• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required as is 20 years of participation in forums (not all true). There are daily reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!

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

Blumlein 88

Grand Contributor
Forum Donor
Joined
Feb 23, 2016
Messages
17,143
Likes
29,856
Another suggestion try amp A on one channel and amp B on the other. Then swap sides and listen again.

I've not followed closely enough to know what switching issues you are having. If it's doable, simply doubling up on switches might help
 

Blumlein 88

Grand Contributor
Forum Donor
Joined
Feb 23, 2016
Messages
17,143
Likes
29,856
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' :).
Yeah series testing has its own difficulty for doing at home. But pink noise and metronomes for test signals is an easy change to try out.
 
OP
F

f1shb0n3

Senior Member
Forum Donor
Joined
Aug 29, 2020
Messages
313
Likes
478
Location
Seattle Area
Yeah series testing has its own difficulty for doing at home. But pink noise and metronomes for test signals is an easy change to try out.
I'll have a Parts Express 8Ohm dummy load arriving tomorrow, if that's all I need for the "hobbyist" version of the comparison of it I'd be interested to try it out.

From your explanation I got this with my first thought on how to put and remove it out of the circuit with 3 switches per channel (excuse the ugly diagram). Downside is it should be switched in the right order to avoid short-circuiting the amp under examination. Wonder if there's an easier or safer way if overall approach is correct.

Edit: removed diagram.
 
Last edited:

Blumlein 88

Grand Contributor
Forum Donor
Joined
Feb 23, 2016
Messages
17,143
Likes
29,856
I'll have a Parts Express 8Ohm dummy load arriving tomorrow, if that's all I need for the "hobbyist" version of the comparison of it I'd be interested to try it out.

From your explanation I got this with my first thought on how to put and remove it out of the circuit with 3 switches per channel (excuse the ugly diagram). Downside is it should be switched in the right order to avoid short-circuiting the amp under examination. Wonder if there's an easier or safer way if overall approach is correct.
View attachment 182524
That you don't want to use. I'll draw something up later, put it here. Don't use what you've drawn.
 

Sal1950

Grand Contributor
The Chicago Crusher
Forum Donor
Joined
Mar 1, 2016
Messages
11,589
Likes
12,794
Location
Central Fl
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.
Sorry, no offense meant. But you must understand this is intended to be a scientific site based on objective observations.
If no one questions the conditions under which folks post their listening impressions here, it would rapidly become just another of the dozens of subjective audio sites. You know, the places where fairy-tales about the sound of the latest $10,000 power cords pile up with no one questioning anyone's listening conditions. "I heard it, so it is so" is the only high standard set for acceptance.
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.
Great idea bud, it would give us a place to link to when the usual completely uncontrolled observations roll in. No guaranty we don't get told to f--k off by the subjective troll but at least new members with an open mind will understand and have a place to start learning and understanding basic listening controls.
 

bo_knows

Addicted to Fun and Learning
Joined
Aug 17, 2020
Messages
697
Likes
650
Location
Dallas, Texas USA
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.

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.
Hi Sal,
Thank you very much for the link to Peter's Audio Legacy read. Phenomenal!
 

tomtoo

Major Contributor
Joined
Nov 20, 2019
Messages
3,240
Likes
3,942
Location
Germany
@fishbone

Still i would be interested about some pictures of class d vs. class ab on your scope. But only with same settings. ;)
 

Sal1950

Grand Contributor
The Chicago Crusher
Forum Donor
Joined
Mar 1, 2016
Messages
11,589
Likes
12,794
Location
Central Fl
Hi Sal,
Thank you very much for the link to Peter's Audio Legacy read. Phenomenal!
No problem. I like to get links to Peter's stuff out on occasion. Lord only knows how much longer biline.ca will continue to host Peter's stuff, he's been gone 5 years now. :(
The site is a goldmine of fun reading, with pdf's of every issue of The Audio Critic still downloadable.
I've got them all saved to my HD. LOL
Filled a few empty nights during the early lockdowns of Covid once again.
 

Blumlein 88

Grand Contributor
Forum Donor
Joined
Feb 23, 2016
Messages
17,143
Likes
29,856
Here a link from the Swedish AES tests. The main link with more detail is gone and was not archived. This one has the basics of how they did the testing.


Here is a simple diagram which should make it clear what they were doing.
amptest5.gif

They used a complex load modeled after a difficult loudspeaker. You can use a power resistor for a first run if you wish. If you don't understand this ask questions prior to doing such a test.

You feed the input of the DUT (device under test or in this case an amplifier) a signal from the preamp. You load the output with a power resistor. You tap across that load with a voltage divider to reduce the voltage. You reduce it equal to the gain of the amplifier. If the amp has 26 db of gain then that is a ratio of 20:1. So once you have done this you can feed the power amp a signal and out comes a signal from the other end equal to the signal level you input. Unity gain.

