Want to build a headphone amp. - Page 1
Forum section: electronics / projects

author: jdraughn
author_rank: Regular Contributor
timestamp: November 10, 2015, 12:19:03 pm
content: Hi all.I am looking to build a little headphone amp and am looking at building this onehttp://sound.westhost.com/project113.htmCould I get some advice on whether that is a decent design or not? Also, I would like to make it as small as possible and I like to work with 0402 and 0603 size resistors and caps if possible. Can anyone tell me what parts should be rated for some wattage? I am guessing that the 4.7 ohm resistors should be of higher wattage. How low can I go? I was thinking of running it with 3 or 4 Li-Ion batteries for the top rail and 3 or 4 Li-Ion batteries for the bottom rail to make it portable.Any gotchas I should be aware of? I have a pair of Sennheiser 555 headphones that I want to build this for. They sound great just running out the headphone jack on my phone or laptop, but from what I have read they should sound a bit better with some real power behind them.I am not set on that schematic and am open to any other circuits. Thanks

author: Richard Crowley
author_rank: Super Contributor
timestamp: November 10, 2015, 01:09:53 pm
content: So if you plug your Sennheiser 555 headphones into a high-power source like a traditional stereo receiver, can you really hear a significant difference?The Elliot design is certainly "decent" but it is not very "portable" in any practical sense of the word. When you have so many (relatively) giagantic components like all the electrolytic capacitors and output transistors, it is not at all clear why you would be concerned about the size of the smallest components (the resistors). Getting them down to 0402 or even 0603 seems pointless when they are already such a tiny part of the size of the whole circuit.

author: homebrew
author_rank: Frequent Contributor
timestamp: November 10, 2015, 03:09:33 pm
content: I don't see the 'superb' characteristics either. It might be a working amplifier - I mean why not. Yet another Class-B design. But I would be almost certain that standard integrated one-chip solutions might have even better audio performance ...

author: DmitryL
author_rank: Regular Contributor
timestamp: November 10, 2015, 03:21:44 pm
content: Why not to build a more decent thing from the same author ?http://sound.westhost.com/highspeed.htmI'm pretty happy with that device.Not for the beginner though..

author: Fungus
author_rank: Super Contributor
timestamp: November 10, 2015, 03:45:54 pm
content: Quote from: homebrew on November 10, 2015, 03:09:33 pmAgree.a) In whose opinion is it 'superb'? Compared to what?b) Taking the exact same signal you're listening to now and passing it through an amplifier can only make it louder, it can't possibly improve it.If you have USB output then you'll have a really hard time beating something like this:http://www.ebay.com/itm/141767703384(seller chosen at random, yes I own one of those and have listened to it a lot)And... that one comes in a nice box. You can get aPCM2704DAC devices without a box for farlessthan that.

author: dom0
author_rank: Super Contributor
timestamp: November 10, 2015, 04:04:07 pm
content: Quote from: blueskull on November 10, 2015, 03:25:11 pmWhat if I told you the diamond buffer is just an emitter follower, too?e:I don't really like highspeed.htm for their fixed ~10 ? output impedance. There are better ways around that.

author: tszaboo
author_rank: Super Contributor
timestamp: November 10, 2015, 04:30:03 pm
content: Quote from: jdraughn on November 10, 2015, 12:19:03 pmI made the same mental mistake years ago. Think of a resistor, where sound goes through it. With higher volumes/amplitudes, it will self heat. Say, temperature of the resistor changes 1 degrees, and you used a 100ppm/degrees resistor. 100ppm is -80dB. It will depend on the circuit whether or not this is audible, or at least it will worsen your THD and other results. just 600uA over a 1K resitor is almost a miliwatt, it will heat up a 63 miliwatt reistor. So I'm afraid, those 0402,0603 resistors are too susceptible to these secondary effects.

author: DmitryL
author_rank: Regular Contributor
timestamp: November 10, 2015, 04:31:52 pm
content: I don't really like highspeed.htm for their fixed ~10 ? output impedance. There are better ways around that.Hmm.. remove 10 ohm resistor and you'll have much lower output impedance

author: suicidaleggroll
author_rank: Super Contributor
timestamp: November 10, 2015, 04:32:46 pm
content: Quote from: Fungus on November 10, 2015, 03:45:54 pm:rolleyes:I know this forum is crazy anti-audiophile, but come on...you can't possibly think that any device capable of generating a 20-20kHz tone is also capable of preserving that tone, without distortion or attenuation when driving any load between 10-1000 ohms, can you? Why even bother having an amplifier or a buffer in the first place? Why not just drive the load straight off the DAC?Why is it that many people here will spend thousands of dollars on multiple 8.5 digit multimeters to measure standard circuits that couldn't possibly need more than 3.5 digits of accuracy, but as soon as any audio-related topic is brought up, anything more than 8 bits of resolution and a single op-amp buffer is "audiophoolery"?The headphone outputs in many devices are shit. Not all, many decent stereo receivers have perfectly adequate ones, but phones and laptops are notoriously crap. Plug a decent set of headphones into most of them with and without an amp and you'd be hard-pressed NOT to hear a significant improvement with the amp. Of course the DAC in most of them is crap too, so adding an amp is only half the battle...OP - I know nothing about that amp, but I do have experience with a lot of AMB's designs. The Mini3 is very portable and works great, and with the optional li-ion battery it lasts for a very long time between charges.

author: Marco
author_rank: Super Contributor
timestamp: November 10, 2015, 04:34:52 pm
content: Quote from: blueskull on November 10, 2015, 03:25:11 pmAssuming a very low impedance source does a diamond buffer actually have better linearity than an A/B stage?

author: dom0
author_rank: Super Contributor
timestamp: November 10, 2015, 04:44:18 pm
content: Not really. If you use transistors with very good complimentary-ness approximately identical collector currents in the first and second stages you'll get some distortion cancellation. It's not really relevant in a closed-loop system.Quote from: NANDBlog on November 10, 2015, 04:30:03 pmThis increases low frequency distortion (the thermal mass plus the thermal resistance to ambient acts pretty much as a 1st order low pass), incidentally low frequency distortion of speakers and headphones is already pretty bad. I would worry more about risk of thermal failure if someone inputs too high input levels and such.

author: DanielS
author_rank: Frequent Contributor
timestamp: November 10, 2015, 05:20:18 pm
content: Quote from: suicidaleggroll on November 10, 2015, 04:32:46 pmI would expect any decent signal generator to do a fairly good job from 50 ohms to infinity at the very least - driving 50 ohms is what they are designed for. But that signal is not straight out of a DAC, it is already internally buffered by op-amps, just like most audio sources do too, but not all sources have low impedance output drivers and even when they do, they are only designed for standard 1-2Vpp line-level output which is nearly useless for driving high impedance headphones like the 120 ohms 555.

