Many thanks to all who replied - the circuit with 120K/0.1uF works
very well.
I want to feed this into an audio ring modulator circuit - (2
transformers, 4 Ge diodes) My carrier is coming in from a mic pre-amp
- which when I checked on my scope looked like a -10 to 10V signal.
The output from the oscillator (currently running at 5v) is too small
to be an effective modulator and really needs to be amplified and
offset to match the range of the carrier.
But what's the end project? Unless you specifically want a modified
signal on the output, you may not want a square wave. A sine-wave would
do the same thing if your intent is merely to translate the audio input up
to a higher frequency. Using a square wave will modify the signal, so
you'll get more than a translation (in electronic music, the modification
is what's wanted) For that matter, if this is a "scrambler", one article
decades ago suggested using a radio for the second signal, making sure to
use the same station at both scrambler and descrambler.
There is nothing magic about a ring modulator. You can get the same
effect with other circuitry, anything that is a double balanced mixer will
have the same effect. Using active components will get around the issue
of needing a strong "carrier" signal, and get away from the need for
audio transformers.
You can find double balanced mixers in all kinds of ICs. Sometimes they
are even deceptive, since they are used as variable gain elements and
using an audio signal instead of a varying DC level will make it a mixer.
Michael
