Buckeye Purifi Eigentakt 1ET9040BA monoblock power amplifier Stereophile Measurements

[pma]

NOTE: Thread has bee superseded by this one:

J

'New Buckeye Measurements'

May 14, 2025

The promised follow-up on the Buckeye Purifi Eigentakt 1ET9040BA amplifier has been published in the June 2025 issue of Stereophile.

You can find my measurements at https://www.stereophile.com/content...ba-monoblock-power-amplifier-new-measurements
and Kal Rubinson's report on his auditioning at https://www.stereophile.com/content...040ba-monoblock-power-amplifier-new-auditions

John Atkinson
Technical Editor, Stereophile

​

• John Atkinson

• 

This is an interesting review -

Buckeye Purifi Eigentakt 1ET9040BA monoblock power amplifier Measurements | Stereophile.com

Sidebar 4: Measurements I performed a complete set of measurements on one of the Buckeye Purifi 1ET9040BA amplifiers. I primarily used my Audio Precision SYS2722 system, repeating some of the testing with the magazine's higher-performance APx555 system. Because class-D amplifiers emit relatively...

www.stereophile.com

and we can see that the amp did not meet the datasheet specs. First, I would like to comment on CCIF IMD 19+20kHz result:

@John Atkinson measured this:

and it should be

Fig.11 Buckeye Eigentakt 1ET9040BA, HF intermodulation spectrum, DC–30kHz, 19+20kHz at 50W peak into 8 ohms (linear frequency scale).

50W peak into 8ohms. Frankly, I do not like "peak power" definitions, so I have measured my 1ET400A at 40W/8ohm (rms) with this result:

It may be seen that the distortion components are at or below -105dBr. What a difference from Stereophile result near -70dBr, it is a huge 35dB!!

I am absolutely sure it is not a difference between 1ET400A and1ET9040BA, but the difference would be in case material. If the Buckey case is made from iron steel, then the coils in the Purifi module become nonlinear (nonlinear core) and the best way to test this is high level 19+20kHz IMD (not the usual 5W). Even 20kHz THD would not indicate the issue.



So, my cordial suggestion to @Buckeye Amps would be to try again with aluminium case. Maybe a bit more expensive, but worth results. Remember the dissimilar faston/binding posts materials.

 

[welwynnick]

So, my cordial suggestion to @Buckeye Amps would be to try again with aluminium case. Maybe a bit more expensive, but worth results. Remember the dissimilar faston/binding posts materials.

Or you could repeat your test with a steel sheet on top of your case?

 

[EdW]

This is an interesting review -

Buckeye Purifi Eigentakt 1ET9040BA monoblock power amplifier Measurements | Stereophile.com

Sidebar 4: Measurements I performed a complete set of measurements on one of the Buckeye Purifi 1ET9040BA amplifiers. I primarily used my Audio Precision SYS2722 system, repeating some of the testing with the magazine's higher-performance APx555 system. Because class-D amplifiers emit relatively...

www.stereophile.com

and we can see that the amp did not meet the datasheet specs. First, I would like to comment on CCIF IMD 19+20kHz result:

@John Atkinson measured this:
View attachment 415219
and it should be


50W peak into 8ohms. Frankly, I do not like "peak power" definitions, so I have measured my 1ET400A at 40W/8ohm (rms) with this result:

View attachment 415220

It may be seen that the distortion components are at or below -105dBr. What a difference from Stereophile result near -70dBr, it is a huge 35dB!!

I am absolutely sure it is not a difference between 1ET400A and1ET9040BA, but the difference would be in case material. If the Buckey case is made from iron steel, then the coils in the Purifi module become nonlinear (nonlinear core) and the best way to test this is high level 19+20kHz IMD (not the usual 5W). Even 20kHz THD would not indicate the issue.

View attachment 415224 View attachment 415225

So, my cordial suggestion to @Buckeye Amps would be to try again with aluminium case. Maybe a bit more expensive, but worth results. Remember the dissimilar faston/binding posts materials.

I’d forgotten about the binding post issues.
Do you think the premature power limiting is down to the case material also? That’s a significant performance shift on the inductors.
But one thing we can learn from this is that building high performance electronics isn’t a LEGO building block job even at audio frequencies. A good test bench is mandatory

 

[Oniiz86]

So, my cordial suggestion to @Buckeye Amps would be to try again with aluminium case. Maybe a bit more expensive, but worth results. Remember the dissimilar faston/binding posts materials.

@pma I believe Buckeye's cases are aluminium according to the website description, "Our cases may not be much to look at, but unlike our competitors who use overseas manufacturing, we have all of our cases manufactured in Nova Scotia, Canada (Protocase, Inc). This is part of our commitment to keep as much of our amplifiers as "home grown" as possible. It also ensures the highest possible quality aluminum and extremely precise CNC manufacturing."

 

[pma]

Even if 1ET400A is pushed to 70W/8ohm (rms), which would be 140W/8ohm of the sine wave with same amplitude as the twin-tone, it keeps very low IMD distortion.

