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Review and Measurements of Purifi 1ET400A Amplifier

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This is a review and detailed measurements of the Purifi 1ET400A Class-D amplifier module. Company was kind enough to send me a complete, assembled kit consisting of two modules, power supply and case, ready to go. They have not disclosed the cost of the unit. Modules will be available to DIY channel in Q4 of 2019.

As cases go, the prototype unit came in an attractive one:


A touch of color on the lid goes a long way to break the monotony of DIY aluminum cases. Someone should take this case, put two giant VU meters in the front and make me happy! :)

Here is a quick teardown:


A single Hypex SMPS1200 is used to power both channels. That feeds two 1ET400A amplifier modules.

A single "Amp Connector Board" feeds both channels using balanced input through an optional gain stage of 13 dB. Here is more detail from documentation on the features of this EVM board:

View attachment 28849

I was pleased to see high-quality Rubycon capacitors used in the amplifier modules:
View attachment 28850

The power supply seems like the stock Hypex SMPS1200:
View attachment 28851

It is remarkable that a high-performance amplifier could be built in such a small enclosure with so few subcomponents.

In use, the evaluation unit would barely get warmer above room temperature. Heat dissipation is simply not an issue here. You could easily put these amps in an enclosed cabinet and not worry.

Note that the main offering here is the 1ET400A. The Amp Connector board is offered as convenience. In that regard, I tested the amplifier with and without the extra gain that the connector board provides. Alas, I wish there was something in between. You get full power with as little as 1.5 volt with the extra gain but need 11+ volts without it. I like to see manufacturers build a gain stage that produces full power at 4 volt which we routinely get out of source products (e.g. DACs).

Amplifier Audio Measurements
As provided, the extra gain stage was active producing this dashboard view at 4 ohm producing 5 watts:
View attachment 28852

Focusing on FFT spectrum of a 1 kHz tone, we see stunningly low distortion product. 2nd Harmonic is barely visible which may actually be the contributions from my source signal. The third harmonic hovers around -130 dB which again, is almost at the limit of what we can measure. Given the ear's 116 dB or so dynamic range, you are assured zero audibility of these distortion products.

THD+N and hence SINAD (signal over noise and distortion) is substantially lower though at 104 dB. Since THD+N is sum of distortion products and noise (+N), the latter is the culprit here. We can see this reflected in SNR measurements:

View attachment 28853

As you see on the left, our noise contributions is essentially what we see for SINAD. Fortunately at full power (right), performance shoots way up to fantastic level of 123 dB.

We can do better though by disabling the pre-gain stage:
View attachment 28854

We gain 4 dB in SINAD resulting this summary ranking:
View attachment 28857

The Benchmark in its low gain mode maintains the championship status still but the 1ET400A gives it serious competition here.

SNR naturally improves with lower gain:

View attachment 28858

Drilling into the distortion (with pre-gain active) we see the vanishing harmonic distortion more plainly:
View attachment 28859

Power is everything in amplifiers so let's see how we do with 4 ohm load:
View attachment 28862

The tables are turned and the 1ET400A produces 257 watts of exceptionally clean power. More could be had if I had run this test with finer resolution and/or allowed the distortion to climb more.

We see the effect of lower gain with reduction of noise at lower power levels although even with the extra grain stage, we are talking very quiet here.

Switching to 8 ohm, the results are similar:

View attachment 28863

Notice the big difference between a commercial amplifier (QSC DAC2422). They have more brute-force power but nowhere as clean as the 1ET400A amplifier module.

Intermodulation distortion versus power gives us another shot at analyzing distortion, this time what is in audio band:
View attachment 28864

The Benchmark AHB2 maintains its less noisy baseline but as we reach full power, the 1ET400A catches up to it and keeps going with more power.

Distortion+noise versus power and frequency yields this (with pre-gain stage on):

View attachment 28865

I was surprised to see the rise in distortion with frequency. I had hoped that the super high gain-bandwidth of the 1ET400A would do away with this. Not an audible concern though as the distortion products here are all in ultrasonic range.

