[sdiy] EXT Re: 808 Q35

Richie Burnett rburnett at richieburnett.co.uk
Mon Jan 30 20:25:09 CET 2017


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.

-Richie, 

Sent from my Xperia SP on O2

---- Needham, Alan wrote ----

>I'm sure I remember reading somewhere that a 'normal' signal transistor could be deliberately damaged to produce more noise, was it a case of reverse-biassing the base-emitter junction until it starts to zener?, then use the device in a normal noise circuit.
>Maybe not very scientific, but if it's that easy I'm surprised Doepfer didn't do it... ?
>
>
>-----Original Message-----
>From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On Behalf Of Florian Anwander
>Sent: 30 January 2017 18:00
>To: *SYNTH DIY
>Subject: EXT Re: [sdiy] 808 Q35
>
>Hi
>
>On 30.01.17 09:37 , matt holland wrote:
>> I didn't think noise circuits were that picky about transistors but I 
>> haven't made any myself.
>Dieter Doepfer once mentioned, that he had to change the transistors for his noise module three times in the recent twenty years. Because the transistors became "less noisy" over their production run.
>
>Florian
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