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Author Topic: Favorable Hypex amplifier review...  (Read 43269 times)

Terry Demol

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Re: Favorable Hypex amplifier review...
« Reply #90 on: May 21, 2008, 09:31:56 am »

zmix wrote on Wed, 21 May 2008 13:42

Terry Demol wrote on Tue, 20 May 2008 22:45

I dug up some measurements on the CI amp here:

  http://www.stereophile.com/solidpoweramps/805cia/index4.html


They actually brought up some compelling points in that review.  Since the Channel Islands amplifier is based on the Hypex modules, I'd like to know what Bruno thinks about their assertions.



I didn't even read the review, was just checking the
measurements.










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zmix

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Re: Favorable Hypex amplifier review...
« Reply #91 on: May 21, 2008, 09:58:15 am »

Terry Demol wrote on Wed, 21 May 2008 09:31

zmix wrote on Wed, 21 May 2008 13:42

Terry Demol wrote on Tue, 20 May 2008 22:45

I dug up some measurements on the CI amp here:
     http://www.stereophile.com/solidpoweramps/805cia/index4.html

They actually brought up some compelling points in that review.  Since the Channel Islands amplifier is based on the Hypex modules, I'd like to know what Bruno thinks about their assertions.


I didn't even read the review, was just checking the
measurements.




I guess I should have been more specific...

I was referring to the text in the measurement results.

It's slightly damning, but very compelling, nonetheless.

I'd like to hear Bruno's rebuttal.

bruno putzeys

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Re: Favorable Hypex amplifier review...
« Reply #92 on: May 22, 2008, 04:14:31 am »

Stereophile always seems to be grappling with measuring class D amps. I've also had problems getting an AP system 1 to return reliable results when measuring audio devices with out-of-band content (noise shaping DACs, class D etc). This is a result of the AP1 having its band-limiting filter downstream of the notch filter. This causes the autorange circuitry to range the detector output based on the carrier residual instead of the audio signal. At low signal levels you don't get any meaningful distortion or noise reading. Starting from the system 2, the AP test sets no longer have this problem, especially the ones fitted with an AES17 filter. Audio Precision's passive external filter is not necessary here (I've never gotten different results with or without) but this filter does allow correct measurements with the AP1.

Anyhow, Stereophile has tried designing their own measurement filter to get round the problem and I am sorry to report that the distortion shown on their plots is entirely due to that filter. I have re-measured the amplifier and got the exact same results as those we publish on our web site.

They were correct in identifying an issue with long-term power output though. This has led to us using slightly larger output inductors in the UcD180 modules for the last two years or so.

As a result of these 2 items, the stereophile review is the only one showing substandard measurements. Subsequent reviews by other magazines have been fully in line with our published specs (bar one where a manufacturer bypassed our input buffer and put in one that distorted more than the amp, not naming names).
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Terry Demol

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Re: Favorable Hypex amplifier review...
« Reply #93 on: May 22, 2008, 05:52:10 am »

Bruno Putzeys wrote on Thu, 22 May 2008 09:14

Stereophile always seems to be grappling with measuring class D amps. I've also had problems getting an AP system 1 to return reliable results when measuring audio devices with out-of-band content (noise shaping DACs, class D etc). This is a result of the AP1 having its band-limiting filter downstream of the notch filter. This causes the autorange circuitry to range the detector output based on the carrier residual instead of the audio signal. At low signal levels you don't get any meaningful distortion or noise reading. Starting from the system 2, the AP test sets no longer have this problem, especially the ones fitted with an AES17 filter. Audio Precision's passive external filter is not necessary here (I've never gotten different results with or without) but this filter does allow correct measurements with the AP1.

Anyhow, Stereophile has tried designing their own measurement filter to get round the problem and I am sorry to report that the distortion shown on their plots is entirely due to that filter. I have re-measured the amplifier and got the exact same results as those we publish on our web site.

They were correct in identifying an issue with long-term power output though. This has led to us using slightly larger output inductors in the UcD180 modules for the last two years or so.

As a result of these 2 items, the stereophile review is the only one showing substandard measurements. Subsequent reviews by other magazines have been fully in line with our published specs (bar one where a manufacturer bypassed our input buffer and put in one that distorted more than the amp, not naming names).


Bruno.

Thanks for pointing that out.

Stereophile really have to get their act together WRT
measurements, they are not doing any favours for manufacturers.

In the absence of AP2, would not something like a Prism Dscope
be at least a major improvement over the AP1.

I checked the graphs from Hypex site of UCD700 and 400 HG series.
They certainly are better than the magazines results. Having said
this, they are still a way off a really good linear amp.

