DIY Amplifiers: Is Purifi EVAL1 the Best Option?

We can always come to a reasonable conclusion about a specific piece of gear through objective measurements and subjective listening. A piece of gear rarely turns out to be a straight-A student, and it's not often that the engineers behind the components completely understood the assignment. In the case of our Project Amp, I still need a name for it; if you think of one comment below, our amp can do things that defy logic and understanding. Find out how good the Purifi modules actually turned out to be in this video!

Parts List:

This description may contain affiliate links, which means I may earn a commission at no extra cost to you if the affiliate links are utilized to make a purchase.

Chapters:
0:00 Purifi EVAL 1
0:30 Intro
1:06 Unboxing and Breakdown
5:39 Measurements
7:20 Sound Quality

#purifi #classdamplifier #diyamplifier

[Nikolajchris]

I've got the Audiophonics HPA-S400ET Amplifier and swapped the LM4562 for both OPA1612 and OPA1656 (which can both be purchased at audiophonics too), with both sounding more detailed than the stock opamps. The nice thing about the audiophonics amp compared to the stock purifi is that you can easily swap the opamps without soldering as they are just socket mounted, letting you swap back and forth.
I prefer the OPA1612 as it gives me a wider and deeper soundstage with super detail and "pitch black background" noise levels to hear sound decay for ever and ever, while my GF prefers the OPA1656 as it puts the singer in clear centerstage while still being very detailed, though a more flat and forward soundscape.

[Espiritiv]

I love my new Buckeye three channel Purifi amp with the 1ET400A modules and custom input buffer. VTV also makes some good amps on these modules

[guyboisvert]

I just bought and assembled the Hyper Nilai 500 Stereo kit. Everything went perfect, no mods needed. Just too bad Purifi / Ghentaudio don't have exactly the right kit. I'm sure the Purifi is as good as the Hypex. I even got the DIY ClassD Preamp, very nice too. My source is an Ayre QB-9 and speakers are the Ryan R610: Sounds marvelous with the Hypex Amp / Preamp combo! I used to have a Rega Elex-R but the Hypex is a nice upgrade: Impression that the amp drives the speakers perfectly, tight basse and refined mids and highs. I'm VERY satisfied!

[wyup]

Interesting job and good description. In comparing the two amps, the preamp used is important for the sound quality because of the impedance bridge between preamp and amp. One important difference between the Eval1 and the Audiophonics board is that Eval1 has only 10.2kΩ(BAL)/5.1kΩ(SE) input impedance compared to HPA-S400ET's 94kΩ(BAL)/47kΩ(SE). So you need at most 510Ω RCA output impedance from the source/preamp to get a minimum recommended 10:1 ratio. Many tube preamps (which go well with class D) have higher than that (like 2kΩ), so it might compromise the Eval1/Purifi performance. Audiophonics and other integrators play safe with their input buffer boards choosing higher input impedances than Eval1 (higher resistors at the input), which some users prefer for SQ. However higher resistors introduce noise aswell, so it's a tradeoff. If your preamp is strong enough, is well buffered and has low output impedance it will play better with Eval1. Regarding the OPA1656 it is curious Bruno recommends it when he chosed OPA1612 for their Eval1 (least measured distortion). More Purifi integrators choose OPA1656 aswell, like Boxem Audio in Europe.

[eubikedude]

6:45 did you do blind ABX testing. REW plots? With/without EQ? What about the Audiphonics (and project one) in bypass mode which bypasses the OpAmp. The Audiphonics one is socketed too so a simple swap, so what did you think of it with the other OpAmp?

[LukeMarthinusen]

Thouroughly enjoyed Mike. I have a big Pass Labs 250w AB monster. But you’ve motivated me to order these parts, have a big of fun and build an amp. Great job. Tx!

[barrowsworm]

My Purifi build uses the Eval-1 with OPA1656 as well. I also used a custom built linear power supply to power the input stage with Belleson discrete regulators to provide +/- 18 VDC to the Eval-1. I never listened without the linear PS on the input stage, so I do not know if using it resulted in any improvement, I just did this because I knew I could design and build a custom linear PS with ultra low noise, and ultra low impedance, so why not. The amp sounds fantastic. I am interested in trying the Hypex Nilai at some point, I have a machined from block Merrill Audio amp chassis here to use for that build, which is a beastly thing.

[Hitsujiomeguruboken]

Two questions: Did you change the Op Amps before the listening session? I just found at the website from Audiophonics, that the HPA S-400 ET has also the OPA 1656 build in. So what’s the reason of the differences in sound? They seem to be 100% IDENTICAL!
Second Question:
Would it be also possible to use SPARKOS Op amps - like the SPARKOS 2602 which is perfect for pimping e.g. the Fosi V3?

[michaelsegel]

This actually a great project and presentation.

If your links are correct, the cost of replacing the op amps is less than $10.00 (tax, shipping, etc... for 2)
I wonder if you would have put in sockets when you replaced the op amp? Can't be much more money...And you'd have more options... right?

[epi]

Man I would love to have VU meters on this build. If one were to build this, how can VU meters be added?

[jerrysnead]

Nice review good to see Mike G he made a ac voltage buffer for my first DIY amp that used the ClassD companies boards, it was a great intro into the "D" side of amps

[khoi]

I use a Legacy Monobloc2 power amp. Fantastic sounding and powerful amp. It does not get hot ever even when I play pretty loud music with lots of bass for a longer period.
Buy used but in excellent shape is the trick :) 😀 but for example here in Canada you must be patient for different brands or models, like my Legacy Monobloc2 which are very rare on the used market :) cheers and happy holidays

[autonomousindividual]

Very different, but I feel you get a better DIY experience with some of the PASS stuff. More soldering and more learning, yet you are almost guaranteed to succeed if you are diligent. As far as 25W vs 2-3, 000 or million - whatever class D can offer, that is a dangerous argument. All depends on the speakers you want to use. I am very happy going down the tube and class A route. I like the soldering but really have problems with the very small SMD parts on class D projects. There is A LOT out there to try. You will be going down a rabbit hole that you'll likely enjoy very much.

[Melissabell]

Awesome stuff!! Just wondering if you could add an 8 pin socket to the board rather than soldering in the new op amp?? This would allow the flexibility of swapping op amps in and out. I would love to see a quick video of you replacing the op amps. Thanks!!

[hilde]

Great video! Mike's system is an amazing reference. I'm very curious about how this Purifi module could be developed further.

[reyiiteleco]

Hello Mike, great video, this open up a new world for me regarding DIY Amp build.
Question, would this class D amp Purify Eval1, 2, 3 would be suitable for current hungry Magnepan 1.7i ?
THANK YOU!.

[fearwolfbrewery]

What do you think about using the VTV input board and putting an opa1656 on it?

[dkokalanov]

Great video! Does you long-term impression confirm your initial enthusiasm?

[John]

How does the Ice amps sound compar d to the Topping B200 mono amplifiers?
Thanks.

[wightmanshawnk.]

Mike, this is an awesome video and project!