Pass ACA Class A Power Amplifier Review

[SEKLEM]

Going to need some Klipsch La Scalas to hear that sweet horrible distortion...

 

[ta240]

Wow... Yeah. You won't make best buddies with the DIY crowd with a review like that. Reality bites sometimes. Thanks for the review.

They can be a touchy group; you know how it is when an entire forum revolves around one person and what they say is the gospel

 

[BDWoody]

They can be a touchy group; you know how it is when an entire forum revolves around one person and what they say is the gospel

Because, having joined today you'd know all about the forum...right?

 

[Deleted member 2944]

Five pages already.

Dave.

 

[617]

Amp Camp and Burning Amp are, to my knowledge, primarily social gatherings, people come together and learn basic electronics skills and show off their weirdo full range speakers.

The fun and accomplishment you get out of making something like this is what you pay for.

There are better performing amp kits out there but they are more complex and harder for a beginner to understand. You can build a neurochrome design, for example.

Trying to design really high efficiency speakers is difficult, and you sacrifice a lot fidelity to get there, but it's fun.

 

[ta240]

Because, having joined today you'd know all about the forum...right?

I read fast.
Like the post where someone said amirm should do the listening test before the measuring so that the listening results wouldn't be affected by the bias of knowing the measurements and they got torn a new one because how dare they say he couldn't be objective. Ironically it wasn't even mentioned that the listening tests should be blind because double blind testing is only required for everyone else.
Or the other post where it was questioned if testing amps with a restive load actually produced accurate results and the reply was "then buy me a $40,000 test rig". That is a bit like NAD saying "if you want us to build amps that test better then pay to have one designed for us".

 

[anmpr1]

1) The other amps that he releases the schematics on and people design boards for can be quite complex to build and setup properly.

2) At the time of the original 'camp' event most of the product costs were absorbed by Mr Pass.

3) The basis of the 'event' was "you've never used a soldering iron? Well, lets build something and learn"

4) Somewhere along the line the amp took on a life of its own. It is sold with his permission due to a very high demand.

1) David Hafler (and a lot of others) were designing useful and easy to put together kits 60+ years ago. Kits that pretty much anyone could assemble. So there is not much excuse for anyone not offering something of value in a kit, that is both easy to assemble and usable, on a day to day basis.

2) As @restorer-john shows, the parts set you back about 15 dollars. A little more with power supply and case. That Mr. Pass subsidized the kit is to his credit.

3) You can buy "My First Soldering Kit" for ten bucks on line. But I admit that learning to use a soldering iron from a world famous audio designer at a 'lunch 'n learn' is not in the same category--experience-wise. However that is, spending $300.00 to build something which will likely wind up in the closet because it's so impractical... well, how meaningful is that?

4) If Nelson Pass is allowing this thing to propagate as a consumer oriented kit product, then obviously he doesn't care that someone is selling what people here are calling 'an experimental lab project' in order to make a profit. So the next question is, "Why would he allow that?" Why would a world famous designer of hi-end amplifiers allow someone to profit off his work, selling an obviously defective (or at least pretty much unusable) amplifier kit, a bag of parts that he gives away when he teaches people at his amp-camp to solder? Why would he do that?

I'm sorry if I can't take this seriously. I just can't. Imagine David Hafler, Hermon Scott, Harry Ashley, Ed Laurent, Stu Hegeman, Erno Borbely, Marshall Leach, Jim Bongiorno, et. al, putting their names on something like this. Good grief!

 

[Sal1950]

Why not build a amplifier that delivers 7 useful Watts ?

"What this country needs is a really good five-watt amplifier"
Paul W Klipsch
Nelson's reputation was built on his design of the Threshold Stasis amps and his work for Adcom, all great amps for their day.

So 'they' sell an exercise with a very nice cabinet and a not 'exercise alike' price that is just that. And NP thinks that is just fine and dandy because they say it is an exercise but gave it the looks of a finished design.

That's the part that bothers me the most. The Pass supporters here keep talking about how it was just an exercise in building a toy from the junk parts box. Why hasn't he come out and condemned this expensive kit as it puts a bad light on him to support it. IMO his integrity should have drove him to say something about this?

Part of the mystique this designer has and exploits, turns on a counter-culture, hippy-Bohemian, "I'll do it my way, damned any convention", eccentric-genius front. The associated look is integral to what he's doing, and it's what his customers both want and expect.

