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Old 20th September 2012, 02:01 PM   #5071
jlaakso is offline jlaakso  Finland
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Originally Posted by analog_sa View Post
Exactly that. There is a subtle change in phono pre noise and a not so subtle collapse of sounstage, change in tonality, reduction in microdynamics...
Wouldn't that imply that PSU of the class D amp is generating noise into your mains network which your sensitive (presumably with high gain) phono preamp picks up?

I am really out my areas of expertise, but how would that be visible in the output of amp if the PSU is generating noise back to mains network? And to make sure, I am not trying to imply anything, I just don't understand
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Old 20th September 2012, 02:17 PM   #5072
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Originally Posted by jlaakso View Post
Wouldn't that imply that PSU of the class D amp is generating noise into your mains network which your sensitive (presumably with high gain) phono preamp picks up?


It is certainly possible to test for this by running the pre on batteries. Common sense though would indicate against the PS being the culprit. Class D gets power from a linear PS utilising EI transformers. It doesn't appear likely that the mains supply gets significantly more polluted than it already is. Arm wiring on the tt, otoh is not screened or twisted over a significant length and can very well act as an aerial.

And then, there is also the question of magnitude. Several volts @500kHz in the speaker cable... And this is why i am curious about the Hypex.

Last edited by analog_sa; 20th September 2012 at 02:20 PM.
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Old 20th September 2012, 03:45 PM   #5073
Julf is offline Julf  Europe
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Originally Posted by analog_sa View Post
I am asking something extremely simple. Hook a scope to the output, set sweep to free running oscillator frequency range (500kHz?) and get a reading of the amplitude.
Well, I still haven't managed to get my nc400's back onto my lab bench - too many other projects. But from the measurements shown in that thread on audiocircle it seems that the output noise is less than 0.1 μW (THD+N, dominated by noise at the low end, is around 0.1 % at 100 μW). That would be 0.6 μV into 4 ohm...
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Old 20th September 2012, 04:22 PM   #5074
bavmike is offline bavmike  Canada
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Originally Posted by wintermute View Post
guys the conversation on the PS Audio DAC is off topic. I'm going to split it off into a separate thread. moved to here --> Dac's for use with the Ncore Amps
Excellent Idea!
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Old 20th September 2012, 05:06 PM   #5075
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Originally Posted by Julf View Post
Well, I still haven't managed to get my nc400's back onto my lab bench - too many other projects. But from the measurements shown in that thread on audiocircle it seems that the output noise is less than 0.1 μW (THD+N, dominated by noise at the low end, is around 0.1 % at 100 μW). That would be 0.6 μV into 4 ohm...

I really don't see how this figure is relevant. Output noise is certainly not measured at 500kHz...
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Old 20th September 2012, 05:24 PM   #5076
Julf is offline Julf  Europe
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Originally Posted by analog_sa View Post
I really don't see how this figure is relevant. Output noise is certainly not measured at 500kHz...
My apologies - I thought output noise was what you were interested in. You are right in that those noise measurements only look at nose up to 20 kHz.
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Old 20th September 2012, 05:30 PM   #5077
tony399 is offline tony399  United Kingdom
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Originally Posted by analog_sa View Post
Is it possible not one of the Hypex fans owns a scope? I asked several times about the amplitude of the output waveform in the absence of signal. Some people queried my motives for such knowledge while others promised to measure at first opportunity. Nothing so far...
NC400 residual.JPG

0.1v and 1us per division
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Old 20th September 2012, 05:43 PM   #5078
Julf is offline Julf  Europe
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Attachment 302304

0.1v and 1us per division
Great! Thanks! So 0,6 V peak-to-peak. I assume that is with open outputs? Wonder how it would look with a normal load...
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Old 20th September 2012, 08:12 PM   #5079
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Attachment 302304

0.1v and 1us per division

Thanks a lot for this. I don't expect a speaker load to dramatically alter this.
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Old 20th September 2012, 08:35 PM   #5080
tony399 is offline tony399  United Kingdom
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Speaker load makes no difference.
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