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Vishay Z-Foil resistors for LM3886
Vishay Z-Foil resistors for LM3886
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Old 9th September 2019, 05:40 PM   #1
FOXYE is offline FOXYE
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Default Vishay Z-Foil resistors for LM3886

Who tried to test the effect of feedback resistors like Vishay Z-Foil for LM3886?
What were your experiences?
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Old 10th September 2019, 01:45 AM   #2
Panelhead is offline Panelhead
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Honestly they cannot do anything but maybe help. Do not know anyone has swapped them and performed measurements to see if there are differences.
The noise floor is very low by design. The impact of MF resistors might be buried deep.
I say this having used Vishay S102 in the feedback positions. But did not try metal film resistors first to see if there were audible changes.
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Old 10th September 2019, 02:02 AM   #3
jameshillj is offline jameshillj  Australia
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In general, the Z-foils impart an emphasized detail sound that appears to be quite 'bright' that can be quite useful in a gain clone amp setup - Susumi MFs (and others too) have a similar sound but not quite the level of detail, transients, etc

The other end of this subjective scale would be the Manganin based resistors - similar detail emphasis but a much 'darker' sound.

There isn't much measured difference at all but a quite distinct difference in the sound, particularly in both the feedback position and the input resistor position for the lm3886 amps.

Curiously, this is apparent in both the voltage gain and 'current gain' circuits

Just my 2 cents ...
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Old 10th September 2019, 11:35 AM   #4
Panelhead is offline Panelhead
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The other option I found to be cheaper is Vishay/Dale RN55E. Many say these are too “sweet” sounding. But the low tempco and tight tolerance are both positives.
I have used these and S102. Not sure I can really hear a difference.
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Old 10th September 2019, 02:42 PM   #5
Fast Eddie D is offline Fast Eddie D  United States
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Those resistors are incredible, and expensive.

I've been using the CMF series resistors for about 5 years now. https://www.mouser.com/datasheet/2/4...ind-111261.pdf Low noise, high stability, low temperature coefficient, high resonance. These resistors make a very audible difference compared to cheaper resistors I've used in the past.

I have to wonder how audible it would be if I used foil resistors. I wonder at what point does it make a difference. The CMF resistors make an audible difference even in an ordinary circuit. I see the better specs on the foil resistors. Does it make a difference compared to other premium resistors?
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Old 10th September 2019, 04:55 PM   #6
jan.didden is offline jan.didden  Europe
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Those foil resistors are very stable, very low temperature and voltage coefficients.

As far as noise is concerned, all resistors have the same noise that depends on resistance value and temperature. Most here will know the famous equation.

There's also 'popcorn noise' or 'shot noise' which you see with some older technologies like carbon film resistors. But modern metal film, whatever the brand, through-hole or SMD, all have essentially the same noise.

As far as stability is concerned, you can easily see that when you have, say, 1k and 20k feedback resistors, and you use 21 identical resistors, all tempcos and voltcos cancel.

Jan
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Old 10th September 2019, 05:32 PM   #7
KSTR is offline KSTR  Germany
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The one issue with Z-foils is that the tempco is only really low in thermal equilibrium of foil and substrate, that means when the AC dissipation in the resistor is kept suffciently low for low temp rise, notably at low frequencies.
The potentiometric approach for a feedback devider can help this (to the amount that matching permits) as Jan pointed out... but meh, rather restrictive given the cost.
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Old 10th September 2019, 06:27 PM   #8
Bare is offline Bare  Canada
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Old 10th September 2019, 08:31 PM   #9
analog_sa is offline analog_sa  Europe
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Vishay Z-Foil resistors for LM3886
Quote:
Originally Posted by jameshillj View Post
In general, the Z-foils impart an emphasized detail sound that appears to be quite 'bright' that can be quite useful in a gain clone amp setup - Susumi MFs (and others too) have a similar sound but not quite the level of detail, transients, etc
Useful observations, thanks!

I am a big fan of the z-foils, only wish they were available at higher power ratings and were much cheaper . Using them in a chip amp appears sacrilegious, yet it may actually make sense as so few are needed.

This raises an interesting question: whether the sound quality of the amp within the same budget is better served by top quality parts or a NASA engineer design.
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