Pass ACA Class A Power Amplifier Review

[dtaylo1066]

M80 mentions H2

https://positive-feedback.com/audio-discourse/the-pass-h2-harmonic-generator/

 

[gene_stl]

A second harmonic generator strikes me as diametrically opposed (in the most rigorous sense) to everything this forum stands for.

 

[RayDunzl]

A second harmonic generator strikes me as diametrically opposed (in the most rigorous sense) to everything this forum stands for.

Unless you want to explore 2nd harmonic distortion.

Then you need a tool.

 

[m8o]

A second harmonic generator strikes me as diametrically opposed (in the most rigorous sense) to everything this forum stands for.

That did invoke a chuckle from me. Otoh tho (and as Ray said), I'd say understanding what H2 does to musical playback in an emperical auditory fashion is very much inline with the science of audio.

For anyone that doesnt want to open the link I provided then locate the figure noted, I'm referring to this.

Now note, H2 (and all) is (are) about 20dB greater here than that of the ACA tested. So the ACA is certainly not altering the waveform with an envelope to that degree; and of course all higher ones are proportionally much higher too. But the actual distortion probably does rest between a sinewave and this, closer to the sinewave.

 

[maty]

Nelson Pass says that too much harmonic distortion is not convenient with complex recordings, such as orchestral or electronic music. How much? H2 at -73 dB to simple recording or maybe at -84 dB is a good compromise to play ALL kind of music.

Of course, the H2 phase is very important too. And the difference in dB from H3.

The vast majority of acoustic instruments are dominant H2.

 

[maty]

To finish -better a new thread- with the dominant H2 and monotonically decreasing harmonic profile, a year ago, in the Hifisonix sx-Amplifier, class A, designed by Bonsai:

https://www.diyaudio.com/forums/solid-state/329814-hifisonix-kx-amplifier-post5598322.html

And the latest design of Hugh Dean (AKSA), with the help of xrk971 and others: Alpha Nirvana 39w 8ohm Class A Amp, 43% efficient SE Class A.

https://www.diyaudio.com/forums/solid-state/344540-alpha-nirvana-39w-8ohm-class-amp.html

And if we increase power to about 12.5w into 8ohm, we still see a nice monotonically decreasing harmonic distortion profile. THD is now about 0.016%

 

[LTig]

A second harmonic generator strikes me as diametrically opposed (in the most rigorous sense) to everything this forum stands for.

Just the opposite. It's an effects box - insert it between preamp and poweramp (like an EQ) and use it or not, depending on your mood, the recording, the weather, what ever. No need to buy flawed gear any longer to get this effect.

 

[solderdude]

nicer than the ACA ..

 

[amirm]

Now note, H2 (and all) is (are) about 20dB greater here than that of the ACA tested. So the ACA is certainly not altering the waveform with an envelope to that degree; and of course all higher ones are proportionally much higher too. But the actual distortion probably does rest between a sinewave and this, closer to the sinewave.

What did you do with all the other tones in your music that are each creating that harmonic spray? You know, those bass tones with much higher amplitude than the violin. Now the harmonics of those bass tones are stomping over the violin tones, including its -20 dB second harmonic.

 

[LTig]

Can anyone look at this design and point to one or two major faults that, if fixed, would improve the performance?

Replace Q4 (FET) by a small signal bipolar transistor. Its much higher gain should help to reduce THD. Have to be careful though WRT stability.

I would try to replace Q4 by an opamp. It should be able to handle 24V supply voltage and be a rail-to-rail type (those often are build for 10V supply voltage, so chose wisely). Now we definitely have to ensure stability, e.g. with an additional cap for a local feedback loop around the opamp alone, and a zobel network at the output to improve stability for higher capacitive loads.

 

[gene_stl]

I agree that if you were trying to study how to synthesize a violin sound electronically you might want to try one of these. or emulate a vintage Marshall or Fender amp.
But I don't see how it contributes to getting to a "straight wire with gain".

 

[RayDunzl]

But I don't see how it contributes to getting to a "straight wire with gain".

As opposed, perhaps, to a more modernistically inclined, LGBTQ (add any initials I may have overlooked) wire?

 

[m8o]

What did you do with all the other tones in your music that are each creating that harmonic spray? You know, those bass tones with much higher amplitude than the violin. Now the harmonics of those bass tones are stomping over the violin tones, including its -20 dB second harmonic.

I'm not sure if we are in agreement; I think we are.
But perhaps I fear the paragraph you quoted isnt being taken in context of my original reply to a question?

I was only saying the distortion applied to -every- tone that makes up the music, is akin to the 'sound of a violin'. Certainly not that everything begins to sound like an -actual- violin. But the texture and timbre of every tone that makes up the music at every instance in time (like the slice of an integral) sort of gets blanketed with the harmonics that make a violin sound like a violin, but with those harmonics applied at a lesser degree (the -20dB).

So are we in agreement? . Please advise if I misunderstood your clarification?

 

[BDWoody]

As opposed, perhaps, to a more modernistically inclined, LGBTQ (add any initials I may have overlooked) wire?

I think that isn't nearly woke enough... I'm sure they would each have their own unique...flavor.

I would think the L wire would sound more...treble focused than the T... Possibly getting a little harsh and screechy at times.

The B might be the most fun for party music, but for misc use, just a generic Q could likely be quite versatile.

 

[restorer-john]

As opposed, perhaps, to a more modernistically inclined, LGBTQ (add any initials I may have overlooked) wire?

Straight wire, Bi-Wire, Trans-sister, male and female- electronics is full of it.

This connector was one of the first I couldn't identify which was male and which female:

It definitely has a bit going on each way...

 

[RayDunzl]

I think that isn't nearly woke enough...

I, being so socially inept and backwards, had to look up "woke" in the modern sense, because, I had no more than some vague idea what it might mean, based on the conversations in which it generally occurs:

woke adjective
chiefly US slang
: aware of and actively attentive to important facts and issues (especially issues of racial and social justice)

First Known Use of woke
1972, in the meaning defined above

Wow. 1972. I only remember first hearing it recently, like, in the last year or so, probably emitted by a potential Presidential votee.

 

[Xulonn]

Wow! This thread has really gone off the rails...

 

[RayDunzl]

I accept full responsibility.

 

[BDWoody]

Wow! This thread has really gone off the rails...

I accept full responsibility.

I hope you both...woke up...

 

[maty]

https://www.diyaudio.com/forums/pass-labs/328357-aca-amp-premium.html

-> https://www.diyaudio.com/forums/pass-labs/328357-aca-amp-premium-post5568768.html

-> https://www.diyaudio.com/forums/pass-labs/328357-aca-amp-premium-post5594355.html