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Measuring 2-channel Buckeye Purifi Amplifier Performance

Rick Sykora

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With Amir busy with house repairs, @Buckeye Amps and I discussed whether I might share some of my efforts to measure his Purifi amplifier as a stop gap until Amir can do so. A couple of disclaimers here as I am NOT an experienced electrical engineer and my QuantAsylum test rig is NOT as capable as Amir's AP analyzer. Should also point out that this amp was built by me using Buckeye's parts. I expect his build is almost identical but could be some slight differences. All said, we still thought this might be useful in the interim.

20210107161508_PhotoLead-QuantAsylum-QA401-QA451.jpg



So first, my basic test rig consists of a QA401 audio analyzer and a QA451 programmable load. The test load provides 4 and 8 ohm resistive loads and includes a 6th order low pass filter help deal with "filterless" Class D amplifiers. The QA451 is capable of measuring up to about 300 watts of power for short bursts. The Purifi amp is capable of a little more than 300 watts but is within the load's limits. All measurements will be done at 4 ohms and the unbalanced outputs are connected to the QA401 inputs using short BNC cables.

The QA401 analyzer has balanced and unbalanced input and outputs and has a couple of different attenuation settings to deal with differing levels of input signals. For this post, am using the unbalanced connections. My measurements are primarily done at lower attenuation and (for the most part) are unweighted. While quite useful and capable, this equipment is not as capable as Amir's (notably for low noise testing), so as shown below, the max SINAD is about 101 dB.

Let's start by showing what the measurement looks like for a 1kHz signal with analyzer output looped back to its input...

1667227769030.png


Note 0 dB is just shy of 1 volt and the SINAD (inverse of THD+N) is just a little over 101 dB. This is an unweighted measurement and so would be a bit better with A weighting.

Adding the QA451 into the loop, but switching to Amir's typical review measure at 5 watts...

1667228824771.png


Note to take this higher input level, had to switch to the higher analyzer attenuation, but still pretty respectable SINAD at 96 dB. With A-weighting is just under 98 dB. By comparison, my Hypex NC252MP measures around 94 dB unweighted.

Let's look at frequency response...
1667233941075.png


Now we'll measure SINAD vs Power...
1667234628361.png

Note single channel output is 334 watts at clipping.

Now with both channels...
1667234853646.png

Power is 325 watts per channel at clipping.

Pretty sure am going to get asked for lower gain measures and will plan to test some of them. Will require some additional gain and/or using a balanced connection.

So, before I rewire the test rig, wanted to see if any other measurements might be desired?
 
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Rick Sykora

Rick Sykora

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As promised, here is a look at the SINAD measurements as we switch between gain settings. The major difference versus my initial measurements is I am using a balanced connection to allow me to drive the lower gain settings to 5 watts. In setting a comparable SINAD, due to the higher voltage, the best SINAD from the QA401 is still 102 dB, but now is attained at -6 dBV (rather than 0 dB for unbalanced connections).


So, first will show the high gain setting...

1667313069471.png

The gain is a now little higher at 31 db and the SINAD is about 92. Note that am driving analyzer output at about -18 dB (versus around -12 for unbalanced). Now let's try the medium gain setting...

1667313356095.png

Gain is around 26 dB and SINAD is about 96 dB. Note the drive level is closer to the unbalanced level at -13 dB. Finally, here is low gain measurement...

1667313681598.png

Gain is around 21 dB with a SINAD of 98 dB. The drive level has now increased to -8 dB to obtain 5 watts of output at 4 ohms. Despite the better lowest SINAD, my analyzer output tops out at 130 watts (with 4 volt drive level) and cannot drive the amplifier to clipping....

1667314400255.png

However, at medium gain, only lose 2 dB of SINAD and (with unbalanced connection able to output 4V), can drive the amplifier to clipping at 400 watts. So if you use balanced connection with a source that can output 4V, you can readily attain great performance from this amplifier.
 
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AndreaT

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Great review. This is the Buckeye 2-channel 1ET400 that sells for $ 1,189. It seems quite powerful over 4 ohm. Any plans to measure power over 8 ohm load?Usually, class D follows closely Ohm's Law, and the power is expected to be half of the 4 ohm measurement. As a side note, I am the happy owner of a Buckeye 2-channel 252MP that has performed flawlessly in the past 2 years.
 

Rottmannash

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Can we expect the 3 channel version to produce similar power across all 3 channels simultaneously?
 

martijn86

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Very clean power, between 2-225W a sinad of >80dB is perfect!
 

