Can you make a really good hifi amp by copying a late 70s schematic + good parts - Page 1
Forum section: electronics / general

author: Beamin
author_rank: Super Contributor
timestamp: June 27, 2018, 01:10:52 pm
content: ? I asked something like this before and got a tons of responses most really good but many rather conflicting. And one person saying those amps that come in DIP packages sound just as good as any high end hifi. So a better idea:Find a service manual for a really good amp from the 70's. Pick one that's not too complex but was known for really good sound quality like a marantz. Hand select the parts to the exact value with better than original tolerances and match the final output transistors to each other. These will probably be the most expensive parts. But if everything is silicon and not germanium you should be able to get the same or equivalent. The transformer might be hard to get the exact one but you would pick an amp that runs off common voltages. One other consideration do these amps have really big chokes in them? If so couldn't you just wind your own making it out of a big toroid since it's just wire with one value you could measure and duplicate? Or do A/B amps not have a choke?Lay it out on a nice hand made PCB and you would have a high end amp for the same price as a best buy amp... Maybe?Maybe make it in sections so you could later add a tube preamp. I know in Macintosh amps the sound quality is mainly in their preamps. Matching tubes might be difficult.When you match the transistors what are you matching, and what do you need to test; a curve tracer or scope? What about tubes? Can you measure tubes on an analog scope with regular probes even though they are high voltage and impedance? ?

author: dmills
author_rank: Super Contributor
timestamp: June 27, 2018, 01:43:41 pm
content: Most of the 70s stuff was done with SLOW output devices, think 2N3055, TIP31 and friends, you can do far better today, but a direct sub would probably hurt stability. The mosfet stuff of the 80's was mostly lateral parts that are well obsolete, in fact finding good mosfets for linear as opposed to switching operation at power is problematic these days.I would grab a copy of "Audio Power Amplifier Design" by Douglas Self, get a recent edition, and build his latest, likely to be as good as anything else out there, and he really doesn't do the tweaky bullshit, maybe also Bob Cordells book.For a valve preamp you are only looking at a couple of hundred volts, so a ten times probe (get one fixed at ten times) and a standard scope is fine.Your major cost is likely in metalwork and power transformer and for a one off you are never going to beat the local box shifter, that is not the reason to play.Regards, Dan.

author: Beamin
author_rank: Super Contributor
timestamp: June 27, 2018, 02:10:02 pm
content: Quote from: dmills on June 27, 2018, 01:43:41 pmAh that's really good to know. I actually came up with this idea when I was a teenager and bought a Marantz for $500 at 50 watts 2 channel. I found that 50 watts was better (both louder and cleaner) then any 100 watt amps including the top of line brands they sold at circuit city or best buy. Best buy didn't have decent amps besides maybe onkyo. So with this in mind I bought a pair of 100 watt speakers. Problem is they wanted true 100 watts like a Marantz 100 watts amp. I tried powering them with a 100 watt amp I bought at circuit city but was even less powerful then the Marantz's 50 watts. It was a Harmon Kardin I think, so I took it back. Plus the Marantz had 20x lower (THD) distortion on the specs the anything the box stores sold. Sony was 0.8%@100w Marantz was 0.03%@50w so big difference. Now I need a clean 100 watts to power them to get the bass/mid bass to come out and make them sound full. I will still build one of these amps at some point. If I had the funds I think they might be fun to build and sell for a small profit. I would totally buy one if I got to check it out and see it.Do you risk damaging the speakers of the amp if the amp is under powered?If the Marantz is Korean built in 2000 the caps won't be starting to go bad yet? I haven't used the thing in years. So it's a "low hour" set. I could see this in some Chinese amps since modern Chinese built TV's are starting to get bad caps five years latter.

author: Benta
author_rank: Super Contributor
timestamp: June 27, 2018, 02:14:58 pm
content: From the 90s and until today, the output bipolars of choice for audio seem to be the Sanken 2SA1216 and 2SC2922.The drivers vary widely.With the Sanken pair, you have to watch stability, as someone mentioned. They are 50 MHz parts, which is way above 2N3055/MJ2955 and 2N3773/6609.

author: NiHaoMike
author_rank: Super Contributor
timestamp: June 27, 2018, 02:27:13 pm
content: Nowadays, there are so many cheap analog input audio amplifier modules that there's little point building one from scratch. For a PSU, telecom "rectifiers" are very cheap on the surplus market.

author: Alex Nikitin
author_rank: Super Contributor
timestamp: June 27, 2018, 03:08:00 pm
content: Quote from: Beamin on June 27, 2018, 01:10:52 pmNo, most likely it would be a waste of time and money (though probably a lot of fun). To make a good amp from scratch requires much more than a "good" schematics and good components. More sense in buying a decent old amplifier and restoring it. If you want something unusual from the schematics point of view, find the 4330 integrated amp from Creek Audio .CheersAlex

author: rdl
author_rank: Super Contributor
timestamp: June 27, 2018, 03:20:09 pm
content: Speaker wattage ratings are for the maximum power it can handle, not what it requires. However, speakers vary in efficiency, so there are considerable differences from one to another in how loud they will be at a given power level.A Creek 4330 has been my main amp for nearly 20 years.These days it's driven from a different source.

