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Buckeye Amps: 2nd Generation Purifi EIGENTAKT 1ET9040BA Amplifier

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-120dB is "high"? With that amount of asymmetry, the expected IM sidebands for 19/20kHz would be well under -100dB. A measurement with something different needs to be looked at carefully to see if there's an error.

These data look excellent to me.
 
I believe JA pre-conditions the amp to warm it up beforehand. This might result in protection intervention at a lower power level than with other testers.
He did indeed, per the review:
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Noticed this bon mot, too, FWIW.

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source: https://www.stereophile.com/content...9040ba-monoblock-power-amplifier-measurements
 
-120dB is "high"? With that amount of asymmetry, the expected IM sidebands for 19/20kHz would be well under -100dB. A measurement with something different needs to be looked at carefully to see if there's an error.

These data look excellent to me.

@SIY - What do you think of the Buckeye 9040AB input impedance specified as 51k ohms in the specification yet measuring 8.4k ohms from 20Hz to 20kHz in the stereophile tests? That seems like a large variation to me. Makes me wonder if this was actually measured by Buckeye?

Could this place a greater load on source devices and potentially impact signal loss or tonal coloration?
 
Regarding the protection kicking in during that review and limiting power, is that protection from the module itself, or does buckeye add its own protection?
 
Could this place a greater load on source devices and potentially impact signal loss or tonal coloration?
If the source was a poorly designed tube one, sure. For any even half-competent design, it's a piece of cake.
For the 9040 module my view is yes -120dB is high. Compare it to measurements of amps using the 1et400 module. These are typically -125 to -130dB.
IOW, better than most AP analyzers. You're in the realm where tiny details in the measurement (like lead dress or the specific analyzer) can cause that level of variation. -120dB is a part per million, for context.

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(source: AP's website)
 
There you go, mistery is solved.

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@SIY - What do you think of the Buckeye 9040AB input impedance specified as 51k ohms in the specification yet measuring 8.4k ohms from 20Hz to 20kHz in the stereophile tests? That seems like a large variation to me. Makes me wonder if this was actually measured by Buckeye?
Could this place a greater load on source devices and potentially impact signal loss or tonal coloration?
It's an unusually large discrepancy, but as SIY says, probably not an issue, as line level connections have quite a lot of latitude. They usually run at 1 or 2Vrms (4V balanced), the player/converter/preamp has an output impedance around 100Ω (25 to 200Ω is most common), and the line level input impedance of either a pre or power amp is usually 47 to 50kΩ. That's a big difference between source and load impedance, and means that most electrical loads are relatively small.

Hypex and Purifi amp modules are different to power amps. They have both low sensitivity and low impedance, needing 10-15V input into as little as 1500 ohms for full power.
That's too much voltage and current for most preamps, which is why integrators like Buckeye Amps use input buffers - both to provide more gain, and to to provide the current needed by the module.

Buckeye specify 51kΩ input impedance, so it ought to be close to that, but it's not as important as power amp / speaker matching, for example. 8.4kΩ is still much higher than 100Ω and only draws a small current. Amir has started doing what John Atkinson often does, and tests line outputs at an unrepresentative 600Ω load. This is an extreme load and often causes a drop in maximum output voltage and a small increase in distortion, but most good convertors and preamps cope well even at this level. Certainly, devices of the calibre that are likely to be used with this power amp won't be troubled.
 
Now all we need to find is a tweeter that can handle 74W continuous for 5 minutes at 20kHz
 
There you go, mistery is solved.

View attachment 415408

@Matias - Could you kindly provide a link for this post from Purifi?

It will be interesting to see if faulty production of shipped 9040BA modules impacts not only HF performance but also impedance and power issues. How can someone determine if they have one of the faulty units from the bad batch? Will manufacturers and Purifi offer a recall for certain serial numbers?
 
As I was working as a contractor with Buckeye at the time, I own a prototype of this amplifier. As I no longer am working with him, cannot comment on the Stereophile review unit. My previous efforts were centered around doing high power testing for various power supplies. As has been stated elsewhere, he was evaluating an AP analyzer, and it would supersede my efforts. Both Dylan and his designer have always been focused on creating a quality product in my experience working with them. Amir has independently posted positive favorability in his dealings with Buckeye as well.

As far as this amp’s power ratings are concerned, I know the Buckeye designer verified it to Purifi’s spec. Dylan told me this at the time so am confident he has acted reputably. So, along with positive past experiences, I was confident to keep the prototype for my own use. As many of us know, he has been busy and so questions around the Stereophile review will take time. Dylan and his designer have demonstrated integrity, but they are a very small operation with family and other priorities. Give them some time and they will investigate and share their findings. As this is just an audio amplifier, suggest we all grab a cup of cheer and enjoy some family time. :)

Happy Holidays!

Rick
 
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As I have said, patience and an adequate amount of data points goes a long way in science.

Luckily, the Stereophile monoblocks were the only affected builds we had shipped with this defect. And while people will ask why we didn't thoroughly test it before sending out for a high-end review...because I do not cherry pick. Our measurement testing involves picking a few components whenever we receive a new batch (amp modules, SMPS', buffer boards, etc) and testing those. It just so happens we didn't pick the bad module from the early batch to test.

All final built amps are tested for functionality and listening impressions (while every so often a random final build is also measured), which these monoblocks did pass (as evidence by Kal's subjective impressions that in practical use it was as superb sounding as expected).

I have reached out to Kal/Stereophile in case they would like to re-measure a new monoblock but I am not at all requesting or demanding that they do.

I will also, as already mentioned, be providing new sets of measurements to hopefully appease those who still want to jump to conclusions of bad engineering on our end.

Thank you all and Happy Holidays!
 
@Buckeye Amps - I noticed this morning the Buckeye spec pages no longer list input impedance for amps sold. Will that be added back to the spec page at a later date? Do you currently have a design target for the input impedance spec of Buckeye amps? Thank you!
 
@Buckeye Amps - I noticed this morning the Buckeye spec pages no longer list input impedance for amps sold. Will that be added back to the spec page at a later date? Do you currently have a design target for the input impedance spec of Buckeye amps? Thank you!
Will be added back, yes. In light of the conflicting results, want to remeasure and reaffirm.

Just bad timing of all of this due to a very hectic build/customer order list and the Holidays.
 
You can probably send Stereophile a new "Manufacturer's Comments" letter with your test results once you replace the modules and retest. Even if they do not want to retest the amp they will likely publish your letter.
 
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