Pass ACA Class A Power Amplifier Review

[solderdude]

This can of things happen when amplifiers are used that are operated outside of their intended limits.
You don't expect a car that can reach 160kph normally to still perform well while driving down a steep mountain at 250kph either.

One should always operate devices within their limits. Trouble starts when owners do not know the limits and use it anyway.
Connecting not suited speakers or exotic cables that need special measures etc.

 

[solderdude]

I have some audiophile friends who is all over older vfets! Don’t know if that’s really snake oil

Let them pick those amps level matched and blind 15x correctly in a row and you will know if they are right or wrong.

 

[SIY]

I have some audiophile friends who is all over older vfets! Don’t know if that’s really snake oil

What was Nelson Pass’s quote? Well, at least they’re not toxic...

 

[CDMC]

What was Nelson Pass’s quote? Well, at least they’re not toxic...

see below.

 

[tomchr]

Would you know where the quote comes from by any chance?

Tom

 

[Hugo9000]

Would you know where the quote comes from by any chance?

Tom

According to his post here, his statement about his Ion Cloud loudspeaker was printed in the Wall Street Journal:

https://www.diyaudio.com/forums/pass-labs/1841-pass-plasma-speaker-history.html#post13712

He discusses the speaker briefly here:

https://www.stereophile.com/interviews/1191pass/index.html

 

[carlob]

Would you know where the quote comes from by any chance?

Tom

https://www.diyaudio.com/forums/pass-labs/1841-pass-plasma-speaker-history.html#post13712

 

[tomchr]

"It also had several flaws, one of which did result in a trip to the local emergency room with breathing problems similar to those sometimes experienced by arc welders and caused by extended exposure to ozone."

Wow. That is epic. Noting says high-end audio like having stators running at 10 kV emitting ozone.

Tom

 

[Sal1950]

If you don’t mind can you provide a link ? Seriously not questioning the authenticity of your answer

Here's a kind reverse approach, the 35+ yo Carver Challenge at Stereophile.
Bob proved by using some measurements and circuit tweaking, he could make his very inexpensive SS amp sound exactly like a very expensive tube amp. Some of the self-proclaimed best ears in the industry had to throw in the towel by the end of the experiment.
https://www.stereophile.com/content/carver-challenge
In the end it still shows that measurement in the hands of someone who knows what he's doing, can be used to determine the sound of a amp

 

[VintageFlanker]

I know and I can explain things which can influence sound, and I can demo that in listening room... my wife or neighbour can hear difference with no problem.

I suppose you tell your neighbour and wife what they're expecting to hear, before and after?

So let me tell you: I can demo literary anything with anybody that way.

PS: I second @SIY on this: if only works when your wife can hear the difference from the other room.

"this forum is not a very good place for any discussion which veers even a bit from its dogma"

"Somehow, Consumer Audio has the monopoly... of knowing something that engineers don't"

Gene DellaSala.

 

[Objectivist01]

Here's a kind reverse approach, the 35+ yo Carver Challenge at Stereophile.
Bob proved by using some measurements and circuit tweaking, he could make his very inexpensive SS amp sound exactly like a very expensive tube amp. Some of the self-proclaimed best ears in the industry had to

I suppose you tell your neighbour and wife what they're expecting to hear, before and after?

So let me tell you: I can demo literary anything with anybody that way.

PS: I second @SIY on this: if only works when your wife can hear the difference from the other room.



"Somehow, Consumer Audio has the monopoly... of knowing something that engineers don't"

Gene DellaSala.

I had experiences in the past when I hear things and my friends don’t until I say it’s there then they magically starts to hear it.

 

[Observer]

I suppose you tell your neighbour and wife what they're expecting to hear, before and after?

So let me tell you: I can demo literary anything with anybody that way.

PS: I second @SIY on this: if only works when your wife can hear the difference from the other room.



"Somehow, Consumer Audio has the monopoly... of knowing something that engineers don't"

Gene DellaSala.

You supposed wrong, I don't tell them what they should hear ... it make no sense.

Gene DellaSala: “I use Kimber 8Tc speaker cables because of their aesthetic”

Cheers

 

[anmpr1]

According to his post here, his statement about his Ion Cloud loudspeaker...

A takeaway, and certainly an argument for a beefy amp is in the linked Stereophile interview. Nelson was designing amplifiers with horribly 'difficult to drive' loudspeakers in mind--the part about the Ion Cloud, and Dayton-Wright XG8 electrostatics. I remember the very popular Apogee speakers. If you ran with that crowd you needed beef--top cow and not 70/30 burger. For most applications in a living room? YMMV

For the little box speakers measured on ASR, it's probably not much of an issue, if it's an issue at all.