author: chemelec
author_rank: Contributor
timestamp: June 27, 2018, 03:24:10 pm
content: QuoteUnder-PoweredAmps result in Square Wave Distortion, Especially at higher Volume levels.Speaker Cones Can't respond fast enough to Square waves, so this tends to tear the Speaker coils off of the Coil form.Eventually resulting in a Badly Damaged Speaker.As to High Quality Amps, The System is only as good as the Worst Component in it.AndYour SPEAKERS are the WORST Part of any Audio System.

author: Alex Nikitin
author_rank: Super Contributor
timestamp: June 27, 2018, 03:24:34 pm
content: Quote from: rdl on June 27, 2018, 03:20:09 pmThank you, it is always nice to see my old design going strong after all these years.CheersAlex

author: dmills
author_rank: Super Contributor
timestamp: June 27, 2018, 03:30:00 pm
content: Audio power is a funny thing, because it typically has a HUGE crest factor, 20dB is not uncommon, so even turned well up that 50W amp was probably averaging under 1W with the very occasional large spike.The way that the US consumer folks insist amps be specified does a poor job of dealing with this reality and actively encourages amps which clip just above their continuous rating, which is stupid design. I suspect your Marantz did not suffer from this, so that 50W was probably RMS Cont, but they may have gone for a design capable of much higher short term peak.Lots of volts from the transformer, with a limited thermal envelope is probably the way to go for HIFI, and use a simple transformer/rectifier cap sort of supply, it will deal with short term overload just fine where a switcher will often go into hickup mode.I second the comment about the speakers generally being the weak link (And the only reason for that "generally", is that sometimes the room is an even bigger issue).Regards, Dan.

author: Beamin
author_rank: Super Contributor
timestamp: June 27, 2018, 03:44:49 pm
content: Quote from: NiHaoMike on June 27, 2018, 02:27:13 pmI'm going for high current low distortion <0.04THD. So I don't want cheap or chinese that would totally defeat the purpose. Yes I could go on ebay and get some pile of shit for a few dollars but I'm trying to upgrade not do a major down grade.

author: Benta
author_rank: Super Contributor
timestamp: June 27, 2018, 03:50:01 pm
content: Quote from: chemelec on June 27, 2018, 03:24:10 pmThis is not the failure mode I've experienced. The woofers and midrange speakers are normally quite well protected from high frequencies by the crossover filter (low pass limiting).What really happens is, that when the amp starts clipping, a lot of power is suddenly transferred to the tweeter range, which causes them to burn out.

author: NiHaoMike
author_rank: Super Contributor
timestamp: June 27, 2018, 04:09:32 pm
content: Quote from: Beamin on June 27, 2018, 03:44:49 pmThere are modules that use TI chips, the leader in the market.Here's one example:https://smile.amazon.com/Sure-Electronics-AA-AB32191-TAS5630-Amplifier/dp/B007ALBNP8/

author: CJay
author_rank: Super Contributor
timestamp: June 27, 2018, 04:10:14 pm
content: Simple answer, no.Old amps were as good as the technology they used/was available, that's not to say they weren't great in their day and a high end 70s amp would be passably OK now but they're nowhere near as good in terms of fidelity as a modern device that's targetted at the same market position, the technology has improved and you can get, in comparison with the old stuff, ridiculously good gear for peanuts these days.I spent a good few years repairing amps for HiFi and PA, the first MOSFET amps I heard were a revelation, at first I thought 'thin bass, lacking 'boom'' but it wasn't that at all, the 'boom' was a product of the old amps just not coping with high bass levels and making it 'smeared' and 'muddy'What I was hearing from the MOSFET amps was actually a lot closer to the actual performance on stage or recording.Note, the amps used on stage were and still are as much a part of the instrument as the strungs on the guitar being played through it so if we're talking amps for performance then you may be better making a faithful copy using the original parts, for recorded music, don't bother.

author: Benta
author_rank: Super Contributor
timestamp: June 27, 2018, 04:52:07 pm
content: Quote from: CJay on June 27, 2018, 04:10:14 pmCJay, you're speaking to my heart. As an old rock guitarist, pairing the instrument to the Marshall/Ampeg/Acoustic/HH was part of the art.

author: ejeffrey
author_rank: Super Contributor
timestamp: June 27, 2018, 05:14:57 pm
content: Quote from: chemelec on June 27, 2018, 03:24:10 pmThat isn't the problem. The amplifier output goes to a crossover, which provides a low frequency signal to the woofer and midrange with no square edges. The fast risetime goes to the tweeter, which has no problem with it.The problem with square waves is that they put a *lot* more power into the high frequency ranges than normal audio and that just overloads the tweeters. A speaker with 100 W "system" power handling probably has a tweeter that can only handle a couple watts. This is normally no problem since few musical instruments put out a lot of power in the upper ranges.Playing a full power 10 kHz sine wave at max volume will destroy your tweeters too.

author: chemelec
author_rank: Contributor
timestamp: June 27, 2018, 06:44:57 pm
content: I Use bi-Amplification, So the Square waves can go to the Woofer.Electronic Crossover for the Tweeter.