Can you comment on sonic differences between something like the
ExtremeA and UCD modules? I know you built extremeA as a
yardstick, and I am thinking it is something along the lines of a
low powered Halcro.


T
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bruno putzeys

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Re: Favorable Hypex amplifier review...
« Reply #94 on: May 22, 2008, 06:37:11 am »

You said it... "good linear amp". Do a test bench shoot-out between a UcD400 and a Pass amp and the contest won't be even close (to spell it out, the UcD amp wins hands down on all counts bar perhaps small-signal bandwidth). Yet, you will not hear audio review magazine making unpleasant remarks toward the Pass' measurement results. I wonder how many people have actually bothered checking. More commonly, measurements simply don't get published in such cases. Apparently putting a lot of weight on the scale and a large number on the till exonerates an amp from having to measure well.

Apart from that, one of the tricks I've used to get UcD to punch above its measured weight is to minimise the frequency-dependence of THD. I hope to find the actual psychoacoustical background of this, but so far I've always found that an amp that does 0.02% consistently over frequency sounds better than one that hits 0.02% at the end of the audio range and performs better at lower frequencies. I have units that do well below 0.001% at mid-range frequencies but I simply can't stand to listen to them.

This is why I'm looking at new control techniques that will get me to <0.001% at all frequencies (without sacrificing output impedance). Until that's finished, UcD remains the best sounding amp I can do in class D.

I've actually not yet had the time to build a pair of Extrema amps to listen to. Sander built a second unit after the measurement session but he managed to sell the pair before I could hear it and since then I've simply not had the time to construct a new pair. That said, I'll eat my hat if it doesn't sonically beat the UcD amps by at least a small margin. After all, the converse would invalidate the scientific approach I take for all my design work. I'm having a set built now so I'll keep you posted.

I was surprised when I was told by a French customer of ours (a rather well known manufacturer of high-end and studio speakers) that they picked the UcD400HG over their Halcro DM58. I haven't heard the Halcros myself, but purely from a logical perspective this result was not expected. Apparently the distortion level on the UcD400 is low enough for other things to matter more. I mean, all other things equal, linear *must* be the better choice if audio performance is the only requirement. If in spite of that my class D amps do unexpectedly well in shoot-outs it must be because all other things simply aren't equal. There are a lot of design shortcuts you can get away with in class A that simply have to be taken fully care of in class D (mostly related to EMC).
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dcollins

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Re: Favorable Hypex amplifier review...
« Reply #95 on: May 22, 2008, 09:04:53 pm »

Bruno Putzeys wrote on Thu, 22 May 2008 01:14


Anyhow, Stereophile has tried designing their own measurement filter to get round the problem and I am sorry to report that the distortion shown on their plots is entirely due to that filter


How could Atkinson not have characterized his filter before making all these false measurements?!

I bet Julian Hirsch would have known better.........



DC

jimmyjazz

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Re: Favorable Hypex amplifier review...
« Reply #96 on: May 22, 2008, 10:53:13 pm »

This stuff makes my head spin, and I'm NOT an idiot.

(I'm not an idiot.  I'm not an idiot.  I'm not an idiot . . .)
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Rivendell61

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Re: Favorable Hypex amplifier review...
« Reply #97 on: May 23, 2008, 12:14:27 pm »

Terry Demol wrote on Thu, 22 May 2008 05:52

 
Stereophile really have to get their act together WRT
measurements, they are not doing any favours for manufacturers.

In the absence of AP2, would not something like a Prism Dscope
be at least a major improvement over the AP1.



Stereophile reported in January '08 that Audio Precision had 'loaned' (!)  them a SYS 2722.
It appears they are using it for at least some of the current test reports.

Previously John Siau of Benchmark had also urged Stereophile to upgrade--noting they were publishing gear test specs which reflected their testing gear limitations, not the performance of the gear tested.

Mark
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Sam Lord

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Re: Favorable Hypex amplifier review...
« Reply #98 on: May 24, 2008, 01:35:21 pm »

Bruno Putzeys wrote on Thu, 22 May 2008 06:37

...I have units that do well below 0.001% at mid-range frequencies but I simply can't stand to listen to them.

Right on, I hate the sound of clean midrange in the morning.

But seriously, it is just silly that Atkinson didn't follow up that HF reading with a phone call to somebody.  I mean, he's been using AP units a long time and measured a boatload of amps.  Julian Hirsch deserves his own thread.

I"m really thrilled about modern Class D, using 4ch of ICE power now.  It's so green and sounds wonderful--a true revolution.  I wonder what modules ATC uses.  And I wish I had an excuse to build a Hypex unit.


