[sdiy] EXT Re: 808 Q35

Michael Zacherl sdiy-mz01 at blauwurf.info
Tue Jan 31 08:45:08 CET 2017


On 30.Jan 2017, at 20:25 , Richie Burnett <rburnett at richieburnett.co.uk> wrote:

> The tr-808 noise circuit reverse biases the base-emitter junction in order to produce noise. I guess this is from avalanche breakdown or zener action of the b-e junction which wouldn't normally see such a large reverse voltage.
> 
> There must be some spread in noise level between transistors as there's a gain trim pot in the noise amplifier circuit.

Hm, I thought that’s the classical approach to operate a transistor in reverse at higher voltage for analogue white noise circuits? But apparently such a transistor can wear out, as I had to change the noise transistor in an Oakley Noise Module recently. And I had to go through like 20 candidates to find the one repalcement with the sound and level I liked.

Michael.




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