author: David Hess
author_rank: Super Contributor
timestamp: June 28, 2018, 02:29:46 am
content: No, just using better parts except if they started out inferior or defective will not significantly improve the performance.Further, layout is critical to avoid ground loops which is not always reflected on schematics.Check out Designing Audio Power Amplifiers by Bob Cordell and Audio Power Amplifier Design Handbook by Douglas Self.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: June 28, 2018, 05:31:05 am
content: Define better.In the 70s I had a similar idea and had a complete schematic and parts list for the best amplifier out there (in the ever so humble opinion of a newly graduated engineer). Went into the local electronics parts haven to buy the parts and found a stack of name brand amps surplussed and selling for less than part of the parts I went in to buy. I bought that, skipped building the amp and have never looked back.Were the specs on the amp I bought as good as what I was going to build? On paper, not quite. Who knows what the as built performance of my amp would have been.Did I learn as much by going this route? No. Building my own would have been better for that. But not doing that amp let me do other things and learn things I wouldn't have learned building the amp.Was the packaged product more pleasing than my homebrew thing was likely to be? Absolutely. Even today, with four decades of practice and experience my housings would barely match up to the commercial products, and then there wasn't even a comparison.Can you trade labor in matching components for better performance? Sometimes, but it depends on the design. In most commercial designs a lot of effort has gone into making the design relatively insensitive to things which are costly in production, like matching. So the design you copy is not likely to benefit. Could another design approach that accepted the penalty of matching perform better? Sure, that insensitivity to product variability usually comes at the expense of something else. Maybe even something you care about. But you won't find that design by looking at high volume products.So the answer depends on you and what you mean by the question.

author: Berni
author_rank: Super Contributor
timestamp: June 28, 2018, 05:51:12 am
content: Quote from: ejeffrey on June 27, 2018, 05:14:57 pmYep you can damage tweeters in such a way.But its very unlikely to happen in a real use scenario. You can very quickly notice low frequency tones clipping even a little bit as it sounds absolutely awful. Also due to standardized line levels its very likely that the audio source is not even capable of putting a large enough signal trough the amplifier to cause such severe clipping.Additionally normal music has quite low "power content". Its often the tiny voice coil in tweeters that gets damaged and that takes a sustained power trough it so it doesn't have a chance to cool down. This is the reason why i usually use a bass test song playing in to a pile of ceramic resistors to test amplifiers. Those tracks are usually almost entirely made up from full scale tones(sometimes even square wave) to push as much power as possible trough the amplifier in order to see if the cooling and power supply is up to the job. The difference can be really seen on my ceramic resistor dummy load, putting 100W of music into it gets it barely warm while 100W worth of bass test gets the resistors to water boiling temperatures.So yeah you can damage speakers if you put the right abusive sort of track trough them(Even if both the amp and speakers are matched in power), but its highly unlikely to happen with any sort of normal music. (Unless perhaps you regard dubstep as normal music and like to listen it at max volume)

author: Beamin
author_rank: Super Contributor
timestamp: July 20, 2018, 11:55:59 pm
content: Quote from: Berni on June 28, 2018, 05:51:12 amYes it is.No it's not.Yahuh!Notunh!Can anyone back up what they are saying? I feel like I'm reading youtube comments where people know absolutely nothing make a statement as if it was fact then post some crazy idiot video on youtube and call it "research". My college education and fancy book learning trumps your research you did on youtube. It's like old wives tales that just because they heard it 100 times it must be true. The internet made the smart people smarter and the dumb people a lot dumber and far more dangerous. I saw a video where a guy drinks turpentine everyday to be "healthy".

author: BrianHG
author_rank: Super Contributor
timestamp: July 21, 2018, 12:07:55 am
content: The truth is if you have a quality design schematic from the 70s, and use parts from the 70s, you will make a good amp.Modern parts, what you might think of as high end parts today, when it comes to the transistors, today, they have been optimized for switching performance, not necessarily linear drive. This can alter the sound, quality and steady function of the amp which was designed with 70s transistors in mind.When it comes to resistors and caps, you have a much better selection for resistors. With today's caps, if you need it, the higher quality ones will cost you money. The life of these components will be better than the ones from the 70s if you pay for the good ones where needed. Be careful of any cap which needs to handle high ripple currents in your design, the odd high end ones from the 70s will need high end ones from today as well.Make your PCB with 2oz of copper at least. Old 70s design PCBs had no soldermask and usually flooded the traces with solder to thicken them up to handle higher current where needed if not everywhere.Everything else is BS. Good luck, rejuvenating old analog circuits from the 70s will be a fun experience and if you choose the right design, don't believe anything said above, and don't strive for that absolute minimal distortion, the design should sound perfectly fine.As for transistors, motorolla/On semiconductor still makes a nice NPN/PNP matched pair designed for linear operation for servo motor and HIFI audio in a TO247 package, designed to maintain at least 100 watts continuous on a generous heatsink. be careful as Chinese crappy knockoffs exist.

author: BrianHG
author_rank: Super Contributor
timestamp: July 21, 2018, 12:28:32 am
content: The modern Onsemi complementary 150watt pair:NJW0281G (NPN)NJW0302G (PNP)Respectable 30Mhz bandwidth and wide safe operating area, plus, averaging 2.50$ each at digikey for originals.NJW3281G and NJW1302G for 200 watt handling.

author: Beamin
author_rank: Super Contributor
timestamp: July 21, 2018, 03:16:27 am
content: Quote from: BrianHG on July 21, 2018, 12:07:55 amThis makes sense. No way am I going to buy some shitty Chinese chip amp and build around then hope it sounds good. That's like building a race car then buying Walmart brand chensing tires to save costs.