author: Fungus
author_rank: Super Contributor
timestamp: November 10, 2015, 06:04:08 pm
content: Quote from: suicidaleggroll on November 10, 2015, 04:32:46 pmAssuming current capability isn't the problem; the only difference between a 10 Ohm and a 1000 Ohm load is the voltage needed to power it to the required level. He's not complaining about the volume level so I don't think increasing the voltage will help. Current drive capability? That's what capacitors are for. Almost any old capacitor will do at 20kHz.Quote from: suicidaleggroll on November 10, 2015, 04:32:46 pmBecause a typical DAC isn't designed to output any possible voltage range, it's assumed you'll connect it to an amplifier. They don't give DACs much current drive ability either, and for the same reason.His laptop/phone already has an op-amp in it and he says his headphones "sound great" when connected. The problems he has (if any) aren't voltage/current related, they're about noise floor, dynamic range, etc. Getting an external DAC is therefore a good start. OK, it doesn't solve the problem of connecting them to his phone, but it's a start. Probably a much better start than building that amplifier. For $8 I'd get one for the laptop. If the phone suddenly sounds a lot worse than the laptopthenstart working on that problem.PS: If you want a PCM2704 with an amplifier they do those too, eg.:http://www.ebay.com/itm/121292071586Yes, I own one. No I can't hear any difference between that and the non-amplified one (not with my headphones anyway, YMMV).Don't worry, there's a whole subculture dedicated to swapping the capacitors in those boxes if that's your thing (or you can justpay a couple of bucks extrafor ELNA brand capacitors - the audiophile's choice)

author: krivx
author_rank: Frequent Contributor
timestamp: November 10, 2015, 06:38:32 pm
content: Quote from: suicidaleggroll on November 10, 2015, 04:32:46 pmHear, hear! Pun intended.

author: suicidaleggroll
author_rank: Super Contributor
timestamp: November 10, 2015, 06:59:03 pm
content: Quote from: Fungus on November 10, 2015, 06:04:08 pmOf course current capability is the problem! What does rail capacitance have to do with the source's output impedance? Or are you actually suggesting putting a capacitor on the output of the source, as if that would help drive a low impedance load?Quote from: Fungus on November 10, 2015, 06:04:08 pmA 5V DAC has plenty of voltage swing for most headphones.Quote from: Fungus on November 10, 2015, 06:04:08 pmSame with the crappy output stage in most phones/laptops...

author: Alex Nikitin
author_rank: Super Contributor
timestamp: November 10, 2015, 07:03:39 pm
content: Quote from: jdraughn on November 10, 2015, 12:19:03 pmI've designed a number of production headphone amps (the first one was in 1994, IIRC and there are some still manufactured). To choose a suitable circuit you need to look at the requirements.Well, let's list main points:1) Portable with a battery supply2) 120 Ohm nominal headphone impedance3) More power and better quality than a usual portable device output.4) Reasonably small size5) Not overcomplicated.#1 and #4 more or less exclude the circuit you've linked.#2 and #3 means a fairly healthy output voltage (and hence the supply voltage too) - at least 3-4V RMS, ~12V p-p, so at the very least 12V supply is required, more is better.If you can leave with two 6V (or even two 12V) batteries, a good choice would be just a quality dual opamp with healthy current output capabilities, for example the LM6172, set for an inverting gain about 5, with 10K volume control on the input and 10 ohm series resistors on the output.CheersAlexP.S. - here is the circuit, you would need a dual switch for the batteries and perhaps an LED to show the power is on.

author: Lightages
author_rank: Unknown
timestamp: November 10, 2015, 08:03:34 pm
content: It is fun to experiment. It is fun to design circuits and build them. There is great satisfaction in having a nice project that is complete and working like you want at the end. If these are your goals in building the headphone amp then be prepared to spend much more than you can buy one for, such as recommended by Fungus. Designing, building, and redoing it all over it again many times until you are happy is not the cheap route.@Fungus:The first USB DAC you pointed to looks like a steal. I am going to get one to play.

author: calexanian
author_rank: Super Contributor
timestamp: November 10, 2015, 09:03:01 pm
content: The op amp driving a B class complementary output assist transistor circuits work reasonably well, but they are a far way off then it comes down to THD from purpose built headphone drivers. If you are just playing around and like the way elliott presents his projects i would recommend just building two low voltage discrete full complimentary power amps at say +/- 10 volts. You will learn about long tail pair stages, biasing BJT's and the basic complementary power amplifier circuit that is at the heart of all of the amp on a chip systems such as the 3886 and such.If you just simply want to build a project there are many many kits out there with everything ready to go.If you want to save money, just buy a cheap rolls headphone amp from guitar center or amazon for $20

author: retrolefty
author_rank: Super Contributor
timestamp: November 11, 2015, 12:11:33 am
content: QuotePot calling kettle black your saying? Difference is the volt-nuts don't obtain their 8.5 meters to measure 'standard circuits' but rather to measure and compare with their other meters. Sort of measurement masturbation?There is some subjective excesses in most all of us when you are talking a favorite endeavor.

author: Fungus
author_rank: Super Contributor
timestamp: November 11, 2015, 07:51:33 am
content: Quote from: retrolefty on November 11, 2015, 12:11:33 am8.5 digit meters are also objective. You can tell if they're working, you can measureexactlyhow much better instrument A is than instrument B.With audio there's a fair amount of subjectivity (and personal taste!) involved. Some people actuallywantdistorted (aka "warm") sound.It also varies depending on what you had for lunch.

author: jdraughn
author_rank: Regular Contributor
timestamp: November 11, 2015, 01:10:06 pm
content: Everyone - thank you for your input. I am going through it all and studying your answers now.

author: krivx
author_rank: Frequent Contributor
timestamp: November 11, 2015, 01:51:23 pm
content: Quote from: retrolefty on November 11, 2015, 12:11:33 amThe response to the 8.5 digit buyers is not nearly as dismissive or even hostile as that for people doing anything to do with audio. An extremely objective design case backed with rigorous data will still get derailed with jokes about magic crystals or claims that amplifiers can only make signals louder. I think it's a shame - low-noise and low-distortion design can be very interesting but it's not received well on the forum.

author: Lightages
author_rank: Unknown
timestamp: November 11, 2015, 02:57:29 pm
content: Quote from: krivx on November 11, 2015, 01:51:23 pmYeah, I think that there are many on the forum here who jump on audio design as being woowoo even if it is practical and science based design. I think that they are just parroting the behaviour of the audiphool bashers without understanding the reasons and therefore bash anything as soon as it refers to audio design.To me a good headphone design needs to be low noise, low output impedance (<2 ohm), and of course low noise/distortion on the order of less than 0.05%.The original circuit referenced by the OP is a good start to play with. Some people just run headphones directly from NE5532 op amps. If this is your first design and project, then going for the smallest parts is not going to make it easy. Start with through hole parts and make it easy to make changes.

author: dom0
author_rank: Super Contributor
timestamp: November 11, 2015, 04:20:10 pm
content: btw. here's a lot of data on headphones:http://www.innerfidelity.com/images/AllGraphs.pdf

author: retrolefty
author_rank: Super Contributor
timestamp: November 11, 2015, 04:28:53 pm
content: Quote from: Fungus on November 11, 2015, 07:51:33 amBoth groups, volt-nuts and audio-nuts, are married to their passions.The audio group judges their equipment and improvements by listening to music not sine waves, so measurements will never be the end all of attempting improvements in their journey to audio nirvana.The volt-nuts (along with time-nuts) are seeking the nirvana of exact repeatable measurements at their finger tips to go forth and make judgments and decisions on circuit and other equipment improvements they dwell in.Both are just examples of human passions pushing towards the edges of extreme behaviors at times. Outside of a commercial endeavor there is probably little justification for anyone to obtain a 8 1/2 digit DMM. Conversely a high end audio reproduction system does not require a budget of tens of thousands of dollars chasing a subjective immeasurable goal.

