[sdiy] SMT transistor for white noise?

[Hugh Blemings]

Hi All,


I'm reminded of "ChaosKey" a design that Keith Packard and Bdale Garbee 
put together to create entropy for the random number generator in the 
Linux kernel.  It's based off a pair of transistors biased up at 
something like 20V and fully open source. https://altusmetrum.org/ChaosKey/


Might be of interest?

Cheers,
Hugh



On 15/12/2025 07:38, Mike Bryant wrote:
> I think you'll find the LM194 and its clones are the only monolithic 
> ones left now.   There were others a few years ago but most others are 
> now two very well matched but separate die in the same package.
> ------------------------------------------------------------------------
> *From:* Synth-diy <synth-diy-bounces at synth-diy.org> on behalf of Ian 
> Fritz via Synth-diy <synth-diy at synth-diy.org>
> *Sent:* 13 December 2025 19:53
> *To:* Gordonjcp <gordonjcp at gjcp.net>
> *Cc:* synth-diy at synth-diy.org <synth-diy at synth-diy.org>
> *Subject:* Re: [sdiy] SMT transistor for white noise?
> Do they have these in monolithic pair packages?
>
> Ian
>
> > On Dec 13, 2025, at 12:27 PM, Gordonjcp <gordonjcp at gjcp.net> wrote:
> >
> > On Sat, Dec 13, 2025 at 11:11:54AM +0000, Mike Bryant wrote:
> >> Too true 🙂   A large percentage of the world's small signal 
> transistors now come from a huge fab in Chongqing and they just brand 
> them to whatever their client wants.
> >>
> >
> > Many years ago I bought a bag of something like 500 of the cheapest 
> Chinesiest BC548-wannabes from Some Dude In Shenzen On eBay, expecting 
> to maybe hand-match a couple of sets of a dozen reasonably close ones 
> for filters.
> >
> > Nope.
> >
> > Any two you pulled out of the bag at random would have the same Vbe 
> down to *microvolts*.
> >
> > So that was a quicker evening than I anticipated.
> >
> > --
> > Gordonjcp
> >
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-- 
I am slowly moving tohugh at blemings.id.au as my main email address.
If you're usinghugh at blemings.org please update your address book accordingly.
Thank you :)
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