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

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f1shb0n3

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From my personal journey , the audible differences can only be audible with highly resolving speakers and with "listening' (not just measuring knowns metric,

I had compare amplifiers that I could not hear the difference when they are driving my Logan bookshelf speakers but can clearly hear the difference when driving highly resolving speakers like B&W 802D3 or Revel Ultima.
I would expect any differences to be audible with good transducers only for sure. Resolving is not a technical term though, could the "resolving-ness" of the speakers in your case have been the higher power requirements of B&W and Revel?

Proper comparison setup is very important, after doing multiple comparisons of amps and DACs myself, I don't accept any subjective impressions as valid unless the setup is right at least.
 

dlaloum

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From my personal journey , the audible differences can only be audible with highly resolving speakers and with "listening' (not just measuring knowns metric,

I had compare amplifiers that I could not hear the difference when they are driving my Logan bookshelf speakers but can clearly hear the difference when driving highly resolving speakers like B&W 802D3 or Revel Ultima.
Typically, bookshelves are easy to drive - most amps will drive them perfectly - well within their optimal performance envelope- and therefore they would most likely sound the same.

The B&W's in particular, the Revel to a lesser degree, are difficult loads - with low impedances - requiring a lot more from an amp... many amps will get pushed to drive such speakers - moving them from the zone where they are "wires with gain" -to zones of performance where various distortions and non-linearities start to impact.... hence they start to sound different.

Pretty much all tests that compare amplifiers well within their optimal performance zone (ie: with speakers that suit them!) - have all amps sounding alike...

The difference are usually the different way, differing designs "fail" under pressure.

So does that mean the amps sound different, or does that mean different amps are suited to different speakers? with ALL amps being suited to "easy" speakers - but fat fewer being suited to difficult ones.... much like people ;)
 

MasterApex

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Typically, bookshelves are easy to drive - most amps will drive them perfectly - well within their optimal performance envelope- and therefore they would most likely sound the same.

The B&W's in particular, the Revel to a lesser degree, are difficult loads - with low impedances - requiring a lot more from an amp... many amps will get pushed to drive such speakers - moving them from the zone where they are "wires with gain" -to zones of performance where various distortions and non-linearities start to impact.... hence they start to sound different.

Pretty much all tests that compare amplifiers well within their optimal performance zone (ie: with speakers that suit them!) - have all amps sounding alike...

The difference are usually the different way, differing designs "fail" under pressure.

So does that mean the amps sound different, or does that mean different amps are suited to different speakers? with ALL amps being suited to "easy" speakers - but fat fewer being suited to difficult ones.... much like people ;)
When connected to these highly resolving speakers such as B&W 802D3 and Revel Ultima, the amplifiers "sounds" different even at moderate volume (80dBA).
So when we say the amps measured the same under optimal zone and therefore should sound the same but they are not with these speakers.
Is that because these resolving speakers are pushing the amps to "non-optimal" zone even at moderate volume?
If so , we need to carefully select amps for good sounding highly resolving speakers.
So with low resolution speakers, any amps just sound the "same" as measurement predicted?
 

Sal1950

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When connected to these highly resolving speakers such as B&W 802D3 and Revel Ultima, the amplifiers "sounds" different even at moderate volume (80dBA).
So when we say the amps measured the same under optimal zone and therefore should sound the same but they are not with these speakers.
Is that because these resolving speakers are pushing the amps to "non-optimal" zone even at moderate volume?
It's because you don't use a bias controlled DBT procedures to compare the two amps.
Close your eyes.
 

dlaloum

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When connected to these highly resolving speakers such as B&W 802D3 and Revel Ultima, the amplifiers "sounds" different even at moderate volume (80dBA).
So when we say the amps measured the same under optimal zone and therefore should sound the same but they are not with these speakers.
Is that because these resolving speakers are pushing the amps to "non-optimal" zone even at moderate volume?
If so , we need to carefully select amps for good sounding highly resolving speakers.
So with low resolution speakers, any amps just sound the "same" as measurement predicted?

Yes I think that is the case... My previous TX-SR876 sounded good with my speakers - my current DRX 3.4 does not sound as good (running on its internal amps) - even though there is no obvious apparent strain, and the volume was well below reference (circa 75db spl at listening seat).

Switching front L&R to either the Quad 606 or the Crown XLS amps, resolved the issue immediately ... And the Crowns are the best sounding option.

