I'm not Neurochome Tom , iv not quite worked out what I am but I definitely can't be trusted around high voltages.
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Pass ACA Class A Power Amplifier Review
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FIFY. (From the "takes one to know one" group of fans.)
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Just remember -- one can be shocked many times... but one can only be electrocuted once.
Measuring high voltages -- Just follow Alanis Morissette's advice:
One Hand In My Pocket
EDIT: PS If my name were Neurochrome Tom -- I think I'd have it tattooed somewhere prominently.
Took me about 3 and a half minutes to understand your advice. Certainly enough time to get shocked many times over.
I kept waiting for her to say her hand was in an insulated glove.
Neurochrome Tom has identified a number of weak points on my end that I haven't properly thought through. I may not even get out of the starting gate on this one. That's probably a good thing to know now rather than later.
You cautioning me about high voltage, and keeping a hand in a pocket and Tom's partial of my possible tool purchases and offering suggestions that have me questioning whether or not I want to make a proper investment into tools I may only need this one time.
On a side note, I did just get my Caintuck F-15 open baffles and I am enjoying them even though they are supposed to not be in their prime just yet.
You may have given Tom something to consider.
I kept waiting for her to say her hand was in an insulated glove.
Neurochrome Tom has identified a number of weak points on my end that I haven't properly thought through. I may not even get out of the starting gate on this one. That's probably a good thing to know now rather than later.
You cautioning me about high voltage, and keeping a hand in a pocket and Tom's partial of my possible tool purchases and offering suggestions that have me questioning whether or not I want to make a proper investment into tools I may only need this one time.
On a side note, I did just get my Caintuck F-15 open baffles and I am enjoying them even though they are supposed to not be in their prime just yet.
You may have given Tom something to consider.
My first build was an ACA. I just bought the boards, then sourced the components separately so I didn't have a lot invested in them. I don't think I spent over a couple hours listening to it. I've always wondered if I did something wrong based on the glowing reviews it receives. Even at low volumes I wasn't impressed. Although, one time I fed it with the 02 Headphone amp on high gain as a preamp and thought it sounded better.
My second build was a single ended tube amp. I don't know if a lot of it was the fun of building it but when I was done it sounded exquisite. Then I chased tweaks, capacitors and tube rolling down the rabbit hole and it never sounded the same. With one set of tubes the highs would sound good, with another the lows sounded good. Whenever I turned it on I'd think it sounded great, but I don't know if it was always in the back of my head that a different tube might sound 'better' but I was never happy long term with it. And when a song would come on that I'd like and turn it up I could hear it struggling. Even a low powered SE like it used 90 watts continuously and put out a fair amount of heat in the summer. Now that I run the stereo 12-16 hours a day and use music to drown out the neighbors, it just doesn't seem optimal.
That amp was in a wood case (treated with fireproofing) so I never got a bad shock off of it. However one I did get careless with one that I used in the garage and sent 400v down one arm, through my chest and out the other. That did not feel good and I probably should have seen someone about it.
I built Rod Elliott's PA3 and I still enjoy its 'smooth' sound. I don't think it is really a high fidelity sound but it is quite pleasing. Only when I turn it up do I find it not as good.
Later after a few other builds I did the Akitika GT-102. To me that is the perfect beginner DIY amp. Bulletproof instructions, no sourcing of parts, no drilling, no figuring out power supplies or adding speaker protection or and of the other tasks that most builds take. It sounds good.
A few more builds down the road and I finally did the Modulus-86. The boards and instructions were very good, but it requires sourcing a case and power supply and speaker protection. Then fitting it all and making sure it is solidly and safely constructed. To me it seems to sound a bit better than the GT-102 but I may be imagining that. I generally found myself listening to this amp the loudest out of any of them. I wouldn't think about it but would notice after awhile that I had it pretty loud. It is clear and strong at higher volumes.
I also build Rodd Elliott's P101A and it is clear and punchy but I'd kind of like a tone control to up the low end a bit on it.
And then finally, after all those years, all those builds and all that money.... I've decided I really like having a remote control for the power, volume and input switching, plus tone controls are nice. So, tomorrow a Yamaha R-N600A is due to arrive. I really enjoyed the building, the planning, the sourcing parts on the DIY builds. I find the process very Zen and I do miss it. However, looking back, I could have bought a really impressive 'forever' amp for the money I've spent. Instead I have a tote full of completed amp boards and a few completed amps in cases that have no resale value.
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When you enter the world of audiophilia you are stepping into an alternate universe.
