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01-11-2010 Post does not mapped to Knowledge Tree
Romy the Cat

Boston, MA
Posts 9,995
Joined on 05-27-2004

Post #: 1
Post ID: 12674
Reply to: 12674
Contact-free volume controls?

The Twogoodears posted on his blog an fascinating message about LDR volume controls.


I never used them and wonder if it might be interesting.


This volume control uses non-contact optical SS devices to change resistance. There are many devises that vary resistance under different conditions – light, temperature, magnetic field, radioactivity, pressure… etc. I am not convinced that they all only by the fact that they have no physical contact are better for sound. I think in the case of the P&S preamp the quality that Twogoodears observe would derive not from the potentiometers itself but from the quality of the buffers that drive the load after the potentiometers.

Still, it might be interesting to hear the thing…

The Cat

"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
01-11-2010 Post does not mapped to Knowledge Tree
Paul S
San Diego, California, USA
Posts 2,468
Joined on 10-12-2006

Post #: 2
Post ID: 12678
Reply to: 12674
Out of the Signal Path?
Well, there's noise, attenuation and impedance to reckon with, at a minimum.

The TAP TVC I use claims that the step circuitry itself is "out of the signal path".  OK, fine; but so what?  Doesn't the voltage have to "cross" something, somewhere, at some point, in order to be divided/attenuated, and doesn't the unwanted voltage/current have to go somewhere from the shuttle point?  There's always plenty of noise to thwart, route and re-route, irrespective of the means of division.  To be "good", any attenuator/pre-amp topology will yet have to deal effectively with the basics.

Does anyone know how the voltage gets turned into light, or if it then gets "re-converted"?  Can any of this happen without some kind of diode effect?

Does the light conversion system itself require power from any source other than the signal?  I would hope any active circuitry was limited to a well-isolated buffer, if only to avoid parasitic noise.

I admit I am leery of "active attenuation" for hi-fi.

Paul S
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