Pass ACA Class A Power Amplifier Review

[restorer-john]

I think this might be the reason why I almost always have not liked the commercial amplifiers. Together with undersized heatsinks and corresponding low idle current and savings on number of pairs of output devices.

But you are a purist, and a designer/builder. You choose not to compromise to fit a price point. That's an admirable trait. The trick with commercial gear was to find the pieces that compromised the least (or not at all) and were priced reasonably.

Many of the Japanese big brands used their top gear as "halo" products, to show off what they could do. Those are the pieces to search out and put in your collection as many were sold almost at give away prices after the '87-'90 crash years.

 

[restorer-john]

I think this might be the reason why I almost always have not liked the commercial amplifiers. Together with undersized heatsinks and corresponding low idle current and savings on number of pairs of output devices.

Good silicon was expensive (and still is). Think of the Sanken diffused emitter and Fujitsu RETs. And current noise. They had to achieve a balance.

 

[MakeMineVinyl]

@kannan
The "voicing" was often done through the lifecycle of a product and most often involved adjusting the rolloffs at each end of the spectrum in order to better demonstrate the relative benefits of upper range models or differentiate them from the bargain basement models. Certain brands "voiced" their low end amplifiers/receivers to sound warm and fat, whereas further up the range, they became ruler flat. This was a choice to sell on the sales floor against competing brands who did the same.

Your reply points to a question I've had for years; other than response tailoring, negative feedback tailoring, and other strictly technical and engineeringly sound techniques, what are the methods (in detail!) which some manufacturers say they use to "voice" their components? "Voicing" is routinely claimed as a development step by some (many) high end audiophile companies - what is involved in this step; rattling chicken heads cut by virgins over the filter capacitors?

I'm serious in asking this question. As my signature suggests, I do this for a living, yet I've never been privy to the voicing rituals claimed by some companies. What am I missing, if anything? I suspect what I'm missing is insanity, but I'd like to hear other's opinions!

 

[SIY]

Your reply points to a question I've had for years; other than response tailoring, negative feedback tailoring, and other strictly technical and engineeringly sound techniques, what are the methods (in detail!) which some manufacturers say they use to "voice" their components? "Voicing" is routinely claimed as a development step by some (many) high end audiophile companies - what is involved in this step; rattling chicken heads cut by virgins over the filter capacitors?

I'm serious in asking this question. As my signature suggests, I do this for a living, yet I've never been privy to the voicing rituals claimed by some companies. What am I missing, if anything? I suspect what I'm missing is insanity, but I'd like to hear other's opinions!

Most of the people in the fashion audio sector I’ve talked to claim that they tune the sound with things like wire type, circuit board materials, resistor brands, that sort of thing. It’s important for marketing purposes in faith-based audio.

 

[MakeMineVinyl]

Most of the people in the fashion audio sector I’ve talked to claim that they tune the sound with things like wire type, circuit board materials, resistor brands, that sort of thing. It’s important for marketing purposes in faith-based audio.

Those techniques are tangential to accepted engineering practice if you squint hard enough. Resistor type can matter if for instance a resistor with high inductance is used in a part of a circuit where that matters. These are the types of things I see mentioned, but some manufacturers imply some mysterious process which transcends all that. To my original point, I've never seen a solid explanation for what exactly they are talking about. And creating some fancy sounding marketing phrase for a well established principle doesn't count.

 

[SIY]

Those techniques are tangential to accepted engineering practice if you squint hard enough. Resistor type can matter if for instance a resistor with high inductance is used in a part of a circuit where that matters. These are the types of things I see mentioned, but some manufacturers imply some mysterious process which transcends all that. To my original point, I've never seen a solid explanation for what exactly they are talking about. And creating some fancy sounding marketing phrase for a well established principle doesn't count.

Nothing that logical. More like, “I use Dale resistors to dial in more warmth, then Vishays for better definition,” kind of nonsense. And of course, silver wire for brightness. Most hilarious are tube amp designers who dread any magnetic-material containing parts, but use tubes and transformers...

 

[MakeMineVinyl]

Nothing that logical. More like, “I use Dale resistors to dial in more warmth, then Vishays for better definition,” kind of nonsense. And of course, silver wire for brightness. Most hilarious are tube amp designers who dread any magnetic-material containing parts, but use tubes and transformers...

Or the concept of a 'modern' tube amp which uses tubes designed in 1933.

 

[BDWoody]

To my original point, I've never seen a solid explanation for what exactly they are talking about.

When pressed, their hands start waving so fast you'd think they were in the Matrix.

 

[restorer-john]

Your reply points to a question I've had for years; other than response tailoring, negative feedback tailoring, and other strictly technical and engineeringly sound techniques, what are the methods (in detail!) which some manufacturers say they use to "voice" their components? "Voicing" is routinely claimed as a development step by some (many) high end audiophile companies - what is involved in this step; rattling chicken heads cut by virgins over the filter capacitors?

I'm serious in asking this question. As my signature suggests, I do this for a living, yet I've never been privy to the voicing rituals claimed by some companies. What am I missing, if anything? I suspect what I'm missing is insanity, but I'd like to hear other's opinions!

