EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier - Page 1
Forum section: electronics / general

author: EEVblog
author_rank: Unknown
timestamp: January 06, 2016, 08:46:11 pm
content: Dave reverse engineers the XuanZu X2-U808 Hi-Fi Headphone Amplifier to see if the valves actually do anything.What is the circuit topology?E180F (6J9) pentode valve datasheet:http://frank.pocnet.net/sheets/009/e/E180F.pdfDoug Ford's Microphone design series:https://www.youtube.com/playlist?list=PLvOlSehNtuHv98KUcud260yJBRQngBKiw

author: Radio Tech
author_rank: Frequent Contributor
timestamp: January 06, 2016, 11:18:49 pm
content: I was really surprised to see that the tubes actually did something in the circuit. As you said it could have worked without them.Nice reversal on the circuit Dave.

author: c4757p
author_rank: Super Contributor
timestamp: January 06, 2016, 11:27:24 pm
content: For the little bit that it's worth, the tubesaredoing something if you want "tube distortion", even a follower configuration will distort (though perhaps with a slightly different profile than a voltage amplifier).Might be interesting to look at an FFT of the output. (Disclaimer, I haven't had a chance to watch all the way through yet, I got about halfway...)

author: thomastheo
author_rank: Regular Contributor
timestamp: January 06, 2016, 11:42:20 pm
content: I was really hoping for a little high voltage boost circuit, and a proper tube based amplifier. Not because it would have better audio output than a set of op-amps, because i don't buy all that nonsense, but because it would be a great little piece of nostalgia. I would totally buy one if it was, novelty or not, but alas.

author: AF6LJ
author_rank: Unknown
timestamp: January 06, 2016, 11:49:54 pm
content: Drawing an analogy to a J-FET is simply wrong.A more apt analogy would be a MOS-FET since there is an insulator between the elements like in a vacuum tube.Sorry Dave Ya got it wrong.

author: Ampere
author_rank: Regular Contributor
timestamp: January 06, 2016, 11:55:06 pm
content: I'm a bit disappointed that they're just being used as buffers (and noise generators), but at least I learned something about tubes.

author: AF6LJ
author_rank: Unknown
timestamp: January 07, 2016, 12:09:23 am
content: Not the kind of thing I would waste my money on.Yah it's Cute, but so much of the electronic trash that comes out of China also has a cuteness factor.

author: Richard Crowley
author_rank: Super Contributor
timestamp: January 07, 2016, 12:09:41 am
content: I have found it to be a pretty reliable indicator that if they put an LED under the fire-bottle to "light it up", then they are going for sizzle and there's no steak there. Move on, nothing to see here.(second time I've used that emoticon in 10 minutes after never using it before.)

author: gadget73
author_rank: Regular Contributor
timestamp: January 07, 2016, 12:17:56 am
content: yay for Chinese numbering. Same "number", but completely different part thats not even remotely close to the original. Nothing like swapping a triple triode for a sharp cutoff pentode and sticking the same number on it for confusion reasons.Honestly the reason that solid state makes no sense to me is because I get electron flow. "conventional" flow is backwards and makes no sense in my head.

author: AF6LJ
author_rank: Unknown
timestamp: January 07, 2016, 12:43:47 am
content: Quote from: gadget73 on January 07, 2016, 12:17:56 amI discovered a long time ago it makes no difference which way the little packets of energy go, it all works out just fine.

author: jolshefsky
author_rank: Regular Contributor
timestamp: January 07, 2016, 12:54:00 am
content: If my really quick look is correct, it looks like you can remove the valves and jumper pin 2 (control grid) to pin 3 (cathode) and get a much lower power, halfway decent headphone amp.

author: V42bis
author_rank: Newbie
timestamp: January 07, 2016, 01:14:12 am
content: If it's not torn down yet, try putting a couple of square wave through it, say 2KHz to check the upper frequency response, should not have significant under or over shoot. Then a 20hz square wave and it should not have signify tilt.

author: N2IXK
author_rank: Frequent Contributor
timestamp: January 07, 2016, 01:17:50 am
content: Quote from: gadget73 on January 07, 2016, 12:17:56 amThe tubes are actually Russian tubes, which can be translated from Cyrillic as 6Sh9P or 6J9P. Equivalent to the European E180F or the US type 6688.Original USSR datasheet:http://www.magictubes.ru/sprav/pdf/6j9p.pdf

author: max666
author_rank: Frequent Contributor
timestamp: January 07, 2016, 01:21:07 am
content: Quote from: AF6LJ on January 06, 2016, 11:49:54 pmNo I think you got it wrong, if the control grid voltage would become positive a grid current would flow, just like in a J-FET.

author: rrinker
author_rank: Super Contributor
timestamp: January 07, 2016, 01:22:33 am
content: My favorite is that one Gigabyte PC motherboard that had a single tube audio amp on it. Talk about silly...

author: gadget73
author_rank: Regular Contributor
timestamp: January 07, 2016, 01:39:41 am
content: Quote from: AF6LJ on January 07, 2016, 12:43:47 amAlso just too many parts to keep track of24v K-A and a cathode follower arrangement? Whats the point? It would give lower output impedance, but feeding into an op-amp its not like that would be required. Not enough voltage to make any useful gain anyway. Wonder how far out of the linear operating range it is.

author: AF6LJ
author_rank: Unknown
timestamp: January 07, 2016, 01:51:46 am
content: Quote from: gadget73 on January 07, 2016, 01:39:41 amIn my opinion there is no point, That is not a good tube for a cathode follower, the designer is not taking advantage of the high input impedance a vacuum tube offers, and as you pointed out the plate voltage (B+) is too low.The designer isn't even trying to prove something.Why not?build a 30W headphone amplifier using all tubes, no output transformer, using an output differential amplifierwith cathode output. (to keep the voltage and impedance low)? Run it on say............125V regulated(+/- 65.5V).That would be a concept amplifier worth building, if for no other reason than to prove the idea.

author: retrolefty
author_rank: Super Contributor
timestamp: January 07, 2016, 01:52:18 am
content: Quote from: rrinker on January 07, 2016, 01:22:33 amI remember seeing a picture of that, couldn't believe it when I first saw it, but then I remembered the golden ear crowd. Suspect it wasn't a big seller. You know that could be somewhat of a collectors item.

author: AF6LJ
author_rank: Unknown
timestamp: January 07, 2016, 01:53:00 am
content: Quote from: rrinker on January 07, 2016, 01:22:33 amI wish I had three hands....This is a triple face palm.

author: retrolefty
author_rank: Super Contributor
timestamp: January 07, 2016, 01:56:14 am
content: Quote from: AF6LJ on January 07, 2016, 01:51:46 amWhy 30 watts, not many headphones can accept even peaks at that level? About the only thing that might differentiate a 'headphone amp' form other audio amps is that it might be designed to only work at the higher output impedance of most headsets.

author: AF6LJ
author_rank: Unknown
timestamp: January 07, 2016, 02:13:19 am
content: Quote from: retrolefty on January 07, 2016, 01:56:14 amIn a word "Headroom" but even 10W would be enough.

author: jitter
author_rank: Frequent Contributor
timestamp: January 07, 2016, 02:39:45 am
content: Quote from: EEVblog on January 06, 2016, 08:46:11 pmA lot of wank indeed. Made for the true audiophile that sees the tubes/valves and just "knows" that these must sound good.Tell the same people that it has SMPSs in there, and it'll fall off it's pedestal in the blink of an eye.Other than guitar amps, which are all about distortion, and for good looks (tubes just look coolwithoutthe blue LEDs), I see very little use for hollow state amplifiers.

author: retrolefty
author_rank: Super Contributor
timestamp: January 07, 2016, 02:44:36 am
content: Quote from: jitter on January 07, 2016, 02:39:45 amStill popular and useful for HF Kilowatt RF amplifiers used on the ham radio bands.

author: BobC
author_rank: Unknown
timestamp: January 07, 2016, 02:58:34 am
content: So, in our world of programmable analog circuit arrays and perfect rail-to-rail opamps, when would you *need* to use a tube? When does using silicon not make sense?I've been fortunate to have worked in a wide variety of fields, including radiation monitoring. Some of the sensors provide signals in the microvolt/nanoamp range, and local gain is needed before forwarding the signal elsewhere. But when the sensor is near the center of an operating nuclear reactor, gain can be tough to find. How to get local gain?Specialty tubes to the rescue! A vacuum is naturally radiation-resistant. But careful selection of materials is needed to make a tube that will have a useful lifetime and still work at high temperatures in the presence of massive levels of ionizing and neutron radiation. It turned out that minor process tweaks to existing tubes did the trick, and a dual-stage high-gain amp provided all the gain needed. (Our work was also used on satellites operating in the van Allen belts.)What finally killed tubes in this application (decades after tubes disappeared everywhere else) was their accelerated aging. Inside a nuclear reactor, a lifespan of a 7 years often isn't good enough.So we had to find ways to get the raw sensor signal away from the reactor to external amplifiers. The cost was moved from the tubes to ultra-low-loss cabling, and the signal was fed to what was basically a logarithmic nano-ammeter.Fun all the way, no matter how you slice it. The conversion to a nearly all-digital system (reducing the circuitry between the ADC and the sensor) was boring in comparison.