Consider this kind of bullshit in an alternative context. Suppose that I took on a commission from the local HAM radio club to present a design for a basic transistor tuned radio frequency receiver. This is to be an introductory project to give club newbies and novices in electronics something to build and to get them listening to whats on the airwaves.
Imagine that I subsequently turned up to the following committee meeting with my example development. It is this stupidly miss-engineered heap of crap that consumes 300W of power, weighs 50kg and won't even come close to matching the performance of a basic crystal set unless it is paired with some kind of boutique or obscure headphones that nobody actually owns. Oh, and I am going to generously charge the newbies and adolescent novices about $400 AUD for the basic kit.
Would this design be a raging success? Would the grown men of the committee and all of the other club members grovel at my feet and start lovingly calling me their Papa?
No! Idiots and weirdos aren't the norm in this arena. I'd be rightly laughed out of the room and likely ejected from the premises with scorn and contempt.
Consider this kind of bullshit in an alternative context. Suppose that I took on a commission from the local HAM radio club to present a design for a basic transistor tuned radio frequency receiver. This is to be an introductory project to give club newbies and novices in electronics something to build and to get them listening to whats on the airwaves.
Imagine that I subsequently turned up to the following committee meeting with my example development. It is this stupidly miss-engineered heap of crap that consumes 300W of power, weighs 50kg and won't even come close to matching the performance of a basic crystal set unless it is paired with some kind of boutique or obscure headphones that nobody actually owns. Oh, and I am going to generously charge the newbies and adolescent novices about $400 AUD for the basic kit.
Would this design be a raging success? Would the grown men of the committee and all of the other club members grovel at my feet and start lovingly calling me their Papa?
No! Idiots and weirdos aren't the norm in this arena. I'd be rightly laughed out of the room and likely ejected from the premises with scorn and contempt.
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That is a lot of anger about audio reproduction.
As far as I'm aware he doesn't make anything off the sales from DIYAudiostore.com He does have PassDIY.com with 3 items for sale. Those ship from his warehouse and come with a nifty PASSDiy sticker
His designs that are for sale on DIYAudiostore site are routinely 'knocked off' by people on the forum that freely distribute the gerber files for their version's of the PCBs, and he will even chime in and give them advice on their designs.
On the subject of stupid, old technology shouldn't all those HAM radio people be ashamed of themselves because they aren't using zoom, facetime or teams to communicate instead of the ancient low quality communication method they are using?
As far as I'm aware he doesn't make anything off the sales from DIYAudiostore.com He does have PassDIY.com with 3 items for sale. Those ship from his warehouse and come with a nifty PASSDiy sticker
His designs that are for sale on DIYAudiostore site are routinely 'knocked off' by people on the forum that freely distribute the gerber files for their version's of the PCBs, and he will even chime in and give them advice on their designs.On the subject of stupid, old technology shouldn't all those HAM radio people be ashamed of themselves because they aren't using zoom, facetime or teams to communicate instead of the ancient low quality communication method they are using?
Those people would not claim that their HAM radio gives superior audio quality, though.
dtaylo1066
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And ICEPower or Hypex amp kit is a good and easy way to learn DIY and also get a quality measuring and sounding unit.
But they would claim that they complete their communications of often planetary distances without using publicly available infrastructure, which is frequently enough not available in circumstances extant at one end or the other.
And for them that’s the challenge, and doing it well isn’t that easy.
Rick “whose ham radio gives close to the best audio quality for communications from here to the other side of the planet when limited to using only two radios, two antennas, and two portable generators” Denney
solderdude
Grand Contributor
The journey can often be more rewarding than the final destination.
The money (and time if that were converted to money) I have spent on the headphone hobby itself could probably have bought me a HE-1 but would not have had the experiences that I have accumulated over decades.
The ACA is a fun educational thing when actually building it rather than buying a finished one. It can even make itself useful and will give pride of builder/ownership.
andrewwnbanks
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No you don’t, but it does add yet more evidence that you have something against any company that makes a component worth more than bargain basement.This is a review and detailed measurements of the Pass ACA Class A stereo power amplifier. It is a DIY design by the famous designer, Nelson Pass, meant to be starter amplifier for people new to audio electronics to build. There are many kits available. The one loaned to me from a long time friend of the forum. The kit seems to cost around US $320 or so.
The ACA sample I received comes in an attractive black case:
The design is a Mosfet output stage with a single stage buffer. Very modest level of feedback (9 dB?) is provided to keep distortion somewhat under control. As you will see, the gain is very low requiring full 2 volt of DACs to drive it to max power.
