Buckeye 3 Channel Purifi Amp Review

[amirm]

This is review and detailed measurements of the Buckeye 3 Channel Purifi amplifier based power amp. It was kindly drop shipped to me by a member and costs US $1,699.

As you see, the case is utilitarian. The amplifier is extremely light making you think there is nothing in the box! The back side shows the features you want, sans RCA inputs:

I like the three gain settings to let you get the best out of your sources. Full power is achieved nearly 2 volts in high gain letting you drive it with many AVRs. Low gain requires 6.5 volts or so.

Three channel configuration is naturally aimed at home theater applications for front left, right and center.

Update: the problem with rising distortion was identified and fixed in new sample. See the new review here: https://www.audiosciencereview.com/...-3-channel-purifi-amplifier-review-2nd.43834/

Buckeye Purifi 3 Channel Amplifier Measurements
Let's start with our warm up test:

Amplifier is stable on power on so no need to leave it on. Now the dashboard:

This is the performance we like to see out of the Purifi module, landing the unit firmly in our top 20 best amplifiers ever tested based on noise+distortion @ 5 watts:

I thought there may be a bit more performance to be had in low gain but that was not the case with SINAD (not shown). However, there is a slight improvement in signal to noise ratio:

Multitone shows the very low distortion floor:

Frequency response is superb for a class D amplifier:

Crosstalk is the best I have measured:

Let's see how much power we get out of two channels into 4 ohm:

The power is consistent with other Purifi amps I have measured. But the rise in distortion is not. I have shared the results with the company and they have identified the issue but no fix as of yet. When there is, I will update the review. Back to amount of power, here is what we have into 2 channels:

The power supply must be quite capable as we only lose a bit of power when driving 3 channels (only two shown):

You essentially have 1000 watts being pumped out.

8 Ohm load still shows good amount of power:

The unknown rise in distortion at higher powers messes up the otherwise clean transfer function of Purifi amplifier modules:

You do have healthy amount of power at 2 ohms (264 watts) before the protection circuit kicks in.

Finally, here is the new power on/off noise test:

There is no pop on noise. There is one while turning off but levels are 0.5 millivolts which should not be an issue. While on, there is a regular pattern of noise. Wonder if it is due to internal microprocessor timer or something like it. Above is with 45 kHz bandwidth by the way. It goes down with 22 kHz.

Conclusions
The Buckeye 3 channel amp was doing superbly in lower power tests. It is attractively priced in a lightweight no-nonsense package. Alas, the power sweep shows rise in distortion. While probably not an audible concern, it is nevertheless a blemish on the otherwise near perfect performance of the Purifi modules. Hopefully the company figures out the issue and provides a fix. I am told when that happens, customers are properly notified and offered the fix.

As is then, I can't recommend the Buckeye 3 Channel Purifi amplifier.

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As always, questions, comments, recommendations, etc. are welcome.

Appreciate any donations using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/

 

[Walter]

This is quite a surprise, but based on Buckeye Amps owner Dylan's track record, I expect the issue to be resolved and a fix available very quickly.

 

[polmuaddib]

Thanks for the review, Amir.
Is that rise in distortion over 10w the only reason you don't recommend this product?
Am I right to think that even with the distortion rise, it's kept around -80 dB under the fundamental?
It's not SOTA, but surely not bad?
Seems like a good amp, even with that dostortion rise, that's why I am asking.
Thanks

 

[hoppy IPA]

dang

 

[amirm]

Is that rise in distortion over 10w the only reason you don't recommend this product?

That's correct. For people who buy this amp, impeccable measured performance is key. For that reason, I think this is a more significant issue that it otherwise would be.

 

[restorer-john]

Thanks for the review, Amir.
Is that rise in distortion over 10w the only reason you don't recommend this product?
Am I right to think that even with the distortion rise, it's kept around -80 dB under the fundamental?
It's not SOTA, but surely not bad?
Seems like a good amp, even with that dostortion rise, that's why I am asking.
Thanks

It points to a poorly designed buffer stage IMO with rising THD as the level and frequency increases. We pretty much know it's not the PURIFI power stages as we've seen enough of them tested to know their THD signatures.

 

[Billy Budapest]

I would have thought with those mostly-great measurements this would have received a “recommended” rating

 

[restorer-john]

I would have thought with those mostly-great measurements this would have received a “recommended” rating

The power vs distortion plots would be a lot worse if it weren't for the 45kHz measurement bandwidth- you can see their trajectory (with the 10kHz and 15kHz) lines dipping due to harmonics being truncated. We are talking about significant levels of HF higher order harmonics.