author: BrianHG
author_rank: Super Contributor
timestamp: July 21, 2018, 04:07:15 am
content: Quote from: Beamin on July 21, 2018, 03:16:27 amDo not discount some of the Chinese class D amps. The problem is that you have no control overs the choice of architecture or main IC & source of the components and the quality of PCB, PCB layout & design. Just placing a few fancy quality caps here and there with the highest spec class D amp IC doesn't necessarily make the amp great.Also, reading deeply into the top Texas Instruments class D amp IC, the 75-100 watts devices, powered to the max, if you look at the THD charts, the 100 watt setup has incredible performance to around 35 watts, then the THD begins nose dive right after that point up to the peak 100 watts. With today's popular music recordings, this is fine for most junk.A properly biased regular analog class B 100 watt amp will have have a fairly consistent THD way up to 80 watts, if really well designed, the THD will be clean up above 95 watts, true RMS level, not peak like the class D amp specs.

author: Beamin
author_rank: Super Contributor
timestamp: July 21, 2018, 04:13:15 am
content: Quote from: BrianHG on July 21, 2018, 04:07:15 am

author: BrianHG
author_rank: Super Contributor
timestamp: July 21, 2018, 03:59:52 pm
content: Quote from: Beamin on July 21, 2018, 04:13:15 amOk, valid question. Let's start with how heat dissipation of a linear amp and a class D switching amp limits you output power.Are you familiar with why it is when you use a mosfet as an on/off switch, switching from 50V VCC to GND, back and forth, fed through an inductor, driving a 10V output into a speaker at around 1 amp load, it will stay cool, where as if you take the same mosfet, but, drive it linear at 1 amp, where the drain is now at your 50v supply voltage and the source output is now at 10v giving your speaker around 1 amp, why that same mosfet will get hot and need a big fat heatsink for those 40 watts of radiated heat? You also have 4 of these for stereo. Also, remember, a class B amp needs to have the output complementary pair transistors fighting each other for a higher quality output without crossover distortion, making a flat continuous level of heat, usually wasting around 50 watts in a good HIFI design.Now, to make things even better for class D, double your amp outputs to drive one speaker, one amp side has a positive voltage signal and the other a negative signal. Now, instead of 50V VCC, you only need 25V VCC since the 2 amps double the output voltage range to the speaker giving you the equivalent to a 50V VCC. The switching class D amp only needs 25V mosfets which today have super low on-state resistance making very little heat if any at all.

author: David Hess
author_rank: Super Contributor
timestamp: July 21, 2018, 05:17:05 pm
content: Quote from: BrianHG on July 21, 2018, 12:28:32 amThose are RETs (ring emitter transistors) or equivalent and they have been around since at least the early 80s in the form of the D44/D45 TO-220 parts and a pile of TO-225 parts like the MJE172/MJE182 which were also used in audio.Not only are they higher bandwidth but they also have a more linear current gain.

author: Richard Crowley
author_rank: Super Contributor
timestamp: July 21, 2018, 05:52:44 pm
content: Quote from: BrianHG on July 21, 2018, 12:07:55 amWhere "good" is defined by 1970 standards.Why do we strain for the last 001% distortion in the electronics when even the best speakers on the planet are lucky to have distortion measured in single digits?Quote

author: Beamin
author_rank: Super Contributor
timestamp: July 23, 2018, 02:40:53 am
content: Quote from: BrianHG on July 21, 2018, 03:59:52 pm

author: Beamin
author_rank: Super Contributor
timestamp: July 23, 2018, 02:52:53 am
content: Quote from: BrianHG on July 21, 2018, 03:59:52 pmAs far as linear range goes what is the other state and what do they use in commercial a/b amps?So are you saying a B amp has push pull transistors? Or is B just one transistor that wastes the current? Does a D use push pull? Or is the advantage of D that it doesn't use push pull?Quote from: Richard Crowley on July 21, 2018, 05:52:44 pmAs far as why I chose those numbers: The speakers I have sound quite good and the Marantz amp that powers them with those specs sounds best. A better amp than that doesn't sound any better to my ears. BUT the speakers are good enough that a Sony or BestBuy ampsound bad/under powered with them, there is no bass or mid bass and the mid range is lacking makin the speakers sound tinny not bright. Why do people assume I am plugging this into a Walmart set of speakers? Try it yourself where you hook up both amps and turn one on and off quickly, the difference is very noticeable. The problem I have with these speakers is most amps are not powerful enough to get a flat bass to treble sound out of them. Also they have separate mids/highs that mount on a wall or book shelf, while I put the woofers back to back diagonal to the room behind furniture. People are always amazed at "How do those little speakers make so much base!?"

author: Richard Crowley
author_rank: Super Contributor
timestamp: July 23, 2018, 03:09:11 am
content: Quote from: Beamin on July 23, 2018, 02:52:53 amApparently I was too subtle in my statement. It doesn't matter WHAT speakers you are listening to.'Even speakers that cost as much as your house almost certainly have distortion measurements that are rarely < 10%. So I question why people pursue the last 0.01% distortion in the electronic path when the transducers (microphones and speakers) have perhaps 10x, 100x or even 1000x higher distortion?Certainly it is easier to design electronics for lower and lower distortion. So it is an attractive "target" for hobbyists and hi-fi marketing gerbs alike.OTOH, microphone and speaker distortion performance is hardly better than 50 years ago (or longer).