I don't think this is at all related to "low resolution speakers" - there are high resolution speakers that are much easier to drive... eg: Quad ESL63 electrostatics.... where with the Gallo's there was a clear differentiation Crown XLS>Quad 606>Onkyo 876 - with the Quad ESL, without doubt one of the highest resolution speakers around, the 3 sounded the same.

If your amp is required somewhere in the frequency range, to drive a low impedance load below what it does comfortably, the resulting changes in distortion become subtly audible... even though it is theoreticaly "idling".

The Quad 606 is "unconditionally stable into any load" to use Quad's own words... where the Onkyo 876 is specified only for speakers of 4 ohm and above... but the Quad design is still much more current constrained than the Crown - Here is where I make the intuitive leap ... that the ability to supply massive amounts of current on demand, without impacting other performance aspects, becomes critical with any speaker having a low impedance (and I am not talking about the nominal impedance for the entire frequency range, but rather, the lowest impedance a speaker reaches at any individual point in its frequency range.

IMO - for many such speakers (Gallo, B&W, Revel) - people underestimate how much current , (possibly instantaneous current) speakers with low impedances require...
 

MasterApex

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Yes I think that is the case... My previous TX-SR876 sounded good with my speakers - my current DRX 3.4 does not sound as good (running on its internal amps) - even though there is no obvious apparent strain, and the volume was well below reference (circa 75db spl at listening seat).

Switching front L&R to either the Quad 606 or the Crown XLS amps, resolved the issue immediately ... And the Crowns are the best sounding option.

I don't think this is at all related to "low resolution speakers" - there are high resolution speakers that are much easier to drive... eg: Quad ESL63 electrostatics.... where with the Gallo's there was a clear differentiation Crown XLS>Quad 606>Onkyo 876 - with the Quad ESL, without doubt one of the highest resolution speakers around, the 3 sounded the same.

If your amp is required somewhere in the frequency range, to drive a low impedance load below what it does comfortably, the resulting changes in distortion become subtly audible... even though it is theoreticaly "idling".

The Quad 606 is "unconditionally stable into any load" to use Quad's own words... where the Onkyo 876 is specified only for speakers of 4 ohm and above... but the Quad design is still much more current constrained than the Crown - Here is where I make the intuitive leap ... that the ability to supply massive amounts of current on demand, without impacting other performance aspects, becomes critical with any speaker having a low impedance (and I am not talking about the nominal impedance for the entire frequency range, but rather, the lowest impedance a speaker reaches at any individual point in its frequency range.

IMO - for many such speakers (Gallo, B&W, Revel) - people underestimate how much current , (possibly instantaneous current) speakers with low impedances require...
I am new in this journey of acquiring more amplifiers and speakers. I usually shop based on just measurement. Recently I have been listening more to different equipment and notice that there are several "audible" sonic quality that does not yet have measurement metric to explain.

For example the sound quality of 100Hz 80dB SPL produced by 12" woofer vs Planar will be audibly different even though the measurement is the same 80dB SPL.

I have observed that the improved materials (e.g. diamond tweeter) or improved driver design does have improved the sound quality in term of more real-life like cymbals, bells, etc or more natural voice, etc. Therefore I called them more resolving.
In reading measurement I did not come to conclusion that the amps will sound different but your explanation helps me....thanks.
 

dlaloum

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With years of planar use (used to sell Quad, then owned Quad ESL's from around 86 to circa 2007...) - finding something more compact, that still gave me much of what I found indispensible in a planar was a challenge... - WAF on the Planar's was not good... the Gallo's were the most "Planar"-ish sounding speaker I heard... (within my budget...) - and they are not quite as resolving as the Quad ESL63/989's I had before were - but they get very close. Additional caveat.... my comparisons between the Quads and the Gallo's in my own home were done using the Quad 606 amp and the Onkyo 876... by the time I purchased the Crowns, the Quads had left the premises - but the addition of the Crown did improve things... and may have brought things to the point where they were with the Quad ESL/Quad 606 setup - but it is very hard (impossible) to tell via aural memory!!

One key thing is the performance of a speaker in a room has a heap to do with the way it broadcasts sound into the space, and the way the frequency response varies by polar position around the speaker.... (which then impacts on the frequency response of the reflected sound, and therefore the overall voicing of the room).

Planars energise a room very differently from Coil/magnet speakers - although certain coil designs are more similar to planars than others.