Not to use his looks as a point of attack, I see that as underhanded, but there's a whole lot of truth in the above statement. The larger percentage of the people who buy his products and get into his DIY projects came out of that generation. That and the reflection to a unkempt genius persona aka Albert Einstein sets the tone for his ventures.

 

[ta240]

2) As @restorer-john shows, the parts set you back about 15 dollars. A little more with power supply and case. That Mr. Pass subsidized the kit is to his credit.

The kits that he subsidized were complete with fancy cases, built in heatsinks and power supplies so they were the much more expensive versions. At the last Burning Amp Festival he just handed out the completed H2 boards for free with a "here, play with these, have fun, experiment".

 

[patient_ot]

Someone mentioned Akitika - would definitely be interested in seeing measurements of some of their stuff. They do offer fully assembled units as well.

 

[tomchr]

I thought I had a cable for this but can't find it. Will need to make another one to test it.

I would greatly appreciate it if you'd test the bridged configuration.

Tom

 

[Sal1950]

Someone mentioned Akitika - would definitely be interested in seeing measurements of some of their stuff. They do offer fully assembled units as well.

https://www.stereophile.com/content/akitika-gt-102-power-amplifier-measurements

 

[Deleted member 2944]

Why does a cable need to be made? Just a standard XLR cable interfaced to a non-psuedo balanced output will yield the bridged configuration, yes??

Dave.

 

[PierreV]

FWIW, looking a bit more into this, there are AP charts here

https://diyaudiostore.com/products/meanwell-24v-5a-psu-with-power-cord

They seem to show the improved design performing much better (also with a 24V power supply)

I probably wouldn't purchase a kit myself, but dropping $327 on it in some ways makes more sense than dropping an additional $300 (or much more) on some device to move some measurement from 100dB to 110dB...

 

[peng]

Let's admit people that this is a BS product not worth $320... Let's not beat around the bush. Let's call this, a turd.

The chassis is the killer, USD149. Another USD49 for the power supply.

 

[RayDunzl]

As a DIY amp with an adjustable bias control, makes me wonder if it was properly biased as that does change the distortion profile. The tell tale hint is that the distortion should go down as the amplifier warms up (for about an hour is the recommendation). Given that @amirm measured an increase in distortion with the amp warmed up, suggests the amp was not properly biased in the first place...

Good point.

https://guides.diyaudio.com/Guide/Amp+Camp+Amp+V1.6+Build+Guide/5

 

[gene_stl]

From what I have observed Amp Camp and Burning Amp etc are Gateway drugs to the high end. Perhaps trying to give a taste of it to those who can't or have not reached the point of spending the absurd amount of money that is required on high end gear. In this day and age power amps are like computer memory , hard drive space and bandwidth. Virtually free. I think spending $327 on this piece of junk would be a very unwise investment. What skills will you have when you are finished. Maybe you will learn to solder and get electrolytics in the right way.

There are lots of amps you can buy new for $300 with free schipping that have two or three hundred watts per channel at very low distortion. If you look for similar amps used they can be had all day long for less than $100. I have two Crown XLS series that I bought for $40 each. 300 wpc. They are a thing of beauty inside. Learning to build power amps is like learning to plow a field behind a mule. There may be some virtue to it, but it is actually silly for most people. (note back in the day the guy who helped me build my boxes built spikkkers for everybody. My role was building amp kits for everybody. I built zillions of Dynakits and Southest Technical Products amp kits. Consequently I am still tempted to build and repair. I repair scientific instrumentation for a living.)

I have in a box a Dyna Stereo 120 that I used to use for 100-1000 Hz. It blew up one channel as they are wont to do. I have been looking at rebuilding it using Akitika's nice stuff which for the ST120 are based on the LM3886 cheep. But doing the whole thing would cost two or three hundred dollars depending on how many of his cute temptations you decided to spring for. You still have a single ended supply amp with a big electrolytic coupling capacitor on the output which if it blows is going to try to take out your spikkers. But rebuilding with all new parts is tempting. This amp was one of the last factory built ones bought from Stereo Discounters after Dyna closed. The Stereo 120 rebuild parts are the same as used in the GT102 Sal mentioned. Like Sal I would rather have that one rather than this supposed class A amp.

 

[garbulky]

So the obvious question is - is this thing broken or badly put together?! That distortion is really poor.

 

[sonci]

If this is bad, imagine how some diy speakers would measure!

 

[gene_stl]

When people build diy speakers they don't build the raw drivers.