Pass ACA Class A Power Amplifier Review

[SIY]

I have no arguments over any of your opinions. To each his own.
I have shared what I hear out of ACA in my system.
Sonic wise, I like the sound of ACA the most with respect to the speaker I use it with.
I have tried ACA on some power hungry speakers including the Totems and Dynaudio, where it falters with dynamics.
But with proper matching it is a superb sounding amp.
Last month it performed superbly on an Altec Lansing 604B.

When you have made comparisons with clean amplifiers ears-only, the sonic opinions can be meaningful. The fun aspect, I’d be the last person to argue about that.

 

[Koeitje]

When you have made comparisons with clean amplifiers ears-only, the sonic opinions can be meaningful. The fun aspect, I’d be the last person to argue about that.

Exactly, a very large group of audiophiles (such as @kannan ) have zero interest in high fidelity. They just want to modify the sound to their liking. Which is fair game.

 

[Observer]

Folks are selling dirty water as tasting good. What else can I say?

There must be a reason on reviewer (your) side for bad listening experience, maybe Topping dac have bad/low output level so you have no enough gain . Once I had Smsl dac , I had to put volume on 12 o'clock on my Verdi Cento (100w@ch) to hear something. Some chinese brands match output/impedance to their cheap amps , but usually don’t match well to “normal” amps . A guy with iPhone test ACA amp, and got good level &sound, here is link:

 

[jan.didden]

Have you read at least some of this forum? Do you really think Amirm got a bad listening experience because he had his gain structure wrong?? That's even less likely than me getting a phone call from Ms. S. Johansson asking me out for a date!

Jan

 

[Observer]

Did you check the video?
Your “guru“ said for ACA ... is that thing on?
Something must be wrong at his place , since 99% percent of people who use ACA dont have problem to determine if amp is on , and they even enjoy the amp.

 

[SIY]

That's even less likely than me getting a phone call from Ms. S. Johansson asking me out for a date!

Jan

Is there something you’re not telling me???

 

[617]

Is there something you’re not telling me???

She actually invited me to her apartment in Paris on a hot June evening, but when I saw her Pass ACA I bailed. Killed the mood.

 

[jan.didden]

Did you check the video?
Your “guru“ said for ACA ... is that thing on?
Something must be wrong at his place , since 99% percent of people who use ACA dont have problem to determine if amp is on , and they even enjoy the amp.

Disclosure: years ago I organised an 'AmpCamp' here in The Netherlands and we build about 20 pairs of ACA's in a day. It was a lot of fun, we had a dad building with his daughter, friends, young and old, and audio people who never held a solder iron before.
They ALL reported how they enjoyed the amp, how great it sounded, and I also kept one set for my self (since sold).

OTOH, Amir's measurements are what they are, you can't argue with them (well you can but you'd make a nice fool of yourself).

So what it boils down to is perception, enjoyment and very personal experiences on one hand, and hard science on the other. I see lots of posts of people trying to 'bend' the measurements to make them conform to their perceptions. Usually that is a meaningless exercise.

Jan

 

[Observer]

So.... you think you can read measurements and buy amp which measure the best?
I heard since 80's many amps who measure very good and they sounded not so good , and others who measure a bit worse but they sound excellent.
You can also find amps who measurements are almost the same, but they sound different. You can't predict how amp sounds when you only read specs/measurements, not to mention that different amps love different speakers. Sonus Fabers - even small one Concertinos are power hungry. I know because I own small ones and big ones. If amp don't match speaker, that does not mean that amp is bad. Then you just plug in ACA a pair of Triangle bookshelf speakers and it will shine. But for that, you need less measurements and more experience.

 

[SIY]

So.... you think you can read measurements and buy amp which measure the best?
I heard since 80's many amps who measure very good and they sounded not so good , and others who measure a bit worse but they sound excellent.
You can also find amps who measurements are almost the same, but they sound different. You can't predict how amp sounds when you only read specs/measurements, not to mention that different amps love different speakers. Sonus Fabers - even small one Concertinos are power hungry. I know because I own small ones and big ones. If amp don't match speaker, that does not mean that amp is bad. Then you just plug in ACA a pair of Triangle bookshelf speakers and it will shine. But for that, you need less measurements and more experience.

That must be it. I need more experience.

 

[jan.didden]

So.... you think you can read measurements and buy amp which measure the best?

Uhhhh ... yes I can. What is so special about that? Or did you mean something else than what you wrote?

Jan

 

[RammisFrammis]

I think the point of using this amp would be for driving very high efficiency horns (especially the high frequency horn of a bi-amped system) where the power needed would always be less than one watt. In situations like this, the total absence of crossover distortion which comes from a class "A" amp overrides any other considerations. At least that is true in my case where I used a single ended triode 2A3 amp for high frequencies with a 105dB/watt efficient horn.

It all depends on the usage - of course the ACA amp would be useless in a home theater system.

 

[SIY]

I think the point of using this amp would be for driving very high efficiency horns (especially the high frequency horn of a bi-amped system) where the power needed would always be less than one watt. In situations like this, the total absence of crossover distortion which comes from a class "A" amp overrides any other considerations. At least that is true in my case where I used a single ended triode 2A3 amp for high frequencies with a 105dB/watt efficient horn.

It all depends on the usage - of course the ACA amp would be useless in a home theater system.

In nearly all AB amps made in the past several decades, crossover distortion is a non issue.

 

[RammisFrammis]

If using speakers of "normal" efficiency, you are correct; if using high efficiency speakers, crossover distortion is very, very much a consideration. Feel the heatsinks of you typical Class A/B amplifier; if they are stone cold or barely warm, the bias is just the minimum to avoid onset of high crossover distortion, nothing more. Especially with amplifier manufacturers who are concerned with energy usage, this is most likely to be the case.

Actually, how bias is handled in "modern" amplifiers is no different than in decades past.

 

[Observer]

Uhhhh ... yes I can. What is so special about that? Or did you mean something else than what you wrote?

Jan

You can’t measure the “sound”, with todays knowledge you can measure just some parts of it.
And using only that in count, you miss the bigger part.

 

[JohnYang1997]

You can’t measure the “sound”, with todays knowledge you can measure only some parts of it.
And using only that in count, you miss the biger part.

I have the feeling that you are trolling here.

 

[SIY]

If using speakers of "normal" efficiency, you are correct; if using high efficiency speakers, crossover distortion is very, very much a consideration. Feel the heatsinks of you typical Class A/B amplifier; if they are stone cold or barely warm, the bias is just the minimum to avoid onset of high crossover distortion, nothing more. Especially with amplifier manufacturers who are concerned with energy usage, this is most likely to be the case.

Actually, how bias is handled in "modern" amplifiers is no different than in decades past.

Unfortunately, measurements do not support that assertion.

 

[Observer]

I have the feeling that you are trolling here.

I am shure that I am not.
How can you explain that Dacs or Amps who mesaure the same sound different?

 

[pkane]

How can you explain that Dacs or Amps who mesaure the same sound different?

Ear wax?

 

[Frank Dernie]

I am shure that I am not.
How can you explain that Dacs or Amps who mesaure the same sound different?

a badly executed comparison.