author: Fungus
author_rank: Super Contributor
timestamp: November 11, 2015, 05:29:36 pm
content: It's understandable that 'volt nuts' are better tolerated in EEVBLOG forums - test gear is the subject matter!I've spent quite a few hours listening to and comparing audio equipment. I've always been of the opinion that most of the audible difference is in the speakers. Once you've spent about $200-$250 on an amplifier then you're pretty much done as far as electronics goes.(nb. This is for home audio. Two speakers, average sized room)Sources? It's all digital these days so it doesn't make any difference.Speakers? You have to spend quite a lot to reach a plateau. Maybe $1500.And ... the best thing you can do to improve most audio setups is to move the speakers around to find the best position/height relative to the listener and add some acoustic conditioning to the room.

author: retrolefty
author_rank: Super Contributor
timestamp: November 11, 2015, 05:34:16 pm
content: Quote from: Fungus on November 11, 2015, 05:29:36 pmYou sir, sound like a 'true' audiophile.

author: suicidaleggroll
author_rank: Super Contributor
timestamp: November 11, 2015, 05:43:24 pm
content: Quote from: Fungus on November 11, 2015, 05:29:36 pmI don't disagree with anything you've said here, and in fact your comments mirror my own equipment to a large degree. All digital sources, I don't care what they are, one nice DAC, about $300 in amps, and about $2000 on a pair of good towers. No room treatment (no way the wife would go for that), but I do have a self-tuning digital RTA/EQ in the mix that does a LOT to reduce resonances at the listening position.My only confusion is why you're fine spending $200-250 on an amp for speakers, but are under the impression that no amp is required for headphones? For little $2 ear buds sure, but a lot of high end headphones are just as hard to power as a small set of bookshelf speakers. There's no way the crappy little chip amp in a phone can do them justice. It can get them to make noise, sure, but that's a long way off from performing correctly.

author: Richard Crowley
author_rank: Super Contributor
timestamp: November 11, 2015, 05:52:04 pm
content: Quote from: Fungus on November 11, 2015, 05:29:36 pmThat wasn't obvious to me upon viewing the title. It is more obvious by spending some time here seeing the videos and forum topics.QuoteAnd, for those of us who produce audio and video, in the MICROPHONES.And generally is it axiomatic that physical to electrical (and vice-versa) TRANSDUCERS have orders of magnitude more impact on the sound than ANY electronics (except, of course, for electronics that is DESIGNED to distort the signal like e-guitar "fuzz boxes" et.al.)QuoteAnd, curiously enough, much the same with microphones (if not more so).QuoteAnd, again, exactly the same with microphones. At least those of us who record "classical" and "natural/ambient" kinds of things. Orchestras, bands, choirs, etc. Selection of which microphone to use in which situation often involves spending hours in the venue during rehearsals to discover just the right spot to put the microphones. Since they don't "hear" like our ear/brain systems do, it is much more critical to get the mic in just the right position to capture the ideal ratio of direct/ambient sound to simulate what our ear/brain systems do for us automatically.And, also in the cine/video world. Our eye/brain systems accommodate a much wider range of exposure and color temperature than ANY film/camera can hope to do. It takes hours/days to "light" a scene or a venue to produce decent pictures that the audience will accept as "natural".Of course modern, "pop" multi-mic, multi-track recording where the musicians may not even be performing "together" (in the same space and/or at the same time) and the song is effectively created in post-production editing is a completely different matter.

author: Richard Crowley
author_rank: Super Contributor
timestamp: November 11, 2015, 06:01:39 pm
content: Quote from: suicidaleggroll on November 11, 2015, 05:43:24 pmOf course, that is a compromise you chose to live with. EQ (even automated by RTA) is only ONE dimension of a 3 or 4 dimensional proper listening space. There are most likely ways of doing acoustic room treatment that your wife would accept. Especially if labeled as "redecoration".QuoteWhile true, it is equally true that you don't need a $200 or more amp to drive even "elite" headphones. There is a fuzzy crossover point where true pursuit of high-fidelity reproduction becomes a completely subjective fetish. Certainly a more socially acceptable fetish than many others.

author: retrolefty
author_rank: Super Contributor
timestamp: November 11, 2015, 06:18:01 pm
content: QuoteI agree with the possible exception of electrostatic headphones? I seem to recall they have rather exotic driving requirements, high voltages? Never listened to any of those types but maybe someone here has and knows if they required a specific amp driver type?

author: Fungus
author_rank: Super Contributor
timestamp: November 11, 2015, 06:30:05 pm
content: Quote from: suicidaleggroll on November 11, 2015, 05:43:24 pmYes, that can be a problem. Speakers are usually unhappy against walls and miserable in corners. They really need to be out in the open and quite close to the listener to sound good.Hint for the non-singles: Mine are on little stands so I can just pick them up and move them to the sweet spot when I need them.Quote from: suicidaleggroll on November 11, 2015, 05:43:24 pmSome sort of amp is required, obviously.My $300 headphones are supposed to be medium-difficult to drive but the $8PCM2704device I linked earlier works just fine. I actually bought another DAC with PCM2704+extra amplifier to compare. There really isn't any difference in sound though (not for me+my headphones anyway, YMMV).Telephones are another story. I've never tried using headphones with one but I know from experience that iPhone outputs are weak (apparently it's because Apple is afraid of lawsuits from teenagers who went deaf because they listened to their music too loud).So... I'll believe you might need an amplifier for headphones connected to a telephone.I don't see why it would be an expensive/exotic amplifier though, eg. TI have a wholeselectionof headphone amps for under $1 (and I'm sure other manufacturers do too).I'm fairly sure you don't need to build something like this to drive your headphones, no matter how exotic they are:

author: langwadt
author_rank: Super Contributor
timestamp: November 11, 2015, 06:31:41 pm
content: Quote from: Fungus on November 11, 2015, 05:29:36 pmspeakers can easily have 10s of percent distortion and all kind of other artifacts so they are the weak link.amplifiers with unmeasurable noise and distortion and a bandwidth way beyond audio is easy

author: Fungus
author_rank: Super Contributor
timestamp: November 11, 2015, 06:41:45 pm
content: Quote from: retrolefty on November 11, 2015, 06:18:01 pmYou don't connect electrostatics directly to an ordinary headphone socket, they come with their own custom amplifier.A lot of them use wall warts for power so I assume you could build a battery pack if you really want to.Unless it's the amp shown below...

author: retrolefty
author_rank: Super Contributor
timestamp: November 11, 2015, 06:45:19 pm
content: Quote from: langwadt on November 11, 2015, 06:31:41 pm

author: Richard Crowley
author_rank: Super Contributor
timestamp: November 11, 2015, 06:56:37 pm
content: Quote from: retrolefty on November 11, 2015, 06:18:01 pmYou reminded me that I have a pair of Koss ESP-9 electrostatic headphones. I am going to go and dig them up and refurbish them.They certainly are much different than your typical "dynamic" (coil of wire and magnet) transducers. They take a high voltage (but very low current) signal. They probably take LESS actualpowerthan dynamic headphones, but much different voltage/current levels. That doesn't mean that it takes thousand-dollar amps to drive it. Simply proper low-distortion, high-voltage drivers. Pretty easy to do with modern semiconductors.The original product came with a largish (~150mm cube) interface box which was mainly a pair of step-up transformers passively driven from the high-power speaker output of your stereo amplifier. I believe they rectified part of the high-voltage signal into the "exciting" voltage required for the transducers (IIRC?)

