🚀 go-pugleaf

In sci.electronics.design, moby@kcbbs.gen.nz (Mike Diack) wrote:

>I'm redesigning a device for blind navigation that I first designed a
>decade or so ago, which requires a transformer to drive an
>electrostatic transducer (sweeping 100..50KHz, around 100v P/P driven
>from a 6v P/P source).
>My first iteration used a (hand wound) Philips 10mm 3E25 toroid. I
>gave one of my original samples to a local transformer outfit and
>asked them to make me something smaller (and tidier!)
>Everything they came back with was bigger than my original.
>I have seen a polarisation tranny inside an AKG C460 microphone which
>is smaller than the size of a frozen pea. 

   That transformer is part of a switching power supply that runs at
an ultrasonic frequency.  The transformers in disposable cameras (that
others mentioned) are for the same thing, running a cheap SMPS at high
frequencies.
   To get any response at all down to 100 Hz you need something at
least the size of a modem phoneline isolation transformer.

>Admittedly this tranny only
>has to handle a single frequency wheras mine carries a sweep, but who

   It's not so much a single frequency vs. a sweep, but what the
lowest frequency is (and the power transferred) that determines the
minimum size of a transformer. 50/60Hz power transformers don't come
any smaller than a wall wart, and ones for significant power are much
larger and heavier.
   For your application, a plate transformer that's normally used
between the 50C5 and loudspeaker of an "All American 5 [tube]" might
work, but the upper 50kHz requirent will likely be a problem.
   One alternative is to make the lower limit something usable for
very small transformers (maybe 1kHz to 5kHz) - this is probably not
acceptable.
    The other is to use one of the tiny switching transformers to make
a high voltage DC supply which runs a transistor amplifier with
high-voltage ouput.

>can make trannies like that or where can the cores be sourced
>(preferably surface mount)
>cheers
>M