Review and Measurements of Purifi 1ET400A Amplifier

[Matias]

Hi Bruno, I see only feedback being employed. Would it make sense to also use feed forward? Why use one or the other (or both)?

Do you consider the 1ET400A the lowest distortion module of this technology, the "sweet spot" of the range so to say? Will higher powered modules have a little higher distortion as well, as per previous works, or that is not the case here?

Also your views on IC versus discrete opamps (measurements and sonics), and opamp rolling to taste in general?

And a wish, if possible make a drop in replacement board to the ICEpower 125ASX2, as it is very popular.

 

[pjug]

Bruno:

In Benchmark's literature, they state the following (https://benchmarkmedia.com/blogs/ap...ory-use-of-the-benchmark-ahb2-power-amplifier):
The important difference between the AHB2 and class-D amplifiers is that the AHB2 does not produce switching noise. Class-D amplifiers are measured with brick-wall AES17 filters that ignore the switching noise above 20 kHz or 40 kHz. Tweeters can demodulate this ultrasonic noise and fold it into the audible band.

Some of us (at least me!) can't help wonder if there could be some kind of harm from having the ultrasonic noise. Really I think I am fairly well convinced that this is harmless, but I would like to hear what you have to say about the above, and your response to any other critical points you have heard regarding Class D ultrasonic noise.

I would also invite @John_Siau to offer any clarification to the above.

 

[rajapruk]

Just for the fun of it, I would like to see THX789 headphone amp overlayed with AHB2 and IET400A on THD+N and power. If possible. For let’s say the first 10W of power.

 

[firedog]

Is Bruno still profiting from the Hypex sales? Because if not, then he might price these DIY kits to compete with the NC400. Otherwise, I imagine they will be priced well above the NC400.
As for the OEM modules, if the NC1200 is any indication, these are going to be costly.

Bruno was only an employee at Hypex and is no longer there. Source: Bruno, as quoted elsewhere.

 

[amirm]

Just for the fun of it, I would like to see THX789 headphone amp overlayed with AHB2 and IET400A on THD+N and power. If possible. For let’s say the first 10W of power.

I can't power the THX with 4 and 8 ohm. Don't want to damage the only sample I have there.

 

[BYRTT]

@amirm re below info/idea (thanks @Joachim Herbert) and all the talk about HF switching noice, any chance you have conventional PSU laying around or can borrow one that fits amp modules specification to show the real world scientific difference in numbers the two PSU between pinky would probably hate more work but think members would love that data case revealed.

A good friend of mine who designed loudspeakers for the German Canton brand always was full of praise for the B&O ICE modules for the professional audio projects he did thereafter.

But he insisted to use conventional power supplies instead of switched ones, claiming a tighter bass performance. Looking at noise figures this might be the way to go for ultimate performance, though a conventional supply will add to weight and price considerably.

But then, who needs ultimate performance when excellent performance is available for a fraction of the cost?

 

[DDF]

Tweeters can demodulate this ultrasonic noise and fold it into the audible band.

This is the only study I'm familiar with and he had no luck reproducing this:
http://www.davidgriesinger.com/intermod.ppt

If you're aware of documented success generating the IM distortion in-band in an audible way with reasonable quality transducers, please share.

 

[Nikke]

@Bruno Putzeys
Hey there and welcome to the forum

When will I be able to buy a 2.1 DIY kit?
Will you sell 2ch boards with integrated power supplies, like the NC252 board?
I browsed around a bit and it seems your retailers play in the range "if you have to ask you can't afford it". My pain threshold is about a grand for each part (so dac, amp and speakers totals about three), any chance this aint going to hurt?
Do you expect to be marketing any speakers or drivers this year? Are you also considering headphones?
What are you looking for in aspiring employees -or do you take any hippie who happens to get past security? Do they have to know what all the technical audio-jargon is or is it enough to guess the hot end of a soldering iron?

Thanks

 

[pjug]

This is the only study I'm familiar with and he had no luck reproducing this:
http://www.davidgriesinger.com/intermod.ppt

If you're aware of documented success generating the IM distortion in-band in an audible way with reasonable quality transducers, please share.

Hi - I'm not sure if you are addressing me, but like I said I am pretty convinced that the ultrasonic noise is not a problem. But that statement appears in the benchmark info so I was hoping to hear what the experts would say @Bruno Putzeys and @John_Siau

 

[Matias]

@Nikke some of your answers may be below.

https://audiophilestyle.com/ca/bits...eaders-qa-with-lars-risbo-bruno-putzeys-r815/

 

[amirm]

@amirm re below info/idea (thanks @Joachim Herbert) and all the talk about HF switching noice, any chance you have conventional PSU laying around or can borrow one that fits amp modules specification to show the real world scientific difference in numbers the two PSU between pinky would probably hate more work but think members would love that data case revealed.

I don't have the wiring harness to power this unit, nor anything with the right voltages.

 

[March Audio]

Bruno:

In Benchmark's literature, they state the following (https://benchmarkmedia.com/blogs/ap...ory-use-of-the-benchmark-ahb2-power-amplifier):
The important difference between the AHB2 and class-D amplifiers is that the AHB2 does not produce switching noise. Class-D amplifiers are measured with brick-wall AES17 filters that ignore the switching noise above 20 kHz or 40 kHz. Tweeters can demodulate this ultrasonic noise and fold it into the audible band.

Some of us (at least me!) can't help wonder if there could be some kind of harm from having the ultrasonic noise. Really I think I am fairly well convinced that this is harmless, but I would like to hear what you have to say about the above, and your response to any other critical points you have heard regarding Class D ultrasonic noise.

I would also invite @John_Siau to offer any clarification to the above.

If a tweeter has no response at the 450 or 500 kHz switching frequency (which they don't) how can it create IM or demodulate into the audible band?

The issue with measurement equipment being disturbed is a separate one and not relevant to what a speaker outputs.

I tried to get time the other week to do some acoustic measurements and for example put some US signals into a tweeter. I failed to Will try to perform this test tomorrow.

 

[amirm]

1ET400A + input buffer <- CMRR?

Here you go:

Strange to see one channel so much better. Both are better than the spec though.

 

[Blumlein 88]

Here you go:

View attachment 28996

Strange to see one channel so much better. Both are better than the spec though.

Yes, I was thinking "Oooooooh! with better than 85 db. And 63 isn't bad, but not as good as 85".

 

[March Audio]

Here you go:

View attachment 28996

Strange to see one channel so much better. Both are better than the spec though.

A small note for those that may not be familiar is that compared to a single ended unbalanced topology, it is 100% better

 

[maty]

Here you go:

Thank you. And yes, a difference of 22 dB is very strange.

But you only has measured the 1ET400A module.

1ET400A + input buffer <- CMRR?

If one is thinking about building a DIY it is very important to know also the quality of the supplied input buffer.

 

[Armand]

Thank you for the CMRR test. Did you use the the simple version or the 10 ohm switching method for pin 2 and 3?
The 10 ohm switching method is better as it detects how efficient the buffer handles differences in output impedance of the connected equipment.
I assume the test frequency was 1kHz?

 

[amirm]

Thank you for the CMRR test. Did you use the the simple version or the 10 ohm switching method for pin 2 and 3?

I tried them all and they produced the same results.

 

[amirm]

I assume the test frequency was 1kHz?

Yes.

 

[restorer-john]

I tried to get time the other week to do some acoustic measurements and for example put some US signals into a tweeter.

US signals (imperial) may not work down under, you need special AUS (metric) signals. Also bear in mind WA AUS signals are different to QLD AUS signals and cannot be compared.