author: Richard Crowley
author_rank: Super Contributor
timestamp: November 11, 2015, 07:06:27 pm
content: Quote from: langwadt on November 11, 2015, 06:31:41 pmAnd microphones, as well. And furthermore, there are many "vintage" microphones with notably UN-flat frequency response. But people have come to like that "sound" and contemporary reproductions of some of those "classics" retain the anomalies despite modern technology that allows much more accurate performance.QuoteAnd mic input preamps, as well. But there are still people who scavenge old tube junk specifically for the "colored" sound of the transformers.And as for D/A converters, it is quite amusing to read which chips are found in both cheap consumer mass-market products AND in premium audiophle and professional products. There is an epic thread over on Gearslutz: "Audio interfaces and their AD/DA chips LISTED"https://www.gearslutz.com/board/geekslutz-forum/542009-audio-interfaces-their-ad-da-chips-listed.html

author: Fungus
author_rank: Super Contributor
timestamp: November 11, 2015, 07:34:56 pm
content: Quote from: langwadt on November 11, 2015, 06:31:41 pmInteresting that everybody is agreeing with this, it's almost the opposite of what HiFi magazines recommend.(usually you "spend at least as much on the amplifier as the speakers")

author: tooki
author_rank: Super Contributor
timestamp: November 11, 2015, 08:08:14 pm
content: Quote from: Fungus on November 11, 2015, 05:29:36 pm^^ This.So much truth. I've been saying the same thing for years.

author: Alex Nikitin
author_rank: Super Contributor
timestamp: November 11, 2015, 08:14:08 pm
content: A bit off-topic however I feel I have to say that:To design a good sounding electronics is not a trivial task. There is much more to it than appears to an electronics engineer who has little to no experience in that very special area. Just as a simple example - yes, transducers are in theory the most non-linear parts of the audio chain. However for that very reason the electronics facing those devices on both ends is difficult to design right. Even a "perfect" amplifier has to work not with a dummy resistive load but with averynon-perfect speaker. So the real importance is how these two devices work together (and that is not an easy thing to get right, believe me, I've designed a number of amplifiers, including some very good ones, and some not so good). It is like in any specialised area of electronics, as soon as you start to dig deep you have to change your perspective and to learn some nuances. And there is usually a good scientific ground to that knowledge, just many things that accepted as of no or little influence in "generic" electronics suddenly become important. In a similar way you pay attention to tellurium copper terminals and plugs, and to your lab temperature down to 0.1 degree precision if you are a volt nut.CheersAlex

author: retrolefty
author_rank: Super Contributor
timestamp: November 11, 2015, 09:30:32 pm
content: Quote from: Fungus on November 11, 2015, 07:34:56 pmThe 'old rule' as i recall is to spend 50% of budget on speakers the other 50% on everything else not just amp.As far as magazines recommendations go recall that they are dependent on ad income so must promote (or at least not discourage) spending.

author: Fungus
author_rank: Super Contributor
timestamp: November 11, 2015, 09:32:33 pm
content: Quote from: Alex Nikitin on November 11, 2015, 08:14:08 pmAs an amplifier designer, how much should a good audio amplifier with, say, 70-100W of power cost on the street?A quick google search for "class ab 100w audio amplifier IC" came up withthisin the first few results.Low noise ... 0.01% THD ... 6 Euros in one-off quantity on Mouser.I suspect the 'amplifier' problem has been studied, the design compromises have been made and it's now available in a monolithic packages from a dozen different manufacturers.

author: Richard Crowley
author_rank: Super Contributor
timestamp: November 11, 2015, 09:33:08 pm
content: Quote from: Fungus on November 11, 2015, 07:34:56 pmThat is because we are speaking in the present tense.Things were significantly different back 50 years ago when "HiFi magazines" were making this recommendation.That was back when people were still using vacuum tubes and "heavy iron" transformers and amplifier distortion figures were integer numbers.

author: Lightages
author_rank: Unknown
timestamp: November 11, 2015, 10:07:04 pm
content: I certainly can see wanting to use a separate headphone amp as many devices have horrible output stages. That is probably getting much less common as good parts are getting to be more like jelly bean parts. Some headphones need a bit more voltage as they are higher impedance so this is where a good headphone amp can help.The bigger concern is the analog output of many notebooks, laptops, and tablets. A USB DAC can get the analog outside of that really noisy environment and into a better isolated one where things can be cleaned up and a proper driving amp for the difficult headphones can be implemented.

author: Lightages
author_rank: Unknown
timestamp: November 11, 2015, 10:17:10 pm
content: Quote from: retrolefty on November 11, 2015, 09:30:32 pmYes, "OLD" rule. The new rule, spend as much as you can on speakers and fixing your room. Almost every amp and sound source made now far surpass the capabilities and fidelity of the sources and amps way back when. The same with headphones. Spend as much as you can on them. If you are spending more than $100 (or even arguably less) on a headphone amp then you have priorities that don't match reality. I find it really funny when some people go crazy over hyped headphones, toob amps, and then listen to 128kbps MP3.

author: Alex Nikitin
author_rank: Super Contributor
timestamp: November 11, 2015, 10:23:56 pm
content: Quote from: Fungus on November 11, 2015, 09:32:33 pmWell, somebody may be perfectly happy with that. I'm not, as simple as that. I generally avoid listening to digital sources of "CD quality" and below altogether, though I've designed several pretty good CD players. On the other hand, high prices are not an indication of quality, my home system (speakers, stands, amplifier, turntable, cables and cassette decks) did cost me probably about £1500 in total (all second hand) and I haven't changed it much for last 7 years or so.CheersAlex

author: Marco
author_rank: Super Contributor
timestamp: November 11, 2015, 10:40:28 pm
content: On the other hand ears aren't even particularly linear.

author: AF6LJ
author_rank: Unknown
timestamp: November 11, 2015, 10:43:09 pm
content: Quote from: Fungus on November 11, 2015, 06:41:45 pmOh But think of all the fun you would have building a power supply...Lots of LIPO batteries, a transistor driven high voltage supply, DC for the heaters....Ah Hell Screw it...Build a vibrator supply....

author: retrolefty
author_rank: Super Contributor
timestamp: November 11, 2015, 10:49:35 pm
content: Quote from: Marco on November 11, 2015, 10:40:28 pmNor are they identical human to human. It's a wonder any subjective description of sound systems is worth offering. Measurement and double blind testing is the only path to audio 'truth' I suspect.

author: Fungus
author_rank: Super Contributor
timestamp: November 11, 2015, 11:16:28 pm
content: Quote from: Richard Crowley on November 11, 2015, 09:33:08 pmI remember them saying it 20 years ago (which was probably when I last read a HiFi magazine).But let's see what the web says today:From:http://www.cnet.com/news/how-to-buy-a-hi-fi-system/"For regular speakers I like the Wharfedale Diamond 10.1 ($349/pair), matched with a JoLida JD301RC integrated amplifier ($425), and a Schiit Audio Bifrost DAC ($349)" (Speakers: 31% of the budget)"If you have a big room, and really want to party, go for bigger speakers, like the Zu Audio Omen Standard ($1,500/pair) with a Peachtree Audio integrated amp/DAC ($1,799)." (Speakers: 45% of the budget)

author: Lightages
author_rank: Unknown
timestamp: November 11, 2015, 11:21:32 pm
content: Quote from: blueskull on November 11, 2015, 10:29:45 pm16 bit is 96db. You cannot add that to the range of human hearing. You need to represent the range of human hearing within those bits....... Hearing damage occurs if you listen to sounds louder than 80db for long periods, 85db for shorter, and for over 90db you better start using hearing protection.Everything you wanted to know about hearing damage but were afraid to ask:https://www.osha.gov/dts/osta/otm/new_noise/

author: Fungus
author_rank: Super Contributor
timestamp: November 11, 2015, 11:24:12 pm
content: Quote from: blueskull on November 11, 2015, 10:29:45 pmIt's enough for playback. Not enough for mixing/recording.