author: BrianHG
author_rank: Super Contributor
timestamp: July 23, 2018, 03:25:07 am
content: Quote from: Beamin on July 23, 2018, 02:52:53 amAs far as class B goes, the NPN transistor pushes up and the PNP pushes down. In many class B designs, there is tuned a little overlap, one fighting the other just a little to make sure both transistors are always conducting, even when one drives all the way to VCC, or in the other direction where the other transistor is driving all the way to GND or the negative rail. In class AB amps, this window where when one transistor pushes, or the other pulls is tuned to a fine point, where, without negative feedback, some crossover distortion artifacts may leak through. So, in class B, we loose a tad of our full power supply range, but when designed right, we guarantee under extraneous circumstances no crossover distorting effect where as with class AB, we waste less heat and drive further to the ends of the power rails, but, with temperature and dynamic loads, distortion is a possibility if not properly designed as it is designed that only 1 transistor is on at a time.Now, for class D, either the high VCC drive mosfet is on, or, the low drive GND mosfet is on, never both at the same time. The high and low mosfet cycles at the amp's switching frequency, something like 768Khz, or even higher at 1.5mhz or 3mhz. This output is fed through a low pass filter inductor and the % of each turn on time, high or low, say 70% high and 30% low means after the output low pass filter, the output will be 70% the voltage of VCC. Since both mosfets are never on at the same time, there is no heat. Since the mosfet switches are something like 0.02 ohm when on, if the processor sends 100% on time for the VCC mosfet and 0% on time for the GND mosfet, the output is practically shorted to VCC driving the speaker to that VCC without any wasted heat. Whether is is at 50% drive, 100% drive, the mosfets are off and on, never acting like a resistor dissipating heat in the device. This is why such small ICs can deliver over 50 watts of power, no sweat.

author: BrianHG
author_rank: Super Contributor
timestamp: July 23, 2018, 03:34:44 am
content: Quote from: Richard Crowley on July 23, 2018, 03:09:11 amWith a 50 watt dynamic load, even your speaker wire will introduce more distortion than this, never mind the resistors and caps in you speaker's crossover block.0.01% may be a valid target for the internals and drive of a pre-amp, not a power amp, especially at full dynamic range.

author: Beamin
author_rank: Super Contributor
timestamp: July 23, 2018, 03:46:58 am
content: Quote from: Richard Crowley on July 23, 2018, 03:09:11 amI know this: Sony and most amps are around 0.8 THD my amp is 0.03 THD and sounds a whole lot better with my speakers. I haven't tried to see if cheaper speakers sound better. I don't think I, nor my speakers would notice any sound that's better and so I am shooting for the same levels at that watt range.

author: Richard Crowley
author_rank: Super Contributor
timestamp: July 23, 2018, 03:59:16 am
content: Quote from: Beamin on July 23, 2018, 03:46:58 amNobody can dispute that. However pinning "sound better" solely on distortion measurement is probably missing the point. There are probably at least half a dozen factors contributing to "sound better" that may or may not have anything to do with measured distortion performance.Can anyone cite a proper test (ABX or double-blind) of 70s era BJT vs. 80s FET vs. 2010 era Class-D? Or is this the same kind of audiophoolery as "magic cables" and green marker on CD disks and wooden knobs? Count me skeptical.

author: Beamin
author_rank: Super Contributor
timestamp: July 23, 2018, 04:05:26 am
content: Quote from: Richard Crowley on July 23, 2018, 03:59:16 amI made a lot of money selling better cables when I was a kid mainly by earning the customers trust buy telling them a $40 "super digital coax cable" was a rip off and to use the cables that came in the box for it there fore creating a need for the over priced monster cables. Did you know monster only sells their cables at %50 of retail price? Not 5% (or less) like most cables. If you are really worried about cables then take cheap component cables that have to pass the signal with minimal loss.

author: Richard Crowley
author_rank: Super Contributor
timestamp: July 23, 2018, 04:14:27 am
content: Quote from: Beamin on July 23, 2018, 04:05:26 amI'm not "worried about cables". I have made my own cables from proper wire and connectors for well over 50 years."Monster" is among the most despicable companies in ANY industry. I'd rather use rusty barbed-wire than anything with the "Monster" brand name on it.

author: BrianHG
author_rank: Super Contributor
timestamp: July 23, 2018, 04:22:02 am
content: Quote from: Richard Crowley on July 23, 2018, 03:59:16 amI can easily make an amp with 1% THD which would blow away his 0.03% THD amp, no frequency coloring, completely flat. There are other things at play here which Beamin cannot take into account without proper measuring equipment and analyzing the 2 amps. THD specs are usually not too meaningful, it just might so happen that his 0.03% amp just better by design and that 0.03% could just also be a measurement at a set of specific frequencies with specific power levels and load.

author: Beamin
author_rank: Super Contributor
timestamp: July 23, 2018, 04:34:46 am
content: Quote from: BrianHG on July 23, 2018, 04:22:02 am

author: Beamin
author_rank: Super Contributor
timestamp: July 23, 2018, 04:38:02 am
content: Quote from: BrianHG on July 23, 2018, 04:22:02 amHer not his (see profile to left). Maybe the 0.03 amp has more power available to drive the speakers? Whats funny is it's only rated 50 watts vs the 100 watt sony I tested. But I have seen lower "watt power" amps that drove higher current and were at least louder then "higher watt" rated amps in car audio.So what else makes your 1% better? I would like to know what to look for when buying.