author: Brumby
author_rank: Unknown
timestamp: January 07, 2016, 03:00:47 am
content: Just one word .... context.

author: helius
author_rank: Super Contributor
timestamp: January 07, 2016, 03:23:51 am
content: Quote from: BobC on January 07, 2016, 02:58:34 amhttp://spectrum.ieee.org/semiconductors/devices/the-quest-for-the-ultimate-vacuum-tube

author: ConKbot
author_rank: Super Contributor
timestamp: January 07, 2016, 03:58:43 am
content: I saw it was a pentode and though "WTf I though you used single end triodes for audiophile cred, pentodes and push-pulls got the distortion too low"Then dave had the schematic drawn out...

author: boffin
author_rank: Unknown
timestamp: January 07, 2016, 04:18:54 am
content: Could you just pull the valve and connect the grid to the anode?

author: Pentium100
author_rank: Frequent Contributor
timestamp: January 07, 2016, 04:20:05 am
content: Quote from: ConKbot on January 07, 2016, 03:58:43 amPentode in SE usually has higher distortion. Connecting it in ultra-linear mode lowers the output power and distortion, triode mode is lowest power and lowest distortion.A JFET has IV curves almost exactly like those of a pentode, however, I do not know of any semiconductor device that has the IV curves of a triode.

author: Brumby
author_rank: Unknown
timestamp: January 07, 2016, 04:23:28 am
content: Quote from: boffin on January 07, 2016, 04:18:54 amNot in this design. The anode goes to the positive rail.You'd have to connect the grid to the cathode - but, yes, your basic idea is ok.Except for one thing - the signal would no longer go through a valve, removing the premise for it being there.

author: Brumby
author_rank: Unknown
timestamp: January 07, 2016, 04:28:55 am
content: The fact that the valve doesn't effectively do anything isn't 'relevant' to the target market. The fact that the signal does, in fact, pass through a valve is enough for them.Also, I find the ultra low distortion figure absolutely hilarious when that target market is after the valve 'sound'.

author: boffin
author_rank: Unknown
timestamp: January 07, 2016, 05:06:23 am
content: Quote from: Brumby on January 07, 2016, 04:23:28 amYes, I meant Cathode; damn electron flow...

author: ConKbot
author_rank: Super Contributor
timestamp: January 07, 2016, 05:52:51 am
content: Quote from: Pentium100 on January 07, 2016, 04:20:05 amYeah I'm not up on valve amps, I thought I had read somewhere that as they progressed the distortion got down quite low (I forget how, thought it was pentodes, apparently not. ) but in doing so, lost the tube amp 'sound'

author: coppice
author_rank: Super Contributor
timestamp: January 07, 2016, 06:15:36 am
content: Quote from: blueskull on January 07, 2016, 06:04:47 amWhat do you consider exact sound reproduction? Our hearing is tied in with our vision, so without the original images we don't hear things as we would in real life. The McGurk effect is the most famous example of this, but it isn't just a speech issue. It happens with musical instruments and other sound sources too. Also, those inner ear monitors might reproduce the super low bass from the lowest pedals of a cathedral organ, but they won't give you that punch in the chest you feel in the actual cathedral, so that's not faithful reproduction, either.

author: Brumby
author_rank: Unknown
timestamp: January 07, 2016, 06:26:06 am
content: Quote from: boffin on January 07, 2016, 05:06:23 amNice try, but I'll call you on that.

author: mikerj
author_rank: Super Contributor
timestamp: January 07, 2016, 09:30:21 am
content: A big fail is that any ripple on the -12v switcher rail is inejcted into the input of the op-amp stages, something you can clearly see on the scope when the amp is powered up. I was hoping Dave was going to put the scope into FFT mode jut to see what kind of crap was coming out of the valve compared to the output of the sig gen.

author: Salas
author_rank: Frequent Contributor
timestamp: January 07, 2016, 09:45:14 am
content: How high is the anode voltage used and how is it created in this headphones amp?

author: kassu
author_rank: Newbie
timestamp: January 07, 2016, 10:06:29 am
content: I think we are all missing the point here. This was sold for about 50 bucks. No true "audiophile" would buy a 50 dollar headphone amp, so this is not "audiophile quality".Now, if you would sell the same thing for 500 dollars, it would be a different story...

author: mikron
author_rank: Contributor
timestamp: January 07, 2016, 10:21:40 am
content: I wonder how much these cheap ceramic caps in the signal path will improve the listening experience...

author: daqq
author_rank: Super Contributor
timestamp: January 07, 2016, 10:38:02 am
content: Dave, didn't you have some dynamic spectral analyzer? It might be interesting to look with it at what comes in vs what comes out.

author: G7PSK
author_rank: Super Contributor
timestamp: January 07, 2016, 11:12:45 am
content: Funny thing is that valve is not in my 1969 Mullard data book, but it is the 1959 book under miscellaneous but there is no data.

author: mikerj
author_rank: Super Contributor
timestamp: January 07, 2016, 11:14:04 am
content: Quote from: Salas on January 07, 2016, 09:45:14 amAbout 24v total (-12 on cathode, +12 on anode) and two small switching regulators are used to create the voltage rails.

author: ciccio
author_rank: Frequent Contributor
timestamp: January 07, 2016, 11:43:44 am
content: I don't want to discuss the electronic design or the performance of this toy.It obviously was designed for a market objective, and the design is done reasonably well.What i discuss is what none of the above posters noted:this toy (and a lot of other tube audio gear on the market) is designed and built without any consideration about product safety.EN60065 (safety requirement for audio, video and similar electronic apparatus) and it's equivalent regulations are violated in at least 2 points:- There are HOT parts accessible to the user (the tubes)- There is a mechanical danger of breaking the glass tubes and cut yourself with the glass.This toy should not be sold, even in China.Best regards

author: timb
author_rank: Super Contributor
timestamp: January 07, 2016, 12:08:31 pm
content: Quote from: ciccio on January 07, 2016, 11:43:44 amWell, you guys heard ciccio, mains voltage and glass objects are dangerous!We better get rid of wall outlets, since the HOT parts are accessible to users... We should also do away with glass cups and bottles as we could cut ourselves!In fact, personal Faraday cages and sippy cups should be mandatory for everyone to prevent electrocution or severe gashes!

author: dr.diesel
author_rank: Super Contributor
timestamp: January 07, 2016, 12:17:49 pm
content: Quote from: ciccio on January 07, 2016, 11:43:44 amLet's not dumb down society even more, complete fail.

author: Fungus
author_rank: Super Contributor
timestamp: January 07, 2016, 12:39:26 pm
content: Quote from: retrolefty on January 07, 2016, 01:56:14 amNot many headphones can accept 30W RMS, but 30W peaks? Sure.

author: Fungus
author_rank: Super Contributor
timestamp: January 07, 2016, 12:41:07 pm
content: No frequency response/distortion/noise measurements? Am leaving disappointed.And why would you "buffer" something that's going to be fed into an op-amp? The op-amp impedance isn't high enough?Still, I guess I'm missing the point. I'm not the target market for this. I'm sure looking at glowing tubeswillimprove the sound quality for many people.

author: retrolefty
author_rank: Super Contributor
timestamp: January 07, 2016, 01:24:45 pm
content: Quote from: Fungus on January 07, 2016, 12:41:07 pmWell at least if a buyer of this amp was expecting and did hear a difference then at least he/she arrived at that conclusion for a whole lot less cash then the 'true believers' that spend ridiculous amounts of money chasing their expectations.

author: ciccio
author_rank: Frequent Contributor
timestamp: January 07, 2016, 01:27:37 pm
content: Quote from: timb on January 07, 2016, 12:08:31 pmHope you are joking.. Glass cups are not electronic devices. There is NOT a safety regulation for them...Wall outlets in any country (outside US and the other who use US type sockets) do not have user accessible parts.If you want to have accessible LIVE part in your house, that's you choice, but no manufacture should be allowed to sell them to you.HOT for me refers to temperature, not mains voltage (in fact the max voltage inside that amp is 12 V dc). Tubes are hot, a child can burn his hands by simply touching it, and the blue LED is an attraction.Serious manufacturers of tube equipment install a perforated shield over the tubes, such as the one in the attachment (randomly chosen on the NET).If the customer removes it to have his evening orgasm whilst looking at red tubes, it is his choice, but the manufactures demonstrates his competence in installing it by default.Other (don't want to say less serious) do not install any protection and maybe don't even have the money for buying a copy of the relevant safety specification.When a problem arise, you will discover that the did not have the money for product's liability assurance too.