author: retrolefty
author_rank: Super Contributor
timestamp: November 11, 2015, 11:31:46 pm
content: Quote from: blueskull on November 11, 2015, 11:26:53 pm

author: Richard Crowley
author_rank: Super Contributor
timestamp: November 11, 2015, 11:33:50 pm
content: From casually browsing their websites, both Zu Audio and Peachtree are "woo-woo" audiophool purveyors (I was going to use a stronger word.)Zu Audio, for example claims for their "premium" Ethernet cable" "Music was more relaxed, information and instrument color was easier to hear but treble and attack was not emphasized. Still, presence was more vivid in a natural way, and bass was both clearer and had better weight." This is for a DIGITAL bitstream of ones and zeroes mind you. Their lack of technical understanding is more than counterbalanced by their vivid imagination.Since we are talking about gear far removed from the mainstream, any statistics we gather from them are just as questionable as the underlying data.

author: Fungus
author_rank: Super Contributor
timestamp: November 11, 2015, 11:35:59 pm
content: Quote from: Alex Nikitin on November 11, 2015, 10:23:56 pmI didn't say you should be, I'm just saying you can probably build a respectable audio amp using those and retail it for under $100.My question to you is: How much would an audio amplifieryou'dbe happy with cost on the street?You're an amplifier designer, I'm not. That's why I'm asking.

author: Fungus
author_rank: Super Contributor
timestamp: November 11, 2015, 11:39:06 pm
content: Quote from: Richard Crowley on November 11, 2015, 11:33:50 pmIn other words, nothing much has changed in the HiFi reviewing business over the last few decades.Quote from: Richard Crowley on November 11, 2015, 11:33:50 pmcnet isn't mainstream?

author: Richard Crowley
author_rank: Super Contributor
timestamp: November 11, 2015, 11:45:02 pm
content: What does cnet have to do with anything? I was looking at the vendors websites directly.Not to say that cnet has any particular credibility, either.

author: Bassman59
author_rank: Super Contributor
timestamp: November 12, 2015, 12:04:48 am
content: Quote from: Fungus on November 11, 2015, 11:24:12 pmDAWs these days work with 64-bit floating-point math.-a

author: Fungus
author_rank: Super Contributor
timestamp: November 12, 2015, 12:38:17 am
content: Quote from: Richard Crowley on November 11, 2015, 11:45:02 pmcnet sent you to those websites.

author: f5r5e5d
author_rank: Frequent Contributor
timestamp: November 12, 2015, 03:03:19 am
content: 16/44 releases today are dithered - with noise shaped dithers tuned to our perception of low amplitude noisewith reasonable psychoacoustic weighting you get more perceived dynamic range than engineering calculated flat bandwidth noise integrationwith good dither and noise shaping you can actually hear a fractional lsb sine tone at ~3kHz more than 10 dB below the flat noise 16 bit calcthe dither + noise shaping is tuned to give best spot noise there, pushing the added dither noise to >10 kHz where our hearing sensitivity is lessCD res could be better than almost anything that was ever initially on classic analog magnetic tape"Loudness War" dynamic range compression however is still a big problem in commercial music releases - entirely due to artist/producer/marketing choice, not technology limitations

author: Alex Nikitin
author_rank: Super Contributor
timestamp: November 12, 2015, 08:22:35 am
content: Quote from: Fungus on November 11, 2015, 11:35:59 pm1) Not that chip, it is not suitable even for a half-decent amplifier.2) The 60W/ch integrated amplifier in my home system had a retail price about £200 in 1998 and was build in China, however I've designed it here in the UK. Another design of mine (40W/ch) from about the same year was made in the UK and sold for £250 retail. I guess that today we need probably to double these prices.CheersAlex

author: Alex Nikitin
author_rank: Super Contributor
timestamp: November 12, 2015, 08:55:47 am
content: Quote from: blueskull on November 12, 2015, 03:13:16 amHmm, I need to check few things before talking or not talking to you. IMHO, "CD quality" (16bit 44.1kHz) is crap compared even to a humble cassette at a standard speed. High resolution digital can be good it done properly (and that is not easy). Main problem for me is that there are very few good quality recordings available on high resolution formats. The introduction of the CD essentially killed the music recording and mastering skills, and the digital processing killed the recorded music quality.CheersAlex

author: Alex Nikitin
author_rank: Super Contributor
timestamp: November 12, 2015, 10:21:09 am
content: Quote from: wilfred on November 12, 2015, 09:11:23 amIf I'll call that project over-engineered it may be an understatement.CheersAlex

author: LA7SJA
author_rank: Regular Contributor
timestamp: November 12, 2015, 11:38:15 am
content: I have buildt a few of this amphttp://nwavguy.blogspot.no/2011/07/o2-headphone-amp.htmland they do sound neutral to my ears and my Audio Analyzer agrees.Johan-Fredrik

author: Marco
author_rank: Super Contributor
timestamp: November 12, 2015, 12:23:40 pm
content: Quote from: Alex Nikitin on November 12, 2015, 08:55:47 amI'd put some money on you not being able to distinguish between a tape playback and a good digital recording of that tape playback.

author: Fungus
author_rank: Super Contributor
timestamp: November 12, 2015, 12:27:16 pm
content: Quote from: Bassman59 on November 12, 2015, 12:04:48 amFloating point is good, but ... double precision? That's overkill. No microphone, ADC or any other source is going to output that resolution. Still, whatever floats their boat. I guess it's free these days.Floating point master, 16 bit integer playback? Seems good to me.

author: Fungus
author_rank: Super Contributor
timestamp: November 12, 2015, 12:38:12 pm
content: Quote from: f5r5e5d on November 12, 2015, 03:03:19 amDithering is explained in that video I posted.Quote from: Alex Nikitin on November 12, 2015, 08:55:47 amIt also mentions cassettes at about the 11 minute mark, right before he gets into dithering(short version: They're only about 6 to 9 bits, but tape hiss is actually an analog version of dithering so they sound better than the number of bits would suggest).

author: Alex Nikitin
author_rank: Super Contributor
timestamp: November 12, 2015, 01:09:35 pm
content: Quote from: Marco on November 12, 2015, 12:23:40 pmI am sure that you would require a DBT and a statistically good result to part with your money- and I won't agree to that because DBT in audio is a con, probably the biggest one, forget poor snake oil purveyors. If you want my subjective opinion, here it is: the chance to distinguish between the tape and it's digital copy depends on the source and the quality of the original tape recording as well as on the tape deck used - if we are talking about a standard speed cassette and a "CD quality" digital. It would be fairly easy for a high quality cassette recording and deck, however (if I want to cheat) it could be even easier for a poor and very noisy recording, because 16bit 44.1kHz are not capable of reproducing an analogue tape noise accurately. For a properly implemented double speed cassette you'll need at least 96kHz 24bit to be competitive. There is a 96kHz 24 bit sample of a choir performance on my web site that I've recorded on a cassette tape four years ago. If you reduce the resolution to 16bits and 48kHz, the quality of that recording noticeably suffers to my ear. I've started to work again (after a gap of 15 years) seriously with tape recorders about seven years ago when I've realised that I am not happy with the digital copies of my vinyl collection, even in a high (96kHz 24bits) resolution. I would prefer to go with digital because of the convenience, but I can not do much about my emotional reaction from music, so I keep it in an analogue domain as much as I can.CheersAlex

author: Fungus
author_rank: Super Contributor
timestamp: November 12, 2015, 01:25:55 pm
content: Quote from: Alex Nikitin on November 12, 2015, 01:09:35 pmWe'll let you choose the cassette, etc., no problem.Quote from: Alex Nikitin on November 12, 2015, 01:09:35 pmAnalog tape noise can be reproduced perfectly, it's mathematically identical to digital quantization noise. Watch the video I just posted. The relevant part is around the 9-12 minute mark but the whole video is worth a watch.The process of dithering is just about reshaping the digital "tape hiss" into something more desirable.