So you take this unity gain signal and send it onto the power amp you have powering your speakers. With what they have labeled volume 2 above and the switch prior to it, that one switch can switch the DUT in and out of the circuit. A perfect amp would sound the same as wire. Now there are plenty of little details of arranging this you'll have to work out. At one time back in the 1990's I had things setup so I could put an amp in and try this in a couple minutes. After that I could switch or have someone switch the amp in and out of circuit. I've not done this since around the year 2000 or so. I don't know if switching amps will cause any issue with the switching frequency noise input into another amp. I do know that unlike the diagram most switching amps are differential instead of one speaker terminal being ground. You'll have to take that into account with how you wire all of this up.

So if someone had this all setup it is no big deal to use, but there is a bit of bother getting that ready to go. Also, I only found one amp that was pure straightwire with gain doing things this way. That was a Spectral DMA-50. Lots of SS amps of quality came pretty close, but only the Spectral was so good you simply couldn't tell if it was in circuit or not. I don't know how many amps the Swedish AES publication tested this way. Or when they stopped doing this. They only found one amp passed their sighted testing and it failed the blind portion. It was a large Audio Research solid state amp. They found one amp that passed both sighted and blind testing for pure transparency and that was a Bryston SST.

It would be nice if some magazine or outfit did such a test with some of the modern amps like a Benchmark, some Hypex, and Purifi based amps and such. Another name for this is amplifier bypass testing. You have a circuit where the amplifier is in circuit and can be bypassed.

So you might want to try other testing I suggested like using pink noise and something like a metronome or different amps on each channel of a stereo setup. Doing the series test will be some bother to do like I said.

You should be able to get a similar result more safely and simply if you connect various amps to speakers, use a voltage divider or auto ranger box and record the speaker terminals with a quality ADC running at least 96 khz. Copy a few pieces of music, and pink noise and maybe a metronome. Then you could play the original files and switch to the recorded files and see if the sound changes. That should be functionally equivalent to the actual series testing of amplifiers. That might be a better direction for you to go here.
 
Last edited:
OP
F

f1shb0n3

Senior Member
Forum Donor
Joined
Aug 29, 2020
Messages
313
Likes
478
Location
Seattle Area
Here a link from the Swedish AES tests. The main link with more detail is gone and was not archived. This one has the basics of how they did the testing.


Here is a simple diagram which should make it clear what they were doing.
amptest5.gif

They used a complex load modeled after a difficult loudspeaker. You can use a power resistor for a first run if you wish. If you don't understand this ask questions prior to doing such a test.

You feed the input of the DUT (device under test or in this case an amplifier) a signal from the preamp. You load the output with a power resistor. You tap across that load with a voltage divider to reduce the voltage. You reduce it equal to the gain of the amplifier. If the amp has 26 db of gain then that is a ratio of 20:1. So once you have done this you can feed the power amp a signal and out comes a signal from the other end equal to the signal level you input. Unity gain.

So you take this unity gain signal and send it onto the power amp you have powering your speakers. With what they have labeled volume 2 above and the switch prior to it, that one switch can switch the DUT in and out of the circuit. A perfect amp would sound the same as wire. Now there are plenty of little details of arranging this you'll have to work out. At one time back in the 1990's I had things setup so I could put an amp in and try this in a couple minutes. After that I could switch or have someone switch the amp in and out of circuit. I've not done this since around the year 2000 or so. I don't know if switching amps will cause any issue with the switching frequency noise input into another amp. I do know that unlike the diagram most switching amps are differential instead of one speaker terminal being ground. You'll have to take that into account with how you wire all of this up.

So if someone had this all setup it is no big deal to use, but there is a bit of bother getting that ready to go. Also, I only found one amp that was pure straightwire with gain doing things this way. That was a Spectral DMA-50. Lots of SS amps of quality came pretty close, but only the Spectral was so good you simply couldn't tell if it was in circuit or not. I don't know how many amps the Swedish AES publication tested this way. Or when they stopped doing this. They only found one amp passed their sighted testing and it failed the blind portion. It was a large Audio Research solid state amp. They found one amp that passed both sighted and blind testing for pure transparency and that was a Bryston SST.
Thanks for digging out this golden info from the archives! Your perspective from experience doing that is great too, provides invaluable context for anyone taking upon the unexpected (by lay people) challenges in amplifier comparisons.

It would be nice if some magazine or outfit did such a test with some of the modern amps like a Benchmark, some Hypex, and Purifi based amps and such. Another name for this is amplifier bypass testing. You have a circuit where the amplifier is in circuit and can be bypassed.

