Pass ACA Class A Power Amplifier Review

[amirm]

Want to see examples of a L mob that go overboard? This very thread, the PS Audio thread, the NAD thread.

People are shocked over the results published. Even I am. Reactions are therefore bound to be negative. It is natural that when covers are pulled off and we finally get some objective data that clashes with our previous understanding, that many people are outraged. You seem to be asking for people to act like robots, or expecting me to run a police force here to clamp people down to stay silent.

The problem isn’t criticism but rather allowing personal attacks or snarky comments on people outside that would never be allowed here,

What? There is no such restriction here. Anyone can come and join the discussion. As for personal attack, the only one I have seen is against me and the forum. And that person remains as a member.

To me they are all indications of a form of tribalism and a form of group catharsism. The danger is that it invites more similar minded people to join feeding on itself and driving out people that don’t.

I am pretty sure if you went to a convention of doctors, they would fit your definition of "tribalism" against the people who don't believe in modern medicine.

So please, put aside these debating tactics, arguments, etc. that have nothing to do with substance of this review. The title of the thread is a review of an amplifier. If you have something to say about that, say it. Otherwise, don't distract us from discussing the topic.

 

[restorer-john]

People are shocked over the results published. Even I am. Reactions are therefore bound to be negative. It is natural that when covers are pulled off and we finally get some objective data that clashes with our previous understanding, that many people are outraged.

You should have seen the torrent of hate I got on another forum when I posted this a year and a half ago:

 

[Sal1950]

I remember building my first amplifier.

LOL, Kool!
My first one was this Knight Kit. It was a neat product that could do a number of things.
Make me into a DJ broadcasting into any nearby AM radio.
I could use it with a mike and speaker for a PA amp or a TT as a phono preamp/amp.
Costs all of $12.95 in 1963. Lots of fun, I loved it!
Might even have out-spec'd the ACA

 

[RayDunzl]

Costs all of $12.95 in 1963

$12.95 in 1963 → $108.66 in 2019

Or thereabouts.

(remembers riding bicycle to store after finding a nickel on the ground, probably to get a balsa glider)

Ouch...

 

[amirm]

(remembers riding bicycle to store after finding a nickel on the ground, probably to get a balsa glider)

Used to tape coins to the nose to make them fly faster!

 

[RayDunzl]

Somebody remind me what was wrong with the Gold Standard again?

 

[Blumlein 88]

Somebody remind me what was wrong with the Gold Standard again?

You'll have to ask Nixon.

 

[Wombat]

$12.95 in 1963 → $108.66 in 2019

Or thereabouts.

(remembers riding bicycle to store after finding a nickel on the ground, probably to get a balsa glider)

Ouch...

View attachment 38210

That was the first thing I would look for in a Christmas stocking.

 

[m8o]

Seems about right.

Doesn't make me want to get my hands on my friend's Aleph 30 any less tho.

 

[cjfrbw]

Very entertaining thread, but didn't read EVERY post here. By all accounts. the builders of these amps really like the sound. Single ended output, which will frequently fall down in measurements. Pass likes it himself, because he has said with little speakers he plays it at his bench with noodling music background. Currently, he has also devised a headphone amp project that has similar topography on the DIY website, and it also puts out about 1 watt@ 0.1 percent distortion.

Maybe Amir can get one of those to bring out the blood howl of ASR. I bet it measures pretty bad, too, by comparison and can even be used for speakers . http://www.firstwatt.com/pdf/art_acp.pdf

However, really, ACA was just a small DIY project that absolute beginners could complete in an afternoon aka just for soldering introduction and entertainment. It was never meant to be taken seriously as an amp, people just liked the way it distorted?? sounded????

So, does the brain have the ability to filter and reconstruct sound THROUGH some kinds of egregious distortion, and even perversely enjoy it?

Remember the $350,000.00 eight chassis Wavac 833 that couldn't even squeeze out a watt at one percent distortion, and required 10-15 percent distortion to even approach it's power envelope of 150 watts? My little Wavac, which probably does no better at a lower power rating, sounds wonderful to the unvarnished ear.

https://www.stereophile.com/content/wavac-sh-833-monoblock-power-amplifier-measurements

Apparently, according to listeners, Wavac 833 is considered a peak audio experience.

I am a bit surprised at how wretched the ACA amp measures, though. You can find kits and fully built Chinese samples on ebay for less than the $327 or so.

