Buckeye 3 Channel Purifi Amp Review

[Rick Sykora]

Looks as though Buckeye's buffer designer also had a dummy load issue. I talked to him today and found he was using some PE dummy loads. I had bought the same ones and returned them. I found they could not be used for measuring low distortion situations. Might have found this sooner but we had limited interaction as it seemed desirable for my testing to be blacker box than his.

Since nobody else complained about the PE dummy loads, I was not sure it was a common problem. In hindsight, seems likely they exhibit the VcR characteristic that Amir discusses here: https://www.audiosciencereview.com/forum/index.php?threads/asr-dummy-load-configuration.8026/page-5

So, the good news is the designer should not have to resort to a pricey AP rental as he was able to get a clean measurement once the PE dummy loads were replaced. More importantly, should also mean he should be able to determine potential remediations fairly soon.

 

[Walter]

@Rick Sykora and @Buckeye Amps I have to really applaud how you are keeping everyone updated on this.

 

[Too Many Notes]

Look as though Buckeye's buffer designer also had a dummy load issue. I talked to him today and found he was using some PE dummy loads. I had bought the same ones and returned them. I found they could not be used for measuring low distortion situations. Might have found this sooner but we had limited interaction as it seemed desirable for my testing to be blacker box than his.

Since nobody else complained about the PE dummy loads, I was not sure it was a common problem. In hindsight, seems likely they exhibit the VcR characteristic that Amir discusses here: https://www.audiosciencereview.com/forum/index.php?threads/asr-dummy-load-configuration.8026/page-5

So, the good news is the designer should not have to resort to a pricey AP rental as he was able to get a clean measurement once the PE dummy loads were replaced. More importantly, should also mean he should be able to determine potential remediations fairly soon.

Been following along and appreciate the update. Sounds like good news. Just placed an order for a 3-channel Purifi and super excited! I have faith the cause of this (minor) distortion issue will be determined and resolved. It's clear that Dylan stands behind his products and his zero-BS approach is very confidence inspiring.

 

[Buckeye Amps]

So, not ready to call the distortion issue officially fixed, but we are very comfortable that we have found the culprit. We have a few more variables/variations to test to be 100% sure, along with a 3rd party measuring/testing as well, but we can reproduce distortion-free measurements by replacing the culprit in every different variation we have tried so far.

The great news: if the results hold up, it will be a super simple fix. Won't say more yet. But for those who have been patient and waiting, I think there is finally light.

 

[Audiomn]

So, not ready to call the distortion issue officially fixed, but we are very comfortable that we have found the culprit. We have a few more variables/variations to test to be 100% sure, along with a 3rd party measuring/testing as well, but we can reproduce distortion-free measurements by replacing the culprit in every different variation we have tried so far.

The great news: if the results hold up, it will be a super simple fix. Won't say more yet. But for those who have been patient and waiting, I think there is finally light.

This is awesome news! <Fingers crossed>

 

[Too Many Notes]

So, not ready to call the distortion issue officially fixed, but we are very comfortable that we have found the culprit. We have a few more variables/variations to test to be 100% sure, along with a 3rd party measuring/testing as well, but we can reproduce distortion-free measurements by replacing the culprit in every different variation we have tried so far.

The great news: if the results hold up, it will be a super simple fix. Won't say more yet. But for those who have been patient and waiting, I think there is finally light.

 

[amper42]

So, not ready to call the distortion issue officially fixed, but we are very comfortable that we have found the culprit. We have a few more variables/variations to test to be 100% sure, along with a 3rd party measuring/testing as well, but we can reproduce distortion-free measurements by replacing the culprit in every different variation we have tried so far.

The great news: if the results hold up, it will be a super simple fix. Won't say more yet. But for those who have been patient and waiting, I think there is finally light.

Great News. Let's have the Buckeye Purifi retested by @amirm and the review updated before we pop the champaign cork. As we have learned, measurements can be tricky and are not a normal function at Buckeye amps yet. Maybe that will change in the future?

 

[pma]

Glad to see that @Buckeye Amps is on the right track. Same care to be followed during measurements, 4 point method preferred.

 

[Too Many Notes]

Great News. Let's have the Buckeye Purifi retested by @amirm and the review updated before we pop the champaign cork. As we have learned, measurements can be tricky and are not a normal function at Buckeye amps yet. Maybe that will change in the future?

Was meant as encouragement and optimism for being on the right track. But sure, let’s be grumps about it.

 

[Audiomn]

Great News. Let's have the Buckeye Purifi retested by @amirm and the review updated before we pop the champaign cork. As we have learned, measurements can be tricky and are not a normal function at Buckeye amps yet. Maybe that will change in the future?

I have confidence that Buckeye’s and Rick’s testing is sufficient and I think we all appreciate Too Many Notes .gif

 

[Buckeye Amps]

Thanks everyone!

It was a very simple fix which is likely how it was overlooked initially (plus the issues with the load resistor when first doing testing and "debugging"). So simple, in fact, I even verified the principle science/theory behind it with Purifi themselves and they backed up what we found. Will also give a shotout when the time comes to a member on here who had the thought of what the issue was days after the review.

Just getting a few logistics in place before making a full post on all the details, options for fixes, etc. Though I know some may still want to wait for the re-test by Amir, which I obviously also support.

 

[Rick Sykora]

Ok, the moment of truth has arrived...

As @Buckeye Amps mentioned, the board designer and I have been going at this diagnosis feverishly. Admittedly, should have found sooner, but I made a critical test error and (as mentioned) the designer had been plagued by a bad dummy load that obscured his measurements until just recently. Since I have been working closely on the troubleshooting, Dylan is allowing me to represent the team to share our finding. In the end, the designer found the cause.

And the culprit is...



