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Amplifier Bakeoff: Purifi Eval1, McIntosh MA252 & Benchmark AHB2

acetogen

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Why would you expect the three amplifiers to sound the same since they have different amplification technologies (A, AB and D)? Even if they measure almost identically there would be subjective differences. You experience that when comparing the upgraded NAD 2200 and the Purifi ones.
 

pma

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You might consider using the mic adequate, but how could you not consider the other method equal to if not better than using a microphone?
I have no problem with electrical measurement. However the noise + calibrated SPL meter like B&K is being used to minimalize amp output impedance influence re interaction with speaker impedance. I know that it should not happen with the amps under test here. However the noise + mike method not to be thrown away.

BTW thanks OP for the test, very interesting.
 

Blumlein 88

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I have no problem with electrical measurement. However the noise + calibrated SPL meter like B&K is being used to minimalize amp output impedance influence re interaction with speaker impedance. I know that it should not happen with the amps under test here. However the noise + mike method not to be thrown away.

BTW thanks OP for the test, very interesting.
Unfortunately the OP used a 1 khz tone, not noise or pink noise.
 

Galliardist

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Why would you expect the three amplifiers to sound the same since they have different amplification technologies (A, AB and D)? Even if they measure almost identically there would be subjective differences. You experience that when comparing the upgraded NAD 2200 and the Purifi ones.
They don't have to measure close to identically, though, do they? What's important is that the differences are inaudible, which requires a high level of performance for each. As soon as they aren't within their performance envelope - for example, if input impedance doesn't match to the output impedance of the source/preamp, or if they are unable to drive the attached loudspeaker due e.g. to insufficient power or gain.

In the case of the test amplifiers, the MA252 (a hybrid integrated amp of good performance) might struggle with the Magico S5 at it's lowest impedence, and may have been driven as if it was a power amp rather than a preamp, the test description isn't clear.
The Purifi amp, if correctly assembled, should drive the speakers with no issues.
The Benchmark amp has to be set up correctly - it has switching input impedance and gain levels - to drive the Magicos, given the expected output from the Topping in preamp mode. Even then, it may not cope.

So, there are legitimate reasons why this test may have shown differences, apart from the level matching question. It is a good idea if indeed you are chasing a "no differences" result, to use easy to drive speakers, a traditional preamp with decent gain, to check everything actually is set up to work together, and probably not to compare power amps with integrated ones. A more reasonable test volume level would help too!
 
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PJ2000

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They don't have to measure close to identically, though, do they? What's important is that the differences are inaudible, which requires a high level of performance for each. As soon as they aren't within their performance envelope - for example, if input impedance doesn't match to the output impedance of the source/preamp, or if they are unable to drive the attached loudspeaker due e.g. to insufficient power or gain.

In the case of the test amplifiers, the MA252 (a hybrid integrated amp of good performance) might struggle with the Magico S5 at it's lowest impedence, and may have been driven as if it was a power amp rather than a preamp, the test description isn't clear.
The Purifi amp, if correctly assembled, should drive the speakers with no issues.
The Benchmark amp has to be set up correctly - it has switching input impedance and gain levels - to drive the Magicos, given the expected output from the Topping in preamp mode. Even then, it may not cope.

So, there are legitimate reasons why this test may have shown differences, apart from the level matching question. It is a good idea if indeed you are chasing a "no differences" result, to use easy to drive speakers, a traditional preamp with decent gain, to check everything actually is set up to work together, and probably not to compare power amps with integrated ones. A more reasonable test volume level would help too!
All the actual recordings we listened to and scored were generally no higher than 90-95 dB. We did try maxing out all the amps to see where they would clip and even the McIntosh could drive the Magicos to decent levels. Frankly none of them were loud enough that any of the amplifiers were straining in any obvious way. The fun piece we used to intentionally tax the amplifiers was 'Poem of Chinese Drum, Hok-man Yim.'
 

Blumlein 88

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I'm also surprised with a 2-5 minute switching time that anything was consistently noticed. With such large switching times you have to have something substantially different. My first guess would be frequency response. Either difference in the low end or a slight slope one way or the other in the upper couple of octaves. Those sorts of things are rather easily heard if large enough.
 

pma

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If this is the speakers used, it looks very good. My only objection would be for use of the acoustical sine 1kHz. The problem of a single sine used in a room are zillions of reflections. For this reason, white noise or pink noise are used for level calibration.

4ohm/-60degrees at 50Hz, this impedance might have been much easier to drive for Purifi than Benchmark. Probably the decisive moment.
 
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acetogen

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They don't have to measure close to identically, though, do they? What's important is that the differences are inaudible, which requires a high level of performance for each. As soon as they aren't within their performance envelope - for example, if input impedance doesn't match to the output impedance of the source/preamp, or if they are unable to drive the attached loudspeaker due e.g. to insufficient power or gain.

In the case of the test amplifiers, the MA252 (a hybrid integrated amp of good performance) might struggle with the Magico S5 at it's lowest impedence, and may have been driven as if it was a power amp rather than a preamp, the test description isn't clear.
The Purifi amp, if correctly assembled, should drive the speakers with no issues.
The Benchmark amp has to be set up correctly - it has switching input impedance and gain levels - to drive the Magicos, given the expected output from the Topping in preamp mode. Even then, it may not cope.

