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Amplifier Bakeoff: Purifi Eval1, McIntosh MA252 & Benchmark AHB2

PJ2000

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We recently got a few folks together to do as close to a 'blind test' as we could of the Purifi Eval1, McIntosh MA252 and the Benchmark AHB2. We had 3 reviewers and a 4th person who switched the gear.

Test Setup: Topping D90SE (balanced outputs) directly connected to each amplifier.
Streamer: Tidal Bluesound Node connected via optical SPDIF to Topping D90SE
Speaker: Magico S5 MKII
Randomization: For each song selection: Each amplifier was randomly assigned a number 1,2,3, A random amplifier order was used for playback.
Level Equalization: For each song/amplifier, a 1K sine wave was used to normalize the level to about 0.1 Db using a calibrated microphone, Focusrite 2i2 and REW before playback of each selection. The level was managed using the Topping D90SE in pre-amp mode and managed to about 90-95 db.
Process: 6 songs. Each song was played and the reviewers wrote comments and then rank ordered amplifiers. Between switches loud music was played to drown out any switching related noises that could indicate which amplifier was being connected.

Some of the selections used:
1. Africa -Toto
2. The Street only knew your name (extended version) - Van Morrison
3. What a wonderful world - Eva Cassidy
4. Beethoven: Triple Concerto in C Major, Allegro - Mutter/Ma/Barenboim
and a few others.

Results: 2 out of 3 reviewers had very similar results with the Purifi in 1st place and the Benchmark in last place in all or a majority of the time, while one reviewer had mixed results from which we couldn't determine a specific pattern.

I was one of the reviewers and I picked the exact same order 100% of the time of the Purifi in the top spot followed by the McIntosh and the Benchmark as a distant 3rd place. What I noticed that distinguished the best (Purifi) from the worst (Benchmark) in my case was the following: The Purifi had better clarity, detail and high end compared to the other two, especially the Benchmark and it was noticeable. It was especially easy to hear differences for me with complex stringed instruments like a strummed acoustic guitar or cello and cymbals and triangles.

This wasn't the result that we were anticipating going into the comparisons. Based on the ASR reviews all of us went into thinking that Benchmark would be far ahead of the other 2 amplifiers based on its measurements. One of the reasons for the bakeoff was that one of the reviewers was seriously considering buying the Benchmark but wanted to do a comparison before. He decided to pan the Benchmark and buy the Purifi instead.

I hate add fuel to this debate about whether amplifiers with great specs can sound different, as I went into this believing that it wasn't possible, but some of the differences we heard weren't subtle. I am really curious as to whether there is some psycho-acoustic reason for this or limitations in what and how we measure these systems to begin with. I actually bought the Purifi Eval 1 and an NAD 2200 which I upgraded based on the measurements from ASR with the assumption that I wouldn't be able to hear a difference and I was quite surprised by the fact that there were differences. One thing I did notice was that my ability to hear a difference was dependent on the speakers used. On a few run of the mill speakers, I really couldn't tell much of a difference as they themselves just don't have the detail resolution of the S5 or the Magnepan LRS.

I must add it was loads of fun and I would highly recommend comparing the Benchmark and Purifi since in theory there should be no real difference that you should be able to detect to see if you can.
 
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Drengur

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the Benchmark is obviously trash, I'll send you my address so you can send it to me for disposal. All jokes aside, can you elaborate on how you went about measuring, the level, and at what distance in each case?
 

amper42

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You had me on the edge of my seat with this comparison until you mentioned the Magnepan LRS was one of the determining factors.
The LRS was my absolute worst speaker purchase and I couldn't imagine accepting any comparison where the measuring stick was so completely flawed. Now go back and do the test again with Revel speakers so I can read this article again. :D:p:facepalm:o_O lol
 
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PJ2000

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the Benchmark is obviously trash, I'll send you my address so you can send it to me for disposal. All jokes aside, can you elaborate on how you went about measuring, the level, and at what distance in each case?
It wasn't my Benchmark, so the owner was the reviewer who had someone inconsistent results. He isn't ready to give up his Benchmark, over his dead body or something to that effect was what he said...

The speakers were about 8 ft apart and mic was on a fixed stand about 6ft from the centerline. It is a Dayton Audio EMM-6. The only components moved throughout the process were the XLR and speaker cables.
 