So you might want to try other testing I suggested like using pink noise and something like a metronome or different amps on each channel of a stereo setup. Doing the series test will be some bother to do like I said.
My first thought was - "Yes, someone has to do it - if magazines won't maybe I should?". Being realistic though, it can be properly done only by an expert in electrical engineering (which I'm not), given the numerous challenges it presents. Hope someone takes it upon eventually and publish their findings!

You should be able to get a similar result more safely and simply if you connect various amps to speakers, use a voltage divider or auto ranger box and record the speaker terminals with a quality ADC running at least 96 khz. Copy a few pieces of music, and pink noise and maybe a metronome. Then you could play the original files and switch to the recorded files and see if the sound changes. That should be functionally equivalent to the actual series testing of amplifiers. That might be a better direction for you to go here.
That's a great idea! I was just about to get into measuring gear with ADI-2 Pro, can also record amplifier output with it and do ABX with digital files using foobar2000, eliminating effects of switches and de-biasing myself. It might also be fun for others to check out and listen for themselves (if I can get proper recordings done).

/ Rolling up sleeves and warming up the soldering iron :) /
 

mrmojo2022

Active Member
Joined
Jan 11, 2022
Messages
159
Likes
90
Sorry, no offense meant. But you must understand this is intended to be a scientific site based on objective observations.

If no one questions the conditions under which folks post their listening impressions here, it would rapidly become just another of the dozens of subjective audio sites.
I agree with your sentiment but Amir posts uncontrolled listening impressions all the time in his speaker reviews. so is this site really any different?
 

Blumlein 88

Grand Contributor
Forum Donor
Joined
Feb 23, 2016
Messages
17,143
Likes
29,856

BDWoody

Chief Cat Herder
Moderator
Forum Donor
Joined
Jan 9, 2019
Messages
5,949
Likes
18,062
Location
Mid-Atlantic, USA. (Maryland)
I agree with your sentiment but Amir posts uncontrolled listening impressions all the time in his speaker reviews. so is this site really any different?

Transducers (motors basically) and solid state devices are in completely different categories.
 

Sal1950

Grand Contributor
The Chicago Crusher
Forum Donor
Joined
Mar 1, 2016
Messages
11,589
Likes
12,794
Location
Central Fl
I agree with your sentiment but Amir posts uncontrolled listening impressions all the time in his speaker reviews. so is this site really any different?
Oh yes, hugely so.
Now we're talking of speakers/headphones only.
Amir presents the numbers and then attempts to relate what he hears in view of them. And add EQ at times talking about it's effects on the perceived sound
.
The only other measurer currently is Stereophiles John Atkinson, and if a product measures bad, he will always phoo phoo his own numbers if the subjective reviewer thinks the DUT sounds glorious.
 
Last edited:

amper42

Major Contributor
Joined
Dec 21, 2020
Messages
1,352
Likes
1,863
Oh yes, hugely so.
Now we're talking of speakers/headphones only.
Amir presents the numbers and then attempts to relate what he hears in view of them. And add EQ at times talking about it's effects on the perceived sound
.
The only other measurer currently is Stereophiles John Atkinson, and if a product measures bad, will always phoo phoo his own numbers if the subjective reviewer thinks the DUT sounds glorious.

I would appreciate having listening tests provided with DACs and Amp reviews in addition to usability issues/features disclosed that are discovered during tests. If a DAC measures really well but the optical/coax ports don't work without dropouts the reader would find that information helpful. Or if a unit sounds good to the reviewer but the measurements are not in the top tier that would be helpful to know too.
 

Sal1950

Grand Contributor
The Chicago Crusher
Forum Donor
Joined
Mar 1, 2016
Messages
11,589
Likes
12,794
Location
Central Fl
I would appreciate having listening tests provided with DACs and Amp reviews
Mostly a waist of time unless it's very bad, which the numbers will reveal.
Otherwise it would be just more subjective BS which Amir doesn't do.
ASR = A NO BS zone and I pray it remains so.
 

amper42

Major Contributor
Joined
Dec 21, 2020
Messages
1,352
Likes
1,863
Mostly a waist of time unless it's very bad, which the numbers will reveal.
Otherwise it would be just more subjective BS which Amir doesn't do.
ASR = A NO BS zone and I pray it remains so.

To me the BS starts when a DAC gets a wonderful ASR measurement/rating but the optical port doesn't work with most TV's or CD players without dropouts and it's not disclosed in the review or updated later. Or maybe the remote control is substandard and doesn't work from a distance without a laser focus on the unit. You don't find this out until much later after you buy it or once customers start posting their dropout stories on ASR and there is no fix. The Topping D90SE is a prime example but there are other DACs in this category too. These are basic function tests that I would appreciate having in ASR reviews. It's not BS, simply full disclosure.
 