I ran this test multiple times, tuning the input voltage. This eventually upset the amp and caused it to shut down when producing 274 watts into 4 ohm before our sweep completed (in green). Documentation clearly states that extra cooling is needed for continuous power.

The Benchmark AHB2 does a lot better since it has much cleaner ultrasonic spectrum:

index.php



Frequency response is exceptionally flat for a class-d amplifier:

View attachment 28866

The output filters in class-d amps can cause variations as we get close to 20 kHz but we see none of that here. Response smoothly rolls off. At 50 kHz, we are down 1 dB.

Crosstalk using my non-optimal setup is still exceptional:
View attachment 28867

I had to pull up the graph to show its crosstalk at 1 kHz. The 1ET400A is that good!

EDIT: here is the broadband spectrum of a 1 kHz tone:
View attachment 28895

We have our switching frequency around 500 Khz and its harmonic at 1 Megahertz. Otherwise pretty clean.

Conclusions
It was just a few years ago that people scuffed at class-D amps not being very clean or good for audiophile use. How the situation has changed. First with Hypex modules and now with the Purifi 1ET400A. Audiophile myths are shattered with use of large amount of feedback and high bandwidth to produce an amplifier which brings transparency to anything you throw at it.

Importantly, the 1ET400A does all of this while producing a ton of power and staying cool and efficient to boot.

There is a subjective aspect to measurements that doesn't come across in the graphs. When I run these tests with switching amplifiers, I often watch the analyzer struggle to get reliable reading, or there are jumps and glitches in measurements. None of that was here. The amplifier basically acted like a traditional class AB amplifier. Indeed, I measured it with and without my AES-17 40 kHz filter and the analyzer was happy both ways. This is when I know there is quality engineering that has gone into design of this amplifier.

Overall, it is my pleasure to strongly recommend the Purifi 1ET400A to DIY and OEM manufacturers.

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

The pink panthers can be pretty lazy at times. I asked them to help clean up the lab and they rolled their eyes and went back to sleep! So I need to hire a housekeeper to keep the walk way clean to my test station. Please donate generously as the hourly rate can be high for such work:

Patreon: https://www.patreon.com/audiosciencereview), or
upgrading your membership here though Paypal (https://audiosciencereview.com/foru...eview-and-measurements.2164/page-3#post-59054).
just curious what's on the back side of 1et400a amp board, could you please post a detailed photo of the 400a back side?
 

mk1classic

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Killingbeans

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just curious what's on the back side of 1et400a amp board, could you please post a detailed photo of the 400a back side?

Components on the PCB? Probably nothing. Just the two FETs and solder points for the through-hole components on the top side.

Putting SMD on both sides of a PCB is a pain in the a$$. That's probably also why it has that 90 degrees tilted daughterboard. Real estate is scarce.
 
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Components on the PCB? Probably nothing. Just the two FETs and solder points for the through-hole components on the top side.

Putting SMD on both sides of a PCB is a pain in the a$$. That's probably also why it has that 90 degrees tilted daughterboard. Real estate is scarce.
I guess there must be more than that, after all this is an amp with superior performance...
 

Julf

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I guess there must be more than that, after all this is an amp with superior performance...
The performance doesn't come from special secret components...
 

Killingbeans

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I guess there must be more than that, after all this is an amp with superior performance...

It's not the amount of components that give you performance, it's what you do with them... Mostly Bruno's tight grip on the balls of the feed back loop.