Below is a cut from Drew Daniels' DIY loudspeaker article (w/4000 watts of tri-amplification), along with his 'subjective' report--note, Drew's thinking had nothing to do with amp classes, TIM, slew rate, fancy circuits and so forth, which he probably thought was mostly irrelevant in any decent amplifier. He also alludes to what people term 'breaking in' a system, which as @amirm has aptly recognized and argued is simply 'getting used to' the new loudspeaker when your ears are accustomed to what went before.

You may wonder why it's necessary to provide a bridged 600-watt amplifier for a driver that will be operated nominally at 1 watt. A 20 decibel musical transient peak requires 100 times the power required by the average signal and a 30 decibel peak requires 1000 times the power required by the average signal. The 600-watt output capability of the amplifier driving the midbass units represents just a bit less than 28 decibels above 1 watt of power reserve for the tracking of transients.

If you are an electrostatic or Bi-polar speaker fan, you will loathe the sound of this system until you get used to it, after that you will loathe the electrostatic and bi-polar types. An analogy of the perceived effect is that this type of system (high-efficiency type) is like removing an electronic compressor from an otherwise good speaker system.

 

[carlob]

I use Kimber 8Tc

Actually cables with high capacitance like the Kimbers can lead to attenuation of the hights and even oscillations/damage if the amp has no zobel network

 

[Observer]

Actually cables with high capacitance like the Kimbers can lead to attenuation of the hights and even oscillations/damage if the amp has no zobel network

You can ask Gene DellaSala about that..... he know Kimber cables.

 

[ta240]

... How can I prove it here on forum, where most of you believe in just one thing"measurment report". It is waste of time.

Politics, religion, and subjective vs objective in audio; the three topics that don't get discussed in polite company. You are right; going to the headquarters for the other side and arguing a different point of view is a waste of time. Some of the technical stuff is interesting but when the candles get lit and the chanting begins it's best to head out.

If you have to peek to hear the difference, you can't actually hear the difference.

That applies to everyone except amirm. When it was suggested once that he should at the very least do his listening tests before the measurements to avoid expecting to hear what the measurements show that was dismissed as insulting.

 

[Objectivist01]

Politics, religion, and subjective vs objective in audio; the three topics that don't get discussed in polite company. You are right; going to the headquarters for the other side and arguing a different point of view is a waste of time. Some of the technical stuff is interesting but when the candles get lit and the chanting begins it's best to head out.



That applies to everyone except amirm. When it was suggested once that he should at the very least do his listening tests before the measurements to avoid expecting to hear what the measurements show that was dismissed as insulting.

So you are saying that subjective sound and whats on measurements can be different ?

 

[JohnYang1997]

Politics, religion, and subjective vs objective in audio; the three topics that don't get discussed in polite company. You are right; going to the headquarters for the other side and arguing a different point of view is a waste of time. Some of the technical stuff is interesting but when the candles get lit and the chanting begins it's best to head out.



That applies to everyone except amirm. When it was suggested once that he should at the very least do his listening tests before the measurements to avoid expecting to hear what the measurements show that was dismissed as insulting.

All the listening tests as I know are done before measurements. It's just written after the measur section.

 

[MakeMineVinyl]

It was mentioned earlier that the amount of standing bias current in a class A/B output stage of a typical amplifier is usually lower than it could be. This is true. There is an unavoidable tradeoff between cost to the user and ultimate performance which all products, amplifiers or anything else, must conform to.

Would you rather pay less money for an amplifier of excellent quality or pay more money for the much larger heatsinks and shipping costs which would support "optimum" bias current for least crossover distortion - which the typical listener would never hear?

However in some systems with very high efficiency and resolving speakers there would certainly be small differences in listening quality between two amplifiers, one with higher verses lower crossover distortion or different spectra of distortion. These amplifiers might measure the same overall THD, but measurements aren't perfect - nothing is. Measurements are extremely useful but in the end sound equipment must be listened to as part of the development process.

 

[Objectivist01]

It was mentioned earlier that the amount of standing bias current in a class A/B output stage of a typical amplifier is usually lower than it could be. This is true. There is an unavoidable tradeoff between cost to the user and ultimate performance which all products, amplifiers or anything else, must conform to.

Would you rather pay less money for an amplifier of excellent quality or pay more money for the much larger heatsinks and shipping costs which would support "optimum" bias current for least crossover distortion - which the typical listener would never hear?

However in some systems with very high efficiency and resolving speakers there would certainly be small differences in listening quality between two amplifiers, one with higher verses lower crossover distortion or different spectra of distortion. These amplifiers might measure the same overall THD, but measurements aren't perfect - nothing is. Measurements are extremely useful but in the end sound equipment must be listened to as part of the development process.

Here we go again! Two amps measured exactly the same would sound the same. And for a quAlity amplifier if all meausrements conforms to certain standards beyond which no audible distortion is heard, they both would sound the same. Any parameter that’s tuned beyond this point which makes an audible change is just not right but just a some addition of subjective eq which he designer is liking. I don’t want my amps to have a permanent eq set on by the manufacturer!