Anyone experienced with Theremins?

[Harry Bissell]

Funny about magnetic field... the SMALLER transformer (with less core area)
is MORE likely to be a problem... Smaller transformers are (as a rule) run
with
the magnetic core at a higher field (closer to saturation) this causes two
problems...

1) Regulation (load/no-load) is worse... often 20-25% (a big one might be
5-10%)
2) More magnetic field can leak out of the core...

There are several "fixes" for this...

1) a Shielded transformer... not the funky brass cover on some... but solid
steel or better
Mu-Metal  (an alloy that SUCKS UP magnetic flux...)

2) A transformer with a "semi toroidal" core... such as the Signal
Transformer "Flathead" series and similar styles for other mfgs.  These
contain flux better than the E-I core (std types).

3) A true Toroidal transformer... the be$t choice but a$ alway$ there are
other factor$ to con$ider if you follow my drift....

I built a hex fuzz where the transformer flux was coupled to the circuits
ONLY when the chassis was closed (so eddy currents might flow...)  I was
already "married" to the design so I made a shield (mu-metal) around the
transformer... which gave it a path that the eddy currents liked even better
!!!  But that is an extreme and expensive solution...

Anyway try your luck... ther is no guarantee that a given transformer will
screw up your circuit anyway... but try it before you drill all the holes....

H^)

Paul Braun wrote:

> It would seem that Harry Bissell typed forth the following:
>
> > A small linear power supply should be no problem...
> >
>
> That was my plan. Line in>Xfmr> bridge> regulator> filter> output.
> Nothing but net.
>
> > Most companies are using wall warts for a couple of reasons...
> > 1) You can easily get a wall wart for any country in the world...
>
> The one in the kit came from RadioShack...
>
> > 2) Safety Regulations... most small wall warts are "Class 2" which
> > means they are inherently current limited... If you short them out
> > continuously they will either self-limit without overheating... or will
> > blow a thermal fuse inside themselves... thereby no risk of fire.
> >
> > This means that Underwriters Laboratories does not have to approve
> > the electronic device (theremin, effect, whatever...)... because it has
> > already approved the power source...
> >
>
> Ahhhh. The CYA theory. Makes sense.
> >
> > 3) It keeps the magnetic field away from the Audio Circuits...
>
> This is my biggest concern. I'm just hoping that with a small
> enough transformer (perhaps in a small metal project box inside
> the wooden case) there won't be enough of a field to matter.
>
> Thanks.
>
> Paul Braun
> Cygnus Productions
> nerdware_nospam at laidbak.com