20200729_185239-1-1024x768.jpg
 

Rottmannash

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Just a note-I have the VTV Purifi amp and am playing through Revel F208's. I had previously not heard anything untoward with this amp/speaker combo, even at very high volumes-until yesterday. I finally heard the "compression" I've heard mentioned. I was playing some Ozzy and decided to see how loud I could either tolerate or until the amp/speaker combo gave up and the amp tapped out first but my ears couldn't have survived more than a few more seconds so glad the amp started acting up. It didn't shut off, it just sounded like the upper freq and lower freq were missing. It was a very odd sensation. At first I wasn't sure what I was hearing but quickly determined the power supply was likely running out of steam. Has anyone else experienced this with the Purifi?
 

mk1classic

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How VTV is setup may not be the same as Purifi's setup as 1et400a datasheet says;

Exceptionally clean clipping and clipping-recovery in both voltage and current domains
o Clips cleanly and recovers immediately without “overhang”. Current limiting is equally instantaneous and glitch free. This guarantees the smallest amount of audible artefacts when pushed into clipping or overload protection.
 

Rottmannash

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How VTV is setup may not be the same as Purifi's setup as 1et400a datasheet says; Exceptionally clean clipping and clipping-recovery in both voltage and current domains o Clips cleanly and recovers immediately without “overhang”. Current limiting is equally instantaneous and glitch free. This guarantees the smallest amount of audible artefacts when pushed into clipping or overload protection. They are identical.
 

Mehdiem

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This is a review and detailed measurements of the Purifi 1ET400A Class-D amplifier module. Company was kind enough to send me a complete, assembled kit consisting of two modules, power supply and case, ready to go. They have not disclosed the cost of the unit. Modules will be available to DIY channel in Q4 of 2019.

As cases go, the prototype unit came in an attractive one:


A touch of color on the lid goes a long way to break the monotony of DIY aluminum cases. Someone should take this case, put two giant VU meters in the front and make me happy! :)

Here is a quick teardown:


A single Hypex SMPS1200 is used to power both channels. That feeds two 1ET400A amplifier modules.

A single "Amp Connector Board" feeds both channels using balanced input through an optional gain stage of 13 dB. Here is more detail from documentation on the features of this EVM board:

View attachment 28849

I was pleased to see high-quality Rubycon capacitors used in the amplifier modules:
View attachment 28850

The power supply seems like the stock Hypex SMPS1200:
View attachment 28851

It is remarkable that a high-performance amplifier could be built in such a small enclosure with so few subcomponents.

In use, the evaluation unit would barely get warmer above room temperature. Heat dissipation is simply not an issue here. You could easily put these amps in an enclosed cabinet and not worry.

Note that the main offering here is the 1ET400A. The Amp Connector board is offered as convenience. In that regard, I tested the amplifier with and without the extra gain that the connector board provides. Alas, I wish there was something in between. You get full power with as little as 1.5 volt with the extra gain but need 11+ volts without it. I like to see manufacturers build a gain stage that produces full power at 4 volt which we routinely get out of source products (e.g. DACs).

Amplifier Audio Measurements
As provided, the extra gain stage was active producing this dashboard view at 4 ohm producing 5 watts:
View attachment 28852

Focusing on FFT spectrum of a 1 kHz tone, we see stunningly low distortion product. 2nd Harmonic is barely visible which may actually be the contributions from my source signal. The third harmonic hovers around -130 dB which again, is almost at the limit of what we can measure. Given the ear's 116 dB or so dynamic range, you are assured zero audibility of these distortion products.

THD+N and hence SINAD (signal over noise and distortion) is substantially lower though at 104 dB. Since THD+N is sum of distortion products and noise (+N), the latter is the culprit here. We can see this reflected in SNR measurements:

View attachment 28853

As you see on the left, our noise contributions is essentially what we see for SINAD. Fortunately at full power (right), performance shoots way up to fantastic level of 123 dB.

We can do better though by disabling the pre-gain stage:
View attachment 28854

We gain 4 dB in SINAD resulting this summary ranking:
View attachment 28857

The Benchmark in its low gain mode maintains the championship status still but the 1ET400A gives it serious competition here.

SNR naturally improves with lower gain:

View attachment 28858

Drilling into the distortion (with pre-gain active) we see the vanishing harmonic distortion more plainly:
View attachment 28859

Power is everything in amplifiers so let's see how we do with 4 ohm load:
View attachment 28862

The tables are turned and the 1ET400A produces 257 watts of exceptionally clean power. More could be had if I had run this test with finer resolution and/or allowed the distortion to climb more.