I don't think I have a proper conceptual handle on this aspect on performance - Things like wide (infinite or semi-infinite) vs narrow baffle, diffraction patterns also have an impact.... thinking back, my preferred Coil/Magnet designs have either been "boxless" like the Gallo, or very wide baffle like Boston Acoustics A400.

But it is absolutely clear that speakers are the most imperfect/flawed part of any audio system - they will have the greatest impact on the sound and the room (with the possible exception of Turntable/Cartridge... which is also a highly imperfect electro-magnetic transducer!).

Hence, in my opinion, you start by picking a speaker that suits you (and your room!) - and then work your way back through the chain...

Once you have your speaker, you can select an appropriate amp to suit.... and an amp that suits your speaker will not impose any voicing... it will be a "wire with gain".... (as soon as you start hearing differences between amps, one or more of the amps involved is failing the "wire with gain" test, and applying some form of distortion...so yeah two or more amps can sound different as a result).

And the rest of the audio chain? - Rapidly diminishing returns! - Digital tech has progressed markedly since CD was released in the mid 80's.... There are plenty of "cheap and chips" components that perform admirably, and the difference in resolving ability between the best of the cheapies and the megabuck audio bling components is very often below the threshold of audibility.... (but seldom below the threshold of measurability.... however associating what we measure with what we hear is more complicated)
 

rdenney

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This is an older thread but some points come to mind as I read it:

1. If we can't detect a difference (when level-matched) sighted, we don't need a controlled test. ABX tests the hypothesis that the difference we hear is not the result of sighted bias. If we don't think we hear a difference, there is nothing to test.

2. The notion of what might make amps sound different interests me, and this thread provides a good context for this. To my thinking, actual differences between amps might be caused by:

a. Inability to maintain linearity in the presence of a given load. It would seem to me that if an amp shows linearity into a 2-ohm dummy load, it should handle a dip to 2 ohms in a speaker, given reasonable capacitive load. So, when I see amp tests that show distortion vs. power into 2 ohms, I think I should see the amp's capability into the usual difficult loads. But if I felt the need to own speakers that were truly difficult (sub-2 ohm impedance somewhere in the spectrum, or a large phase angle coupled to an impedance dip), I'd want to see testing against a similar load. Stereophile has their simulated speaker load, which is not particularly difficult but which is probably relevant to most people with reasonable speakers. DonH56 has written cogently about this topic on ASR. It takes a particularly beastly load to create an audible effect (and even then the effect is only relevant for that load).

b. Clipping. Nearly all tests are conducted at steady state, or at listening levels specifically designed to keep the amp within its power envelope. Power output is usually tested separately. The question is how often a real signal might include peaks that clip an amp without us realizing it. The only way to know for sure would be to record the output of the amp and study the waveform. Or, we can depend on the clipping indicators in amps supplied with them, but usually with very little specificity on how sensitive they are to differences between input and output waveforms. I recall an analysis done by one magazine that found that their test protocol caused amps under test to clip to distortion levels high enough to potentially be audible. Frequency-response behavior with broadbanded input (like, say, pink noise) at clipping is rarely tested. I'd be happy testing low percussion music recorded very loudly, using a scope output or recorded waveform to determine the clipping point for a consistently used test track.

c. Distortion, which I define broadly as any difference between output and input (meaning that clipping effects are one example of distortion) across the frequency spectrum. Distortion at low frequencies is, to my ears (and I have tested this) more critical than distortion at high frequencies, particularly harmonic distortion, simply because the harmonics more quickly rise into audibility relative to the fundamental. This is particularly true when the low-frequency signal-under-test has no harmonics--a clean sine wave--which is thankfully rare in music. To my ears, distortion is really hard to hear when playing actual music, particularly harmonic distortion. Nearly all musical sources present a range of harmonics as part of their characteristic sound, so harmonics added by an amp would have to be loud enough to overcome the masking effect of the source material.

d. Frequency-response linearity. Most amps not subject to above issues are exceptionally good here, unless they are trying not to be. I have amps that roll off in the top octave by some fraction of a dB by the time they reach 20 KHz. I think even those with good high-frequency hearing would be hard-pressed to demonstrate their ability to hear such in a blind test.