I put "voicing" in quotes, because nine times out of ten, it's just tweaking the response curve. In the case of the mid 70s and early 80s low-mid range amplifiers and receivers, it was blatant. Rolled off lowest octaves, mid bass bump and sometimes a bit of treble boost. I've seen some shocking examples with audiophile favourites and so-called "giant killers". The thing with all the reviews in the 70s/80s was they used say a B&K paper plotter with a 50dB pot range which was then printed about an inch high in the HiFi magazines. Everything looked ruler flat!

As for the thought of revered "gurus" waving their magic hands over designs and tweaking a bit of wire here and a special "custom" formulation of capacitor electrolyte there, it's all pretty much BS.

 

[amirm]

AmpCamp is a sweet sounding amplifier irrespective of your criticisms. I have also read some other reviews of yours like the ATCs. Sorry mate the world thinks otherwise and so do I. I am highly critical of your listening skills which I presume are extremely poor as compared to your measuring skills.

I have listened to AmpCamp. There is nothing sweet sounding about it. If you think it sounds sweet it is your imagination talking. Unlike your opinion, measurements back my opinion.

In my opinion Toppings do not deserve the credit you reap on them, Audio GD is quite a good DAC and your reviews are off track therein...Teac sits at the top of the pile for me.

Your opinion is without value because you can't demonstrate it to be true. What matters is what you can prove, not what you think just like any other audiophile. We exist because people like you run around make proclamations with no foundation. We exist because we can objectively and from engineering point of view demonstrate what is good and what is bad. Come back with something other than pure audiophile myths and then we can talk. Until then the random stuff you say is spitting in the wind.

 

[DonH56]

There's a story on the 'net someplace by an engineer working at a form where certain components were chosen by a few select people with basically no technical expertise or rationale... He left. Famous guy, I'll leave it to somebody else to find it...

 

[kannan]

I have listened to AmpCamp. There is nothing sweet sounding about it. If you think it sounds sweet it is your imagination talking. Unlike your opinion, measurements back my opinion.


Your opinion is without value because you can't demonstrate it to be true. What matters is what you can prove, not what you think just like any other audiophile. We exist because people like you run around make proclamations with no foundation. We exist because we can objectively and from engineering point of view demonstrate what is good and what is bad. Come back with something other than pure audiophile myths and then we can talk. Until then the random stuff you say is spitting in the wind.

As I had said in the earlier post, no more repartee from my end as I have well made my point.
The world of audiophile will move on without your types or mine.

At one pole ATCs will continue to rule the roost and at the other end AmpCamps still will have thosands of happy users inspite of its such a very low profile.

Have a great day.

 

[aschen]

I only sort of skimmed through this thread, but I am thinking of ordering one of these things. It will be fun to assemble with my 9 yo son. I was thinking of ordering some full range fostex speaker kits from madisound as well, coupled to an old rega TT I have and tube preamp I have lying around. Putting a chip amp in a box seems less fun and insightful, an my EE skills don't permit anything more ambitious.

I am shooting for the highest distortion, lowest fidelity $1500 stereo money can buy! I think it will be a whole lot of fun to assemble and look cool as a 3rd system. Sometimes its about the journey not the destination.

I think Nelson Pass is as cool as they come, and I think he knows precisely what this amp is and isn't. I think he is more than capable of designing state of the art amps if he was so inclined but is enjoying (and has had commercial success) messing around with esoterica

 

[AudioTodd]

I only sort of skimmed through this thread, but I am thinking of ordering one of these things. It will be fun to assemble with my 9 yo son. I was thinking of ordering some full range fostex speaker kits from madisound as well, coupled to an old rega TT I have and tube preamp I have lying around. Putting a chip amp in a box seems less fun and insightful, an my EE skills don't permit anything more ambitious.

I am shooting for the highest distortion, lowest fidelity $1500 stereo money can buy! I think it will be a whole lot of fun to assemble and look cool as a 3rd system. Sometimes its about the journey not the destination.

I think Nelson Pass is as cool as they come, and I think he knows precisely what this amp is and isn't. I think he is more than capable of designing state of the art amps if he was so inclined but is enjoying (and has had commercial success) messing around with esoterica

EXACTLY and very well put. I love my Pass XA25 for the fun of it - and am trying to decide on a First Watt model to buy - as this hobby is more than just listening to music for me. If I want total accuracy, as I sometimes do, I have a full Benchmark system augmented with a Gustard X16 for that and I doubt it will ever be beat for that use. Otherwise I pretend to hear differences from the Pass and tube amps I listen to LOL!!

 

[mhardy6647]

I only sort of skimmed through this thread, but I am thinking of ordering one of these things. It will be fun to assemble with my 9 yo son. I was thinking of ordering some full range fostex speaker kits from madisound as well, coupled to an old rega TT I have and tube preamp I have lying around. Putting a chip amp in a box seems less fun and insightful, an my EE skills don't permit anything more ambitious.

I am shooting for the highest distortion, lowest fidelity $1500 stereo money can buy! I think it will be a whole lot of fun to assemble and look cool as a 3rd system. Sometimes its about the journey not the destination.