author: f5r5e5d
author_rank: Frequent Contributor
timestamp: July 23, 2018, 06:37:57 am
content: Dr Geddes is occasionally active onhttp://www.diyaudio.comas are amp designers, including Self, Cordell, Pass, Curl ...http://www.gedlee.com/Papers/The%20Perception%20of%20Distortion.pdfis an overview of Geddes take on distortion perceptionmore in the other distortion papershttp://www.gedlee.com/Papers/papers.aspxbasically low order distortion not too audibledistortion at low levels (crossover distortion) can be very audibleGeddes has looked at amplifier distortion as levels decrease into the noise with long averagingclaims it can be a good test of cheap commercial amps - he used $200 Pioneer HT amps from Costco to demo his $4k speakersJJ's papers could also help with understanding that there have been advances in understanding audio perceptionhttps://audiosciencereview.com/forum/index.php?threads/jjs-signal-processing-and-psychoacoustics-master-library.2066/

author: CJay
author_rank: Super Contributor
timestamp: July 23, 2018, 10:14:59 am
content: Quote from: Beamin on July 20, 2018, 11:55:59 pmI can speak from experience, I can't provide documentary evidence thought, it was very common to have to replace tweeters that had a voice coil, especially in PA applications where the volume had been tuirned up to 11(usually nightclubs or mobile DJs), we fixed it by fitting Motorola Piezo tweeters, I can't remember ever having to replace one of those unless it had been physicaly damaged.

author: CJay
author_rank: Super Contributor
timestamp: July 23, 2018, 10:23:38 am
content: Quote from: BrianHG on July 21, 2018, 12:07:55 amPartly, yes to the 'heavy' copper, it definitely won't hurt and is worth doing but the tinning was, AFAIK, also to prevent corrosion, not just for current handling.

author: luiHS
author_rank: Frequent Contributor
timestamp: July 23, 2018, 10:36:22 am
content: If you want a high quality amplifier, look for any scheme with tubes,Class A (without crossover distortion), buy good quality components like Hammond output tube transformers. The 300B tubes are the best or if you can not spend a lot of money, then use 6550, KT88 or EL34 tubes.You will never get such high quality with transistors and much less with integrated power circuits, that's the worst.As for the preamplifier, it is not true that it is the most important, unless you are going to use a turntable for vinyl, either with magnetic capsule, or much better with mobile coil capsule, then the preamplifier is crucial, basically to avoid the background noise.

author: langwadt
author_rank: Super Contributor
timestamp: July 23, 2018, 10:42:46 am
content: Quote from: luiHS on July 23, 2018, 10:36:22 amhttps://en.wikipedia.org/wiki/Poe%27s_law

author: BrianHG
author_rank: Super Contributor
timestamp: July 23, 2018, 06:17:39 pm
content: Quote from: CJay on July 23, 2018, 10:23:38 amI'm talking about 70s 50-100watt designs with that huge 1/4inch thick layer of solder blobbed all over the traces around the power transistors.

author: BrianHG
author_rank: Super Contributor
timestamp: July 23, 2018, 06:28:35 pm
content: Quote from: Beamin on July 23, 2018, 04:38:02 amUnfortunately what I buy is out of your price range. But, for 50 watts per channel, or even a true 75 watts per channel/100 watts peak, you can build something really good for under 200$ total, so long as you can find a good torroid transformer with 4 big ass computer grade high current DC filter ripple capacitors. The transistors, and or ICs will be in the 40-50$ range the heatsinks should also be in that range leaving 100$ for the torroid and DC power caps and A good 35 amp bridge rectifier.Here is a photo of the amp I use, though, it is way overkill for your 50-75 watts... As you can see, not complex at all, but this design output can sustain 15 amps X 2 channels continuous. Though, this amp has a rating of THD and IM less than 0.25%, I can guarantee it will pulverize your 0.03% amp into the dirt.

author: BrianHG
author_rank: Super Contributor
timestamp: July 23, 2018, 06:35:59 pm
content: Note that the less in a properly designed amp, usually the better, here are example photos of some quality amps:Hint: None of these amps have a distortion anywhere low as 0.03%...

author: BrianHG
author_rank: Super Contributor
timestamp: July 23, 2018, 06:53:29 pm
content: If you want low distortion, Class AB, easy to build, just use this IC from TI:http://www.ti.com/product/lm3886Use 1 per channel, or 2 per channel if you want a bridged output.Make a stiff power supply near the IC's limit voltage, though it doesn't need to be regulated.Get a big ass heat sink and you're away.A different low distortion option would be to use 2 high voltage, medium current opamp from TI, each feed the bases of the transistors I mentioned earlier and with a 2x 0.2 ohm series resistors at the emitter with the center tied to your speaker output. A little more experimenting and adjusting here, but, you can easily make a 100w / channel amp closer to the specs of a high performance, high current output amp like the pro-ones listed above, though, the distortion will be closer to 0.2%, not 0.03% like the TI LM3886 all in one IC.

