Pass ACA Class A Power Amplifier Review

[maty]

With commercial SS, 0.1% THD and 1% THD if tubes is what I set for power.

ACA is an exercise, an entertainment. With H2 about -40 dB -> like a SET tube amp profile -> THD 1%.

 

[tomchr]

You are talking the same thing. IMD mains related lines. The reason is very low PSR rejection of such circuits, together with high PSU ripple due to high idle current. That's why ACA uses SMPS instead of linear PSU (transformer, bridge rectifier, filter). SMPS does not have mains line issues, it may have HF EMI issues. You may also go with high filter capacitances for linear supplies, which helps, but again it is a kind of overkill, similar to produced heat.

I know... I design such contraptions for a living. I went single-ended for my HP-2 DIY headphone amp. I used an RLC filter to get rid of the SMPS HF hash and opamps with stellar PSRR to prevent any remaining power-supply related noise from reaching the amp output. The result is quite good (as you can see in attached residual noise measurement).
I do recognize that a headphone amp draws less current than a Class A power amp, but there's no technical reason you couldn't design a Class A power amp to have similar performance.

Tom

 

[pma]

I do recognize that a headphone amp draws less current than a Class A power amp, but there's no technical reason you couldn't design a Class A power amp to have similar performance.

Tom

Yes but I do not know why should I do it with the project that was made 18 years ago just for fun and as simple as possible and that was built by absolute beginners. This is a closed chapter. BTW, if idle current is decreased to the level of headphone amplifier needs, mains lines intermodulation goes away. I can also show you clean noise floor of the line level amplifier, however I thought this thread was about ultrasimple power amplifiers with very compromised parameters.

 

[pma]

So before I dismounted the toy, I made some more measurements - 3 kinds of IMD vs. amplitude and THD vs. frequency at 1W/4ohm. The measurements of mosfet power follower, simplest 2-transistor amplifier (1xMOSFET + 1xDarlington - CCS) give almost same results as Amir had shown in ACA measurements. That was my goal, to show that Amir's measurement correspond to real behavior of these simple amplifiers. These amplifiers may be nice as DIY starting project for absolute beginners, but have nothing in common with the task we request from good amplifiers - to yield exact amplified copy of the input signal at the output.

Mosfet Power Follower - THD and IMD vs. output voltage for 4ohm load

Mosfet Power Follower - THD vs. frequency at 1W/4ohm

 

[readerA]

I'd love to see how you plugged in this gear for the … listening test?
I run a more or less comparable set of audio-gear, and sorry, but what you have put there is just some alternative reality.
But it's okay.
It's also fine to let your readers believe they can do better for 1/10 of the price. Power supply, chassis, connectors and everything included of course.

I will leave you with video from my favorite and most famous entertainment Master: Bixby Snyder. https://youtu.be/85cL1HisrNc

 

[pma]

I'd love to see how you plugged in this gear for the … listening test?
I run a more or less comparable set of audio-gear, and sorry, but what you have put there is just some alternative reality.

I had a complete two channel Mosfet Power Follower amplifier, in the past, in the box with similar construction like one you will find here:


https://www.audiosciencereview.com/...wood-ka-5010-amplifier-clone.9902/post-267371

This is my "alternative reality", Sir.

 

[BDWoody]

I'd love to see how you plugged in this gear for the … listening test?
I run a more or less comparable set of audio-gear, and sorry, but what you have put there is just some alternative reality.
But it's okay.
It's also fine to let your readers believe they can do better for 1/10 of the price. Power supply, chassis, connectors and everything included of course.

I will leave you with video from my favorite and most famous entertainment Master: Bixby Snyder. https://youtu.be/85cL1HisrNc

Well, that helped clear things up.
Want to post some data from your 'comparable audio-gear' and enlighten us all as to what wonderfulness we are missing?

That'd be great.

Nobody is telling you not to like it (sounds like you have one...). Lobbing some silly post like that without anything other than 'nuh uh' as the main point seems a little...I dunno...lacking?

 

[Xulonn]

It's also fine to let your readers believe they can do better for 1/10 of the price. Power supply, chassis, connectors and everything included of course.

"fine"? Or actually true if you substitute "know" for "believe"? Attempted snark that actually reflects reality?

It's also good to let your readers know they can do better for 1/10 of the price. Power supply, chassis, connectors and everything included of course.

Edited - Since the quoted person apparently could not comprehend my logic-based snark, I edited the above "not-really-a-quote"

 

[amirm]

I'd love to see how you plugged in this gear for the … listening test?

I connected the speaker using speaker wires to it. I plugged in the AC power. And I powered the input via a top performing DAC with its own volume control. Very, very complicated so I am glad you asked!

 

[Thomas savage]

I connected the speaker using speaker wires to it. I plugged in the AC power. And I powered the input via a top performing DAC with its own volume control. Very, very complicated so I am glad you asked!

But did you have someone competent check all those connections to make sure they were all correct.

 

[amirm]

I will leave you with video from my favorite and most famous entertainment Master: Bixby Snyder. https://youtu.be/85cL1HisrNc

Not even worth that one dollar in my book unless you want to claim you have built something you don't understand. But sure, if you want to just play, use parts out of a junk drawer.

