Amplifier comparison: March Audio P452 (Purifi 1ET400A) vs Buckeye Hypex NC502MP vs AIYIMA A07 (TPA3255) vs Onkyo TX-NR737 (125W Class AB)

[f1shb0n3]

Some random thoughts on the whole process of comparing speakers, amplifiers and such -
Listening intently to find differences which are hard to hear is improving my appreciation for music in unexpected wonderful ways:

• I can now listen and appreciate music for the fine details and nuances of instruments, dynamics, spacial presentation, etc. in addition to the song as a whole. I could do that before to an extent with focus, now it happens naturally.
• Found a lot of new music and expanded the genres I enjoy! Soundtracks, orchestra, indie rock, vocal harmonies, etc.
• After intently listening to good recordings, some of my old favorites started sounding like crap, pop music being worst offender A bit unhappy about it, but these are the "sacrifices" necessary for "science"

 

[Sal1950]

I can now listen and appreciate music for the fine details and nuances of instruments, dynamics, spacial presentation, etc. in addition to the song as a whole.

Unfortunately if your not using strickly bias controlled DBT conditions your adding sonic qualities to recordings that you (want-think should) to be there. No one is immune bias induced imagination.

After intently listening to good recordings, some of my old favorites started sounding like crap, pop music being worst offender

Just often the consequence of listening on better gear. No one ever heard any problem from the mp3's on their boom-box.

 

[f1shb0n3]

Unfortunately if your not using strickly bias controlled DBT conditions your adding sonic qualities to recordings that you (want-think should) to be there. No one is immune bias induced imagination.

I've essentially acquired a bias towards better sounding music, not a bad one
I like to embrace my biases and utilize them for improving my listening experience - learned this from subjectivists, it works!

I've not heard appreciable differences in amplifiers yet and enjoying my music as well on the "bottom-tier" Onkyo AVR amp as the SOTA Class D Purifi amp, in sharp contrast to my bias towards "well-engineered and well-measuring" gear.

Just often the consequence of listening on better gear. No one ever heard any problem from the mp3's on their boom-box.

So true!

 

[Sal1950]

I've not heard appreciable differences in amplifiers yet and enjoying my music as well on the "bottom-tier" Onkyo AVR amp as the SOTA Class D Purifi amp, in sharp contrast to my bias towards "well-engineered and well-measuring" gear.

Yet you claim to hear differences in the amps "crisper highs" without taking step one to apply a proper scientific approach to your testing procedures. These claims could possibly hurt the sales of the Bucheye vs Purifi but IMHO and are most likely bias induced.
These types of reports are not the type we do here, there's a hundreds of sites to tell fairy-tales on.
Tighten ship and then present the evidence.

 

[f1shb0n3]

Yet you claim to hear differences in the amps "crisper highs" without taking step one to apply a proper scientific approach to your testing procedures. These claims could possibly hurt the sales of the Bucheye vs Purifi but IMHO are most likely bias induced.
These types of reports are not the type we do here, there's a hundreds of sites to tell fairy-tales on.
Tighten ship and then present the evidence.

I'm doing it for my own education and being fully transparent in my journey so far. Would have been totally lost without the help I got here.

To be clear and avoid confusion - I hear no appreciable differences in any of the amps at all (still) when volume matched (except expected noise differences close to tweeter). I use these amps in my systems and have been perfectly happy with each of them and would recommend them to anyone! I'm not doing the comparison to pick winners - I will continue using all these amps anyway, just want to understand the nature of differences (if any) to inform my future purchasing decisions.

If I can ever pass a volume-matched A/B test and have confidence in it, I will shout from the rooftop here, caps and all so you won't miss it

 

[dlaloum]

Given you are testing with KEF R3 speakers, and the impedance of the speakers is (as Measured by Amir) 8ohm nominal with a drop to around 3 ohm at the woofer crossover...

The requirements on the amplifier performance envelope are by no means difficult... a little bit of grunt is needed due to the 3.2ohm minimum - which will require a bit of current - but it's not like it is dropping down below 2 ohm.

There is nothing there that should put any of the amps into the difficult zone, where nasties are exposed - they should all behave like "wires with gain".

It is worthy of note, that the most difficult part of driving these speakers is in the bass area - and that is where you are noticing minor differences

Although you described your comparisons between the other amps - you made no description comparing to the Onkyo?
Was there no noticeable difference?