We see the effect of lower gain with reduction of noise at lower power levels although even with the extra grain stage, we are talking very quiet here.

Switching to 8 ohm, the results are similar:

View attachment 28863

Notice the big difference between a commercial amplifier (QSC DAC2422). They have more brute-force power but nowhere as clean as the 1ET400A amplifier module.

Intermodulation distortion versus power gives us another shot at analyzing distortion, this time what is in audio band:
View attachment 28864

The Benchmark AHB2 maintains its less noisy baseline but as we reach full power, the 1ET400A catches up to it and keeps going with more power.

Distortion+noise versus power and frequency yields this (with pre-gain stage on):

View attachment 28865

I was surprised to see the rise in distortion with frequency. I had hoped that the super high gain-bandwidth of the 1ET400A would do away with this. Not an audible concern though as the distortion products here are all in ultrasonic range.

I ran this test multiple times, tuning the input voltage. This eventually upset the amp and caused it to shut down when producing 274 watts into 4 ohm before our sweep completed (in green). Documentation clearly states that extra cooling is needed for continuous power.

The Benchmark AHB2 does a lot better since it has much cleaner ultrasonic spectrum:

index.php



Frequency response is exceptionally flat for a class-d amplifier:

View attachment 28866

The output filters in class-d amps can cause variations as we get close to 20 kHz but we see none of that here. Response smoothly rolls off. At 50 kHz, we are down 1 dB.

Crosstalk using my non-optimal setup is still exceptional:
View attachment 28867

I had to pull up the graph to show its crosstalk at 1 kHz. The 1ET400A is that good!

EDIT: here is the broadband spectrum of a 1 kHz tone:
View attachment 28895

We have our switching frequency around 500 Khz and its harmonic at 1 Megahertz. Otherwise pretty clean.

Conclusions
It was just a few years ago that people scuffed at class-D amps not being very clean or good for audiophile use. How the situation has changed. First with Hypex modules and now with the Purifi 1ET400A. Audiophile myths are shattered with use of large amount of feedback and high bandwidth to produce an amplifier which brings transparency to anything you throw at it.

Importantly, the 1ET400A does all of this while producing a ton of power and staying cool and efficient to boot.

There is a subjective aspect to measurements that doesn't come across in the graphs. When I run these tests with switching amplifiers, I often watch the analyzer struggle to get reliable reading, or there are jumps and glitches in measurements. None of that was here. The amplifier basically acted like a traditional class AB amplifier. Indeed, I measured it with and without my AES-17 40 kHz filter and the analyzer was happy both ways. This is when I know there is quality engineering that has gone into design of this amplifier.

Overall, it is my pleasure to strongly recommend the Purifi 1ET400A to DIY and OEM manufacturers.

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

The pink panthers can be pretty lazy at times. I asked them to help clean up the lab and they rolled their eyes and went back to sleep! So I need to hire a housekeeper to keep the walk way clean to my test station. Please donate generously as the hourly rate can be high for such work:

Patreon: https://www.patreon.com/audiosciencereview), or
upgrading your membership here though Paypal (https://audiosciencereview.com/foru...eview-and-measurements.2164/page-3#post-59054).

Hi Amir. I recently joined this forum and in the process of translation from myth-based to scientific-based audiophile. I took my first step by accepting EQ is a good thing, and hence, purchased my beloved RME ADI-2 recently.

