On Sun, Jul 8, 2018 at 3:01 PM, Andre Majorel aym-htnys@... [cgs_synth] <cgs_synth@yahoogroups.com> wrote:On 2018-07-06 11:04 +0000, mikejburnham@... wrote:
> For the Serge Noise circuit it specifies the noise transistor
> as 2n/PN4250 but these are stupidly expensive nowadays
>
> Is it possible to use BC557? Are they noisy enough? BC557C
> probably best?
Not a month ago, Tony Allgood posted this to Analogue heaven :
Noise in reverse biased transistor junctions can be
surprisingly variable in quality. One of my designs, the 5U
Oakley Noise/Filter module, requires selection of the noise
transistor which is a BC547.
Originally I had thought that the process of selecting the
best noise transistor was to find the loudest one. But oddly,
the loudest ones actually didn't sound as good as the quieter
ones. The loud ones were often prone to random bursts of noise
while the quieter ones produced a more even and wide band
noise. The BC547 sounded better than the BC550 too.
Going by that, the BC557 would be worth trying. And possibly
better than the BC560, if whatever parameters distinguish them
have the same effect on the PNP as they do on the NPN.
--
André Majorel http://www.teaser.fr/~ amajorel/
--
Message
Re: A couple of parts questions
2018-07-08 by Ken Stone
Agreed. When I was shipping transistors with my PCBs, it was not the loudest that I chose, but rather the one that put the signal level where I wanted it.