[sdiy] Help with (lack of) noise circuit

Oren Leavitt obl64 at ix.netcom.com
Tue Dec 24 22:29:20 CET 2013



On 12/24/2013 3:15 PM, Ian Fritz wrote:
>
>>>  > If you can find one, try a 2N2712.
>>>
>>> Why that transistor in specific?
>>
>> 2N2712s have a higher noise output in reverse bias. I've found I don't
>> need as much amplification on these guys.
>
> Disagree with this choice! They have a high output, but the noise has a
> large non-white component at low frequency.  The best noise transistor I
> found was from a large batch of 2N3904's, selected for the flattest
> spectrum.  It had the *lowest* output level of the batch.  I have
> 2N2712, and it sounds terrible by comparison.
>
> Ian
>

Yeah, I'll concur - old transistors get "yellow" with age :) The 2N2712 
is rather "colored". The quieter guys are flatter on the overall noise 
spectrum.
I have an old process 1N47xx Zener diode that "whistles" if you put just 
the right current through it.

- Oren




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