[sdiy] Overdriving 4069UB

Seb Francis seb at burnit.co.uk
Tue Jan 3 00:28:32 CET 2006


Harry Bissell Jr wrote:

> */Seb Francis <seb at burnit.co.uk>/* wrote:
>
>     Hi Harry,
>
>     This is the current circuit:
>     http://burnit.co.uk/sdiy/stuff/mosfet_distortion.gif
>
>
>     Yep, that's right - with a 1uF cap before the 10K resistor. I
>     experimented with also adding DC bias to the CMOS input to make the
>     distortion more symmetrical, but I found that it didn't make much
>     difference.
>
> It would not make a difference. The circuit will self bias to the 
> crossover
> point between the N and P transistors because of the feedback resistor.
>
Actually even the 3rd stage which doesn't have a feedback resistor seems 
to self-bias (it just takes a while to settle).  Maybe I should stick a 
few megs across it just for stability .. but then again I quite like a 
bit of instability in my analog sound, and by the time the signal gets 
to the 3rd stage it's pretty much rail to rail so the bias point makes 
less difference.

> Kind of cool, that....
>
Yeah, I thought so :)

Seb





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