Of these, it seems to me that only clipping is the effect normal people are likely to face in their home setups, unless they buy big amps and always listen at low levels. I know that I have have seen the clipping indicators flash on my (350-watt into my 6-ohm-nominal Revel speakers) NC502MP when playing highly dynamic and percussive source material. I would think a cleanly recorded mechanical metronome would be perfect for this--it can be played very loudly without summoning the constabulary. I have one such and maybe a good enough microphone to give that a try.

But people who routinely listen at low levels are the sorts who think, "I don't need a big amp--I only listen at low levels." Then, when the occasion arises that they want to crank it up--hello, clipping! Those occasions seem to me to include "putting an amp through its paces" in the context of a home "test". They then report differences here as being characteristic of the amps, rather than reflecting their excursion (so to speak) outside the amp's operating envelope.

I offer this as a summary of what I read in this thread, where subjective impressions were dismissed as phantoms when they might have had more concrete causes, but without having to insist that amps are routinely different within their linear range driving the sorts of speakers most people use. The point is not to dismiss subjective impressions, but rather to explain them, if possible, to validate them (or not).

Rick "not quite sure how I ended up reading this thread weeks after the fact" Denney
 
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f1shb0n3

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This is an older thread but some points come to mind as I read it:

1. If we can't detect a difference (when level-matched) sighted, we don't need a controlled test. ABX tests the hypothesis that the difference we hear is not the result of sighted bias. If we don't think we hear a difference, there is nothing to test.

2. The notion of what might make amps sound different interests me, and this thread provides a good context for this. To my thinking, actual differences between amps might be caused by:
...
Rick "not quite sure how I ended up reading this thread weeks after the fact" Denney
Thanks for your detailed explanation on expected audible amplifier differences!

I'm not yet done with amplifier comparisons, essentially I'm at "don't hear any difference", but knowing I'm not an experienced listener and realizing how hard it is to intensely focus on sound details for a long time, planning to do some amplifier audio sample recordings (when I find some free time to solder a rig for it) to compare digitally and Foobar ABX. The causes which might lead to audible differences you listed might be verifiable with such recordings.
 

Axo1989

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... 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.
Pink noise and metronomes? Sounds like some of my favourite tracks from Autechre.
 

regan

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Thanks for your detailed explanation on expected audible amplifier differences!

I'm not yet done with amplifier comparisons, essentially I'm at "don't hear any difference", but knowing I'm not an experienced listener and realizing how hard it is to intensely focus on sound details for a long time, planning to do some amplifier audio sample recordings (when I find some free time to solder a rig for it) to compare digitally and Foobar ABX. The causes which might lead to audible differences you listed might be verifiable with such recordings.
Did you continue to compare the amps? Would you say there is no significant difference between them?

I'm willing to build a R3+A07 but still hesitant.
 

regan

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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...

View attachment 182416

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?
I'm looking to power an R3 and sb1000pro with an A07. Do you think this amp is good enough for the system?
 

Walter

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I'm looking to power an R3 and sb1000pro with an A07. Do you think this amp is good enough for the system?
It won't matter for the sub, since it is powered. For the R3, I would personally want something better like a Hypex 252-based or Yamaha A-S series amp, or a good second hand amplifier. Or possibly even something based on the new, higher powered Infineon chip would suffice, like the SMSL A300 or the Sabaj A20a. But if your budget is stretched, the A07 would certainly be serviceable for a few months until you can afford better. And it is also possible you won't find any audible difference.
 

item

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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.
This seems sensible. It's easy to lose sight of the wood for the trees: objective measurement is the second-class citizen of educated listening – not least because the objective (purpose, endpoint and goal) of audio equipment is brain experience. There's a reason why sight tests aren't conducted double-blind ABX. It's unhelpful to wave away reported experience as 'irrelevant expectation bias'.

The site is about 'audio science', not 'equipment science' - it would be helpful to have more discussion about greater rigour in the evaluative phase of the listening process.
 

item

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This is an older thread but some points come to mind as I read it:

1. If we can't detect a difference (when level-matched) sighted, we don't need a controlled test. ABX tests the hypothesis that the difference we hear is not the result of sighted bias. If we don't think we hear a difference, there is nothing to test.
There's a crucial, and unfortunately widespread, fallacy here that results from focusing on the wrong thing. Perhaps a dedicated thread would be in order to examine the relevance of double-blind ABX testing when the objective is testing perception. 'What is audible?' is a hard question to answer, but you're on the wrong path to useful insights if you begin from the position that audibility itself isn't relevant.
 
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