 

[Chrispy]

Some random thoughts on the whole process of comparing speakers, amplifiers and such -
Listening intently to find differences which are hard to hear is improving my appreciation for music in unexpected wonderful ways:

• I can now listen and appreciate music for the fine details and nuances of instruments, dynamics, spacial presentation, etc. in addition to the song as a whole. I could do that before to an extent with focus, now it happens naturally.
• Found a lot of new music and expanded the genres I enjoy! Soundtracks, orchestra, indie rock, vocal harmonies, etc.
• After intently listening to good recordings, some of my old favorites started sounding like crap, pop music being worst offender A bit unhappy about it, but these are the "sacrifices" necessary for "science"

Curious, have you trained at all for listening or have you tried Amir's listening skills video or ?

Always good to use the gear to listen the actual recordings Concentrating on the recording is a more useful thing than concentrating on an amp in my experiences over the years. I find amp differences insignificant in general among my various amps, and going thru more than my informal testing for preference just isn't all that interesting (and can be difficult to do). Better recordings are always better than poor recordings (in terms of the way the gear works....a good performance will shine thru of course, just make you wish it was better handled at the recording level).

 

[Sal1950]

I'm doing it for my own education and being fully transparent in my journey so far. Would have been totally lost without the help I got here.

I applaud your desire to learn and acquire knowledge. I only offer my advice on the proper path to gain a accurate baseline for your learning.. First take the time to set up that proper level matched DBT using the best procedures at your disposal. It's really not that difficut at all. Then when you start to get answers to any question you have, they will be the correct ones.

If I can ever pass a volume-matched A/B test and have confidence in it, I will shout from the rooftop here, caps and all so you won't miss it

You can't pass or fail these tests, only collect data on your question.
Do the two amps under test really sound different ?
If you can identify A from B near 100% of the time, then yes some difference exists.
If not near 100%, running the test a lot of times will start to accumulate data showing the statistics on the likely hood of there being a difference or your just guessing.

 

[f1shb0n3]

Given you are testing with KEF R3 speakers, and the impedance of the speakers is (as Measured by Amir) 8ohm nominal with a drop to around 3 ohm at the woofer crossover...

The requirements on the amplifier performance envelope are by no means difficult... a little bit of grunt is needed due to the 3.2ohm minimum - which will require a bit of current - but it's not like it is dropping down below 2 ohm.

There is nothing there that should put any of the amps into the difficult zone, where nasties are exposed - they should all behave like "wires with gain".

It is worthy of note, that the most difficult part of driving these speakers is in the bass area - and that is where you are noticing minor differences

Thanks for the analysis - I don't know how to interpret the MTF graph myself. I'm using R3 to compare amps because they are my new shiny speakers, but I also have DBR62 and they are a harder load I think (lower sensitivity and Amir's review mentions beefy amp needed). Would listening on them help reveal differences between amps better?
I'd expect lower powered amps will lose dynamics at the hard frequency range at lower volume compared to the more powerful amp. Definitely want to hear an amp towards its limit as part of the education and comparison, the AIYIMA 07 (TPA3255) is the one I'll look to max out eventually for such test, don't think I have any speakers around that would get Onkyo AVR, Purifi or Hypex amps to struggle to drive.

Although you described your comparisons between the other amps - you made no description comparing to the Onkyo?
Was there no noticeable difference?

Currently listening to Onkyo vs Purifi on R3 - first proper volume-matched comparison I do, assuming these amps will be the most different from the set. No differences heard yet, but continuing to listen and not finished with the comparison.

After done with the Onkyo, l'll listen to Hypex and TPA3255 vs Purifi. Planning to take my time with it, it's obviously very hard to hear differences and might take me awhile to improve my listening skills.

Curious, have you trained at all for listening or have you tried Amir's listening skills video or ?

No training. Seen Amir' video, understand proper procedures for blind testing and know basic statistics to evaluate, but I'm not there yet in the process.
I'm aware of Harman's old "How to listen" app, but not sure if it's relevant to amplifier comparisons as it teaches recognizing mostly tonality differences.
I'd appreciate pointers to listener training materials if anyone knows any!

Concentrating on the recording is a more useful thing than concentrating on an amp in my experiences over the years. I find amp differences insignificant in general among my various amps, and going thru more than my informal testing for preference just isn't all that interesting (and can be difficult to do).

