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DIY Class A Amp
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xarkkon
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Haven't done either of those but did the Amp Camp Amp despite the poor reviews here. Was an easy build to do with everything all in there. Would recommend for learning purposes. Pretty much no power though so don't expect a lot out of them. I use them well enough on 87db speakers but have to turn it up pretty loud to get to reasonable levels.
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Nobleman
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I’ve never had a serious class A amp so wanting to hear the difference. Currently using an Audiolab 6000A and love it. It drives my Maggie’s quite well but it’s only 75wpc so have to turn up the volume quite high. Which is why I’m considering a class a build. As a self taught technical person I’m worried about adjusting the bias Of class a amps. Is that difficult? Should I just get a Hypex NCxxx instead?
MAB
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Class A will typically have less power than other amp types. Hard to buy or build Class A amp even close to 100 WPC. Bias adjustment is likely low on the list of obstacles!!!
Are you thinking of building a Hypex kit? That will likely be an upgrade from your Audiolab amp, the additional power is substantial. Depending on your Magnepan model, they may appreciate that! And the build is straightforward.
I built this class A amp https://sound-au.com/project3b.htm and learned a lot but I also do not recommend them especially if you need a lot of power i.e. more than 20 watts or so. They are not difficult to bias. The reason class A amps are so expensive to build is because of the heat sinks and power supplies. They draw and dissipate maximum power all the time which means the heat sinks have to be huge and the power supply has to deliver clean power constantly which means lots of capacitance and probably chokes. This is very much different that other amps that only dissipate power when it is called for. The bottom line is they are expensive, inefficient, heavy, large, and heat up your room. While they "sound and measure" fine so do many other amps without all the drawbacks. There really is no advantage but they are kind of fun to build if you have the time and lots and lots of money.
You should look up Tom Christiansen ( a member and poster here) Neurochrome line of amplifiers. A newish hobbyist without a distortion analyzer is not going to come anywhere near their performance. He sells built circuit boards as well as unpopulated boards and a bunch of very nice peripherals.
neurochrome.com
I have three Pioneer series twenty/elite M-22 power amps which are class A. They are rated about 30 watts per channel. I use them in a multi amp system where they drive the Mid range and tweeters directly. I would never hook them up to a pair of Maggies. They put out about 50 watts when they start clipping visibly.
DIY Audio Engineering Gear for Audiophiles | Neurochrome
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MAB
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Here is a classic example of Class A vs. Class A/B. Built into the same chassis, the M-22 is Class A 30 Watt, the M-25 is Class A/B 120 Watt.
stereonomono.blogspot.com
stereonomono.blogspot.com
I want one of each!!! But the M-25 is the more useful of the two for most setups!
Pioneer M-22
Blog High-Fidelity Stereo. Vintage Audio and Hi-Fi Equipment, info, specifications, descriptions,
stereonomono.blogspot.com
Pioneer M-25
Blog High-Fidelity Stereo. Vintage Audio and Hi-Fi Equipment, info, specifications, descriptions,
stereonomono.blogspot.com
MAB
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I am dying of envy.
Agreed! Not quite the best application for those amps!
I got these before the M25 was imported to the USA.
In your case (Maggies, 75W not enough) it would be utterly insane to go class A. I drove my old MG 1.6 with Denon POA6600 (250W mono blocks) successfully. A class A poweramp of 250wpc would dissipate 2 kW. Might be fine if you live in Northern Alaska and use an electric heater anyway.
Go for a decent class D poweramp.
Zek
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You'll never know until you try.
In the last century, I made a Super Hiraga A-30 amplifier that has about 30W/8 ohms. The case must have large heatsinks due to the large quiescent current on the output transistors, in addition there is a large transformer with a large electrolyte bank (about 300,000 uF) in the power supply, which is quite expensive.
Such a Hiraga was good for my speakers with an impedance of 8 ohms and a sensitivity of about 89dB, but it did not have the power to push the AR9 speakers whose impedance drops to 2 ohms.
MAB
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Nothing about Class A will have better sound quality, it will be less powerful and you will likely run out of power while listening which will cause it to actually sound worse! The alleged benefits of Class A are simply not audible. For instance, I have a Yamaha CA-2010 amplifier which has both Class A/B and Class A modes. Class A has 1/4 the power of Class A/B operation. It just doesn't sound any different, but the unit sure runs hot in Class A and has noticeable clipping if I run it too hard!
I don't want to say it's all hype, but Class A doesn't makes sense for most applications especially where power is required.