MacCali

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Great review. This is the Buckeye 2-channel 1ET400 that sells for $ 1,189. It seems quite powerful over 4 ohm. Any plans to measure power over 8 ohm load?Usually, class D follows closely Ohm's Law, and the power is expected to be half of the 4 ohm measurement. As a side note, I am the happy owner of a Buckeye 2-channel 252MP that has performed flawlessly in the past 2 years.
Hmmmm maybe wrong here, as it is a different module, but isn't that Audiophonics amp 400ET a better buy than this? 1241 euros for non EU sales and I just bought something from them the other day and the euro was like 6% lower than the american dollar and also no tax o.o
 
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Rick Sykora

Rick Sykora

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Can we expect the 3 channel version to produce similar power across all 3 channels simultaneously?
Would expect so. Pretty sure @Buckeye Amps sent 3 channel amp to Amir. So maybe Amir can test.

As you can see, my test rig maxes out at 2 channels.
 
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Rick Sykora

Rick Sykora

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Great review. This is the Buckeye 2-channel 1ET400 that sells for $ 1,189. It seems quite powerful over 4 ohm. Any plans to measure power over 8 ohm load?Usually, class D follows closely Ohm's Law, and the power is expected to be half of the 4 ohm measurement. As a side note, I am the happy owner of a Buckeye 2-channel 252MP that has performed flawlessly in the past 2 years.

Should be able to post an 8 ohm power graph when I have some time. :)
 
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Rick Sykora

Rick Sykora

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Hmmmm maybe wrong here, as it is a different module, but isn't that Audiophonics amp 400ET a better buy than this? 1241 euros for non EU sales and I just bought something from them the other day and the euro was like 6% lower than the american dollar and also no tax o.o
It seems a nice unit, but after shipping still is a bit more than the Buckeye.

The Buckeye amp has auto-on option and does not appear the Audiophonics offers.
 
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Rick Sykora

Rick Sykora

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Here is THD+N performance at 8 ohms and medium gain. One channel driven with balanced connection...
1667389225871.png

At 8 ohms, clipping is at 206 watts.
 

MacCali

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It seems a nice unit, but after shipping still is a bit more than the Buckeye.

The Buckeye amp has auto-on option and does not appear the Audiophonics offers.
Shipping for over 500 is only 25 euros.

Honestly makes no difference it’s only 4 db, but if it is cheaper because of this war situation than maybe it can be a feasible option.

Warranty would be another factor, not sure how long either company does provide
 
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Rick Sykora

Rick Sykora

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Shipping for over 500 is only 25 euros.

Honestly makes no difference it’s only 4 db, but if it is cheaper because of this war situation than maybe it can be a feasible option.

Warranty would be another factor, not sure how long either company does provide

For US, only shipping option was UPS at 54 Euros, but splitting hairs in my opinion.

The prices are close enough that would not be my major factor in my decision. :cool:
 

57gold

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Have a buddy putting a system together around some new Monitor Audio speakers, suggested a Purifi-based amp. He was concerned that many of these "companies" are just guys assembling parts and that if he has an issue with the equipment down the road, will they still be in business to do repairs. He was favoring an NAD Purifi amp because of this...any guidance I can can share with him?
 
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Rick Sykora

Rick Sykora

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Have a buddy putting a system together around some new Monitor Audio speakers, suggested a Purifi-based amp. He was concerned that many of these "companies" are just guys assembling parts and that if he has an issue with the equipment down the road, will they still be in business to do repairs. He was favoring an NAD Purifi amp because of this...any guidance I can can share with him?
There are existing ASR threads where this has been discussed in depth. An amplifier from a small company is riskier but often is a much better value. As for the major Purifi or Hypex parts, if the original company is not able to fix, they can be repaired by a local electronics repair shop. If there are custom parts, will depend on the shop.

NAD, ATC make some fine amps and, if he prefers to pay for the added peace of mind of a larger company, it's his money. :)
 

Billy Budapest

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There are existing ASR threads where this has been discussed in depth. An amplifier from a small company is riskier but often is a much better value. As for the major Purifi or Hypex parts, if the original company is not able to fix, they can be repaired by a local electronics repair shop. If there are custom parts, will depend on the shop.

NAD, ATC make some fine amps and, if he prefers to pay for the added peace of mind of a larger company, it's his money. :)
Also good to keep in mind: for whatever reason, the Purifi implementations by the “big guys” do not appear to perform as well on the test bench as the ones from the smaller companies.
 

LTTelamon

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Great to see this. I’ve been running this amp for a few months now and love it (replaced Emotiva PA-1 Stealth monoblocks feeding my Philharmonic BMR Towers). It’d be fun to eventually see it tested with Amir’s rig to land it officially on the rankings, but I appreciate this post in the meantime.
 
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