Pass ACA Class A Power Amplifier Review

[wwenze]

I'm here thinking out loud:

If we mod it to add an op-amp input stage and use global feedback, would performance vastly improve?

 

[JohnYang1997]

I'm here thinking out loud:

If we mod it to add an op-amp input stage and use global feedback, would performance vastly improve?

No. Output power is limited.
Also in that case why not just build an amp that performs better to begin with.
It's probably gonna be an ok headphone amp.

 

[solderdude]

I'm here thinking out loud:

If we mod it to add an op-amp input stage and use global feedback, would performance vastly improve?

Distortion will be much lower, output power the same and the 'fun' part of the design will be out the door as well as it's 'special' qualities which people attribute to it.
This amp is what it is, making changes alters the design and performance.
One needs to take it for what it is.

The only possible change could be to increase power supply voltages, heatsink size and output power capabilities. But why bother other than for the fun of the built.

 

[anmpr1]

One needs to take it for what it is.

I know what you mean, but I would rewrite your conclusion to state: "One needs to not take it, because of what it is."

Seriously and all humor aside, I appreciate the 'ampcamp' thing: getting together with friends, meeting new people, and sharing an experience (can we even do that these days?). But from a productive standpoint, it would make more sense to pretty much build any other kit than this little Nelson Pass toy. Maybe a tube guitar head, or even a combo amp kit. Something useful.

Where is David Hafler now that we need him?

 

[RichB]

I know what you mean, but I would rewrite your conclusion to state: "One needs to not take it, because of what it is."

Seriously and all humor aside, I appreciate the 'ampcamp' thing: getting together with friends, meeting new people, and sharing an experience (can we even do that these days?). But from a productive standpoint, it would make more sense to pretty much build any other kit than this little Nelson Pass toy. Maybe a tube guitar head, or even a combo amp kit. Something useful.

Where is David Hafler now that we need him?

... and one time at amp camp, I stuck...

- Rich

 

[gvl]

I'm contemplating to build one with my son just for fun and for him to learn something new. If you source all the parts yourself and can live with a less fancy enclosure the cost is $150 or less for a 2ch single ended version.

 

[DonH56]

Where is David Hafler now that we need him?

Passed away quite a few years ago, alas. R.I.P.

 

[maverickronin]

... and one time at amp camp, I stuck...

 

[cistercian]

Is that a dual triode? It is even fatter than my 833A!

 

[maverickronin]

Is that a dual triode? It is even fatter than my 833A!

The page I found the image on claims it's 35KV 40A Soviet radar tetrode...

 

[AnalogSteph]

The ACA in balanced mode would make a good - albeit somewhat impractical - amplifier for horn tweeters. I'm reading about 88 dB of SNR ref. 50 mW / 4 ohm, or 104 dB ref. 1 W / 8 ohm, and the gain is low enough that you should be able to just connect your DCX2496 without having to worry about attenuators and such.

Now could you come up with an amplifier that retains the ACA's few positives (low noise, ease of assembly) while not embarrassing itself on the bench right away, being much less toasty, and adding the odd feature? Oh, absolutely. I've got some ideas already. This may actually be worth doing, given that this sort of grey area between headphone amplifiers and speaker power amps isn't very well-explored.

 

[Ralf Stocker]

More than once I almost bit on getting one of these kits. But fortunately, I always realized there were a lot of better things to do with $300. Still, when you see and hear Mr. Pass, you can see why the kit is popular, and his 1st Watt and Pass Labs stuff sells..

For $22 more you can get a Yamaha as301:
Yamaha A-S301BL Natural Sound Integrated Stereo Amplifier (Black) https://www.amazon.com/dp/B00MXUCN0A/

Hope Amirm tests one of the as301/501/701/801 sometime soon

And this for $130:
Yamaha R-S202BL Stereo Receiver https://www.amazon.com/dp/B01EMQI2CU/


Amirm, great to see a 'break' from DACs for some amps!

What is the difference between an engineer and a guru? What is the difference between engineering and designing?

 

[KEW]

I have read speculation that the Outlaw M2200 and NHT A1 are designed by ATI. Do you know if this is true? Would you even be allowed to disclose it if it were true?

