[sdiy] single 9 volt battery white noise source

[David G. Dixon]

> This circuit looks good...except the IC's are powered by dual 9Volt
> batteries. Looking for a single 9V battery as I'm wanting to add a
> noise source to a thingamakit http://bleeplabs.com/thingamakit/

Ah, yes.  Still, wouldn't it still work if the base were simply grounded
instead?  According to the 2N3904 datasheet, the emitter-base breakdown
voltage is 6V, so 9V should do the trick, no?  Is there something I'm
missing here?  In fact, a survey of all the small-signal transistors
available in the TO-92 package suggests that V_EB0 ranges from 4V to 7V.  Is
a higher voltage than this required to generate "avalanche breakdown"?

I found a couple more single-polarity supply noise sources in addition to
the one posted by Dave Leith care of aerogramma:

http://electronicdesign.com/Articles/ArticleID/6356/6356.html

http://www.maxim-ic.com/appnotes.cfm/an_pk/3469

Google-search "noise generator reverse biased" for all sorts of ideas.

According to good ol' Forrest Mims, the simplest noise source is a
forward-biased diode.  The Forrest Mims Circuit Scrapbook contains a very
useful description of several noise circuits, including one by John Simonton
of PAiA fame.  The Google search will bring it up.

> 
> On 7/17/09, David G. Dixon <dixon at interchange.ubc.ca> wrote:
> > > Reading thru the documentation for the Rainmaker seems that this would
> >  > be the best solution. Is the following really the case?
> >  >
> >  > quote" Common designs use invariably Zener diodes or reverse-biased
> >  > transistors base-emitter junctions as white noise generators. The
> main
> >  > snag of these circuits is that a supply of at least 12V is required,
> >  > therefore a big battery pack or (more commonly) mains supply is used
> >  > as power source."
> >
> >
> > Ray Wilson's Sound Lab uses the reverse-biased E-B junction method, on a
> 9V
> >  supply, and it works just fine (presuming you choose a transistor which
> >  actually makes noise!).
> >
> >