Now, I am planning to purchase a “transparent” amp to take my journey to the next level. I chose to go with OEM, and preferably stablished brands, hence I don’t mind the premium price. I had NAD C298 or Benchmark AHB2 in mind. A few people in this forum recommended C298. However, there are a few that say DIY or VTV amps with Purifi are better than OEM. Some also expressed concern about continues-gain-control that might result in imbalance. Others say, there would be no audible difference between Purifi amps. I understand that you haven’t tested the NAD C298 yet, but I was wondering what’s your take on this? Is it possible that an OEM Purifi amp be inferior in quality compared to VTV or DIY? In any case, what model, brand do you recommend? My
My current setup is Bluesoudns Node, RME, Yamaha NR602, KEF LS50. In the near future my speakers will be upgraded to floor-standing speakers, so, a bridge-able amp would be a plus. I live in Canada.
 

mk1classic

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Hi Amir. I recently joined this forum and in the process of translation from myth-based to scientific-based audiophile. I took my first step by accepting EQ is a good thing, and hence, purchased my beloved RME ADI-2 recently.

Now, I am planning to purchase a “transparent” amp to take my journey to the next level. I chose to go with OEM, and preferably stablished brands, hence I don’t mind the premium price. I had NAD C298 or Benchmark AHB2 in mind. A few people in this forum recommended C298. However, there are a few that say DIY or VTV amps with Purifi are better than OEM. Some also expressed concern about continues-gain-control that might result in imbalance. Others say, there would be no audible difference between Purifi amps. I understand that you haven’t tested the NAD C298 yet, but I was wondering what’s your take on this? Is it possible that an OEM Purifi amp be inferior in quality compared to VTV or DIY? In any case, what model, brand do you recommend? My
My current setup is Bluesoudns Node, RME, Yamaha NR602, KEF LS50. In the near future my speakers will be upgraded to floor-standing speakers, so, a bridge-able amp would be a plus. I live in Canada.
So far Vera Audio P150/600 is the only one with bridgeable 1ET400A amplifier modules (that I know of). Their build quality looks to be better than most other 1ET400A based amplifiers, but the price also reflect this.
 

mk1classic

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NAD C298 and M23 are also bridgeable.
If that is the case, I don't see why you should not buy a NAD C298 if easily available in Canada. I expect NAD has full access and more to Purifi Audios experience database with the amplifier modules. They also may have a larger technical division than any of the "boutique" brands like Vera, VTV, Rouge etc. But NAD do design for ROI - price point and will have to take end price into account. Other smaller brands may design and build more to show of what they are capable of supplying.

The review in Stereophile seems to give a nice feedback and measurements, you will most likely not go wrong with either the C298, M23 or any other less "professional" brands.

 

Mehdiem

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If that is the case, I don't see why you should not buy a NAD C298 if easily available in Canada. I expect NAD has full access and more to Purifi Audios experience database with the amplifier modules. They also may have a larger technical division than any of the "boutique" brands like Vera, VTV, Rouge etc. But NAD do design for ROI - price point and will have to take end price into account. Other smaller brands may design and build more to show of what they are capable of supplying.

The review in Stereophile seems to give a nice feedback and measurements, you will most likely not go wrong with either the C298, M23 or any other less "professional" brands.


Thanks for your reply. I had never heard of Rouge before, but I just looked them up. They seem decent, and the price is not very far from C298, they are actually cheaper. Nevertheless, I think NAD might have a better residual value? Plus I can get it here for 25% off from someone I know. I have a few questions though,
(1) you noted that NAD might have some technical divination from boutique brands, do you think this divination would be audible? In that case, I prefer to go with the former, as I maintain a more long-term perspective in my purchase.

(2) my speakers (LS50) are said to be inefficient, and that I need a high-current amp. Is C298 considered high-current? What quantitative measurement specifies this factor?

(3) I understand that class D with Purifi is a different animal than class AB. But I want to know how does this compared to Rotel 1590 (especially if I later want to feed floor standings such as BW 702 S2) by bridging them?
 

Julf

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(2) my speakers (LS50) are said to be inefficient, and that I need a high-current amp. Is C298 considered high-current? What quantitative measurement specifies this factor?

Both hypex and purifi modules are definitely high current. and they actually specify exactly that parameter - output current.
 

mimaximax

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Can someone explain what issues prevented the Purifi team to advise for bridging 1et400a amps?
 
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