Review and Measurements of Purifi 1ET400A Amplifier

[maty]

Many of those who buy these expensive modules do so only for the outstanding measurements, hence the logic of the request to improve a parameter that does not shine for its excellence.

That said, for me the good measurements are necessary condition that not enough to have a great sound. A sound that is not only spectacular but also closer to the real one if acoustic instruments are used in the recording and, above all, that it excites when listening to some superb recordings, making us forget that they are reproductions and not live music.

 

[PierreV]

That said, for me the good measurements are necessary condition that not enough to have a great sound.

If reading about the thickness of an aluminum case or some set of numbers has an impact on your perceived SQ, this is the textbook definition of subjectivity. It is not because you have a half baked theory on EM interference (which apparently isn't shared by the users with professional EM interference experience around here) or because you have thoughts on CMRR (which apparently were mostly dismissed by one of the most successful and transparent contemporary amplifier designer) that those suddenly become universal objective factors.

As a hobbyist, you always have the option of doing extensive and documented double blinded tests to prove your point. Why don't you give it a shot? And, when you have identified and proven the effect of those issues, why not start your own business around it?

that it excites when listening to some superb recordings

There's a measurement for that too: it is called the WTF FFS (Worth Tapping Feet For Fabulous Sound).

 

[maty]

What is the point of having an amplification module with exceptional measurements if the rest does not accompany it? The weak point/link or bottleneck of our audio system will always be the limiting factor.

Then put the 1ET400A in a wooden box and... We have to have some coherence in our audio system.

 

[March Audio]

@Bruno Putzeys, Have you considered improving the CMRR in the final design? Via 1ET400 module or the input coneection board.

@maty Amir measured the CMRR. Whilst it needs explaining as to why one channel was lower, the "good" channel was 85dB which is absolutely fine.

Question. Do you see any issue in the other measurements that would indicate problems caused by poor CMRR?

No thought not. With respect you need to stop obsessing about certain things when you dont understand what the implications of the numbers (or case thickness ) are.

 

[pos]

This quite extensive response to pretty much all the questions asked (including mine) is honestly more than I expected and very much appreciated!

As a follow-up to my question about the input board: I didn't expect (or want) a different Input buffer board, just having the clarification it will come with this exact one is good, so the measurements here are representative.

Still a few question left, maybe for latter?

@Bruno Putzeys :

https://www.audiosciencereview.com/...fi-1et400a-amplifier.7984/page-13#post-196619

https://www.audiosciencereview.com/...fi-1et400a-amplifier.7984/page-13#post-196679

 

[maty]

CMRR value is the only weakness that I detect but, unlike the PSRR, the responsibility for the improvement can be transferred to another part of the amplifier already built. As there is still no module without buffer, there is more than enough time for it to be taken into account during its design and subsequent measurement, module and/or buffer.

The input connection board of the kit is only for testing. If, on top of that, improves the CMRR, then very little business would be left to the future assemblers of the 1ET500A.

The Hypex NC400 and the NC500 stopped being interesting to me for a long time. The NC1200 did not even think about it because of its excessive price. I was only interested, with class D, in the IcePower 1200AS2 but I ended up discarding it.

On the other hand, the 1ET400A does interest me a lot, depending on how it ends up being implemented and the final cost with the other components that I have thought about for a long time. Of course, I will never be among the first to building, I can wait. That others verify if the sound is also exceptional with the type of recordings that I usually listen to.

 

[tktran303]

I’ve didn’t think it was possible to beat a dead horse at the same time as missing the wood from the trees.

Guess I’m learning new things every day.

 

[maty]

...60dB will bomb proof you against anything that may happen from one end to the other end of a very noisy chassis, but not against an unknown signal source at the far end of 100 metres of microphone cable. If you expect your product to see a lot of CM noise, invest in a proper input stage. We can't put one on the module because that would also make it more expensive for anybody else, certainly if we also want that buffer to have distortion and noise specs comparable to the amplifier.

About the famous 22dB difference: the input of the module is literally just a pair of resistors feeding into a virtual short, which also receives feedback from the output though another pair of resistors (one to speaker out, one to speaker gnd). CMRR as tested here is determined by the pairwise matching of these resistors. So you would indeed expect the occasional unit with excellent pair matching by sheer luck, and hence much higher CMRR.

It took me a bit to understand why CMRR and PSRR were mentioned in one breath in some posts but of course that must be because, at DC at least, CMRR and PSRR are linked in operational amplifiers. That’s not the case here. CMRR of the amplifier is something that the user can improve at libitum with a modicum of circuitry, whereas PSRR can’t be improved externally unless you want fix things in the supply. Many amplifier companies like to turn a weakness in their design into a sales argument by drawing attention to their big transformer and huge bank of caps, but it seems to me that the better design is the one that doesn’t need such desperate measures. I’d like the PSU performance to affect only the clipped output power – as it does in this review – but not other performance specs.

