[sdiy] EXT Re: 808 Q35

[Michael Zacherl]

On 31.Jan 2017, at 14:29 , Jacob Watters <jacobwatters at gmail.com> wrote:

> If this is the case, then what is a better method for creating white noise? I have seen some CMOS options that create pseudo random squarewaves, but they seem to use a lot of components compared to the transistor option. I was considering just using a tinyAVR instead.

I think that’s how semiconductor technologies changed: None of my vintage synths’ noise sources show such wear out symptoms. It might be that the much smaller size of contemporary dies contributes to the expenses caused by reverse operating a transistor. So it’s probably to expect that small modules utilising SMT parts may show that wear more likely.

> On Tue, Jan 31, 2017 at 2:45 AM, Michael Zacherl <sdiy-mz01 at blauwurf.info> wrote:
> 
> 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.

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