author: CJay
author_rank: Super Contributor
timestamp: July 23, 2018, 07:14:15 pm
content: Quote from: BrianHG on July 23, 2018, 06:17:39 pmHence 'not just'

author: Gyro
author_rank: Super Contributor
timestamp: July 23, 2018, 07:29:10 pm
content: Quote from: BrianHG on July 23, 2018, 06:53:29 pmThe LM3886 does have a pretty good reputation in the 'Chipamp' comunity. Here's a useful site on it...https://www.neurochrome.com/taming-the-lm3886-chip-amplifier/

author: BrianHG
author_rank: Super Contributor
timestamp: July 23, 2018, 07:48:08 pm
content: Quote from: Gyro on July 23, 2018, 07:29:10 pm@Beamin, just read the neurochrome website. The TI LM3886 done right, feeding an 8 ohms speaker at 50w will give you a distortion below 0.01%. Closer to 0.015% if you count the peak 20Khz at full power at that frequency... That's 3x better than your current amp.

author: Zero999
author_rank: Super Contributor
timestamp: July 23, 2018, 09:00:52 pm
content: Quote from: Richard Crowley on July 23, 2018, 03:59:16 amNot class D vs class AB, but here's an interesting double-blind study done comparing several amplifier designs, back in the 70s, which showed no one can tell the difference, with everything else being equal.http://www.keith-snook.info/wireless-world-magazine/Wireless-World-1978/Valves%20versus%20Transistors%20DCD.pdfNo doubt if the same test were conducted today, comparing amodern class D design with an older solid state design and an ancient valve design, the results would be the same.

author: David Hess
author_rank: Super Contributor
timestamp: July 23, 2018, 10:48:10 pm
content: Or follow the instructions in the two books linked earlier for a completely discrete low distortion "blameless" design. Even the simplified versions are in the 0.01% range.Another option is theLT1166 Power Output Stage Automatic Bias Systemwhich can be used by itself but achieves much lower distortion within a feedback loop. This might be combined with a "blameless" design to avoid the thermal compensation of a class-AB output stage.

author: BrianHG
author_rank: Super Contributor
timestamp: July 23, 2018, 11:20:53 pm
content: Quote from: David Hess on July 23, 2018, 10:48:10 pmWhat an interesting little chip. I had no clue something like that existed. One of my early home made bipolar amps replicated it's function by using 2 normal, medium output current op-amps, one driving the NPN's base and the other driving the PNP's base in a push-pull output emitter follower. The 2 series resistors at the output emitters and the fixed voltage offset at each op-amp's inputs created my regulated bias current, correcting for the thermal warming Vbe offset characteristics of the power transistors. Worked like a charm. It had an excellent 75 watt performance with 100w peak. I biased the thing to around 50 watts idle. Boy did it get toasty, but, it had such a warm filled rich sound.

author: NiHaoMike
author_rank: Super Contributor
timestamp: July 23, 2018, 11:55:09 pm
content: Quote from: Hero999 on July 23, 2018, 09:00:52 pmIsn't the whole point of a tube amp the specific kind of distortion they make that alters the sound in a good way?

author: David Hess
author_rank: Super Contributor
timestamp: July 24, 2018, 12:30:49 am
content: Quote from: BrianHG on July 23, 2018, 11:20:53 pmThe design I came up with long ago used a complementary common base input stage to drive current mirrors and produce an output. The supply current to the common collector output stage was monitored on alternate half cycles from one collector when it should be idle and fed back to the biasing of the complementary common base input stage to trim the idle for every stage. Full power bandwidth with 2MHz output transistors was about 500kHz, power supply rejection was surprisingly high, and stability and transient response were ideal. The first version used a stack of diodes for thermal compensation and it ran away on a hot day; a Vbe multiplier might have worked better.The next design I might try is a power version the one shown below which could be considered a voltage feedback operational amplifier driving a current feedback amplifier which neatly avoids the problems of achieving high full power bandwidth at the expense of input noise.

author: Alex Nikitin
author_rank: Super Contributor
timestamp: July 24, 2018, 07:10:36 am
content: Quote from: NiHaoMike on July 23, 2018, 11:55:09 pmNo - unless it is a guitar amp or another "effect processor" .CheersAlex

author: Zero999
author_rank: Super Contributor
timestamp: July 24, 2018, 08:16:27 am
content: Quote from: NiHaoMike on July 23, 2018, 11:55:09 pmThat might have not been the case when the study was done. Back then (I can't be sure, as I wasn't around) I think audiophiles were still convinced that old glassware sounded better than solid state. In any case it proves that if a decent amplifier is not over-driven, it will not cause any audible artefacts, irrespective of whether it's solid state or thermionic.