author: N2IXK
author_rank: Frequent Contributor
timestamp: January 07, 2016, 01:34:03 pm
content: Those tubes aren't going to get more than warm running at 24V. Certainly not hot enough to be considered a burn hazard.The perforated shields are needed over POWER amplifiers, which have output tubes which actually get hot in use.

author: c4757p
author_rank: Super Contributor
timestamp: January 07, 2016, 01:40:55 pm
content: Oh no, a child might burn his hand on a hot thing or cut himself on a sharp thing! REGULATE!Don't grab hot things, don't smack glass things, and teach your children the same. FFS people.Unfortunately I think we still need to be fairly careful with high voltages. A lot of people don't understand electricity very well, and it can be an invisible hazard... though I still think some countries overdo it on the regulations there, dunno. Not sure exactly how much I think is appropriate there. But hot and sharp? Come on.

author: @rt
author_rank: Super Contributor
timestamp: January 07, 2016, 01:46:57 pm
content: Well you still know if the operator at the other end has valve audio preamp even if you have a solid state receiver.Similarly an old 50’s SW valve radio is the best audio for HF I’ve yet heard.Quote from: retrolefty on January 07, 2016, 02:44:36 am

author: tszaboo
author_rank: Super Contributor
timestamp: January 07, 2016, 01:50:29 pm
content: Quote from: AF6LJ on January 07, 2016, 01:53:00 amWhile it is possibly waste of natural resourses, there are dual triode tubes, like the 12AX7. That can be used to to amplify the DAC output, going to the headphone out.

author: dr.diesel
author_rank: Super Contributor
timestamp: January 07, 2016, 01:51:27 pm
content: Quote from: c4757p on January 07, 2016, 01:40:55 pmYup, regulate, and where you can't sue to make millions. Pretty much sums up today's philosophy, pathetic and depressing.

author: mikerj
author_rank: Super Contributor
timestamp: January 07, 2016, 02:23:28 pm
content: Quote from: ciccio on January 07, 2016, 01:27:37 pmWe must also ban all incandescent lamps, cookers, toasters, heaters, kettles etc. Use of a soldering iron will be a capital crime.Won't someone think of the children?

author: Richard Crowley
author_rank: Super Contributor
timestamp: January 07, 2016, 02:25:32 pm
content: Quote from: @rt on January 07, 2016, 01:46:57 pmThat is just audiophoolery.The only reason firebottles are still allowed is because there are so few of them left compared to incandescent lights which are quickly going illegal across most of the populated parts of the planet.

author: jolshefsky
author_rank: Regular Contributor
timestamp: January 07, 2016, 03:08:07 pm
content: Quote from: ciccio on January 07, 2016, 01:27:37 pmAlas, very noisy people love the idea of an unregulated world. They think everyone's life and health is disposable, especially the stupid. They think that they are so smart as to avoid all danger. They don't realize that young children are incredibly ignorant (and will hopefully be able to grow out of it someday). They don't realize that there are ordinary lapses in attention or awareness that, rather than causing a permanent disability, could simply be met with an "oops" if there were some protection in place.So rather than assessing whether a danger is a necessary part of the object (e.g. knives need to have sharp edges) or whether it is just cheap, lazy design (e.g. not putting a guard around a rotating fan), their knee-jerk libertarian reaction is to declare that all suggestions to insist on design that is rooted in human behavior (and error) are worse than worthless, coddling the incompetent.

author: krivx
author_rank: Frequent Contributor
timestamp: January 07, 2016, 03:34:48 pm
content: Small-bottle tubes tend to run about 50C at the glass. This would make them quite a bit less of a danger than a household radiator.

author: Pentium100
author_rank: Frequent Contributor
timestamp: January 07, 2016, 04:33:52 pm
content: I built my tube amp without the shield. I actually told somebody that it was OK if he wanted to touch the tubes while the amp was on, it's just that parts of the glass were about 150C.Small tubes do not get hot enough to burn a hand when touched, unless they are used at the maximum plate dissipation the ratings allow. Power tubes do get quite hot, especially in class A amplifiers.Quote from: jolshefsky on January 07, 2016, 03:08:07 pmThere is a need for some common sense, especially if the danger is not all that great. Let's say somebody does touch the 150C tube or pick up a soldering iron on the wrong end. At most, they will get some small burn (unlike spilling hot oil on your hand, touching something hot usually invokes the reflex of taking the hand away and that stops the damage), it may be painful, but not lethal or permanent. I however, will insulate live mains wires so the cannot be touched even if I am connecting them temporarily (for a few minutes) or I will use an insulating transformer because touching a live wire can kill.Incandescent lightbulbs get hot too, and table lamps usually do not have protection from touch. How did the human race not go extinct because it was possible to touch a hot lightbulb?We should not have instructions that tell not to put a cat in a microwave oven (or a regular over for that matter) and we should not reward the people that do it even though the instructions did not forbid it. Some things should be understood by all and parents should teach those things to their children. If they don't do that, then maybe those genes should have a reduced chance of reproducing...Lets say you have a sauna. You can pour water on the hot stones to increase the humidity. Do you really need an instruction to tell you that 1) stones are hot, do not touch them and 2) do not pour gasoline on them?

author: Brumby
author_rank: Unknown
timestamp: January 07, 2016, 04:44:55 pm
content: Quote from: Pentium100 on January 07, 2016, 04:33:52 pmYou never know......

author: G7PSK
author_rank: Super Contributor
timestamp: January 07, 2016, 04:49:53 pm
content: Quote from: Pentium100 on January 07, 2016, 04:33:52 pmObviously not valves with a top hat anode connection at 750 Volts then.

author: station240
author_rank: Unknown
timestamp: January 07, 2016, 05:06:45 pm
content: Heh, I remember when Silicon Chip finally after years of complaints finally made something with a valve pre-amp in it.They deliberately over drove the input signal to the valve, so it flattered the top of the curve, for that 'choob' sound.This on the other hand has a unity gain of 1, don't think the Chinese understand what valve amps are really about. Could be interesting to modify this in various ways, eg more gain, higher voltage HT, changed input/output levels. Perhaps it's next owner could consider this.Quote from: kassu on January 07, 2016, 10:06:29 amYou mean once you add the cloth power cord, oak plinth and gold plated sockets. Oh and replace the blue LEDs with orange ones.Actually it would be an interesting experiment to do that, put it up on ebay, and see what idiot buys it.

author: xygor
author_rank: Regular Contributor
timestamp: January 07, 2016, 05:57:30 pm
content: The grid is positive wrt the cathode!?It's running in enhancement mode (to borrow a mosfet term). The data sheet gives data for depletion mode. I suppose that's a consequence of running the plate voltage so low. It's not a mode that's characterized on the data sheet. What do the curves look like for this mode? A spice model probably couldn't be trusted to give the correct result for this region of operation.

author: Salas
author_rank: Frequent Contributor
timestamp: January 07, 2016, 06:04:46 pm
content: Quote from: mikerj on January 07, 2016, 11:14:04 amThanks. There seems to be a small usable area for the 6J9 in such low B+ but in grid current territory.Hence the input coupling capacitors I suppose.

author: Salas
author_rank: Frequent Contributor
timestamp: January 07, 2016, 06:16:03 pm
content: Quote from: xygor on January 07, 2016, 05:57:30 pmLook herehttp://klausmobile.narod.ru/testerfiles/6j9pe.htm

author: N2IXK
author_rank: Frequent Contributor
timestamp: January 07, 2016, 06:33:21 pm
content: Quote from: G7PSK on January 07, 2016, 04:49:53 pmAmpeg introduced their famous SVT series amplifiers using 6146 tubes (which have plate caps), but quickly shifted to 6550 tubes without the caps. Users getting zapped when changing tubes was at least part of the reason behind the change.

