Designing for Ultra-Low THD+N in Analog Circuits

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#4
Worth reading

xstreme said:
By Bruce Hofer, Chairman & Co-Founder, Audio Precision
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For those with an electronics degree/job/background -
  • a nice reminder of everything we should not have forgotten about noise and distortion mechanisms in passive components (but that I don't see current graduates knowing)
  • plus some updates on his opinion of the SOTA
  • plus a nice distortion estimation technique


Capacitors seem to remain The Black Art of audio- his comments remind me of stuff Bob Pease used to mention in Pease Porridge. And also implied by Thorsten Loesch (1998 cable article) and someone else on capacitor film corrosion
 
#10
Would anyone care to comment on the point made about metal foil resistors and "modulation distortion" at low frequencies?
 

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#11
Extraordinary claims and pathalogicial science

CZ101 said:
Would anyone care to comment on the point made about metal foil resistors and "modulation distortion" at low frequencies?
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He's claiming that he has measured a time variant component of resistance of the same order as the resistor value.

Before I do any more than "oh, really?" I'd like to see a reproducible experiment described, preferably reliably reproduced by others.

At the moment it's a claim (and right now I don't care enough to correspond with the author to get an experiment definition - bills to pay etc.)
 
#12
http://www.diyaudio.com/forums/part...on-distortion-foil-resistors.html#post3518344

jcx said:
it appears that Hofer is saying that some bulk metal foil don't perform proportionately as much better than some thin film just considering TCR

a guess would be that the extreme low TCR are obtained in part by balancing mechanical strain and TC of substrate and foil - so there is a more complicated thermo-mechanical effect that doesn't work to full benefit above fractional Hz and below kHz

but the foil still has as low TCR as any thin film as far as I know – so it shouldn't actually be worse than thin film – just not as much better as might be expected by the DC TCR ratios

it would be useful to know which “some bulk metal foil” are that show this – Z foil? - differ between chips, leaded, “naked”, fully encapsulated? as well as the numbers, plots
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#13
Could it be related to the issue that low Tc (at DC and very low frequencies) can be obtained either by using low Tc materials, or by balancing much higher positive and negative Tc against each other. For example, the thermal expansion of a substrate can be balanced against thermal conductivity changes in the resistive material. In the latter case if the two effects have quite different time constants, which will be common, then the Tc can rise for intermediate frequencies.

Oops- just noticed that jcx said the same thing two days ago.
 
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