@Bruno Putzeys What is the tolerance of these two resistors?

If they are 1% then it will be easy and cheap to increase the CMRR: if we change these two resistors with 0.1% tolerance we will have much better CMRR always. Of course, better with 0.01% but more expensive.

 

[March Audio]

@Bruno Putzeys What is the tolerance of these two resistors?

If they are 1% then it will be easy and cheap to increase the CMRR: if we change these two resistors with 0.1% tolerance we will have much better CMRR always. Of course, better with 0.01% but more expensive.

@maty you are still not understanding. This does not need to be done. The overall cmrr is set by the input stage/buffer. This will be implemented by the vendor.

 

[amirm]

@maty you are still not understanding. This does not need to be done. The overall cmrr is set by the input stage/buffer. This will be implemented by the vendor.

This is the key point. This module is not a complete amplifier. It needs a front-end. The one provided will be available for purchase and does an excellent job anyway. Let's not keep arguing this.

 

[maty]

1ET400A has a own buffer with the OPA1612 if I am not wrong. This opamp has very good PSRR and CMRR.

Those 22 dB of difference in the CMRR measurement between the two modules are excessive, maybe these resistances have a tolerance of 5% or 10%.

As it is not yet in mass production phase in China?, I suppose that the cost of improving them will be minimal (two resistors with 0.1% tolerance). It would be necessary to make the calculations and the pertinent measurements.

 

[March Audio]

1ET400A has a own buffer with the OPA1612 if I am not wrong. This opamp has very good PSRR and CMRR.

Those 22 dB of difference in the CMRR measurement between the two modules are excessive, maybe these resistances have a tolerance of 5% or 10%.

As it is not yet in mass production phase in China?, I suppose that the cost of improving them will be minimal (two resistors with 0.1% tolerance). It would be necessary to make the calculations and the pertinent measurements.

You are assuming that the resistors are the cause of that mismatch between the channels. Very unlikely to be the case. I think I will leave Bruno to explain it to you.

 

[maty]

That is why I ask. If so, the solution would be cheap and it would be on time. It would again be evident that what is really important is the correct implementation of the components.

In that case, the future boutique ensamblers of the 1ET500A should use resistors with 0.01%, whose extra cost could be assumed perfectly given the very high price they charge, at least with Hypex NC500 and, sure, with Hypex NC1200.

 

[BYRTT]

1ET400A has a own buffer with the OPA1612 if I am not wrong. This opamp has very good PSRR and CMRR.

Those 22 dB of difference in the CMRR measurement between the two modules are excessive, maybe these resistances have a tolerance of 5% or 10%.

As it is not yet in mass production phase in China?, I suppose that the cost of improving them will be minimal (two resistors with 0.1% tolerance). It would be necessary to make the calculations and the pertinent measurements.

Hi maty you really up on the horse about those resistors but for diy'ers as yourself think it can be a easy fix now remember if source unit have tolerance it won't help fix 1ET400A so diy precision fix that source unit too

 

[maty]

But they are probably SMD resistors. If the solution were as easy as the change of those two resistors we would be in a situation in which everyone wins.

It is best to wait for the answer.

 

[pirad]

Rather than worrying about buffers and CMRR, I'd much prefer to see an input DAC module feeding the Purifi amp directly.

 

[March Audio]

That is why I ask. If so, the solution would be cheap and it would be on time. It would again be evident that what is really important is the correct implementation of the components.

In that case, the future boutique ensamblers of the 1ET500A should use resistors with 0.01%, whose extra cost could be assumed perfectly given the very high price they charge, at least with Hypex NC500 and, sure, with Hypex NC1200.

You are unlikely to be satisfied with his answer.

 

[FrantzM]

But they are probably SMD resistors. If the solution were as easy as the change of those two resistors we would be in a situation in which everyone wins.

It is best to wait for the answer.

Maty

Perhaps designing your own amplifiers or modules then submitting it (them) to Amir for testing would be the most satisfying outcome for you (and some of us). I am not sure Amir is yet able to test thought-experiments-type products .. then again one never knows.

 

[maty]

Again: It is best to wait for the answer.

Perhaps the improvement produced by better resistors is too small.

 

[pirad]

Maty,
To match the Purify amp you need to go transformers. 120dB can be achieved when impedances are within 0.0001% tolerances.
InGenius resistor matching with laser trimming is only 0.005% and gets you meager 90dB CMRR. The pro world uses transformers.
Obviously your equipment is in such a noisy environment that only transformers can answer your expectations.
(and you get galvanic isolation as bonus)
http://sound.whsites.net/articles/balanced-2.htm