No, it is not. The reason for this speculation is that many of Outlaws amps were made by ATI.

Outlaw outsourced the M2200 from the same facility that makes Parasound amps (per M code)
Outlaw also sources from another vendor per this post where M code corrects me (I wrongly assumed all Outlaw non-ATI electronics were made at the Parasound facility):

https://forums.audioholics.com/foru...-processor-vs-avreceiver.113662/#post-1292881


Scroll down to post number 12 in the link above to see M code's statement on the m2200.

 

[solderdude]

What is the difference between an engineer and a guru? What is the difference between engineering and designing?

The designer invents, the engineering is tasked with creating an actual product.

A guru is just a designer and/or engineer that is adored by followers that like the products or the stories that are told (or made up) around the product.
These individuals are the ones that feel an engineer/designer needs to have an honorary name. Some stay humble others make use of their honorary 'title'.

 

[DonH56]

The designer invents, the engineering is tasked with creating an actual product.

A guru is just a designer and/or engineer that is adored by followers that like the products or the stories that are told (or made up) around the product.
These individuals are the ones that feel an engineer/designer needs to have an honorary name. Some stay humble others make use of their honorary 'title'.

Well crud, now I have to scratch "design" off my business card where it says "analog design engineer"...

My take:

The usual distinction that is made is not among design, engineering, and "guru" but between mathematicians and scientists who focus on theoretical aspects of things versus engineers that reduce the theory to practice, i.e. make something you can use. There is lots of creativity, design, inventivity, and all that jazz for engineers too, it is just usually more focused on the practical than the theoretical.

A "guru" is a subject matter expert, theoretical or practical. And there is no hard line between "theoretical" and "practical" -- it's a continuum, with a person dealing with theory one day and implementation the next, and back and forth.

Some folk do distinguish between R&D engineering and manufacturing engineers. And some scientists look down upon engineers and vice-versa. I've never felt the need to raise one speciality above another; I've had to accept that I cannot know everything, and have forgotten much of what I did know. I make no claim at always following the sage advice of a famous trumpet teacher but wish I did: "You do not have to blow out another's candle to make your own shine brightly."

 

[amirm]

Unless we are talking about industrial design, an engineer is also a designer and the terms are used interchangeably in US.

 

[solderdude]

Well crud, now I have to scratch "design" off my business card where it says "analog design engineer"..

You can be both ... and be considered a guru as well.
You business card could say: analog guru

 

[DonH56]

Old, old, old...

The Girl in the Chair Story:

• A girl was placed on a chair across the room.
• A mathematician, physicist, and engineer were placed behind a line at the other end of the room. They were told they could walk to the girl but each step had to be half the size of the first.
• The mathematician immediately started wailing that it was theoretically impossible to ever reach the girl, but turned around to the blackboard babbling about limit theories and starting writing all sorts of intricate equations to see if a new proof could be found.
• The physicist cried "not in the macro world" and began mumbling about discontinuities in space-time, uncertainty principles and such, then also turned to begin scribbling on the blackboard.
• The engineer took a big step forward, then another...
• The mathematician and physicist, seeing that, turned and yelled "Don't you understand, you can never reach the girl!"
• Without pausing or looking around the engineer replied "I'll get close enough!"

And that, my friends, is why I became an engineer.

 

[RichB]

I side with Merriam-Webster.

Definition of guru
1: a personal religious teacher and spiritual guide in Hinduism

2a: a teacher and especially intellectual guide in matters of fundamental concern has been a guru to many young writers
2b: one who is an acknowledged leader or chief proponent became the guru of the movement
2c: a person with knowledge or expertise : EXPERT a computer guru

IMO, it's best to keep mysticism out of engineering.

- Rich

 

[ctbarker32]

I built this amp many moons ago and enjoyed the experience. I thought it sounded okay but of course the measurements are an eye opener. The paradox of High-End Audio.

Steve Guttenberg just posted a video about the Amp Camp Amp. It captures the total experience of building this amp very well. I have always liked Steve and his reviews even though some of his positive reviews (Border Patrol DAC - an audio scam IMHO) are questionable. He will at least review low cost gear and acknowledge that good audio doesn't need to be expensive.