author: Alex Nikitin
author_rank: Super Contributor
timestamp: November 12, 2015, 01:57:32 pm
content: Quote from: Fungus on November 12, 2015, 01:25:55 pmWho are "we".1) I am not playing these guessing games, I have no time for that.2) I am not forcing anybody to share my point of view, I'm just expressing it. Feel free to disagree.Quote from: Fungus on November 12, 2015, 01:25:55 pmI have enough experience with all kinds of D-A and A-D processes for almost 50 years, thank you.CheersAlex

author: Marco
author_rank: Super Contributor
timestamp: November 12, 2015, 02:02:07 pm
content: Quote from: Alex Nikitin on November 12, 2015, 01:09:35 pmIt would be interesting to do a nice ~22 kHz minimum/linear phase high order low pass which rolls off over a couple kHz (brick wall filters are a bad idea) with 48 kHz decimation, round to 16 bit numbers and re-interpolate to 96 kHz with a high quality Sinc filter for a low resolution high resolution file.I'm not good enough at DSP to do it without spending too much time though :/

author: Fungus
author_rank: Super Contributor
timestamp: November 12, 2015, 02:28:33 pm
content: Quote from: Alex Nikitin on November 12, 2015, 01:57:32 pmSure, but I have doubts about what people are claiming, eg. that 96kHz, 24 bits isn't good enough.(If itreallyisn't good enough then you need to take a look at your equipment and/or process, not the bitrate).

author: f5r5e5d
author_rank: Frequent Contributor
timestamp: November 12, 2015, 07:47:46 pm
content: for headphone amp projects they are more often found with accompanying audiophoolerybut projects that have been posted, worked over, have comments in forums can be useful learning tools:Forums - Head-Fi.org Communityis an enthusiast site - with a diy sub forumwww.Head-Case.org-the obligatory spin-off "opposition site" of those critcal of head-fi's fanboyism and reputed commercial slantHeadwize is inactive but archived atHeadWize Library - Projects[edit: may have to dig on archive.org]you can still read/search the design/build threads for several popular diy projectssome diy project collections - now getting dated but useful links:HeadWize: DIY Workshop > Current DIY Headphone Amp OfferingsandDIY projects, kits - Head-Fi.org Community

author: dom0
author_rank: Super Contributor
timestamp: November 12, 2015, 08:28:04 pm
content: Quote from: Fungus on November 11, 2015, 09:32:33 pmIn a way, yes. Monolithic amplifiers can be very good and have excellent performance/price ratio. Discrete amplifier designs are still almost alwayscrapthat simply won't last (e.g. class AB output stages with Ube multipliers)In commercial applications class D is extremely important, too, of course. Not just for low end applications, but also for high-end applications. Today you will often find that even ICs designed for low end markets incorporate not simply PWM modulators but actually quite good SDMs. Class D can surpass 0.005 % THD+N today (actually, ten years ago, but let's not nitpick on time lines).Quote from: Richard Crowley on November 11, 2015, 06:01:39 pmWell said!QuoteYou should immediately visit a university clinic. Someone there is probably interested in doing some hearing tests with you.As a matter of fact, increasing the Fs from 48 kHz to XYZ kHz does not add any information in the audio band (<20 kHz)at all, and never has.Quote from: blueskull on November 11, 2015, 10:29:45 pmCalling bullshit. To, like, all points you make. Your dynamic range calculation is just utterly wrong (at 30 dB SPL average you are unable to perceive a 100 dB dynamic range). Studios, just by the way, use 24 bits or 32 bit float not because 16 bits aren't enough, but because dozens of post-processing filters simply add a lot of noise. Using a high resolution format keeps that noise waaaayy below anything someone can hear.QuoteUh, no, that's not how digital volume control in practical DACs/SDMs work. They won't reduce the effective dynamic range until quite some volume reduction, typically -50... -60 dB, because they directly fiddle around inside the modulator and don't simply scale the input PCM stream (which, yes, would proportionally reduce dynamic range. So in systems where no DAC volume control is used 24 bits makes sense - it still doesn't make sense to distribute 24 bit media.)

author: Richard Crowley
author_rank: Super Contributor
timestamp: November 13, 2015, 12:04:04 am
content: Quote from: blueskull on November 12, 2015, 08:43:31 pmPlease cite a convincing number of examples. I find that almost impossible to believe.Certainly there are high-end audiophool devices that use 24-bit DAC, not because they actually have any effect on the performance, but simply for "bragging-rights". And because with modern, mass-market monolthic technology, a 24-bit DAC costs only a few pennies more than 16-bit. Furthermore, remember that outside SACD (which not 1 in 10000 people has ever seen) there is no 24-bit CONTENT to play. Not to mention that every year there are a vanishingly small segment of the customer base who even listen to uncompressed audio of ANY word-depth.QuotePlease cite a convincing number of examples. I find that almost impossible to believe.QuoteAre there designs that operate the DAC at "full-scale" and then adjust the audio level in the analog domain? That has been a widespread practice from the low end to the high end practically since day-one. It is true that some designers have come to understand the downside of controlling reproduction DAC levels in the digital domain and are returning to analog controls.

author: Richard Crowley
author_rank: Super Contributor
timestamp: November 13, 2015, 04:12:11 am
content: 24-bits can record a dynamic range of 145dB. I can't think of ANY audio gear out in the Real World that has even that kind of dynamic range between its noise floor and full-scale clipping. You might be able to approach that dynamic range under carefully controlled laboratory conditions.32-bits can handle a dynamic range of 192dB. That is essentially the absolute limit of sound that can be produced in normal atmospheric pressure at sea-level. Of course no transducer (microphone or speaker) can handle anything remotely resembling that. Selling 32-bit audio DACs to consumers is essentially the very definition of AUDIOPHOOL.Most people who live in the Real World can't even appreciate the full 96dB dynamic range of 16-bit. Most of us live in a 60dB (11-bit) world between the quietest we can experience without travelling to the Deep Woods, vs. watching big jets taking off at the international airport.32-bit audio is simply a manifestation of the "Bit-Depth Wars" and has no practical value in the Real World (unless you have a vivid imagination.)

author: Synthetase
author_rank: Regular Contributor
timestamp: November 13, 2015, 04:50:09 am
content: Haven't had time to read the whole thread, but to the OP I can say I've built this amp and it works very well (it's also NOT a class B amplifier, it's AB). Distortion is too low to measure with my equipment. It drives practically any load with ease and I use it to drive a pair of HD800s (although I modified its output impedance to 4R for this task).However, it's not portable. If you're looking for portability, you could try P109 from the same site. It's easy to build on a piece of prototyping board and it's cheap.