 

[RayDunzl]

So, does the brain have the ability to filter and reconstruct sound THROUGH some kinds of egregious distortion, and even perversely enjoy it?

Maybe.

One bit is "enough".

https://soundcloud.com/ray-880875693%2Fonebitpaul

 

[cjfrbw]

I'm shocked that is even discernible the way it is at one bit. Two bit Paul must be almost hi fidelity yuck yuck!

 

[Sal1950]

My first one was this Knight Kit. It was a neat product that could do a number of things.

The best part of all was that Allied Radio's main store on Western Ave in Chicago was just short 15 minute ride from my house and my dad was always up for taking me there on a Sat or Sun to do some dreaming. We didn't have any money but he never minded spending some time with me to let me indulge my gear fantasy poking around there. RIP pop, you were the best!

 

[RayDunzl]

I'm shocked that is even discernible the way it is at one bit.

The sample is so short because, even with "1 bit" sound, SoundCloud recognized the longer version and blocked it.

"SoundCloud
Hi Ray,
It looks like your track
"OneBitPepper"
might contain or be a copy of "With A Little Help From My Friends" by The Beatles, which is owned by owned by EMI Catalogue in certain territories.
As a result, your track has been removed from your profile for the time being.

Thank you,
The SoundCloud Copyright team"

Jeez.

 

[restorer-john]

The best part of all was that Allied Radio's main store on Western Ave in Chicago was just short 15 minute ride from my house and my dad was always up for taking me there on a Sat or Sun to do some dreaming. We didn't have any money but he never minded spending some time with me to let me indulge my gear fantasy poking around there. RIP pop, you were the best!

That's awesome, Sal! Great memories. How much fun was an AM transmitter, huh? I loved making them too and 'jamming' the neighbours...

I remember Dad and I going to HiFi stores on Saturday mornings in early 1970s as they were open usually from 9am until midday. I even persuaded him to take me to a store on Bridge Rd Richmond called "Ham Radio" and I'd rat through this big bin of PCBs they had at the front door really cheap, like a lucky dip. I was allowed to buy one or two things only. Other kids were buying lollies and gum/football cards...

From my point earlier, imagine if all the Amp Camp attendees were kids, not adult audiophiles? That would be awesome.

 

[RayDunzl]

We had the Eico HF-81 and a matching mono FM tuner, built with my 8 year old help on the dining room table about 1962 or so.

It was very mysterious. Sound was fine.

 

[Blumlein 88]

We had the Eico HF-81 and a matching mono FM tuner, built with my 8 year old help on the dining room table about 1962 or so.

View attachment 38218

It was very mysterious. Sound was fine.

I still have one of those. Haven't tried it in some time, but last time I did (2010'ish) it worked still.

 

[solderdude]

Audiophile/boutique build by abza.

Amp Camp Amp build log! (Nelson Pass Amplifier)
https://www.avforums.co.za/index.php/topic,77452.0.html

Pictures optimized

View attachment 38169

View attachment 38170

At x watts?

H2 at -60 dB.
H3 at -73 dB.


View attachment 38171

At 1 watt?

H2 at -75 dB, great value!
H3 at -78 dB.

Good numbers if we have loudspeakers with high/very high sensitivity as my calcs.

The X Watt is actually almost 1W (0.98W into 8 Ohm) = 0.1% THD and 0.075% @ 1kHz (so the dashboard tells us)
Amir measured 0.3% in the version he has.

Where you say 1W it is 13dB below 1W = 0.05W = 0.02% THD (calculated)
Amir measured 0.06% in the version he has.

The by Amir measured amplifier thus has 3x worse distortion than the one you posted.

For both cases (0.1W and 1W) with the numbers of the measurements you posted I would say audibly transparent at these levels.
Doesn't take away the fact that due to the simplicity of the design it won't fit in the homes of the majority of ASR members.

 

[cjfrbw]

The sample is so short because, even with "1 bit" sound, SoundCloud recognized the longer version and blocked it.

The Beatles stuff is heavily surveilled for copyright. Must be quite the profit center still in order for all those lawyers to keep sniffing everywhere for malfeasance. I posted a You Tube video of my system playing a vinyl record of a Beatles cut, and they nixed it right away, even at that remove from the original.

 

[maty]

You know, I would like more H2 at -73 dB or -84 dB at 1 watt, H3 at least 10 dB less if I would like harmonics over -90 dB. ALWAYS dominant H2. But, after add delay from JRiver MC 64-bit DSP, I have more depht and I can adjust it depending on the kind of music...