author: dzseki
author_rank: Frequent Contributor
timestamp: July 24, 2018, 09:30:58 am
content: Hi-Fi (let alone High-End) is a though topic, there is no ultimate solution, but opinions and preferences...Relying only on THD measures may be misleading, as these parameters are born with some sort of static tests. To my understanding in the 70’s-80’s enthusiast engineers found out what TIM (Transient InterModulation) is. Until that amplifier designers focused on high open loop gain, and relied on the global feedback loop to decrease THD. Indeed this way it is possible to get very good THD measures for the borchure, but the trade off here is that the open loop bandwidth is low, which implies that the feedback loop „speed” is also bad. High TIM is the result of this suffering, and is often even noticeable when listening to music on such amplifiers.Making a Low-TIM amplifier is a design concept, which relies highly on symmetrical circuit layout, and on more local feeedback loops rather than big global feedback.There is plenty of information on the net over this topic, IMHO, this is the real game changer in the amplifier construction.But this is only one aspect of the things, because a lot depends on actually what music do you listen usualy. Electrical music (Yello, J.M. Jarre, etc.) may sound very impressive on virtually any sound system, which may not be the case with a brass big band style music...I enclose a mid 80’s amplifier schematic, which uses classic semiconductors but feature the „novel” circuit arrangement already, this amplifier was a part of Hungarian made active studio monitors, each amplifier drove a single speaker after active crossover network. It is a rather complicated circuit but if one takes the time to analyze can see each component have a good reason to be there...

author: CatalinaWOW
author_rank: Super Contributor
timestamp: July 24, 2018, 06:49:37 pm
content: Quote from: dzseki on July 24, 2018, 09:30:58 amThis post is a good example of why audio discussion often ends in hurt feelings and fist fights.It starts with good factual information. TIM is a real thing and very credibly one of the sources of "poor" listening experiences on some styles of music.Then goes on with irrelevant or partially relevant statements. Symmetrical layout has little, if anything to do with TIM, though it does have some other benefits and definitely helps the aesthetics. Local feedback is one approach, but not "the" answer to reducing TIM (or to getting low THD while minimizing the use of feedback loops).Even if the original designer and/or this poster understands the details of a particular approach there will be a lot of folks misunderstanding, quoting and fighting over these particular implementations of a design and their efficacy in generating a good listening experience.

author: Zero999
author_rank: Super Contributor
timestamp: July 25, 2018, 08:18:53 am
content: Quote from: CatalinaWOW on July 24, 2018, 06:49:37 pmI'd head of intermodulation and knew that non-linear amplifiers can cause it, but hadn't heard of transient intermodulation distortion, which seems like a different name for what I already knew. The trouble is, when dzseki started talking about symmetrical layout, I started to smell BS, which made me question TIM and the rest of the post.Although layout can be important, in audio amplifiers, especially for high current paths and high impedance nodes, it's not as critical as in an RF circuit (unless it's a class D amplifier). There's no need to do anything crazy such as making it look a certain way i.e. symmetrical.The LM3886 has a more than acceptable level of intermodulation distortion, probably better than many old discrete designs from the 70s.http://www.ti.com/lit/ds/symlink/lm3886.pdf

author: dzseki
author_rank: Frequent Contributor
timestamp: July 25, 2018, 09:38:08 am
content: I may have been imprecise in my previous post, sorry, but at least gave some practical aspect to it (posted a schematic that the OP may appreciate).While I have to admit there is no hard definition for a symmetrical layout for a low-TIM power amplifier, it is just all of them appear to be fully symmetrical (that I know of).And while CatalaniaWOW started his post with this:QuoteThen he goes on with qualifying my post (without any actual evidence or alternative solution offered) which eventually lead to the hurt feelings in me.And now this trail goes on with Hero999’s suspicion on me BS-ing, which makes me curious where is it stated the LM3886 excels in low-TIM, because Intermodulation Distortion is not the same as Transient Intermodulation Distortion.EDIT: added an article about TIM too.

author: GeorgeOfTheJungle
author_rank: Super Contributor
timestamp: July 25, 2018, 09:51:35 am
content: Quote from: David Hess on July 24, 2018, 12:30:49 am"Op Amp Applications Handbook" by Walter G. Jung :-) I had all his cookboks, were the best back in the day!

author: dzseki
author_rank: Frequent Contributor
timestamp: July 25, 2018, 10:04:21 am
content: Quote from: Hero999 on July 24, 2018, 08:16:27 amInteresting find, it is often overlooked that tube amplifiers emplyos different feedback structure (current feedback vs. the voltage feedback of the solid state amplifiers) this results in (an inherent) non-linear frequency response that depends on the actual speaker's impedance (and the woofer's impedance resonant point dominates here), this behaviour is contributed as the "warm sound" of the tubes.

author: Zero999
author_rank: Super Contributor
timestamp: July 25, 2018, 12:42:36 pm
content: Quote from: dzseki on July 25, 2018, 09:38:08 amDon't take it personally. It's impossible to distinguish between an honest error and deliberate bullshit. If this was about most other subjects related to electronics, one would normally assume any inaccuracies are honest mistakes, but because audio is full of bullshit, one's judgement is biased to presuming the worst.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: July 25, 2018, 07:07:50 pm
content: Sorry I hurt your feeling dzseki. But I stand by my comments. Which included a mention that you probably knew what you are doing.The key points - you made an assertion that symmetrical layout is needed to control TIM. I don't believe this is true, and you have partially retracted that statement. Persons with limited understanding will take your original comment and run with it, leading to spreading conflict and misunderstanding. As far as I can understand the only benefit to symmetrical layout for TIM is to make sure that unintended signal paths are balanced resulting in identical TIM in each channel which is a possible listening benefit. Symmetrical layout has other benefits unrelated to TIM which are sufficient unto themselves. Matching TIM is a speculative benefit.You asserted that "the" way to control TIM is the reduced and local feedback. I agree that it is a way, and perhaps one of the best. Again a path for the relatively uninformed to start a religious war over the "right" way to design amplifiers.