I arrived to the same mindset myself too - not listening to "amps", but the details of the recording and overall experience with it. As for amp differences, I want to figure it out this once, be done with comparing amps for life so i can focus only on the music not gear going forward. After doing the same comparison exercise with DACs too though

 

[dlaloum]

The DBR62 also has a "difficult" patch with the crossovers - shown in Amir's impedance graph - but it only drops down to 5 ohm

So in terms of being relatively inefficient - it will need a bit more power to get to the specified SPL, but it won't need a heap of current, so it won't strain the power supplies.

The Kef R3 dropping to 3 ohm will use a lot more current - making the power supplies work harder - but still not a difficult load

If you were running these (testing) with 10W tube amps - you might push them into their difficult zones.... but in your case with all the amps capable of 100W+ and all of them being decent quality, with current reserves and headroom.... I doubt the amps would be under any pressure (at least not at any sensible SPL !!)

The advantage of what I would call "normal" designs, as opposed to exotica!

Look at the Gallo Reference 3.5 impedance at 20khz:

It drops down to well below 2ohm - luckily at the high end, where typically you don't need too much power - but in doing similar comparisons - it was the high end where I felt the differences between amps were (marginally) audible... (confirmation bias? - possible.)

Also if you look at impedance for electrostatics - here is a Martin Logan... dropping down to 1.5 ohms:

These kinds of speakers tend to be difficult for some amps.

 

[f1shb0n3]

Yet you claim to hear differences in the amps "crisper highs" without taking step one to apply a proper scientific approach to your testing procedures. These claims could possibly hurt the sales of the Bucheye vs Purifi but IMHO and are most likely bias induced.
These types of reports are not the type we do here, there's a hundreds of sites to tell fairy-tales on.

I've been a follower and participant in this community myself for the past year and a half and believe to be following some reasonable scientific approaches. Where I don't, I get a correction (like this one) and incredible support and advice from knowledgeable professionals and experienced HiFi enthusiasts such as yourself for which I'm immensely grateful!

What I'm really struggling to figure still is - How to properly preface, explain, rationalize or disambiguate expressed subjective listening experiences with audio gear to avoid misleading people, hurting manufacturers or the integrity of this website as an established objective science-based audio forum?
Could be an interesting topic to explore in a separate thread. For now, I'll continue with a bunch of gear evaluations because that's the best fun I've had with audio my entire life and I'm learning a ton. I'll continue "blogging" about it on ASR while trying my very best to not mislead people in any way with unvalidated or non-scientific subjective impressions. Any tips on how to be better about it would be appreciated!

Example - my not-well-prefaced subjective experience statement in reference:

I hope my experience is useful to some planning to compare amps - wanted to emphasize how I incorrectly volume-matched the amps by ear before getting the ‘scope and heard “crisper highs and more detail” on Purifi when it was actually louder by 0.5dB.

Yes, some might miss that I'm saying incorrect volume matching leads to this experience and consider it a claim of subjective or objective differences between volume-matched different gear. How to say it properly though to avoid confusion or triggering anyone's "smells like subjectivism" sense while browsing the forum? I suspect it's a struggle for others too.

 

[Sal1950]

Currently listening to Onkyo vs Purifi on R3 - first proper volume-matched comparison I do, assuming these amps will be the most different from the set. No differences heard yet, but continuing to listen and not finished with the comparison.

I only want to point out to you how much you already appear bias to believe that a audible difference "should" exist in this compare. Maybe yes, maybe no, but if you try your best to make the test closely controlled you can avoid even your own bias. Many of us here have been down this same path and arrived here with a heavily objective slant due to what we learned from
our testing experiences.

I don't know if you're aware of Peter Aczel, now RIP, but most all of is writing and legacy is still on-line. Take a bit to read this short page, specially #6 as it applies directly to this conversation. I believe we're close to 20 years since he pen'd this but see how close his crystal ball was.

Web 'Zine Page 1

What I'm really struggling to figure still is - How to properly preface, explain, rationalize or disambiguate expressed subjective listening experiences with audio gear to avoid misleading people, hurting manufacturers or the integrity of this website as an established objective science-based audio forum?

There's only one way, using the same approach Amir uses.
If you apply proper scientific controls to your listening approach, you can be most reasonably comfortable that the subjective findings you present will be accurate to fact and not illusionary.

 

[tomtoo]

@fishbone

Its great what you do. But its very importend to know, if you realy like to be honest to your self. Its not allowed to know what is playing.

 

[f1shb0n3]

@fishbone

Its great what you do. But its very importend to know, if you realy like to be honest to your self. Its not allowed to know what is playing.