And not just my opinion by the way. Here is Rod Elliot on the same design: https://sound-au.com/project36.htm

If this is your idea of high-fidelity, I suggest staying low here until you learn both the electronics and performance aspects of amplifiers.

 

[amirm]

Rod goes on to say about the output power stage of the ACA Amp:

The recommended MOSFET by Nelson is IRFP240. What is the application for that? From IR website:

Switching is its design goal. There, you are going from on to off quickly, not what we want in audio where we operate the transistor proportionally to provide amplification. Linearity is poor as a result which the low feedback gain of ACA amp fails to attenuate by much.

Straightforward engineering shows why this is a design optimized for part count and assembly effort, and not any attempt at high fidelity. People who want to claim otherwise, need to first learn about electronic design. Building these amps doesn't make you so.

 

[amirm]

But did you have someone competent check all those connections to make sure they were all correct.

Yes, twice. Once by our female dog. And second, by the male one. Both barked at the end, confirming proper connections and scents.

 

[restorer-john]

Yes, twice. Once by our female dog. And second, by the male one. Both barked at the end, confirming proper connections and scents.

Ah, that's where I've been going wrong! You have a bidirectional canine cable tester. My single ended undirectional feline cable tester is much faster, but less accurate.

 

[readerA]

"fine"? Or actually true if you substitute "know" for "believe"? Attempted snark that actually reflects reality?

Nah. I actually said (well, wrote) It's also fine to let your readers believe they can do better for 1/10 of the price. Power supply, chassis, connectors and everything included of course.

Of course, it's up to you to decide if you want to take this as a challenge. Dare to show your community?

 

[readerA]

I connected the speaker using speaker wires to it. I plugged in the AC power. And I powered the input via a top performing DAC with its own volume control. Very, very complicated so I am glad you asked!

See. That's basically what I do with my gear–which is similar in specs though way simpler and cheaper than yours. My ACA doesn't even have that nice Power-supply, just the wall mart. But mine makes some noise on some 88dB-bookshelve-speaker, from a Usb-DAC.
Thus I can't believe you really plugged it the right way 'round (Just as canine sometimes tend to confuse front and back ends) when you state that you performed ... a .... wait a minute – a listening test?

Is this thing on?

That is the expression that immediately came to mind after I hooked up the ACA amp to my Sonus Faber Concertino bookshelf speaker. Granted, the Concertino is spec'ed at 86 dB efficiency but come on, I could barely hear it. There was no bass naturally. But not much above that either. And this was with my Topping DX3 Pro at full volume.

For grins, I plugged the US $74 tiny little SMSL SA100 Amplifier which I recently reviewed into the setup. Now the speakers came alive, with lots of bass, great dynamic range, and detail.

So much for, erm, serious testing and stuff like that.

I'm not talking about high-fidelity, as you aren't neither. I'm (we're?) talking about loudness, volume, you know, "is this thing on"... c'mon, if you barely can't hear it with this setting you have, you'd be better off counting the revolutions of a record-player.

If this is your idea of high-fidelity, I suggest staying low here until you learn both the electronics and performance aspects of amplifiers.

Ha. Never said anything about "high fidelity". I'm talking about a fun peace of gear. You should read carefully and respond accordingly.

 

[BDWoody]

 

[Xulonn]

Of course, it's up to you to decide if you want to take this as a challenge. Dare to show me?

OMG, you are actually not aware of my post quoting your original silly statement and creating a snarky response? I edited my previous post to help you comprehend the point I was trying to make.

I am aware that others in this thread (which you seem to have not read in its entirety) have already met your challenge. And I am familiar with the prices of audio electronics cases, PS's, and connectors for DiY'ers. $300 is a ripoff.

What's next from you? A double-dog dare? To build a pile of audio crap? No thanks. I built my first amplifier kit back in about 1968. I'll stick with my $400, 70wpc, vintage 1993 Classé A/B amplifier.

 

[readerA]

"fine"? Or actually true if you substitute "know" for "believe"? Attempted snark that actually reflects reality?



Edited - Since the quoted person apparently could not comprehend my logic-based snark, I edited the above "not-really-a-quote"

OMG, you are actually not aware of my post quoting your original silly statement and creating a snarky response? I edited my previous post to help you comprehend the point I was trying to make.

I am aware that others in this thread (which you seem to have not read in its entirety) have already met your challenge. And I am familiar with the prices of audio electronics cases, PS's, and connectors for DiY'ers. $300 is a ripoff.

What's next from you? A double-dog dare? To build a pile of audio crap? No thanks. I built my first amplifier kit back in about 1968. I'll stick with my $400, 70wpc, vintage 1993 Classé A/B amplifier.

1968? Not bad.
For the rest of this conversation, you‘re right. It‘s silly. You‘re bullshitting and I know it even if I didn‘t measure anything.
33 1/3 rpm btw.

 

[Thomas savage]

1968? Not bad.
For the rest of this conversation, you‘re right. It‘s silly. You‘re bullshitting and I know it even if I didn‘t measure anything.
33 1/3 rpm btw.

I can't work out what your point is but can you dial down the obnoxious and rude tone of your posts please .

If your wondering to which posts I'm referring, all of them.

thanks