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Old 25th September 2003, 06:45 PM   #1
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Default "non direct" volume control

Hello everyone,

It has been a while since I have posted somthing here and it is good to be back.

I have read a lot of material about pots, stepped attenuators etc.
as a volume control devices. did not like any of them because the sound is going in via resistors caps and selector connections.

The one idea I was considering is a tube amplification stage with variable gain in such a way that the sound is going through the tube instead of the pot, and the pot is there olny for stage gain change (the sound is not going through it).

Have you ever seen circuits like that? How successful ware they, and how good do thay sound?

Thanks.

Glass painter.
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Old 25th September 2003, 06:52 PM   #2
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Glass painter,

What you propose is a VCA, a voltage controlled amp. There are many ways to do that, but it will be very, very difficult to improve on a good pot. Why? Firstly, it remains to be seen whether the gain stage is "better" than a passive pot. Also, variable gain stages often have also variable performance, meaning that the distortion & noise performance will generally vary with gain. Lastly, think about the concept. Presumably, a DC control voltage from the pot would control the gain. So, any noise, pop, crackle on the pot, which you find so objectionable, will modulate the gain to get the noise, pop, crackle at the signal output.

If you can accept a solid state solution to try it out, look up the AD or TI VCA's. They are very high performance.

Jan Didden
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Old 25th September 2003, 07:09 PM   #3
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Hi,

Gain contol devices using tubes are often used in studio gear as limiters.

A very common tube for this application is the ECC189/6ES8.

Whether this is useable as a logarithmic audiocontrol I don't know.

BTW, either way it's still going to need some components that are likely to degrade performance.

The better volctrls are rotary attenuators where performance can approach complete transparency.

Another way that's reported to sound very good are transformer
based volume ctrls.

Cheers and welcome back,
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