author: timb
author_rank: Super Contributor
timestamp: January 07, 2016, 06:35:12 pm
content: Quote from: jolshefsky on January 07, 2016, 03:08:07 pmThe sad reality is that the majority of people's lives *are* disposable. People want to think every life is sacred and everybody is a unique special snowflake. They're not.There's billions of people alive on this pale blue dot, if any one of them disappeared tomorrow, 99.999999...% of the rest wouldn't notice or care. It happens every day.If every life *was* sacred then the money and time first world countries (whose quality of life and mortality rates are pretty damn good) spent on THINK OF THE CHILDREN causes would instead go to *actual* children who are drinking filthy water and starving to death in third world shit holes, the world might be a better place.But it's not. Instead, it goes to making sure little Johnny doesn't suffer the physical and emotional trauma of getting a boo-boo. Proving that people are greedy, selfish and value some lives more than others.Sent from my Smartphone

author: retrolefty
author_rank: Super Contributor
timestamp: January 07, 2016, 07:04:59 pm
content: Quote from: timb on January 07, 2016, 06:35:12 pmTHINK OF THE CHILDRENWhen people, organizations, political parties, religions, etc use that term they don't mean all the children, just theirs and the immediate group or area they most closely associate with. That is not concern for all children of all areas of the world and with all religious or non-religious groups.It's not unlike the NIMBY syndrome which also shows up just as frequently. People will almost always first apply their own self-interests whatever they are, which is also the underlining foundation of a capitalistic world, which has so far proven to be the most successful system yet developed. Maybe someday the outer space Aliens will arrive and impose a better system on all of us that is 'more fair and 'equal outcomes' for everyone. However it that happens I'm sure we will find faults with the Aliens system of government.

author: xygor
author_rank: Regular Contributor
timestamp: January 07, 2016, 07:08:06 pm
content: Quote from: Salas on January 07, 2016, 06:16:03 pmWhat's the difference in meaning of "Grid" and "Grid Drive" in the voltmeter section? Is this the voltage across a grid current sense resistor?A modern tube tester. Cool!

author: retrolefty
author_rank: Super Contributor
timestamp: January 07, 2016, 07:12:34 pm
content: Quote from: xygor on January 07, 2016, 07:08:06 pmA grid is a physical thing, conductive circular mesh surface placed between the cathode and anode of a tube. Grid drive is a voltage (AC + any required DC bias value) that will effect/control the current conduction between the anode and cathode terminals.

author: xygor
author_rank: Regular Contributor
timestamp: January 07, 2016, 07:19:07 pm
content: Quote from: retrolefty on January 07, 2016, 07:12:34 pmLet me rephrase: Grid Voltage and Grid Drive Voltage. It's specific to the tube tester.Edit: Salas' tube tester.

author: xygor
author_rank: Regular Contributor
timestamp: January 07, 2016, 07:21:28 pm
content: Remove the tube and the cathode resistor. Short the grid connection to the cathode connection at the tube socket. Voilà!Edit: spelling.

author: Sylvain
author_rank: Contributor
timestamp: January 07, 2016, 07:54:18 pm
content: Really interesting ...I didn't know anything about valve tubes before watching this video.One question that poped up in my mind : could the "quality" of the 6V supply affect the quality of the sound by modifying the power of heating element (and thus the electron flow) ?

author: Richard Crowley
author_rank: Super Contributor
timestamp: January 07, 2016, 08:01:40 pm
content: Quote from: Sylvain on January 07, 2016, 07:54:18 pmIn some primitive (or high-power) tubes, the heater is also the cathode. But for almost all tubes used for audio, the cathode is a metal tube/oval with the heater filament wires INSIDE for indirect heating. So the actual current through the heater isn't really "in the circuit". Most tube heaters were operated directly from mains-frequency (50/60Hz) AC power. The thermal mass of the heater completely swamps out any effect from the sine-wave power of the heater current waveform. In exactly the same way that nobody can actually perceive "flicker" from an incandescent lamp operating at mains frequency.Of course if circuit design or execution is sloppy, (or component failure) it is possible for the heater AC "hum" to get into the signal path. But that is an exceptional condition and not commonly found in properly designed circuits."Golden ears" audiophools imagine they can "hear" the difference between AC and DC power in an indirectly-heated filament tube. But they imagine lots of other things also, so that comes as no particular surprise.

author: krivx
author_rank: Frequent Contributor
timestamp: January 07, 2016, 08:09:43 pm
content: Quote from: Richard Crowley on January 07, 2016, 08:01:40 pmPeople building high-gain (high distortion) guitar amplifiers have reported that power the heater of the first tube with DC can cut down on hum that is otherwise inductively coupled through the heater wiring. It shouldn't do much in linear amplifiers. Apparently noisy DC on heaters can result in signal noise as well, surprisingly enough.

author: Pentium100
author_rank: Frequent Contributor
timestamp: January 07, 2016, 08:14:08 pm
content: Quote from: G7PSK on January 07, 2016, 04:49:53 pmNo. I also do not particularly like the higher voltages, you know, when the wires have to be a certain distance apart or they would arc over. I have seen insulated top connectors, those would reduce the chance of getting zapped.Quote from: Richard Crowley on January 07, 2016, 08:01:40 pmDepending on the tube and the circuit design, in some cases a small current can flow between the cathode and heater, introducing hum. Of course this is only noticeable in something like a phono preamp where the input signal is a couple of mV. After all, pretty much all tubes were used with AC powered heater. Only battery operated devices had DC heaters (and most tubes designed for battery operation were directly heated) back in the day when tubes were common.

author: rrinker
author_rank: Super Contributor
timestamp: January 07, 2016, 08:17:56 pm
content: It was common for small 6.3V transformers to be called "filament transformers". Guess why. Younger players may rarely if ever come across that term.

author: N2IXK
author_rank: Frequent Contributor
timestamp: January 07, 2016, 08:20:43 pm
content: Quote from: krivx on January 07, 2016, 08:09:43 pmThe usual heater construction is a folded wire inserted inside the cathode sleeve. In tubes specifically designed for low level audio preamp applications, a twisted/coiled heater wire was used to help cancel out the electromagnetic field that could couple into the cathode circuit and result in hum. An example is the 7025, which is a 12AX7 with a coiled heater, specifically designed for audio applications.Another trick was to use the input stage heaters as cathode resistors for the push-pull output stage. In this way, they were operated on DC current, without the expense of additional transformer windings/rectifiers/filter caps.

author: Salas
author_rank: Frequent Contributor
timestamp: January 07, 2016, 08:39:07 pm
content: Quote from: xygor on January 07, 2016, 07:19:07 pmIts not my tester, I just have a TV7 mutual conductance military tester, when the Klausmobile is a Russian curve tracer project that I don't think it ever went commercialhttp://www.klausmobile.narod.ru/projects/pr_02_kmtt_e.htmA famous digital one was the Italian Audiomatica Sofia (great-expensive-obsolete) from the same guys that make the Clio electro-acoustic measurement systemThe most accessible tracer today maybe is the µTracer 3+ kithttp://www.dos4ever.com/uTracer3/uTracer3_pag0.html

author: Salas
author_rank: Frequent Contributor
timestamp: January 07, 2016, 09:11:08 pm
content: Quote from: xygor on January 07, 2016, 07:08:06 pmCould be a sense voltage yes. Grid drive is overdriving a valve by pushing it to grid current leaking territory with near zero and above zero voltage swing, but there is also capacitor blocking possibility when AC coupled. i.e. to peg on big transients until discharged. Nasty distortion effect. It takes a DC coupled buffer driver stage either valve or Mosfet to really push it. Especially for power tubes where it makes sense. In this one its just a starved tube drive necessity to go down there because of little anode voltage available. The guys who made this headphone gadget amp wanted to have tubes for show off or to just spice it up too, but it looks they knew how to work with valves even in weird modes nonetheless.

author: jitter
author_rank: Frequent Contributor
timestamp: January 07, 2016, 09:44:28 pm
content: Quote from: coppice on January 07, 2016, 06:15:36 amIMHO, there's absolutely nothing like the live sound of instruments (that are NOT electronically amplified in any way). How could a speaker, of which the membrane that must reproduce the sound is of a different shape than any instrument, ever come close to reproducing the sound faithfully? Oh, it does a good job at trying, but it doesn't come close to the real thing.I have a good hifi system that even audiophiles wouldn't frown upon, and I am satisfied with it, but there's nothing like a live acoustic instrument. Perhaps that's one of the reasons why I recently took up learning to play the guitar (but it's also got something to do with doing it yourself).

author: TheGreatGooglyMoogly
author_rank: Contributor
timestamp: January 07, 2016, 10:17:06 pm
content: Finally posting two questions...One: the output stage has one amplifier driving another unity buffer, then paralleling the outputs. Does this not introduce distortion or other issues due to the propagation delay of the NE5532? I know it has a global feedback, but seems like it would still have issues. A better solution would seem to parallel both amplifiers? Maybe I'm wrong - not an expert on audio buffers, but want to become one.Two: I have read numerous times never to use SMT ceramic capacitors in audio paths since they 'microphone' and distort the signal. Is this the case or no?Bonus rant... I HATE HATE HATE blue LEDs under tubes. Looks lame and doesn't let the pretty 'natural' glow out. If anything put an amber one in. Blah!