So, there are legitimate reasons why this test may have shown differences, apart from the level matching question. It is a good idea if indeed you are chasing a "no differences" result, to use easy to drive speakers, a traditional preamp with decent gain, to check everything actually is set up to work together, and probably not to compare power amps with integrated ones. A more reasonable test volume level would help too!
Makes sense. I've heard in another board that it is always recommended to have an analog preamp in between a given source and a power amplifier. This applies whether the DAC source has a preamp mode or not.
 

eddantes

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Welp - you guys will need to have another go at this. As mentioned before - voltage at output, or at the very least pink noise to match levels... And secondly, y'all need to invest in a switch, because you need near instant switching as audio memory is so darn short.
 

Willem

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Makes sense. I've heard in another board that it is always recommended to have an analog preamp in between a given source and a power amplifier. This applies whether the DAC source has a preamp mode or not.
This is audiophile nonsense. Really, the feed from a good DAC like the RME ADI-2 is just perfect and does not need anything. A modern DAC with volume control is quite simply nothing other than a traditional preamplifier, but now with digital inputs. In the case of the ADI-2 it even has traditional goodies like tone and balance controls, filters, dynamic loudness and a lot more.
 

pma

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And secondly, y'all need to invest in a switch,
New, and non-trivial issues, then. You would kill low output impedance of Purifi and Benchmark by inserting an unpredictable nonlinear switch contact resistance. And probably some lousy wiring with high resistance.
 

JayGilb

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Thanks for the test and the write up. Interesting results.

If you ever do another test try using a 2 in 6 out DSP and route a copy of the L/R signal pair to each amp. Level matching will only have to be performed once and should be easy to do via software. Resolution will depend on the DSP software.

Use a simple speaker switch like a board with multiple banana jacks where the person switching can just pause the music and connect a set of jumpers between the amp jacks and the speakers.
 

eddantes

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New, and non-trivial issues, then. You would kill low output impedance of Purifi and Benchmark by inserting an unpredictable nonlinear switch contact resistance. And probably some lousy wiring with high resistance.
Yep thats true - I imagine most of the switches on amazon leave something to be desired. I believe there was a request for @tomchr to build something high quality... but considering he'd building into a market of dozens, I doubt it will ever happen. Maybe he can rent them out :)

Still - without rapid switching, I remain highly skeptical as to the reliability of the test.
 

DSJR

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Setting levels with a tone at 110dB? I'd respectfully suggest most domestic systems and even smaller pro systems can't playat that level well.

Brings back memories when I used a Densen DeMagic CD player 'demagnetiser' or whatever it claims to so... The racket from the speakers effed my ears for twenty minutes or more even before I ran from the room and I swear the sound was worse for that listening session. I tried this disc with zero volume and it make not one iota of difference, so I suggest the noise from the speakers 'conditions' the ears first..

What's that to do with the thread topic - purely the effects a LOUD 1kHz signal might have on one's ears irrespective of the amp used...

Of course I cannot dispute the OP's findings, but I'd honestly recommend the suggestion above to use an electrical meter instead of possibly messing the group hearing up. The Benchmark may be the least powerful of the amps compared and as said above, if the amp isn't set up quite right for the signal level feeding it, I just wonder if that may have had something to do with it? Just thinking here (and we all know how dangerous that can be ;) )
 

phion

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Benchmark ABH2
Test Setup: Topping D90SE (balanced outputs) directly connected to each amplifier.
Did you use the Low Gain mode on AHB2? If so, I don't think D90SE's output has enough range to drive that (you'll need close to 10V). You will probably need a Pre90 or some other preamp in between them.
 

pma

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Setting levels with a tone at 110dB? I'd respectfully suggest most domestic systems and even smaller pro systems can't playat that level well.

Agreed. This info makes the review a bit untrustworthy. Also imagine the speaker distortion at 110dB SPL sine ..... And it has survived ....
 

acetogen

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This is audiophile nonsense. Really, the feed from a good DAC like the RME ADI-2 is just perfect and does not need anything. A modern DAC with volume control is quite simply nothing other than a traditional preamplifier, but now with digital inputs. In the case of the ADI-2 it even has traditional goodies like tone and balance controls, filters, dynamic loudness and a lot more.
I agree, but the RME is really 2in1 piece of gear (actually 3 if you include the headphone amp), it does have a full preamp as part of the integration. Does that apply to the Topping 90SE that they used in this bakeoff? My guess is probably yes others might disagree. I do have the cheaper E30, which can handle volume, but I'd gather it wouldn't be suitable for the tests they are trying to carry out here, especially without the full suit of measurements.
 
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PJ2000

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Thanks for the test and the write up. Interesting results.

If you ever do another test try using a 2 in 6 out DSP and route a copy of the L/R signal pair to each amp. Level matching will only have to be performed once and should be easy to do via software. Resolution will depend on the DSP software.

Use a simple speaker switch like a board with multiple banana jacks where the person switching can just pause the music and connect a set of jumpers between the amp jacks and the speakers.

Yeah it would be nice to have had a 'switch' as that would have made the process faster allowing for more samples also. We will think about that for next time.
 
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