Very very important indeed! I'm finding surprising value in a very simple exercise of randomly rotating the box in my hands with eyes closed and randomly switching switches until I lose track of which side is which and switch and listen without conscious knowledge of which one is which. I plan to improve my switching box to be fully symmetrical to remove the hand-felt cues about which is A or B, that will be even better!

 

[f1shb0n3]

I only want to point out to you how much you already appear bias to believe that a audible difference "should" exist in this compare. Maybe yes, maybe no, but if you try your best to make the test closely controlled you can avoid even your own bias. Many of us here have been down this same path and arrived here with a heavily objective slant due to what we learned from our testing experiences.

Biases in sighted comparisons are unavoidable and I believe should be clearly expressed for full transparency instead of pretending they don't exist. Full de-biasing through double-blind ABX testing is the gold standard, the standard we should definitely apply to any scientific inquiry or manufacturers claiming audible subjective improvements with their products. Does this standard apply to your average enthusiast (like myself) who wired up a couple of amps to compare them and is asking for help on this forum?

I'm afraid I might not be able to meet this high standard you imply. When your prior statement also included an offer to go away to other websites "to tell fairy-tales on" it makes me feel even less welcome posting here. I guess that's a good strategy to keep the forum clean from "subjectivists" who only tell fairy tales. Let's not go overboard with it though.

I don't know if you're aware of Peter Aczel, now RIP, but most all of is writing and legacy is still on-line. Take a bit to read this short page, specially #6 as it applies directly to this conversation. I believe we're close to 20 years since he pen'd this but see how close his crystal ball was.

Web 'Zine Page 1

Thanks for the link - haven't read it, will check out! Indeed I've missed an important step in my "scientific inquiry" - look at prior publications.
Hey, I called my effort "scientific inquiry" - from now on all standards apply full force

 

[tomtoo]

@fishbone
You are absolutly welcome!!

Nothing is perfect. What counts is learning by doing.

 

[Blumlein 88]

I've sort of had in mind putting together a best practices thread for sighted comparisons. They'll always be second class citizens to blind tests, but aren't always useless. The natural way audiophiles usually do this unfortunately are nearly guaranteed to mislead.

Item #1: You must have an excellent volume match between devices. (I think you've learned that in this thread)

Item #2: Go back and read item #1, I mean it, it is a must have job #1 don't pass go if don't do this.

Item #3: Use pink noise. Frequency response differences are the #1 reason two things sound different. Pink noise makes pretty small FR differences stand out clearly. It also has an advantage vs music. There are no short always changing details where we can trick ourselves upon hearing over and over that one time it was just a little plainer and clearer than another time.

After that I'm at a bit of a loss. I do have one hint. The Swedish JAES did series amplifier testing. I've done that. I found it much more revealing than side by side comparisons. Basically you put an amp, loaded with a speaker like load, between source and the amp driving the speakers. You can switch it in and out of circuit to see if you hear a difference The Swedish test almost never found a transparent amp sighted and always followed it with blind testing to confirm. The hint however is what they found the most revealing signal. It was a recording of a metronome. It was exactly repetitive and had lots of transients and harmonics. I wish someone could find out which recording of one they used. I think it points out something useful though in that an exactly repetitive signal does what pink noise does in that it makes you less likely to hear a fleeting not-repeated portion of music and think it sounds different. You'll hear the same signal again, and again and again every 2 seconds.

So pink noise will cover FR, and something like a metronome will cover transient dynamic power differences in amps. Those two right there might pretty well work as well as anything that can be done sighted and by home audiophiles. Not as much fun as sitting with pals sipping a nice wine or some nice bourbon and listening to musical favorites while casually deciding about new gear, but perhaps a lot more effective in finding real differences (and finding times you don't really hear a difference).

Anybody have any thoughts about this?

Maybe I need to go find a metronome and record it myself.

 

[f1shb0n3]

I've sort of had in mind putting together a best practices thread for sighted comparisons. They'll always be second class citizens to blind tests, but aren't always useless. The natural way audiophiles usually do this unfortunately are nearly guaranteed to mislead.

Item #1: You must have an excellent volume match between devices. (I think you've learned that in this thread)

Item #2: Go back and read item #1, I mean it, it is a must have job #1 don't pass go if don't do this.

Item #3: Use pink noise. Frequency response differences are the #1 reason two things sound different. Pink noise makes pretty small FR differences stand out clearly. It also has an advantage vs music. There are no short always changing details where we can trick ourselves upon hearing over and over that one time it was just a little plainer and clearer than another time.