Blumlein 88

Grand Contributor
Forum Donor
Joined
Feb 23, 2016
Messages
17,143
Likes
29,856
To me the BS starts when a DAC gets a wonderful ASR measurement/rating but the optical port doesn't work with most TV's or CD players without dropouts and it's not disclosed in the review or updated later. Or maybe the remote control is substandard and doesn't work from a distance without a laser focus on the unit. You don't find this out until much later after you buy it or once customers start posting their dropout stories on ASR and there is no fix. The Topping D90SE is a prime example but there are other DACs in this category too. These are basic function tests that I would appreciate having in ASR reviews. It's not BS, simply full disclosure.
I agree with much of this, but I don't know about the dropouts and such. They are so random. The D10B thread people complain of popping when switching sample rates and mouse noise getting in, and so on and so forth. I don't doubt them. But I have one that has done none of that. I'm glad I didn't see those and shy away from the D10B. Which I got it for its bridge capabilities too.
 
OP
F

f1shb0n3

Senior Member
Forum Donor
Joined
Aug 29, 2020
Messages
313
Likes
478
Location
Seattle Area
To me the BS starts when a DAC gets a wonderful ASR measurement/rating but the optical port doesn't work with most TV's or CD players without dropouts and it's not disclosed in the review or updated later. Or maybe the remote control is substandard and doesn't work from a distance without a laser focus on the unit. You don't find this out until much later after you buy it or once customers start posting their dropout stories on ASR and there is no fix. The Topping D90SE is a prime example but there are other DACs in this category too. These are basic function tests that I would appreciate having in ASR reviews. It's not BS, simply full disclosure.
Makes a lot of sense - if electronics above certain level of objective measured performance are transparent for all intents and purposes, the most important info people need from a review should be features, stability, compatibility, etc. My relevant example - Motu M2 is working great on my Mac, but a friend with a Windows 10 laptop has it stop playing audio randomly 2-3 times per week. He doesn't care about the SINAD at all or a random reviewer's subjective experiences of it, he needs it to work and not stop while he's doing teleconferencing for work.

Maybe to get to where we focus only on the right things about gear, we have to first convince enough people about the stuff that doesn't matter.
 

Pdxwayne

Major Contributor
Joined
Sep 15, 2020
Messages
3,219
Likes
1,163
I'll use this thread as my personal blog in The Quest to find The Answer to The Question about Amplifiers. My subjective one, informed by the best science known to me. Both the question and the answer are to be figured out, my first revision of the question is: "What are the audible differences between different power amplifiers?"
I have a few amps laying around and using my near-field to mid-field desk setup of KEF R3, I'm equipped with all gadgets and cables to make a proper comparison of amplifiers using my own ears.

Trigger warning: no objective claims will be made, only subjective experiences will be expressed! :p
Feel free to question them if you wish, this is ASR after all! :) Any comments or questions will be appreciated!

Products involved
  • March Audio P452 Class D amplifier using Purifi 1ET400A chip with Alan's custom input buffer. Amir's review of a comparable model by Nord, I expect P452 to measure not too far from it.
Nord Three SE 1ET400A Dual Mono Stereo Amp With  Sonic Imagery 990Enh Audio Measurements.png


Nord Three SE 1ET400A Dual Mono Stereo Amp With  Sonic Imagery 990Enh Power into 8 Ohm Audio M...png


Nord Three SE 1ET400A Dual Mono Stereo Amp With  Sonic Imagery 990Enh Frequency Response Audio...png
Buckeye 6ch Nc502mp Measurements distortion multichannel amplifier.png


Buckeye 6ch Nc502mp Measurements Frequency Response multichannel amplifier.png


Buckeye 6ch Nc502mp Measurements Power 8 multichannel amplifier.png
AIYIMA A07 TPA3255 Measurements 32v 5 amp power supply.png
AIYIMA A07 TPA3255 Measurements 32v 5 amp power supply Frequency Response.png
AIYIMA A07 TPA3255 Measurements power into 8 ohm.png
  • Onkyo TX-NR737 AVR with 125W Class AB amplifiers. No measurements are available to my knowledge, looking for comparable ones for reference.

Diagram of the setup

View attachment 181454
Picture
View attachment 181456

Status so far
Volume matching is a serious challenge, still working to confirm I'm within 0.1dB.
Heard distinct differences between Purifi and Hypex and between Purifi and Onkyo AVR so far with my best attempts in volume matching.
Details on specifics comparisons and exact settings will follow.

Updates from the thread below
One thing I am very curious about is your own hearing sensitivity.

I have a thread that track all the tests I have done at

For example, can you sense 0.5db of sound pressure difference?
See

How good are you in sensing distortions?
I have a thread here:

There are many other tests I have done you can also try, after you let us know your results for the two tests I mentioned.

: )
 
Top Bottom