The binding post connection tab.

Unknown to @Buckeye Amps when he bought the binding posts, the tab is primarily made of steel. Steel is a relatively poor conductor and like a loose or oxidized connection can cause distortion. As with some others, I thought the culprit was the input board, but fortunately it was not. Honorable mention goes to @pma. Within his first few posts in this thread, he mentioned problems with ferrous materials in the signal path. We just had to find it.

Anyway, @Buckeye Amps is working on lining up parts and plans to address this issue in customer units and his production. He will share more details soon. Both of us are planning corrective actions to avoid this issue recurring.

P.S. (for those wanting some additional insight, please read on...)

I mentioned a critical error on my part. Tbh, there may have been more than one, but the key one was when I tested the amp speaker binding post by replacing it with a different binding post that also had a steel tab. Later when I tested the Purifi EVAL1 board (with built-in banana jacks) alongside the Buckeye board, the Purifi passed the test. At that point, was pretty convinced the culprit was the input board. I then tried several ways to alter the board grounding, but none worked.  So, the troubleshooting effort turned towards the board designer as he had more intimate knowledge of the design. Lesson learned!

 

[Buckeye Amps]

Which also means none of those who chose the speakON upgrade option are affected.

 

[amper42]

Ok, the moment of truth has arrived...

As @Buckeye Amps mentioned, the board designer and I have been going at this diagnosis feverishly. Admittedly, should have found sooner, but I made a critical test error and (as mentioned) the designer had been plagued by a bad dummy load that obscured his measurements until just recently. Since I have been working closely on the troubleshooting, Dylan is allowing me to represent the team to share our finding. In the end, the designer found the cause.

And the culprit is...

View attachment 263237

The binding post connection tab.

Unknown to @Buckeye Amps when he bought the binding posts, the tab is primarily made of steel. Steel is a relatively poor conductor and like a loose or oxidized connection can cause distortion. As with some others, I thought the culprit was the input board, but fortunately it was not. Honorable mention goes to @pma. Within his first few posts in this thread, he mentioned problems with ferrous materials in the signal path. We just had to find it.

Anyway, @Buckeye Amps is working on lining up parts and plans to address this issue in customer units and his production. He will share more details soon. Both of us are planning corrective actions to avoid this issue recurring.

P.S. (for those wanting some additional insight, please read on...)

I mentioned a critical error on my part. Tbh, there may have been more than one, but the key one was when I tested the amp speaker binding post by replacing it with a different binding post that also had a steel tab. Later when I tested the Purifi EVAL1 board (with built-in banana jacks) alongside the Buckeye board, the Purifi passed the test. At that point, was pretty convinced the culprit was the input board. I then tried several ways to alter the board grounding, but none worked.  So, the troubleshooting effort turned towards the board designer as he had more intimate knowledge of the design. Lesson learned!

Rick,
Are these same steel binding post connection tabs on the NC502MP? If so, could these amps be improved as well?

 

[danzilla31]

Which also means none of those who chose the speakON upgrade option are affected.

I just read this entire thread. And your patience humility and desire to go above and beyond fixing this for your customers has just blown me away.

I would've bought this Purifi amp as is without the fix because even with the distortion (which is inaudible) where are you going to find a purifi amp that sounds as good as it does for the price you are offering.

I'm not bashing the members on here who thought this was an issue I do understand that for many buying this amp its about buying perfection.

But how you've handled this has completely won me over. Within the year I do plan on replacing all of my class ab amplifiers with class d in my theater room for better rack space and obviously less weight and heat. And when I do I will be going 100% with you and your company

 

[Buckeye Amps]

Rick,
Are these same steel binding post connection tabs on the NC502MP? If so, could these amps be improved as well?

They use the same tabs, yes.

However it remains to be seen if they would make a difference for the NCxxxMP series. Amir will be reviewing an 8ch NC502MP that will also have new tabs swapped in.

I say remains to be seen for the NCxxxMP because if you look at the data sheet for the Rev4 NC502MP, for example, there is a subtle rise in distortion that occurs starting around 10W. So it will be interesting to see what Amir shows in that regard when the time comes (compared against the older NC502MP amp of mine that was reviewed nearly two years ago).

 

[Matias]

Now I wonder if rising distortions at the power knee of the modules have also something to do with materials used, but that is for another topic. Thanks for detailing the hunt for the guilty, very interesting!

 

[Sokel]

If it was for a random guy saying that the binding post would make a difference lots of people here would put him in the snake oil territory.
It was fortunate that it came for someone who has tested stuff,so...
Happy ending!

 

[pma]

If it was for a random guy saying that the binding post would make a difference lots of people here would put him in the snake oil territory.
It was fortunate that it came for someone who has tested stuff,so...
Happy ending!

It is a big, big difference between randomly expressed opinion and hypothesis based on evidence and experience. Sometimes it may happen, however, that even the 1st is an important hint. Sometimes, there should not be an inflation of "snake oil" recommendations .

To check the high current related issue (nonlinear contact resistance, ferro, ...) it is good to measure with and without load. Nonlinear contact issues need heavy load, high current.

 

[Rick Sykora]

Rick,
Are these same steel binding post connection tabs on the NC502MP? If so, could these amps be improved as well?

Currently do not have any Buckeye Hypex amps on hand to try and only one older NC502MP. Agree with @Buckeye Amps that the difference may be revision dependent. As you know, have been busy with Nilia builds and need to get back to Directiva work. Since the designer found this issue, he has had the ball lately…

Will work with the team to better characterize. Am confident Dylan will do his best to ensure customers concerns are addressed.

P.S.

I do have a Buckeye Purifi amp and have been running with the old binding post tabs. I will replace the tabs when I have the chance, but we are still talking quite low distortion even with the old tabs.