Note: I came to the issue of the high odd distortion components in the high level 19+20kHz test by chance, when I was testing an LC filter for BW restriction. The difference in-box/out-box. Then found the same with class D amplifier modules that use filter coils. Aluminium case is a must. Never the iron case. That separates top implementations from cost-effective implementations.

 

[Multicore]

50W peak into 8ohms. Frankly, I do not like "peak power" definitions, so I have measured my 1ET400A at 40W/8ohm (rms) with this result:

I don't know what "50W peak" means to describe test tones. I know two possible meanings: peak-to-peak but this doesn't apply to Watts afaik and peak power refers to a short a duration burst test signal but I don't see how that applies here.

It may be seen that the distortion components are at or below -105dBr. What a difference from Stereophile result near -70dBr, it is a huge 35dB!!

I don't think your test result can be compared with the Stereophile test without knowing its levels, i.e. what "50W peak" means. It might have been an error in the write up and the word "peak" should not have been there.

There's another curios power spec in the Stereophile text "mix of 19kHz and 20kHz tones at 50Wpc peak into 8 ohms" (2nd last para). What's "Wpc". I guessed maybe "per channel" but it's a single channel amp. The caption for the graph repeats that but without the "pc" suffix.

 

[pma]

@pma I believe Buckeye's cases are aluminium according to the website description,

But look at the photo from Stereophile:

Look at the bent corners and material thickness (thin). This does not look like Al at all. I hope @Buckeye Amps will clarify. Al would ask for milling, straight shapes and screws.

 

[Old_School_Brad]

It says it's aluminium on the webshop.

Buckeye Amps

Buckeye Amps utilizes the most advanced audio amplifier technologies available. Authorized seller for Hypex and Purifi Class D amplifiers. Based in the US. Free shipping and worldwide service!

www.buckeyeamp.com

 

[Multicore]

A magnet is not attracted to the case of my Buckeye. It's a Hypex amp but the case looks like the image above. It's unlikely to be sainless (inox) steel.

 

[pma]

It says it's aluminium on the webshop.

OK, let us wait for the answer from @Buckeye Amps related to the amplifier sample under test. Otherwise, there is no other explanation for the very high skirts in the 19+20kHz IMD, which do not correspond with the datasheet. The other and only explanation would be a core non-linearity in the AP class D measuring filter, but I hope it is not the case. I am not sure if @John Atkinson would reply here.

Datasheet:

 

[MaxwellsEq]

I was confused by this from @John Atkinson

As the Buckeye is a class-D design, there was no need to precondition it before the testing. Nevertheless, out of habit I operated the amplifier for 30 minutes at a moderate power into 8 ohms before starting the testing.

My bold

 

[Old_School_Brad]

I was confused by this from @John Atkinson

My bold

Yeah, stumbled over that one too...

 

[MaxwellsEq]

I suddenly had one of those existential logic jumps - why do we (still) precondition amplifiers before testing. I always did it, and assumed it was a chance to spot temperature-related faults, or it would give the amplifier a chance to be stable before being beaten up by some aggressive signals. But it's an unrealistic test, really - other than tube amplifier owners, who turns on their amplifiers half an hour before use and plays tone to get things stable?

 

[Sokel]

Case is aluminum,we have read that many times,I can't be the cause of such high IMD.
Combined with the power collapse I would be more inclined to believe that it's just a faulty module,it happens.

 

[SIY]

If I saw that in a measurement, my first reaction wouldn't be looking at effects whose impact is usually orders of magnitude lower than seen here, but rather trying to validate the measurement chain.

Or you could repeat your test with a steel sheet on top of your case?

Great control experiment if the hypothesis is "the case is the problem."

 

[Old_School_Brad]

I suddenly had one of those existential logic jumps - why do we (still) precondition amplifiers before testing. I always did it, and assumed it was a chance to spot temperature-related faults, or it would give the amplifier a chance to be stable before being beaten up by some aggressive signals. But it's an unrealistic test, really - other than tube amplifier owners, who turns on their amplifiers half an hour before use and plays tone to get things stable?

A guess would be because a heat sink at room temperature won't generate airflow, but once preheated, it allows convection to continuously remove heat from the components.

 

[Multicore]

A guess would be because a heat sink at room temperature won't generate airflow, but once preheated, it allows convection to continuously remove heat from the components.

But you're just elaborating how it is unrealistic. We expect to turn on the sounds and party immediately. @MaxwellsEq makes an interesting point.

 

[yys310]

The other and only explanation would be a core non-linearity in the AP class D measuring filter, but I hope it is not the case. I am not sure if @John Atkinson would reply here.

I don't think so.
The NAD C298 is also based on Purifi
Stereophile
200W into 4ohm.
Still far from the module's performance but at least shows much better performance compare to the measurement on buckeye.

 

[JSmith]

validate the measurement chain

Agree... something seems off.


JSmith

 

[Old_School_Brad]

But you're just elaborating how it is unrealistic. We expect to turn on the sounds and party immediately. @MaxwellsEq makes an interesting point.

Neither for nor against, but in a load test scenario, it’s reasonable for the sake of protecting the equipment. Or giving it the best possible heat dissipation.