Here is the back side:
I did not mess with it but I am assuming the single XLR allows bridged mono operation.
Power is provided by a very beefy external switching power supply which outputs 24 volts with up to 5 amps or 120 watts. All of that is put to "use" in generating copious amount of heat. I was told by the owner to let it warm up for a few minutes. As you will see in the measurements, this actually made the performance worse, not better.
Overall, this is a very nice package if it performs.
Amplifier Audio Measurements
As usual, we start with our dashboard with 5 watt output into 4 ohm. Normally this is well below the max power but not in this case as we see later:
View attachment 38083
Gosh... What happened to aiming for high fidelity? This is a distortion-factory if there ever was one. The notion that it is mostly second harmonic does not hold true either. Welcome to the bottom of our amplifier ratings:
View attachment 38084
Let's dig into distortion spectrum at lower power level of just 1 watt:
View attachment 38085
Second harmonic is more dominant than at 5 watt but it doesn't stay there that long. Here it is at 2 watts:
View attachment 38086
Our 32-tone signal resembling "music" paints an ugly picture as a result:
View attachment 38087
I was pleasantly surprised how quiet the unit is though:
View attachment 38088
Frequency response is also very well extended:
View attachment 38089
You may be able to make an AM radio out of this thing.
Back to ugliness, here is our power versus distortion+noise into 8 ohm load:
View attachment 38091
Oh gosh again.... Only 7 watts of power with SINAD of 38 dB?
Things don't get much better with 4 ohm load:
View attachment 38092
We now have distortion climbing into near 10% category at max power of just 7.4 watts/channel.
There was little variation of response with respect to frequency:
View attachment 38093
Distortion level is so high that it is masking secondary sources of it.
Making sure this unit matches the reference, I compared them to what Nelson Pass has published:
View attachment 38094
We are getting very good agreement. So this is what the unit is supposed to do. Nelson stays with 1 watt output which shows the performance to be better.
EDIT: I noted on the dashboard that the gain was much lower than the spec. I am told that version 1.6 which I tested now has a spec of 10 dB for gain so we are good.
EDIT 2: See this link for bridged mode measurements: https://www.audiosciencereview.com/...ass-a-power-amplifier-review.9741/post-262036
Listening Tests
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. Yes, the amp started to cry when I turned it up much but until that point, it left the ACA so far in the dust it was not even funny.
Conclusions
As a starter hobby amplifier to get some sound coming out of a speaker, with relatively few components, the Pass ACA Class A Amp does the job. Build it, have fun with it and then put it aside and get a proper amplifier. Amplifiers need to have a lot more power. And much less distortion. We are not even close here folks.
Do I need to tell you that I can't recommend the Pass ACA for hi-fi listening? I hope not.
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As always, questions, comments, recommendations, etc. are welcome.
I suspect the above review is going to make me many enemies in DIY audio circles. So I need hire a bodyguard and get some serious insurance for my bodily parts from Loyd's of London. Both cost good amount of money so please donate generously using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
vs.
So what is it? No good reviews on budget gear, or only budget gear gets good reviews?
tmtomh
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I don't think you understand what the term "evidence" means.
What makes you think that?
It is true it is mainly performance that is praised not niceness of enclosure or feel of controls, though they are mentioned but this item is far from high fidelity at any price.
The amplifier in a cheap smart speaker is probably better than this.
Jim Taylor
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We at ASR advocate The Scientific Method. The data it collects is the dispassionate (unemotional) numerical representation of values discovered in the efforts to understand the universe.
Under no circumstances does the Scientific Method prevent people from developing personal opinions or preferences. It does, however, provide evidence whether those opinions or preferences are demonstrable. Because ASR is evidence-based, we prefer that which can be demonstrated. This includes (among other things) 1) performance level-vs.-cost and 2) the blanket (and sometimes obliquely humorous) classification of "snake oil".
Posts which show no demonstrability, and are not based on evidence or data, are not useful for criticism. In particular, it is not useful to make accusations regarding other people's motivations. That would fall, I believe, under the classification of "ad hominem".
Many members here have disagreements with (various) other members, but they retain a certain degree of civility. One of the reasons for that is the aforementioned requirement for evidence. Another is simply the realization that impolite behavior, if left unchecked, ruins the utility of websites and reduces their memberships.
As regards the review of the ACA amp which @Amir posted ... the conclusion was upheld by the data provided. If you admire the ACA amp and have a preference for it, that is entirely up to you. No one can prevent you from having that preference ... nor should they. But to make disparaging remarks and incorrect conclusions regarding the review and the motivations of the reviewer (who happens to be the owner of this site) are not a really good idea. If you still doubt Amir's motives, please read this:
A bit about your host....