author: N2IXK
author_rank: Frequent Contributor
timestamp: January 07, 2016, 10:28:02 pm
content: In high quality audio gear, ceramic caps (not just SMT ones) are generally frowned upon as coupling capacitors because they exhibit a change in capacitance with applied voltage due to the piezoelectric effect. Some are worse than others, however.

author: xygor
author_rank: Regular Contributor
timestamp: January 07, 2016, 10:33:04 pm
content: Quote from: TheGreatGooglyMoogly on January 07, 2016, 10:17:06 pmIt depends. Class 1 (NPO, C0G, U2J,etc.) are pretty good.Class 2 (X7R, Y5R, Z5U, etc.) can be pretty bad especially higher values in smaller packages. If the signal has frequencies for which the capacitive reactance is much smaller than the impedance of the rest of the circuit, it's not too bad. This would be the case for interstage coupling. Otherwise the lower frequencies cause intermodulation distortion. This would be likely be the case for filters and equalizers.

author: EEVblog
author_rank: Unknown
timestamp: January 07, 2016, 10:53:52 pm
content: Quote from: Richard Crowley on January 07, 2016, 08:01:40 pmI've heard that is you hook up the filament backward the audiophiles can hear Paul McCartney whispering to them.

author: Groucho2005
author_rank: Regular Contributor
timestamp: January 07, 2016, 11:03:12 pm
content: Quote from: TheGreatGooglyMoogly on January 07, 2016, 10:17:06 pmProbably insignificant for audio frequencies. Anyway, the bias of the tube (12V anode-cathode voltage, 2.5 mA cathode current) is so atrocious that the distortion of that "buffer" will dominate everything (which is of course by design). It's not unlike operating a BJT in it's saturation area which is ridiculous for a linear amplifier.Tubes have a reputation of having high distortion which is not true if the circuit is designed properly.If anyone is interested, here is an article on designing a tube audio buffer without any snakeoil and audiophoolery by Stuart Yaniger:http://syclotron.com/?page_id=2380

author: f4eru
author_rank: Super Contributor
timestamp: January 07, 2016, 11:21:13 pm
content: Quote from: kassu on January 07, 2016, 10:06:29 amIn china, 50 dollars are like 500 dollarsQuote from: jitter on January 07, 2016, 02:39:45 amThat's the reason of rubbing off the ICs : people not recognizing that this is a SMPS would not be able to search the ICs

author: TheGreatGooglyMoogly
author_rank: Contributor
timestamp: January 07, 2016, 11:35:30 pm
content: Quote from: xygor on January 07, 2016, 10:33:04 pmI'll bet literal bottom dollar that they are Y5V. Maybe X5R, but larger than 0.1uF C0G are virtually non-existent and very expensive (have used a 0.1uF C0G before).

author: Richard Crowley
author_rank: Super Contributor
timestamp: January 07, 2016, 11:41:15 pm
content: This will all be moot soon. Apple is dropping the 3.5mm analog output jack completely.If you don't want to use wireless (Bluetooth) headphones, there will be digital headphones that plug into the Lightning connector.No word on how you will plug in BOTH you headphones AND your charger, sync cable, etc.Not letting the audio loose in the analog domain means they can enforce DRM right to your eardrums.

author: retrolefty
author_rank: Super Contributor
timestamp: January 07, 2016, 11:46:59 pm
content: Quote from: Richard Crowley on January 07, 2016, 11:41:15 pmWow is that for real? So in the near future the Apple user can't pipe his/her music to a typical analog audio amp/speaker system via a analog jack unless it's an approved and compatible amplifier?Don't own anything Apple, so no problem here.

author: Richard Crowley
author_rank: Super Contributor
timestamp: January 08, 2016, 12:10:02 am
content: Quote from: retrolefty on January 07, 2016, 11:46:59 pmhttp://www.fastcompany.com/3055208/its-true-apple-will-drop-the-headphone-jack-to-make-the-iphone-7-slimmer-and-simplerhttp://mashable.com/2016/01/07/phone-7-headphone-jack-rip/#8OX.TxjEJuqQhttp://9to5mac.com/2016/01/05/apple-dropping-removing-headphone-port-iphone-7/http://www.digitalmusicnews.com/2016/01/05/you-can-kiss-your-3-5mm-headphone-jack-goodbye/http://www.forbes.com/sites/gordonkelly/2014/06/05/apple-to-abandon-headphone-jack-suddenly-beats-deal-makes-sense/http://appleinsider.com/articles/16/01/07/another-rumor-claims-iphone-7-will-drop-headphone-jack-gain-waterproofing-wireless-charginghttp://money.cnn.com/2015/11/30/technology/iphone-7-headphone-jack/http://www.engadget.com/2015/11/28/next-iphone-may-use-lightning-audio/http://www.cultofmac.com/399993/apple-would-be-stupid-to-drop-the-iphone-headphone-jack/

author: Fungus
author_rank: Super Contributor
timestamp: January 08, 2016, 12:53:35 am
content: QuoteBut will it bend?

author: rrinker
author_rank: Super Contributor
timestamp: January 08, 2016, 02:06:00 am
content: Quote from: EEVblog on January 07, 2016, 10:53:52 pmWho are you kidding, everyone knows Paul's dead, they told us that many many moons ago.Or maybe his ghost lives amongst the vacuum in the valves.

author: gadget73
author_rank: Regular Contributor
timestamp: January 08, 2016, 02:58:17 am
content: Quote from: N2IXK on January 07, 2016, 08:20:43 pmThis is always a cute trick. I have a Fisher TA-600 that uses this system. One of the phono tubes developed a heater-cathode short, and that particular cathode was grounded. It did some unhappy things to the bias on the output stage.There are certainly some interesting bits of economy used on electronics at times. One of the oddest I've seen on a tube amp was the original bias supply in my big Bogen PA amps. It used a 0.47 uf cap off the 300 VAC winding to feed through a diode to get the negative DC supply. That now has a small 6vac transformer fed backwards to run the bias supply.Tube amps have long been a contentious thing in the electronics world. Audio guys tell you they sound better. Measurement devices tell you they are shite on a stick. Personally I say they are both true. Tube amps measure badly but are pleasing to listen to. Its the difference between steam power and internal combustion engines. By every measurable way the IC engine wins, but we still like steam trains.

author: gadget73
author_rank: Regular Contributor
timestamp: January 08, 2016, 03:16:03 am
content: Quote from: Fungus on January 07, 2016, 12:39:26 pmI do not suspect that your ears would though. It takes such a tiny amount of power to run a set of cans that even a watt of power would give you ample dynamic range for anything you want to listen to, even at levels that would make your ears bleed. There are a few designs out there for straight cathode drive can amps with low tube count. A 6AS7 works nicely for OTL headphone amp duty.

author: Pentium100
author_rank: Frequent Contributor
timestamp: January 08, 2016, 04:08:00 am
content: I have a headphone amp with a white cathode follower made from ECC88s (voltage gain stage is another ECC88). Works quite well, even with 32ohm headphones. Though I currently use 300ohm headphones (did not specifically search for the high impedance).As for why I need a headphone amp - not all devices I have provide a headphone output and I did not want to use a speaker amp for the headphones all the time (too easy to accidentally turn on the speakers in the middle of the night).

author: jitter
author_rank: Frequent Contributor
timestamp: January 08, 2016, 06:58:57 am
content: Quote from: EEVblog on January 07, 2016, 10:53:52 pmI thought he was dead... we're supposed to be stuck with Faul now...

author: boffin
author_rank: Unknown
timestamp: January 08, 2016, 08:04:39 am
content: Quote from: retrolefty on January 07, 2016, 11:46:59 pmIt's more annoyinghttp://www.patentlyapple.com/patently-apple/2015/09/apple-granted-an-alternative-headset-connector-patent-that-may-never-see-the-light-of-day.htmlAn Apple headphone plug that will/might work in other devices, but not other devices into an Apple device, unless you pay their patent licensing fee.

author: timb
author_rank: Super Contributor
timestamp: January 08, 2016, 08:13:04 am
content: Just because they're removing the 3.5mm jack, doesn't mean it won't still output analog audio. They could very well push the analog audio over a couple of pins on the Lightning connector. The older 30-pin connectors did that. You would then use a simple Lightning to 3.5mm adapter.If they don't do analog transport over the Lightning port, they'd be to just stick a DAC in the adapter.Or they won't remove it from the phone at all. 99% of Apple rumors are wrong, so perhaps it's best not to spread FUD just yet. Also, Apple patents *a ton* of stuff. Of that, a small number makes it into production.Either way, you'll still be able to use headphones, I guarantee that. It's sort of a basic requirement.

author: AF6LJ
author_rank: Unknown
timestamp: January 08, 2016, 03:48:00 pm
content: Quote from: timb on January 08, 2016, 08:13:04 amThere is a trend to remove the analogue link to the outside world, the copyright people want to make it hard to plug that phone (or whatever) into a recording device. They think we are all criminals and want to share our music with the world.