After that I'm at a bit of a loss. I do have one hint. The Swedish JAES did series amplifier testing. I've done that. I found it much more revealing than side by side comparisons. Basically you put an amp, loaded with a speaker like load, between source and the amp driving the speakers. You can switch it in and out of circuit to see if you hear a difference The Swedish test almost never found a transparent amp sighted and always followed it with blind testing to confirm. The hint however is what they found the most revealing signal. It was a recording of a metronome. It was exactly repetitive and had lots of transients and harmonics. I wish someone could find out which recording of one they used. I think it points out something useful though in that an exactly repetitive signal does what pink noise does in that it makes you less likely to hear a fleeting not-repeated portion of music and think it sounds different. You'll hear the same signal again, and again and again every 2 seconds.

So pink noise will cover FR, and something like a metronome will cover transient dynamic power differences in amps. Those two right there might pretty well work as well as anything that can be done sighted and by home audiophiles. Not as much fun as sitting with pals sipping a nice wine or some nice bourbon and listening to musical favorites while casually deciding about new gear, but perhaps a lot more effective in finding real differences (and finding times you don't really hear a difference).

Anybody have any thoughts about this?

Maybe I need to go find a metronome and record it myself.

Wow, that’s a megaton of useful info and a lot to explore on amplifier comparison! Thanks!

Another issue I discovered, similar to what @restorer-john pointed out - my AB switches are not great and actually affect the comparison adversely - sometimes they don’t make good contact even when fully pressed and is perceived as a shift of the mono phantom center. For “even more proper” comparison I would need an AVA ABX Compararor, but at $1400 it goes beyond my reasonable cost for a little hobby experiment.

I’d appreciate suggestions for better AB switch to use that’s reasonably priced if anyone have found!

 

[Blumlein 88]

Wow, that’s a megaton of useful info and a lot to explore on amplifier comparison! Thanks!

Another issue I discovered, similar to what @restorer-john pointed out - my AB switches are not great and actually affect the comparison adversely - sometimes they don’t make good contact even when fully pressed and is perceived as a shift of the mono phantom center. For “even more proper” comparison I would need an AVA ABX Compararor, but at $1400 it goes beyond my reasonable cost for a little hobby experiment.

I’d appreciate suggestions for better AB switch to use that’s reasonably priced if anyone have found!

Maybe mono testing is better.

 

[boXem]

I've sort of had in mind putting together a best practices thread for sighted comparisons. They'll always be second class citizens to blind tests, but aren't always useless. The natural way audiophiles usually do this unfortunately are nearly guaranteed to mislead.

Item #1: You must have an excellent volume match between devices. (I think you've learned that in this thread)

Item #2: Go back and read item #1, I mean it, it is a must have job #1 don't pass go if don't do this.

Item #3: Use pink noise. Frequency response differences are the #1 reason two things sound different. Pink noise makes pretty small FR differences stand out clearly. It also has an advantage vs music. There are no short always changing details where we can trick ourselves upon hearing over and over that one time it was just a little plainer and clearer than another time.

After that I'm at a bit of a loss. I do have one hint. The Swedish JAES did series amplifier testing. I've done that. I found it much more revealing than side by side comparisons. Basically you put an amp, loaded with a speaker like load, between source and the amp driving the speakers. You can switch it in and out of circuit to see if you hear a difference The Swedish test almost never found a transparent amp sighted and always followed it with blind testing to confirm. The hint however is what they found the most revealing signal. It was a recording of a metronome. It was exactly repetitive and had lots of transients and harmonics. I wish someone could find out which recording of one they used. I think it points out something useful though in that an exactly repetitive signal does what pink noise does in that it makes you less likely to hear a fleeting not-repeated portion of music and think it sounds different. You'll hear the same signal again, and again and again every 2 seconds.

So pink noise will cover FR, and something like a metronome will cover transient dynamic power differences in amps. Those two right there might pretty well work as well as anything that can be done sighted and by home audiophiles. Not as much fun as sitting with pals sipping a nice wine or some nice bourbon and listening to musical favorites while casually deciding about new gear, but perhaps a lot more effective in finding real differences (and finding times you don't really hear a difference).

Anybody have any thoughts about this?

Maybe I need to go find a metronome and record it myself.

The series testing is the way I test preamps. It's fairly easy.
For the amps the recurring question is to find the proper simulated load. As a pro, I will try to use something really difficult for the amp. For a 'normal' person, the ideal would be to use a load as close as possible from the speakers.
Concerning the test signals, applauds in a concert hall are also quite revealing, even if less 'metronomic' .