author: Fungus
author_rank: Super Contributor
timestamp: November 13, 2015, 07:42:38 am
content: Quote from: dom0 on November 12, 2015, 08:28:04 pmI was wondering about that...When I looked for amplifier ICs on TI's website there were no class A/AB chips for anything over about 5W. All their power amplifiers are class D. "Class D" is even in the category title for their power amp section ("Mid/High-Power Class D Amplifiers")I haven't really been paying attention lately but I guess the world has moved on from when class D was only for "subwoofers and cars", and gone are the days when amplifiers were designed around their heatsinks.Unless you're an audiophool, in which case heatsink design is alive and well:nb. I'm not knocking the sound quality of class A/AB amplifiers, it just seems like newer technology is making them obsolete.

author: tooki
author_rank: Super Contributor
timestamp: November 13, 2015, 10:35:42 am
content: Quote from: blueskull on November 11, 2015, 11:26:53 pmNope. Because it's a bandwidth-limited signal, no additional data is required to achieve perfect (in the literal sense) representation of the sine wave through sampling, nor does additional data add anything. More bits simply reduce noise, but for this, 16 bits is already more than enough. Did you actually watch the video? He demonstrates this very concept.

author: dom0
author_rank: Super Contributor
timestamp: November 13, 2015, 12:39:01 pm
content: QuoteActuallyanysignal band limited to the sampling band.Quote from: Fungus on November 13, 2015, 07:42:38 amAh, their parametric search has a few bugs. TI still has a few AB power stages in their lineup, namely LM3886, LM3875, LM3856, LM4780 (=Two LM3886 dice packaged together). They also have a few HV input stages (LME49810, LME49811, LME49830, LM4702, ...), but I think they're starting to discontinue them.I don't think AB is obsolete just yet, for two reasons. First, class D has become very, very good, but still can't quite reach the best linear power amplifiers. Second, audio PAs are quite often found in laboratories as cheap drivers for stuff - in a laboratory people might not like the additional EMI introduced by a class D amplifier -- although it's inside (inter)national regulations.--As I mentioned above 24 bit DACs mostly make sense when you do digital volume control by scaling the PCM stream, which is a quite common thing to do.

author: Fungus
author_rank: Super Contributor
timestamp: November 13, 2015, 01:43:56 pm
content: Quote from: dom0 on November 13, 2015, 12:39:01 pmAlso for recording or any source where you might not have optimal levels set.

author: Richard Crowley
author_rank: Super Contributor
timestamp: November 13, 2015, 03:11:12 pm
content: Quote from: Fungus on November 13, 2015, 01:43:56 pmYes, definitely. I always use 24 bit when recording live events. Because it gives you the dynamic range to handle the kinds of unexpected peaks encountered especially from amateur performers. And especially when recording multi-track where you can't keep an eagle-eye on every microphone.And in post-production editing, most DAW products use 32-bit arithmetic internally. But creating a final delivery mix more than 16 bit is essentially pointless. For that matter, MP3 is far more often the delivery format of choice.

author: Lightages
author_rank: Unknown
timestamp: November 13, 2015, 04:43:52 pm
content: The OP wants to build a headphone amp and he has to wade through a flood arguments over digital bit depth and digital theory?

author: retrolefty
author_rank: Super Contributor
timestamp: November 13, 2015, 05:03:49 pm
content: Quote from: Lightages on November 13, 2015, 04:43:52 pmAbout par for this site. It's part of the drama that draws us like bees to honey.

author: Richard Crowley
author_rank: Super Contributor
timestamp: November 13, 2015, 06:34:14 pm
content: "Topic drift" is par for virtually ANY un-moderated online forum. Quite often, the "drift" turns out to be more interesting (and informative) than the original question/topic.

author: retrolefty
author_rank: Super Contributor
timestamp: November 13, 2015, 07:08:18 pm
content: Quote from: Richard Crowley on November 13, 2015, 06:34:14 pm

author: Fungus
author_rank: Super Contributor
timestamp: November 13, 2015, 07:58:07 pm
content: Quote from: Lightages on November 13, 2015, 04:43:52 pmThe OP's question was answered on the first/second page. He can stop reading there if he wants to.

author: AF6LJ
author_rank: Unknown
timestamp: November 13, 2015, 08:09:03 pm
content: Quote from: Richard Crowley on November 13, 2015, 06:34:14 pmI totally agree; in the case of this thread the original topic was interesting, the thread managed to get better.This whole bit depth / bit rate discussion has been going on for some time in the software defined radio community, especially since twelve bit DACs come up short in terms of performance.

author: Lightages
author_rank: Unknown
timestamp: November 14, 2015, 03:50:57 am
content: So "Fuck the OP and his post, we want to talk about something completely different!"? Sorry, but I don't get it. Why not start another thread if you want to talk about something completely different instead of hijacking? I thought this forum was better than that.I guess this is one of my pet peeves, thread crapping and hijacking.

author: Lightages
author_rank: Unknown
timestamp: November 14, 2015, 03:53:44 am
content: jdraughn:I would try building the first headphone amp you linked to and see how it goes. It is a good test to see how your construction and packaging techniques are. After that you can maybe improve or change the design, or try another. It is fun to experiment but don't worry about making it small until you have your final design that you like the most.

author: Marco
author_rank: Super Contributor
timestamp: November 14, 2015, 06:18:24 pm
content: Quote from: Lightages on November 14, 2015, 03:50:57 amThis is off topic for this entire forum, yet you have the audacity to complain about it being off topic for the post

author: Richard Crowley
author_rank: Super Contributor
timestamp: November 14, 2015, 07:04:08 pm
content: Quote from: Lightages on November 14, 2015, 03:50:57 amYes, apparently you don't get it. This is NOT "something completely different" it is an analysis of WHY people think they need special magic circuits for rather prosaic applications like accurately driving dynamic headphones. And furthermore a comparison of what we have available today in terms of monolithic ICs vs. what they had to work with decades ago when those circuits were designed.

author: Lightages
author_rank: Unknown
timestamp: November 14, 2015, 07:21:31 pm
content: Quote from: jdraughn on November 10, 2015, 12:19:03 pmjdraughn:What have you decided to build? I am curious.

author: Zero999
author_rank: Super Contributor
timestamp: November 14, 2015, 07:29:15 pm
content: I've recently used a TDA2003 amplifier module to drive several 50R headsets (mono only). It works fine gives reasonably decent sound quality. I did have some problems with it having poor supply rejection but thas was fixed with an RC filter followed by a TIP121 Darlington transistor on the positive rail.

author: dom0
author_rank: Super Contributor
timestamp: November 14, 2015, 07:33:00 pm
content: Very poor PSRR is normal with car audio ICs. Lots of people still don't get, that these ICs are unsuitable for use with transformer + filter supplies (and how bad these ICs actually are compared to even the stuff 20 years ago - it's 70s-90s car audio, maximum bang, minimum cost, quality doesn't matter).

author: madires
author_rank: Super Contributor
timestamp: November 14, 2015, 08:00:05 pm
content: I've built a small amp based on the TDA1519B for my PC speakers and it includes a headphone output with a 120 Ohms series resistor. It's powered by the PC's 12V rail (LC filter) and runs quite well. As long as I don't turn the output to max the audio is decent, also for headphones.The TDA2822M might be a good amp for headphones.

author: Lightages
author_rank: Unknown
timestamp: November 14, 2015, 08:18:47 pm
content: Why, WHY, would you put a 120 ohm resistor in series? High impedance outputs are a guarantee that you will have frequency anomalies.