author: Oskar
author_rank: Newbie
timestamp: January 08, 2016, 04:22:01 pm
content: That's funny that the tube is just a buffer. Thanks for using the DS1054Z and highlighting the channel control issue. That does not take the DS1054Z off my to purchase list.Nice video.

author: Fungus
author_rank: Super Contributor
timestamp: January 08, 2016, 06:16:19 pm
content: Quote from: Oskar on January 08, 2016, 04:22:01 pmNot just a buffer, the electric heater in the tube will add 'warmth' to the electrons.What audiophile doesn't want warmed-up sound?

author: Richard Crowley
author_rank: Super Contributor
timestamp: January 08, 2016, 06:58:03 pm
content: Quote from: timb on January 08, 2016, 08:13:04 amSure. Apple headphones (or Apple-licenced headphones) at an inflated Apple price.It's plays nicely into their "Walled Garden" scheme where they control EVERYTHING including the customer.I am extraordinarily dubious about this.

author: Fungus
author_rank: Super Contributor
timestamp: January 08, 2016, 07:04:34 pm
content: Quote from: Richard Crowley on January 08, 2016, 06:58:03 pmNah, there's no conspiracy.It's a phone. The whole point is that it's wireless and the music plays remotely while you select songs on the screen. Bluetooth sound is built into everything these days. You don't connect a cable when you listen to your iPhone in your car, why should you do it at home.It's the way the iTunes generation rolls, Apple is just going along.

author: jdamewood
author_rank: Newbie
timestamp: January 09, 2016, 06:28:59 am
content: Quote from: max666 on January 07, 2016, 01:21:07 amThen the cathode follower would be 180° out of phase from input signal.Preemptive call to myself as being wrong, if needed.

author: Pentium100
author_rank: Frequent Contributor
timestamp: January 09, 2016, 07:15:45 am
content: Quote from: jdamewood on January 09, 2016, 06:28:59 amThe cathode follower output is in phase with the input. When the control grid voltage becomes more positive than it was at idle, more current flows trough the tube causing higher voltage drop on the cathode resistor. If the control grid voltage becomes positive with respect to cathode, then some grid current flows, but the plate current is increased even more.I have attached the IV curves of a Russian 6?2? (6N2P) tube, which is similar to 12AX7. It shows the effect of a positive grid voltage.

author: gildasd
author_rank: Frequent Contributor
timestamp: January 09, 2016, 07:18:13 pm
content: Quote from: Richard Crowley on January 08, 2016, 06:58:03 pmThe day Apple removes the 3.5 is the day I buy a Samsung...Apple in ear head speakers are nice, but in my use, worn under noise protection ear muffs, they last only a few weeks before splitting open.Cheap PVC based models last until the conductors split.I like Apple products, but my brand loyalty breaks down when said brand tries to shag me, in a fashion frowned by the ecclesiastical hierarchy, without so much as the courtesy of a reach around.

author: gadget73
author_rank: Regular Contributor
timestamp: January 10, 2016, 04:28:32 am
content: Quote from: jdamewood on January 09, 2016, 06:28:59 amCathode followers are in-phase with the input signal, anode follower would be 180 out of phase.

author: 13hm13
author_rank: Frequent Contributor
timestamp: January 10, 2016, 07:27:03 am
content: Quote from: AF6LJ on January 06, 2016, 11:49:54 pmI think Dave meant in a GENERIC way: tubes and FETs are voltage amps (not current).

author: jitter
author_rank: Frequent Contributor
timestamp: January 10, 2016, 07:35:10 am
content: The way I understood the analogy is electrons flowing through a vacuum are being effected by the electrical fields on the grids. Hence the analogy to the FE part of a FET.

author: AF6LJ
author_rank: Unknown
timestamp: January 10, 2016, 01:52:08 pm
content: Quote from: 13hm13 on January 10, 2016, 07:27:03 amThat's true The J-FET analogy just doesn't work.

author: Brumby
author_rank: Unknown
timestamp: January 11, 2016, 02:07:05 am
content: Quote from: 13hm13 on January 10, 2016, 07:27:03 am+1After all, it's a tear-down style examination, not a quantum physics analysis.

author: rch
author_rank: Regular Contributor
timestamp: January 11, 2016, 11:33:35 am
content: +1. To those of us brought up on valves, JFETs are just like valves, and bipolar transistors are alien and odd!

author: Richard Crowley
author_rank: Super Contributor
timestamp: January 12, 2016, 06:22:15 pm
content: From the BBC yesterday....QuoteI don't agree that if Apple ditches the 3.5mm connector, it spells doom for that connector in the Rest Of the World. But, at least as far as I am concerned, it just reinforces my distain for everything Apple. If I were a dumb consumer appliance-operator, I would probably have a different opinion.

author: helius
author_rank: Super Contributor
timestamp: January 12, 2016, 09:37:50 pm
content: I very much doubt the cross section of "£1,000 headphone users" who plug them into iphones is significant. Aren't all products in that range either 600 ohm, electrostatic, or otherwise not driveable from low-output equipment?

author: rch
author_rank: Regular Contributor
timestamp: January 12, 2016, 11:01:19 pm
content: Quote from: helius on January 12, 2016, 09:37:50 pmApple users may well be able to purchase £1000 headphones which look just like £3.50 headphones to the rest of us.(DOI moderately keen Apple user.)

author: timb
author_rank: Super Contributor
timestamp: January 12, 2016, 11:15:53 pm
content: It's a rumor guys. It's either not going to happen, or if it does they will still be pumping analog out through the Lightning port, which will allow you to use a $5 passive adapter. I guarantee that.It's pointless to get worked up over an Apple rumor. This particular one has been floating around since the iPhone 3GS. (This same rumor was about the iPhone 4 not having a headphone port.)These get started one of three ways:1) Some Apple Rumors Blog makes up some BS and tech sites pick it up as news.2) Apple files a patent for "Method of transporting digital audio directly to headphones" and someone interprets that to mean the headphone port is being killed.3) Someone at Apple says, "Gee wouldn't it be nice if we didn't have to deal with external ports, we could make phones that were paper thin!" This gets repeated like the Telephone Game and eventually someone posts it on Twitter as "Apple to remove headphone ports!"In this case, it's likely a combination of all three. If anyone wants to start a pool on Apple removing the headphone port in the 7, I'll throw down $100 right now squarely in the Not Happening category.

author: jitter
author_rank: Frequent Contributor
timestamp: January 13, 2016, 06:33:42 am
content: Yeah, and that hyped rumor is talking about a 3.5 mm jack like that's the smallest jack there is...which it is not.More than a decade ago I bought a HP PDA which already did away with the 3.5 mm jack and used a 2.5 mm jack instead. Thoughtfully HP supplied a 2.5 mm to 3.5 mm adapter...So wether or not Apple stops using the 3.5 mm jack is really not that interesting, it's been hyped because it's Apple that (allegedly) does it. And even if they were to do it, I have no doubt that aftermarket converters would become available for very little money very quickly.I hear people say: "Yeah but that costs extra..." Well, if you're prepared to buy overpriced stuff to begin with, a few more dollars/euros/whatever isn't going to hurt your wallet that much...

author: gildasd
author_rank: Frequent Contributor
timestamp: January 13, 2016, 10:37:52 am
content: Of the thing I find that Apple has to improve, thinness and size are not on my list.Battery life, WIFI sensitivity and others come to mind.In any case it goes in a rubber case...

author: Fungus
author_rank: Super Contributor
timestamp: January 13, 2016, 01:34:36 pm
content: Quote from: jitter on January 13, 2016, 06:33:42 amApple will charge $20 for their legacy headphone compatibility system.

author: krivx
author_rank: Frequent Contributor
timestamp: January 13, 2016, 01:36:54 pm
content: Quote from: Fungus on January 13, 2016, 01:34:36 pmIf it's an analog breakout cable then eBay will charge $3

author: Richard Crowley
author_rank: Super Contributor
timestamp: January 13, 2016, 02:03:39 pm
content: Quote from: timb on January 08, 2016, 08:13:04 amPlease explain how you think they could do that since there are no analog pins on the Lightning connector, and no re-assignable pins, either.And furthermore, the Lightning connector is not only proprietary, but contains active circuitry to ensure that ONLY Apple-provided (or Apple-licensed) gear can connect. (Read: $$$)Ref:https://en.wikipedia.org/wiki/Lightning_(connector)

author: Richard Crowley
author_rank: Super Contributor
timestamp: January 13, 2016, 02:08:25 pm
content: Quote from: krivx on January 13, 2016, 01:36:54 pmIt cannot be an analog cable because Apples proprietary Lightning connector is digital-only.Furthermore Lightning requires an active ID/authentication chip available only by licen$e from Apple.That ensures that you won't be able to buy sensibly-priced accessories like simple cables, adapters, etc.Apple must enforce their lucrative proprietary Walled Garden scheme.Of course, the knock-off artists in Asia have proven themselves to be very clever.So it seems within the realm of possibility that they can produce a counterfeit authentication chip.Of course, then Apple could pull an FTDI stunt and brick all your counterfeit gear.

