🚀 go-pugleaf

In article <BsDu8n.6zC@acsu.buffalo.edu> v064mb9k@ubvmsb.cc.buffalo.edu (NEIL GANDLER) writes:
>
>	I recently wrote in asking about dual audio pots but just discovered
>an alternative. The key is a simple multiplexor using the versatile 4066b
>cmos I.C. I simply allowed two channels of audio to share one channel of
>resistance alternately switching between the two. Normally you would hear 
>distortion or audio noise or clicks but I used an inverter for one of the
>channels and a 555 to provide a high frequency signal using a 10pf cap
>to run at extremely high frequencies. It works! Im not sure if its anything
>inovating or new but it just made designing my stereo receiver that much
>easier. I no longer have to search for hard to find and expensive pots.
>The multiplexor circuits costs less than $3. I welcome any comments or
>questions. 

The CMOS switches sound bad to my ears.  Your best bet is probably to use
a pair of operational transconductance amplifiers, which are basically
amplifiers whose gain is controlled by an input voltage.  You can then tie
the gain inputs together to a pot, and adjust the gain on both channels
at the same time (and the tracking is much better than any pot).  This is
what most of the newer mixing boards use these days.

You can also use the CMOS volume controls, but again, I don't like the
sounds of the things.  The CMOS switches seem to have a lot of low-level
nonlinearities, but they're cheap enough that you might want to give them
a listen anyway.  The multiplexer is an ingenious idea, though I don't
think I'd want to use it in a high quality audio application.
--scott