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PJ2000

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You had me on the edge of my seat with this comparison until you mentioned the Magnepan LRS was one of the determining factors.
The LRS was my absolute worst speaker purchase and I couldn't imagine accepting any comparison where the measuring stick was so completely flawed. Now go back and do the test again with Revel speakers so I can read this article again. :D:p:facepalm:o_O lol
I love my LRS's, they take a bit of tweaking, which is part of the experience. But that is neither here nor there. The testing was done with the Magico S5MkIIs. My comments about the LRS were more personal and subjective.
 
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PJ2000

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I applaud the attempt. Unfortunately the level matching was not done correctly. Acoustic measurement is not accurate enough. What is needed is electrical measurement of the outputs.
Next time I will whip out the Multimeter or Oscope. So why do you believe that the error in measurement of the acoustic signal is large enough to skew the results? Do you believe that to be a systematic error or random, and why?
 

MediumRare

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Can you post the data, please? A few other items:
- Was the order of the amps randomized?
- What was the interval between the song/amp combos.
- What was the SPL for the level matching?

Thanks!
 

MusicNBeer

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Maybe the Benchmark is defective. Unless you measure it, no way to be sure.
 
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PJ2000

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Can you post the data, please? A few other items:
- Was the order of the amps randomized?

Yes, please see the text. A random number was assigned to each amp, and then a random order was selected for playback on top of that.

- What was the interval between the song/amp combos.

~10-15 minutes between songs
~2-5 minutes between Amps to reconfigure and calibrate level.
- What was the SPL for the level matching?

110 db.

 
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PJ2000

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Maybe the Benchmark is defective. Unless you measure it, no way to be sure.
Possible, but nothing obvious like noise or distortion etc. Unfortunately we don't have a second one to test. If someone lives in the SF Bay area and wants to volunteer one, we could re-test it.
 

MediumRare

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Yes, please see the text. A random number was assigned to each amp, and then a random order was selected for playback on top of that.



~10-15 minutes between songs
~2-5 minutes between Amps to reconfigure and calibrate level.


110 db.
Thanks for all that. The data would be interesting to analyze. Without seeing that and the strength of the finding, I believe the gap between the different amps make it hard to have the auditory memory necessary for a reliable AB. Does anyone know the time gap between speaker changes in the Harman/Toole research?
 

PierreV

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Test Setup: Topping D90SE (balanced outputs) directly connected to each amplifier.
Streamer: Tidal Bluesound Node connected via optical SPDIF to Topping D90SE
Speaker: Magico S5 MKII

Thanks for doing the test on very good speakers and the writeup!

This wasn't the result that we were anticipating going into the comparisons. Based on the ASR reviews all of us went into thinking that Benchmark would be far ahead of the other 2 amplifiers based on its measurements. One of the reasons for the bakeoff was that one of the reviewers was seriously considering buying the Benchmark but wanted to do a comparison before. He decided to pan the Benchmark and buy the Purifi instead.

I think the anticipated result would be "no difference" - yes, the benchmark performed better in tests here, but the difference with the purify should be in the non-audible territory: both are supposed to be audibly transparent.
 
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Galliardist

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So... what impedance and gain settings did you use on the AHB2? They need to be correctly set to provide sufficient gain. If you don't do this they won't drive the Magicos properly as they are a difficult load.
Potentially too difficult for the Mac, in fact. At 100W into 8 ohm, and 160 into 4, at the volume level used they might not provide enough power for the Magico which is specified as nominally 4 ohms and goes down close to 3 before taking phase into account. IIRC this amp also has a clipping protection feature that could change the sound under these conditions.

Regarding your last comment about speaker resolution. Since we are kind of expecting no difference with well performing amps within spec, it's more likely that the amps under comparison could both drive those other speakers adequately, and you are hearing a difference where at least one amp was not suitable for the speaker and volume level used.
 

pma

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I applaud the attempt. Unfortunately the level matching was not done correctly. Acoustic measurement is not accurate enough. What is needed is electrical measurement of the outputs.
There are people who would disagree, especially if noise is used as a signal instead of the sine and if the mike position is fixed.
 

Blumlein 88

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There are people who would disagree, especially if noise is used as a signal instead of the sine and if the mike position is fixed.
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?
 
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