author: krivx
author_rank: Frequent Contributor
timestamp: January 13, 2016, 02:31:09 pm
content: Quote from: Richard Crowley on January 13, 2016, 02:08:25 pmThe Wikipedia page posted above says that Apple sell a Lightning to 30pin (previous Ipod/IPhone connector) adapter and that it supports analog audio. Google brings up lots of knockoffs of this adapter, so maybe the work is already done?

author: Brumby
author_rank: Unknown
timestamp: January 13, 2016, 02:35:37 pm
content: I would not be comfortable trusting Apple to give me what I want - and I certainly am not one of the 'faithful' that accepts whatever is served up as being the best option.I like to think and decide for myself on a few things....

author: Fungus
author_rank: Super Contributor
timestamp: January 13, 2016, 04:07:42 pm
content: Quote from: Richard Crowley on January 13, 2016, 02:08:25 pmApple could just stick a new connector on the bottom with more pins.It's not like they've never released an iPhone that was incompatible with previous-gen peripherals.

author: jitter
author_rank: Frequent Contributor
timestamp: January 13, 2016, 08:44:10 pm
content: How has this thread gone from a valve amplifier to an Apple thread?

author: Richard Crowley
author_rank: Super Contributor
timestamp: January 13, 2016, 08:52:46 pm
content: Quote from: jitter on January 13, 2016, 08:44:10 pmDiscussion of the future of headphone interface (connector, impedance, etc.) is threatened by Apple's rumored decision to drop the industry-standard analog headphone interface (3.5mm or 6.35mm=1/4 inch) presumably in favor of digital and likely wireless interface. Rendering the valve headphone amps, already arcane, to the category of downright obsolete as well.

author: bob808
author_rank: Frequent Contributor
timestamp: January 24, 2016, 12:41:33 pm
content: Dave is making waves amongst audiophools:http://www.stereo.net.au/forums/index.php?/topic/96224-Audiophools-and-cables

author: Brumby
author_rank: Unknown
timestamp: January 24, 2016, 02:53:36 pm
content: Much of the reaction is predictable - but one post made me smile.This is probably the most honest attitude I have come across:"My take is, even if there are no variables - all cables sound the same, all amps sound the same, all CD players and turntables sound the same (which of course I don't think is the case) the Fact that we Perceive improvements and gain increased enjoyment from them (even if in fact they aren't there) it's WORTH it. Perception is reality; not fact."I have to agree that perception is the key factor in the appreciation of anything. If someone feels happier about something that isn't real, then I can just shake my head and walk by quietly.But have someone try to convince another that the extra $$$s are worth it - and I have a real problem.

author: Brumby
author_rank: Unknown
timestamp: January 24, 2016, 02:56:41 pm
content: Then there was this:"His parents should have put the lid back on the red cordial."Yeah - sometimes you can wonder about that... but, in the end, it's an honest opinion that's as entertaining as hell.

author: rrinker
author_rank: Super Contributor
timestamp: January 24, 2016, 05:27:50 pm
content: I laughed out loud at this one:what irritates also are clowns like the guy in the video, he didn't really offer any factual information nor present as someone really capable of doing so. At one point he mentions 'sheilding' as though it's a snake oil selling term and holds up his basic black IEC power cable as though it's performance can't be bettered.LOL doesn't offer facts?

author: Pentium100
author_rank: Frequent Contributor
timestamp: January 24, 2016, 08:03:49 pm
content: Even if, for example, the signal from a reel to reel tape deck is inferior to the signal from a CD player (most likely with my tape decks and tapes, definitely for some recordings I have), it is still more enjoyable to me to listen to music while watching the big reels spin.Tubes usually do alter the signal (SE amplifiers, for example, usually have a lot of 2nd order harmonics), so it's a matter of preference. I, for example, prefer the sound of my (lo-fi) tube tape recorder for some music even though other music on it sounds bad.

author: c4757p
author_rank: Super Contributor
timestamp: January 24, 2016, 08:17:29 pm
content: Quote from: bob808 on January 24, 2016, 12:41:33 pmThat thread is excellent.

author: kalleboo
author_rank: Regular Contributor
timestamp: January 24, 2016, 09:30:41 pm
content: Quote from: krivx on January 13, 2016, 02:31:09 pmAnd it actually contains a small DAC!Quote from: krivx on January 13, 2016, 02:31:09 pmThe cheap ones I've seen in stores all say "Does not support Audio/Video" on the box, e.g. this one on Amazon:http://www.amazon.com/DP-30-Pin-Adapter-Apple-Lightning/dp/B00D48Q4OG

author: Fungus
author_rank: Super Contributor
timestamp: January 25, 2016, 07:34:07 am
content: Quote from: kalleboo on January 24, 2016, 09:30:41 pmI don't trust it, it will have jitter.Bring back the true analog output!

author: krivx
author_rank: Frequent Contributor
timestamp: January 25, 2016, 08:53:17 am
content: Quote from: Fungus on January 25, 2016, 07:34:07 amYou don't trust the DAC in a cable, but a DAC inside the phone is OK?

author: rch
author_rank: Regular Contributor
timestamp: January 25, 2016, 10:48:28 am
content: Quote from: blueskull on January 25, 2016, 10:23:17 amIf it is mainly going to used to listen to music recovered from .mp3s I think that is a purely academic concern. Even I can often hear gross compression artifacts, and I'm not musical.

author: Fungus
author_rank: Super Contributor
timestamp: January 25, 2016, 02:36:19 pm
content: Quote from: krivx on January 25, 2016, 08:53:17 amI thought the "true analog" would have given it away, but nooooo....

author: Brumby
author_rank: Unknown
timestamp: January 25, 2016, 02:42:25 pm
content: The truth be known,Funguswants his brick mobile phone back...

author: gildasd
author_rank: Frequent Contributor
timestamp: January 25, 2016, 03:23:45 pm
content: Quote from: Brumby on January 25, 2016, 02:42:25 pmCould a person even make* an all analogue GSM phone?*That fits in the bed of a Medium Pickup and runs off no more than a Honda Handy generator of 700W.

author: mikerj
author_rank: Super Contributor
timestamp: January 25, 2016, 05:16:24 pm
content: Quote from: c4757p on January 24, 2016, 08:17:29 pm'Audiophiles' are a very excitable bunch.

author: bob808
author_rank: Frequent Contributor
timestamp: January 25, 2016, 05:18:06 pm
content: I start to feel less and less sorry for them. I feel they should pay as much as possible for their arrogance

author: Yansi
author_rank: Super Contributor
timestamp: January 25, 2016, 06:13:49 pm
content: Quote from: AF6LJ on January 06, 2016, 11:49:54 pmSorry for the late reply, but comparison to a jfet is pretty much right.Both the tube's grid and jfet's gate behave the same way. Small capacitance for negative voltages, a diode for positive voltages (with respect to cathode / source).

author: AF6LJ
author_rank: Unknown
timestamp: January 26, 2016, 04:06:57 pm
content: Quote from: Yansi on January 25, 2016, 06:13:49 pmJ-FETs have a lower impedance there is physical contact between elements, and a J-FET cannot operate with current flowing on the gate, a vacuum tube can.I hate to put too sharp of a point on it but;Drawing that analogy dumbs down the whole discussion. Vacuum tubes are unique as an active device, even though they share some commonalities with solid state field effect devices.

author: bktemp
author_rank: Super Contributor
timestamp: January 26, 2016, 04:45:04 pm
content: Quote from: AF6LJ on January 26, 2016, 04:06:57 pmA J-FET can be operated with a current flowing into the gate. If the junction gets forward biased, current will flow. And this will decrease the drain-source resistance further.The operating principle may be different, but electrically their behaviour is similar (Id/Ug curve), except J-FETs work on a much lower voltage than tubes and drain and source are interchangeable.At the end of the tube era some tubes were substituted with a J-FET input stage driving a larger transistor.

author: Brumby
author_rank: Unknown
timestamp: January 27, 2016, 04:23:26 am
content: Quote from: AF6LJ on January 26, 2016, 04:06:57 pmA simplification it may be - but that comment was still more intelligent than the product.

author: Yansi
author_rank: Super Contributor
timestamp: January 27, 2016, 02:28:40 pm
content: I don't feel offended when talking about the JFET analogy for tubes.It is an analogy, not a direct replacement having same operation voltage and same high impedances...