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bruno putzeys

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Re: Favorable Hypex amplifier review...
« Reply #99 on: May 26, 2008, 04:44:16 am »

Sam Lord wrote on Sat, 24 May 2008 19:35

Bruno Putzeys wrote on Thu, 22 May 2008 06:37

...I have units that do well below 0.001% at mid-range frequencies but I simply can't stand to listen to them.

Right on, I hate the sound of clean midrange in the morning.

If the same amp produced just as little distortion at 20kHz it'd been marvellous. Somehow distortion becomes more noticeable if it rises with frequency, even if it is quite low in absolute terms. Which led me to the somewhat counterintuitive practice of shifting the dominant pole(s) out of DC to 20kHz. This must be the only really "unscientific" thing I do.
Sam Lord wrote on Sat, 24 May 2008 19:35

I wonder what modules ATC uses.

IIRC, all of their speakers use homegrown linear amplifiers.
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Sam Lord

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Re: Favorable Hypex amplifier review...
« Reply #100 on: May 26, 2008, 08:45:22 pm »

Bruno Putzeys wrote on Mon, 26 May 2008 04:44

If the same amp produced just as little distortion at 20kHz it'd been marvellous. Somehow distortion becomes more noticeable if it rises with frequency, even if it is quite low in absolute terms. Which led me to the somewhat counterintuitive practice of shifting the dominant pole(s) out of DC to 20kHz. This must be the only really "unscientific" thing I do.

I'm sorry Bruno, your meaning was clear.  I was trying to be silly while admiring your midrange THD figure in Class D. (I assumed you were speaking of your own testbeds.)

I think your f vs THD approach is quite reasonable, given your own listening impressions and those of many others like myself and yikes, Stereophile.  I too believe (unscientifically) there is usually a sound penalty when high-harmonic THD numbers are far worse than the 2nd and 3rd harmonics, even when averaged passband THD numbers are much lower.   Actually I look at speaker drivers this way too, examining out-of-band junk.  

Bruno Putzeys wrote on Mon, 26 May 2008 04:44

IIRC, all of their [ATC] speakers use homegrown linear amplifiers.

Thanks. I expect they'll use Class D once they get religion.  And congratulations on the technical achievements and success of your Hypex designs.
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Bogic Petrovic

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Re: Favorable Hypex amplifier review...
« Reply #101 on: July 23, 2008, 06:35:52 am »

Bruno Putzeys wrote on Mon, 26 May 2008 10:44

....
Somehow distortion becomes more noticeable if it rises with frequency, even if it is quite low in absolute terms. Which led me to the somewhat counterintuitive practice of shifting the dominant pole(s) out of DC to 20kHz. This must be the only really "unscientific" thing I do.
....


Hi Bruno,

Your "unscientific" method of frequency independent THD, can be find in some other professional audio devices (not power amplifiers, but... never mind)

You can see what I measured on my PCI audio interface (in analog loopback) today Very Happy

http://www.bozoel.com/images/thd_vs._freq.png

setup:
Measurement software: STEPS (prof. Ivo Mateljan), -3dBFS output level, sweep method is used, 12pts. per oct., measuring range 20Hz - 20kHz,
Card setup: +4dBu IN and OUT range, -7dB attenuation on Lynx built-in digital mixer, left channel only, all other muted, no dither, 24bit, 192kHz (only way to view a start of "rise" of THD, is using higher S/R)

Regards,

jdg

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Re: Favorable Hypex amplifier review...
« Reply #102 on: July 02, 2009, 03:45:47 pm »

just adding some info to this thread.

had a fuse pop in my hypex yesterday 10min before a session and had to hook my dunlavys to the pass x.250 thats in here.


man, what a total difference. and i didn't like it.
im not saying it was better or worse, its just not what i was used to, and it freaked me out.

the difference was with the pass, my speakers became sooo much more relaxed and smooth.  like i just got a shot of ativan.

the low end was firm, and the top end was free.


hypex is back up this afternoon, and everything is back to normal.

the lows are a bit more obvious, but the highs are much more focused.


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T. Mueller

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Re: Favorable Hypex amplifier review...
« Reply #103 on: August 03, 2009, 11:01:59 am »

I've done only a touch of surfing after reading this thread and the other related threads... are there wiring diagrams or other documentation available for the UCD400 kits?  Or anywhere online?

Thanks in advance.  Great discussion on here.

EDIT: I found this: http://www.gweep.net/~rocko/UcD400/

Can anyone attest to the accuracy of the BOM and the correctness/completeness of the discussion?

EDIT #2: (sorry for this, but here's the link, finally: http://www.diycable.com/main/pdf/exodus_docs.pdf)
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