MRC01
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I drive my Maggies (3.6/R) with an Adcom 5800. It's class AB and biased so that it's class A (both sides conducting) up to about 10 watts output. Sounds and measures great, with 400 wpc both channels driven it has enough power to drive the inefficient 3.6/R to their limits. But only just barely. Bass tones just loud enough to cause the panels to rattle against the stops have the amp's distortion lights just beginning to flicker. When doing that it can draw 1800 VA and will occasionally blow a 20 amp breaker when you first turn it on.
The maggies need a lot of power to come alive, and they have very low distortion in the mids & treble. If you want to get the most out of your maggies, any good amp with at least 400 wpc continuous power will do the job. You don't need class A, and there's no way you'll get pure class A at that power level.
The maggies need a lot of power to come alive, and they have very low distortion in the mids & treble. If you want to get the most out of your maggies, any good amp with at least 400 wpc continuous power will do the job. You don't need class A, and there's no way you'll get pure class A at that power level.
OP
Nobleman
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Thanks. I had a Luxman L510 back in the day which ran 1/4 power in class A but I could not hear any difference. Which is why I always wanted to try a high power pure class a amp. I understand the the benefit of class as that they eliminate transistor switching noise by keeping them on I.e the plus voltage bank push and the minus bank pull and the biasing is used to complete and align the sine wave. Is it that not a huge benefit to reduce noise?
MRC01
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True, but only for very small signal amplitudes. Which means class A/B solves the same problem more efficiently. The A/B doesn't even have to be biased very high, though many are.
OP
Nobleman
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AR9 Brings back memories…those were beautiful speakers. I was in love with them for quite some time. What happened to Acoustic Research?You'll never know until you try.
In the last century, I made a Super Hiraga A-30 amplifier that has about 30W/8 ohms. The case must have large heatsinks due to the large quiescent current on the output transistors, in addition there is a large transformer with a large electrolyte bank (about 300,000 uF) in the power supply, which is quite expensive.
Such a Hiraga was good for my speakers with an impedance of 8 ohms and a sensitivity of about 89dB, but it did not have the power to push the AR9 speakers whose impedance drops to 2 ohms.
MAB
Major Contributor
No, there will be no practical improvement in distortion and noise.
1/4 power in Class A is typical, same for the CA-2010 and the Pioneer M-22 and M-25 examples I cited. And also typical is the THD for these classic Class A designs is typically reduced in half compared to Class A/B, see for instance the Yamaha CA-2010:
Both modes have vanishingly low levels of distortion!
The Pioneer M-22 also has half the distortion of the M-25, both are incredibly low distortion amps. I will never be able to hear the difference, maybe a bat can but I can't! But for sure Class A will begin to audibly distort at noticeably lower volume!
These figures are from Classic amps, and I believe the published values. I really don't know how much further SOTA for Class A vs. Class A/B operation has come since these were created decades ago, but Class D has exceeded this level of distortion.
The way I discovered Neurochrome was the statement by Sigfried Linkwitz , on his webpage, "I don't know how to measure such low distortion." Tom C's amps have like three zeros to the right of the decimal. they start with a good clean chip (the LM3886) and then add a servo corrector in the feedback loop. Every bit as good as class A.
It is important to have enough power. I my case the class A amps are hooked directly to drivers in a multi-amp (active crossover) set up. Most passive crossover networks eat a lot of your power.
When I hear or read that a system "drops to two ohms" that tells me the crossover network is parallel (as most are) and that it is a too many way system to have a passive crossover.
I tried to help someone bi or tri amp an Infinity system from back in the day. It was like a five way plus it had a rearward firing tweeter for "ambience" which I would have unhooked, which impedance wise made it like a six way system. It is no wonder that the impedance gyrated. Instead of finding an amp that is comfortable driving a below two ohm(and very reactive) load, dissect it apart and multi amp it. You get lots more headroom and better performance in a lot of ways. And the benefit of a four or five way speaker system.
It is important to have enough power. I my case the class A amps are hooked directly to drivers in a multi-amp (active crossover) set up. Most passive crossover networks eat a lot of your power.
When I hear or read that a system "drops to two ohms" that tells me the crossover network is parallel (as most are) and that it is a too many way system to have a passive crossover.
I tried to help someone bi or tri amp an Infinity system from back in the day. It was like a five way plus it had a rearward firing tweeter for "ambience" which I would have unhooked, which impedance wise made it like a six way system. It is no wonder that the impedance gyrated. Instead of finding an amp that is comfortable driving a below two ohm(and very reactive) load, dissect it apart and multi amp it. You get lots more headroom and better performance in a lot of ways. And the benefit of a four or five way speaker system.
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