author: AF6LJ
author_rank: Unknown
timestamp: January 27, 2016, 03:02:10 pm
content: I am not offended; I feel the analogy dumbs down the subject.

author: Yansi
author_rank: Super Contributor
timestamp: January 27, 2016, 04:59:26 pm
content: You seem to have a better analogy, don't you?

author: AF6LJ
author_rank: Unknown
timestamp: January 27, 2016, 07:08:38 pm
content: Quote from: Yansi on January 27, 2016, 04:59:26 pmThis one situation where an analogy serves no good.Go learn how vacuum tubes actually work.Just as a small example the J-FET analogy doesn't explain why a tetrode under certain conditions draws negative screen current.Bad analogies are a trap for young players.

author: Pentium100
author_rank: Frequent Contributor
timestamp: January 27, 2016, 09:23:57 pm
content: JFET is similar to a pentode (operating with the screen and suppressor grids connected to fixed voltages), but I do not think there is a solid state device that has the IV curves of a triode.

author: Groucho2005
author_rank: Regular Contributor
timestamp: January 27, 2016, 09:34:01 pm
content: Quote from: Pentium100 on January 27, 2016, 09:23:57 pmYes there is, Static Induction Transistor (SIT), some info here:http://www.firstwatt.com/sitintro.html

author: helius
author_rank: Super Contributor
timestamp: January 27, 2016, 09:43:53 pm
content: Quote from: Groucho2005 on January 27, 2016, 09:34:01 pmI was reading with interest until he said "First, it allows a single gain stage...without a feedback loop or degeneration." As is widely known, a triode amplifier doesn't work "without feedback": the feedback happens internally.

author: AF6LJ
author_rank: Unknown
timestamp: January 28, 2016, 04:14:44 am
content: Quote from: Pentium100 on January 27, 2016, 09:23:57 pmI haven't seen one...In this day and age vacuum tubes are for the most part at the end of their technological evolution. The last place you will find vacuum tube tech used in are devices like ion implanters, Ion discharge machining and similar industrial applications, where the work is being done inside a vacuum with an electron emitter and grids, anodes and the like to accelerate ions.Vacuum tubes are still fun to play with.

author: mikerj
author_rank: Super Contributor
timestamp: January 28, 2016, 07:42:20 am
content: Quote from: blueskull on January 28, 2016, 02:50:46 amWhere did you get the 200W input from? I see 18dB gain and 10W output.The distortions figures are quite impressive for a single transistor power amp with no feedback, try getting anywhere near that with a single bipolar or MOSFET.

author: Yansi
author_rank: Super Contributor
timestamp: January 28, 2016, 11:35:15 am
content: AF6LJ: Yolo, there are also mosfet tetrodes. Usually HF stuff. Also behaving well like a tetrode (pentode) valve, having the g1 input capacitance ridiculously low.

author: AF6LJ
author_rank: Unknown
timestamp: January 28, 2016, 01:31:18 pm
content: Quote from: Yansi on January 28, 2016, 11:35:15 amI know about dual gate MOS-FETS They don't behave fquite like a tetrode but are a beast all their own.

author: Groucho2005
author_rank: Regular Contributor
timestamp: January 28, 2016, 03:47:27 pm
content: Quote from: mikerj on January 28, 2016, 07:42:20 amGo to the product page and look at the SIT1/SIT2 amplifier pages. Yes, this is an extremely inefficient design and there are barely any speakers it can drive properly.

author: mikerj
author_rank: Super Contributor
timestamp: January 28, 2016, 03:51:08 pm
content: Quote from: Groucho2005 on January 28, 2016, 03:47:27 pmThat's simply because they are Class A designs, which are inherently inefficient. Pure class A amps with reasonable power outputs are room heaters, irrespective of the type of power output device.

author: Fungus
author_rank: Super Contributor
timestamp: January 28, 2016, 03:53:47 pm
content: Quote from: Groucho2005 on January 28, 2016, 03:47:27 pmIt's a class A amplifier, so... that's just the way they work.They're good for cold winter days. With a small enough heatsink you can even cook eggs.

author: Groucho2005
author_rank: Regular Contributor
timestamp: January 28, 2016, 05:02:03 pm
content: Quote from: mikerj on January 28, 2016, 03:51:08 pmYou have to differentiate a bit. Theoretically, a Class-A amplifier can have up to 50% efficiency. A Class A amplifier with complementary bipolar or MOSFET output devices comes very close to that number.However, a single ended class a triode amp, which is very popular in the audiophile/audiophool community, will barely reach 10% efficiency which seems pretty insane but there are people who wouldn't have it any other way.

author: rrinker
author_rank: Super Contributor
timestamp: January 28, 2016, 08:17:33 pm
content: The Class A design was used as a selling point for the receiver I had in college. Well, at full volume (this sucker goes to 11!), it would barely get warm. But at normal listening levels - yes, I could fry eggs right in my dorm room. All was fine until I developed a habit of going to sleep with the volume really low for background noise - fried the outputs twice on it.

author: Brumby
author_rank: Unknown
timestamp: January 29, 2016, 02:01:13 am
content: That's the one thing about Class A amplifiers I always remembered .... If you want them to run as cool as possible, you had to run them at full volume.

author: retrolefty
author_rank: Super Contributor
timestamp: January 29, 2016, 02:35:01 am
content: Quote from: Brumby on January 29, 2016, 02:01:13 amThat sounds like a myth to me? Can you link to an analysis to support that.

author: Brumby
author_rank: Unknown
timestamp: January 29, 2016, 04:32:04 am
content: Hmm...My text books are buried somewhere if not long gone - and Google hasn't been too helpful. I've found some references to power dissipation in Class A amplifiers, but nothing that gives me what I was looking for - which would be a chart of power dissipation vs output power.It is my understanding that pure class A amplifiers draw maximum power from their supply at no signal (and therefore no output). While not being particularly critical of my reading over the years, unless I've read it wrong, as power increased to the load, there is a corresponding drop in the power dissipated by the amplifier. Therefore the amplifier runs cooler at maximum output.I'm open to correction if I've got that wrong.Will still keep looking for something to back it up - but I can't spend any longer on this right now.

author: mikerj
author_rank: Super Contributor
timestamp: January 29, 2016, 10:20:34 am
content: Quote from: Groucho2005 on January 28, 2016, 05:02:03 pmNot true for an equivalent design to the one shown in the SIT datasheet. The efficiency of a simple class A design is no better than 35% at full load, and much worse at low outputs or under quiescent conditions. Efficiency can be improved by using active loads rather than a simple resistor or transformer coupling, but even then you are unlikely to reach 50% efficiency.

author: Groucho2005
author_rank: Regular Contributor
timestamp: January 29, 2016, 11:05:33 am
content: Quote from: mikerj on January 29, 2016, 10:20:34 amI suppose you missed my use of the words "theoretically" and "up to". Also, efficiency obviously relates to the maximum power output.Lastly, transformer coupling is much more efficient than using active loads.

author: gadget73
author_rank: Regular Contributor
timestamp: February 03, 2016, 01:47:19 am
content: Quote from: retrolefty on January 29, 2016, 02:35:01 amSome amplifiers will switch in and out of Class A operation depending on output demands. At low levels it runs a room-warming Class A bias level, with some crank it switches to a more sane AB1 bias level and the heat drops accordingly. A straight Class A amp chugs out essentially the same heat with the volume at 0 or 11.

author: Brumby
author_rank: Unknown
timestamp: February 03, 2016, 02:10:32 am
content: Quote from: retrolefty on January 29, 2016, 02:35:01 amBest I've come up with so far...http://www.analog.com/library/analogDialogue/archives/40-06/class_d.html

author: coppice
author_rank: Super Contributor
timestamp: February 03, 2016, 04:41:05 am
content: Quote from: retrolefty on January 29, 2016, 02:35:01 amIt comes directly from the definition of class A. A pure class A amp draws a constant amount of power. At zero output it all ends up as heat in the amp. At maximum output some ends up in the load, so less ends up as heat in the amp.

author: Brumby
author_rank: Unknown
timestamp: February 03, 2016, 04:49:47 am
content: That's what I was talking about! Thank you.

author: FM
author_rank: Newbie
timestamp: July 05, 2016, 10:30:54 pm
content: Quote from: jolshefsky on January 07, 2016, 12:54:00 amCan anyone confirm that method to bypass the tubes?It would lower the power by a lot?I wish another video was done on this amp about bypassing the tubes.This amp gets criticism for the tubes not doing much, but if bypassing the tubes doesn't lower the power output, it's a lot of power for the price, and bypassing the tubes means no need to buy replacement tubes when the stock ones wear out. And it gets rid of the tube distortion, of course.I have one and like it, but it'd be great to be able to bypass the tubes. If the power output would be the same.