This is a bit about your host, Amir Majidimehr. I am writing this as to give more context to people reading my technical reviews and measurements. I have realized that without this context, many assume I am yet another blogger spitting out graphs. That is very true but let’s see if we can...
www.audiosciencereview.com
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How do you figure this? All Amir has done is measure the amplifer and post his results.
Now one thing I can guarantee you is that I'm sure Nelson has been made aware of this 6 year old review and if he felt there was any error in the measurements posted he would have been thrilled to point them out here.
I've been a fan of much of his design work for decades and even today I still run 5 power amps he designed for Adcom. Those were done back in the day when his main concern was designing amps that were accurate input to output, etc. Sadly at some point his focus changed from excellent technical design, to "voiced amps" and making money from the subjective HIGH END community.
To quote John Atkinson from a 2018 review,
"As with the other Pass Labs XA-series amplifiers we have reviewed, the XA200.8's top-octave decrease in linearity (fig.7) is associated with some higher-order intermodulation products that were fairly high in level when the amplifier was asked to drive an equal mix of 19 and 20kHz tones at high power into 4 ohms (fig.11). Even so, the second-order difference product at 1kHz, which will be more audible than the higher-order products, lies at a low –74dB (0.05%)."
Pass Laboratories XA200.8 monoblock power amplifier Measurements | Stereophile.com
Sidebar 3: Measurements Before performing any measurements, I ran one Pass Labs XA200.8 (serial no. 29556) for an hour at one-third its measured maximum power into 8 ohms—thermally, the worst case for an amplifier with a class-AB output stage but not for a true class-A amplifier, which runs at...
In the last line of this review he tries to cushion the bad measurement results with a claim of their low audibility.
So why then did Nelson design in these failing grade measurements if not to voice the amp to add something inaccurate to the sound of the input? It's far from a "straight wire with gain" design for a $42,000 in 2018 product.
As to the case in point of the amp measured here, it's results are so "off the rails" for a High Fidelity amp sold in 2019 I don't know how he could look any other HiFi EE in the eye.
Shame on you Nelson !
If you look at the stuff this guy posts, it's clear he doesn't care about any of this. He rails at Amir about not liking cheap stuff in this thread. But also rails against Amir about not liking expensive stuff in other threads. Totally incoherent.How do you figure this? All Amir has done is measure the amplifer and post his results.
Now one thing I can guarantee you is that I'm sure Nelson has been made aware of this 6 year old review and if he felt there was any error in the measurements posted he would have been thrilled to point them out here.
I've been a fan of much of his design work for decades and even today I still run 5 power amps he designed for Adcom. Those were done back in the day when his main concern was designing amps that were accurate input to output, etc. Sadly at some point his focus changed from excellent technical design, to "voiced amps" and making money from the subjective HIGH END community.
To quote John Atkinson from a 2018 review,
"As with the other Pass Labs XA-series amplifiers we have reviewed, the XA200.8's top-octave decrease in linearity (fig.7) is associated with some higher-order intermodulation products that were fairly high in level when the amplifier was asked to drive an equal mix of 19 and 20kHz tones at high power into 4 ohms (fig.11). Even so, the second-order difference product at 1kHz, which will be more audible than the higher-order products, lies at a low –74dB (0.05%)."
Pass Laboratories XA200.8 monoblock power amplifier Measurements | Stereophile.com
Sidebar 3: Measurements Before performing any measurements, I ran one Pass Labs XA200.8 (serial no. 29556) for an hour at one-third its measured maximum power into 8 ohms—thermally, the worst case for an amplifier with a class-AB output stage but not for a true class-A amplifier, which runs at...www.stereophile.com
In the last line of this review he tries to cushion the bad measurement results with a claim of their low audibility.
So why then did Nelson design in these failing grade measurements if not to voice the amp to add something inaccurate to the sound of the input? It's far from a "straight wire with gain" design for a $42,000 in 2018 product.
As to the case in point of the amp measured here, it's results are so "off the rails" for a High Fidelity amp sold in 2019 I don't know how he could look any other HiFi EE in the eye.
Shame on you Nelson !
This was both obtuse and hilarious, I love it when Audiophiles compare their wealth and their alleged competence:
Audioquest Niagara 1200 Review (Power Conditioner/Surge Protector)
One should respect people; one needn't respect all of their opinions and/or statements. Yes, and there is a respectful way to reply to opinions that one does not share. We should all strive to be so generous whenever possible.
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