author: dom0
author_rank: Super Contributor
timestamp: November 14, 2015, 08:28:48 pm
content: The response of headphones is optimized for ~1 ? drive impedance and/or 120 ? drive impedance.

author: Lightages
author_rank: Unknown
timestamp: November 14, 2015, 11:30:42 pm
content: Where did this 120 ohm source requirement for headphones come from? Headphones range from maybe 16 ohms to 600 ohms. A 120 ohm source guarantees problems.

author: Lightages
author_rank: Unknown
timestamp: November 14, 2015, 11:38:16 pm
content: OK, found the reason people want to use a 120 ohm source. From Wikipedia:Quoteon this page:https://en.wikipedia.org/wiki/Headphone_amplifierRead the whole article section on output impedance.So as I said, a 120 ohm source is detrimental. You want less than 2 ohms.

author: Zad
author_rank: Super Contributor
timestamp: November 14, 2015, 11:43:59 pm
content: Build it and see. Anything is better than the hundreds of theoretical designs discussed in Internet forums!Personally, for portable use I wouldn't bother with external transistors, I'd stick to a pair of op-amps, or a TPA6120 (current feedback amp, needs reasonable PCB design), but like I say, the best headphone amp is the one you actually build, not the one sat on a drawing board.

author: Lightages
author_rank: Unknown
timestamp: November 14, 2015, 11:47:01 pm
content: Yup, Zad, I totally agree. Even trying out a 5532 op amp, or some in parallel, would be a good and easy start.Like this simple one:https://easyeda.com/DiyGuy/NE5532_Based_Headphone_Amplifier_Circuit-53XfxrJ1i

author: f5r5e5d
author_rank: Frequent Contributor
timestamp: November 14, 2015, 11:52:59 pm
content: wanting low Z output over audio brings another bit of EE into play with feedback amplifiers and the capacitance of the headphone cable potentially resulting in loop oscillations"Zobel" series RC to gnd on a amplifier output to give damping is often seenpower amps for audio often use a series isolating Z such as inductor or L||Rop amp based headphone amps sometimes just use a R, at least for higher Z headphones 10-25 Ohms added in series doesn't give big FR error with typical single driver headphones

author: SeanB
author_rank: Super Contributor
timestamp: November 15, 2015, 08:47:39 am
content: My first PC amplified speakers was literally a car audio amplifier, driving 2 4R 10W speakers in plastic enclosures. Added a LC filter to the 12V supply taken from the PC, random choke from the scrapped radio it was sold with in the auction, and a 2200uF 16V capacitor from the same radio. Did the job for around a decade, stayed there with motherboard upgrades and was eventually scrapped when I changed case to fit an ATX supply in to power the then new Pentium Pro processor I bought.

author: madires
author_rank: Super Contributor
timestamp: November 15, 2015, 12:33:29 pm
content: Quote from: Lightages on November 14, 2015, 08:18:47 pmWhen I built the amp I've found several references claiming 120 Ohms to be the standard impedance for headphones. Another interesting thing is that the impression of the sound level is quite similar to my normal speakers. So I can just plug in the headphones and don't have to adjust the volume. Extra point for convenience

author: suicidaleggroll
author_rank: Super Contributor
timestamp: November 15, 2015, 02:18:39 pm
content: Quote from: madires on November 15, 2015, 12:33:29 pmThat still doesn't explain anything. This is not RF, you don't want to match the impedance. Headphones, like all speakers, have a very dynamic impedance. At one frequency they might be 120 ohms, while at a different frequency they might be 50, or 200. By sticking a a 120 ohm resistor in series, you've created a frequency-dependent voltage divider, so you frequency response is going to ride the headphone's impedance curve. That's not a good thing.Quote from: madires on November 15, 2015, 12:33:29 pmThere are a hundred other ways of accomplishing that without screwing up the frequency response of the headphones.

author: mich41
author_rank: Regular Contributor
timestamp: November 15, 2015, 02:45:39 pm
content: Headphones already have substantial voicecoil resistance in series with the "actual load" (i.e. moving diaphragm around). As I understand, getting reasonable FR involves matching this series resistance with any case resonance, damping, etc.The 120R standard was meant to give headphone designers some way to predict the total series resistance for given voicecoil resistance, which is something they control.120R fails miserably with multiple armature IEMs which contain highly reactive crossover networks.It isn't clear whether manufacturers really target 120R amps or not in actual products, I have never seen solid data on this.

author: f5r5e5d
author_rank: Frequent Contributor
timestamp: November 15, 2015, 07:06:55 pm
content: 120 ohms is dead as a standard - not much use with 1Vrms DAP and 16-32 Ohm IEMmatching Z is the wrong concept in driving speakers and headphones - in audio the long accepted assumption is that amplifiers are nearly Zero output Z Voltage Sources and most loudspeakers and headphones are built with that expectation, give their flattest frequency response when driven from a Vsource or at least most are most accurate to whatever FR they were designed for when driven from a Vsourcebut you can find exceptions too - some laud "current drive", others think some particular output Z may complement a specific loudspeaker or headphone - Sennheiser makes a amplifier for their 300 Ohm HD800 headphones that has 40 Ohms output Zbut matching Z really isn't a thing in audio amplifier/loudspeaker or headphones

author: dom0
author_rank: Super Contributor
timestamp: November 15, 2015, 09:22:15 pm
content: Quote from: suicidaleggroll on November 15, 2015, 02:18:39 pmI think the idea originated somewhere in maybe the 70s where it was common practice to just use a voltage divider from the main output (of the power amplifier for speakers) to drive the headphone jack on the front-panel. I guess transistors were expensive.

author: madires
author_rank: Super Contributor
timestamp: November 16, 2015, 12:22:21 pm
content: Quote from: dom0 on November 15, 2015, 09:22:15 pmI think you're right. The series resistor is a simple and inexpensive solution to whack in a headphone jack. If you want to add it the proper way you would add a small amp around 1W and maybe a dedicated volume control.For me the 120 Ohms resistors are fine since I don't wear headphones regularly and I can't say that the non-linear (regarding frequency) voltage divider causes any major issues for me. Maybe it's a perfect match for the frequency response and impedance of my inexpensive headphones

author: retrolefty
author_rank: Super Contributor
timestamp: November 16, 2015, 03:57:58 pm
content: Quote from: madires on November 16, 2015, 12:22:21 pmEven in the 70s some manufactures had models that did it right. I have A Sony 2000F (high voltage FET stereo preamp) that had a dedicated amp for headphones with their own dedicated volume control.http://www.thevintageknob.org/sony-TA-2000F.htmlMany, (at least me lol), still think the 70s was the high point in consumer stereo hi-fi equipment. This was pre PC computer days when a persons hi-fi system was the first to get disposable income spent for quality and performance.There was lots of competition from the Japanese manufactures that drove quite a horse-power race in receivers and amps. I have a Pioneer SX-1980 receiver that has 270 WPC rms and weighs like 90 pounds!Anyway your correct in that most stereo receivers just used resistor drop on output to drive the headphone jack(s).But a few higher end pre-amps included a separate headphone drive.

author: AF6LJ
author_rank: Unknown
timestamp: November 16, 2015, 04:27:51 pm
content: Quote from: retrolefty on November 16, 2015, 03:57:58 pmI would agree once you got past the consumer junk and poorly designed power amplifiers that had too much stage gain and required massive amounts of negative feedback.