[sdiy] uPC1406 as log VCA

[Michael Bacich]

On Mar 29, 2006, at 12:15 PM, anthony wrote:

> I have a couple of these uPC1406's that I scavanged from some  
> digital cable receivers. Basically it's a double log-response  
> voltage controlled attenuator. The log-response sounds interesting  
> although I have read that a linear VCA and a log envelope sounds  
> better, I know I have some uses for log VCA's in a very small package.
>
> I guess it wouldn't take much effort to try one out on a  
> breadboard, but I was wondering what anyone's first thoughts might  
> be. My guess is that there will be a lot of control voltage  
> bleedthrough and it will be mostly useless. Still having 4 log  
> VCA's in two 9-pin SIL's...

There seem to be a lot of similar voltage controlled attenuator IC's  
out there, in various package types.  All appear to be designed for  
use in video subsystems or broadcast recievers, probably for some  
sort of amplitude modulation stuff.  A common characteristic of these  
parts seems to be a fairly  limited range of attenuation -- typically  
around 20 to 40 dB max, at least according to spec sheets.  This may  
prove not very effective for synth use, where we need more like 80 dB  
range.

Please do let us know if you manage to get it working, and what the  
result is like.


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