 

[Buckeye Amps]

This was not expected and was not an attempt to have a known/flawed product pushed through review.

While we did robust testing during development and prototyping, I cannot account for why this issue was not identified or observed early on. But I do take full responsibility.

As Amir briefly acknowledged, now that we are aware of and able to reproduce the issue on our end, we have been testing furiously to identify the exact cause so we can produce a fix.

Transparency and communication with the community has been one of the "pillars" I've tried to build my business upon. As soon as we identify the exact issue and the appropriate fix, it will be implemented ASAP, including for current customers as needed.

 

[Chrispy]

This was not expected and was not an attempt to have a known/flawed product pushed through review.

While we did robust testing during development and prototyping, I cannot account for why this issue was not identified or observed early on. But I do take full responsibility.

As Amir briefly acknowledged, now that we are aware of and able to reproduce the issue on our end, we have been testing furiously to identify the exact cause so we can produce a fix.

Transparency and communication with the community has been one of the "pillars" I've tried to build my business upon. As soon as we identify the exact issue and the appropriate fix, it will be implemented ASAP, including for current customers as needed.

While I was just conteplating what the impact to you was....there you are!

 

[pma]

It points to a poorly designed buffer stage IMO with rising THD as the level and frequency increases. We pretty much know it's not the PURIFI power stages as we've seen enough of them tested to know their THD signatures.

We would need to see measurements of spectra of THD and IMD at about 20W, 100W, 150W to be able to say what is happening. We would probably see spectral mess and noise floor rise. Cummulative plots like THD+N with integrating character are unable to reveal origins of the issue seen.

 

[restorer-john]

We would need to see measurements of spectra of THD and IMD at about 20W, 100W, 150W to be able to say what is happening. We would probably see spectral mess and noise floor rise. Cummulative plots like THD+N with integrating character are unable to reveal origins of the issue seen.

Yes, but we also have the two 4R and 8R THD vs Po plots, and notice, the rise starts at approximately the equivalent voltage output. That suggests to me anyway, that it is not the amplifier stage itself as the current flow has doubled for 4R as compared to 8R and the PSU is holding up into 8/4 and 2 and 3ch.

It would be interesting to see the low/med/high gain switch sweeps for THD vs Power Output.

 

[pma]

Yes, but we also have the two 4R and 8R THD vs Po plots, and notice, the rise starts at approximately the equivalent voltage output. That suggests to me anyway, that it is not the amplifier stage itself as the current flow has doubled for 4R as compared to 8R and the PSU is holding up into 8/4 and 2 and 3ch.

It would be interesting to see the low/med/high gain switch sweeps for THD vs Power Output.

It seems that the rise of distortion ( from noise) starts at 10W/4 ohm and also at 10W/8 ohm. That would be at output voltage approx. 6.5V/4 ohm and 9V/8 ohm …

 

[Kevinfc]

The case doesn’t look very well manufactured. There’s large gaps all along where the top and bottom meet.

 

[Futility]

What does it mean for customers who currently have these amps on order / in production / ready to be shipped?

I just received a UPS notice of label creation. Should I ask to hold off shipping until the fix?
How long is it going to take to identify the issue and rectify it? It has already been over 9 weeks.

 

[Sokel]

I don't think this rise in distortion is new with Buckeye.
Here's the last year's review of the 6-ch NC502MP,we see the same pattern:

 

[marcom22]

I don't think this rise in distortion is new with Buckeye.
Here's the last year's review of the 6-ch NC502MP,we see the same pattern:

It's Correct ....... very strange.

 

[amirm]

I don't think this rise in distortion is new with Buckeye.

Certainly not a new thing with amps in general. It is however new/unusual with Purifi amps.

 

[Sokel]

Certainly not a new thing with amps in general. It is however new/unusual with Purifi amps.

If I remember correctly a guy in diyAudio had a similar problem which turned out to be as simple as proper grounding.
But it was a long time ago,don't think I will find it.

 

[Dennis_FL]

This was not expected and was not an attempt to have a known/flawed product pushed through review.

While we did robust testing during development and prototyping, I cannot account for why this issue was not identified or observed early on. But I do take full responsibility.

As Amir briefly acknowledged, now that we are aware of and able to reproduce the issue on our end, we have been testing furiously to identify the exact cause so we can produce a fix.

Transparency and communication with the community has been one of the "pillars" I've tried to build my business upon. As soon as we identify the exact issue and the appropriate fix, it will be implemented ASAP, including for current customers as needed.

Any future plans to test the latest Hypex design?