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In Reply to: RE: Everything in moderation? posted by Tre' on July 13, 2016 at 16:08:39
I should have said it Thermal Noise. Every device has it when a signal passes through regardless of how immeasurably and small form of distortion (noise) is generated. Thermal Noise in active devices (diodes, rectifiers, transistors, valves) are much worse than most passive devices such as transformers, caps, resistors; etc.
The good thing is all that happened way outside of AF band so we won't likely hear it (or we can in some ways?).
Bias drift due to thermal instability in transistors also happened in valves (I think it's called Red Plating)?
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.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.
Follow Ups:
Thermal Noise, yes all active devices add some.
In a power supply there is usually a capacitor to ground following the last active device so that noise is shunted to ground and does not continue to the amplifier circuits.
Tubes are much more thermally stable than SS devices. If a tube "red plates" there is something wrong with it or the Bias supply.
In a cathode biased push pull stage (using a common cathode bias resistor) when one tube goes bad and stops conducting the bias voltage is cut in half and that will cause the other (good) tube to red plate.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
I am sure it's a very common approach in SS circuits where high frequency noise is shunted using 0.001-0.1uF decoupling cap to Ground. But in SET and DHT preamps, I think shunting the extra noise to Ground is probably not such a great solution where ground bus noise should be kept to minimal.As to the sonic benefits of regulator, I have to take Paul words and try and see if I too can hear a difference.
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.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.
Edits: 07/13/16
Two things caught my attention in this "sub-thread." First, semiconductor diodes and rectifiers are not active devices. (I assume the reference was to semiconductors, as "valves" was a separate item.) Second, tubes are not more thermally stable than SS. No one would even think about building a free-running HF oscillator using tubes if stability was the goal. I have also seen audio tubes like the 6BL7 and others exhibit slow current drift (with constant voltages applied) requiring more than half an hour to stabilize. This would be unacceptable in its SS counterpart. Just sayin'...
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Buy Chinese. Bury freedom.
I stand corrected and thanks for correcting my mistake. It's funny how I forgot and still make the same mistakes in this past 20 years of calling diodes and rectifiers as active devices. They are passive semiconductors. But I think they can be just noisy as an active devices when it comes to thermal noise.
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.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.
Don't most SS PP output stages have active offset sensing (or transistor temp sensors) and servo circuits that are continually adjusting the bias to prevent thermal runaway?"
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 07/14/16
Self-heating and susceptibility to same are very much dependent on the specific application. Tubes and transistors each have their caveats in this regard, so I don't think any generalization is accurate.
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Buy Chinese. Bury freedom.
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