[sdiy] sync circuit woes

Tom Wiltshire tom at electricdruid.net
Thu Nov 20 17:43:16 CET 2008

On 20 Nov 2008, at 15:36, Dan Snazelle wrote:

> the only real issue (and its not too big of a deal) is some  
> OVERLOADING in the mixer (audio summmer) circuit.
> its just a typical 100k summer like you would see on a vco but with  
> a 50k pot before each sum. it seems that with all the inputs being  
> quite loud (except the clean guitar which seems quiet in comparison  
> even though it has almost X10 of gain) when they all get past 5  
> there is some distortion that results.
> is this typical of an opamp mixer?

It is if you're using it to mix a lot of +/-5V oscillator signals.  
You've only got (at most) 30V of headroom, so 10V signals will soon  
max it out. If you've got +/-10V signals, it'll be even worse. If  
you've got 100K input resistors, try reducing the op-amp's feedback  
resistor by a factor of 2 or 3 or 4.


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