I think Nelson Pass is as cool as they come, and I think he knows precisely what this amp is and isn't. I think he is more than capable of designing state of the art amps if he was so inclined but is enjoying (and has had commercial success) messing around with esoterica

You will have fun and you will like the audible results of the fruits of your labo(u)rs!
Well, I can pretty much guarantee the first part; the second part's an anecdotal SWAG based on my own feelings about a somewhat tarted-up ACA here that I've listened to on a variety of high-sensitivity loudspeakers.

 

[Deleted member 26571]

There are ten thousand posts in the ACA thread at diyaudio.com. Measured objectively, the ACA is providing thousands of man-hours of enjoyment to someone for some reason. The hand wringing evident in this thread on ASR is not a good look.

 

[tmtomh]

There are ten thousand posts in the ACA thread at diyaudio.com. Measured objectively, the ACA is providing thousands of man-hours of enjoyment to someone for some reason. The hand wringing evident in this thread on ASR is not a good look.

I definitely agree that the ACA amp is givng lots of enjoyment to some folks - and good for them! It's a DIY project and quite useful for both learning and using.

Your "hand-wringing" comment, though, is just silly. As many comments in this thread indicate, lots of folks enjoy talking about this amp and discussing the pros and cons, as well as the technical issues involved with the amp and (as in many ASR threads) the somewhat schizophrenic nature of audiophile culture when it comes to tech specs and measurements. Just because folks might engage in a conversation that is critical of something does not mean they are not engaging in a conversation that they find absorbing, educational, and enjoyable - and I would also imagine many ASR members are engaging in this thread while happily enjoying listening to their favorite music on their own equipment.

 

[Harmonie]

There are ten thousand posts in the ACA thread at diyaudio.com. Measured objectively, the ACA is providing thousands of man-hours of enjoyment to someone for some reason. The hand wringing evident in this thread on ASR is not a good look.

Of course, this hobby is all about enjoyment.
If you are happy, that's the most important.

 

[Deleted member 26571]

Thanks for the reply. I'm evidently not a long-time or frequent contributor to ASR, but I've been reading this forum daily for a few months now and I understand its purpose and culture. I see a range of comments in this thread, a fraction of which I would call genuinely dismissive or hostile to the amplifier, its designer, and/or its builders. Others seem to judge the amplifier against an objective standard that the it was never intended to meet.

I'm an electrical engineer by training (though I don't work in the field) and I daresay I know as much or more about audio amplifier design than the majority of ASR members. The ACA is not something I would build for myself personally. But I know exactly what Nelson Pass' design philosophy is and what the purpose of this amplifier is. Even though I'm not interested in building the amplifier myself, I find the concept interesting and it makes be happy to see people enjoying playing with this circuit.

The hardest part of any DIY project is building the box. The official ACA enclosure is a sweet-looking thing. I would have a hard time duplicating it for under two hundred dollars. If I had one of these amps, I would use it to drive horns or desktop speakers and have fun with it on its own terms.

I have even less interest in owning a Chinese Class D desktop amp than I have in the ACA. There are people who have built and listened to the ACA who are genuinely satisfied with its sonic performance. I feel no compulsion whatsoever to comment disparagingly on their subjective experiences.

Back in the day I had a chance to listen to a Pass Aleph 3 and I was astonished by how good it sounded. Objectively good in terms of the state of mind I experienced listening to it, for whatever reason. I don't think any of Pass' commercial products are particularly good deals and some of them are way over the top, evidently designed to appeal to the sort of buyers that make ASR readers roll their eyes... to put it politely. Personally, I don't feel the slightest outrage or indignation at the existence of this three hundred dollar oddity. It is what it is. Anyone who is looking for a state-of-the-art DIY power amplifier project would do quite well to check out the Wolverine thread that's currently underway at diyaudio.com.

What I'm about to say will probably bring a lot of criticism down on my head, but ASR is not science. We do not listen with meters. Our brains do not objectively transcribe auditory stimuli into perceptual experiences. The idea that an amplifier should be a "straight wire with gain" is a defensible position to take, but it does not and cannot tell the whole story without taking into account the extraordinary perceptual processing that takes place in our brains. I find this forum useful because of the measurements, but the bulk of the discussion contributes nothing to the science behind audio engineering.

I find most subjective review magazines and websites to be nonsense. Sometimes I find myself getting bent out of shape when I see ads and reviews for snake oil products. But then I think about how much us-versus-them hatred there is in this world and I ask myself just how much I am really being harmed by snake oil audiophoolery. I am forced to conclude: not very much.

Live and let live, I say.

 

[LTig]

What I'm about to say will probably bring a lot of criticism down on my head, but ASR is not science. We do not listen with meters. Our brains do not objectively transcribe auditory stimuli into perceptual experiences. The idea that an amplifier should be a "straight wire with gain" is a defensible position to take, but it does not and cannot tell the whole story without taking into account the extraordinary perceptual processing that takes place in our brains. I find this forum useful because of the measurements, but the bulk of the discussion contributes nothing to the science behind audio engineering.

You are quite wrong in this since the task of an audio chain is to reproduce as faithfully as possible at its output what was fed to its input. This is physics and electronics, not psychology.