[sdiy] LC osc for AF

[John L Marshall]

Toby,

I can't tell if you got the answer that you are looking for. Here are some
ideas:

1. Hartley oscillator; tapped coil, maybe 10% to 20% and capacitor in
parallel. In a transistor circuit, top of coil to base through blocking
capacitor, tap to  emitter, bottom to ground.

2. Colpitts oscillator, tapped capacitor, and inductor in parallel. similar
connection.

3.Tickler feedback with a second small winding close coupled to the tank.
The tank may be in the base circuit or the collector circuit.

I just checked "The ARRL Handbook for Radio Amateurs" there are FET circuits
for Colpitts and Hartley.

BTW "The Handbook", while intended for hams, is loaded with really good
information on topics that appear on this list such as, grounding, EMI,
testing, general theory, and so on. Published yearly. Teory doesn't change
get an old one cheap.

Another thought. Use an opamp and put the series LC in the positive feedback
path and something non-linear (lamp or diodes)  in the negative feedback
path. The L and C will oscillate just fine. You just need to give it a small
kick to keep it going. Give it too big of a kick and and the sinewave clips.


Take care,
John
www.sound-photo.com
---------------------------------------------------------------------------

----- Original Message -----
From: "Toby Paddock" <tpaddock at seanet.com>
To: <synth-diy at dropmix.xs4all.nl>
Sent: Friday, April 18, 2003 6:31 AM
Subject: [sdiy] LC osc for AF


> Could someone point me to some
> Audio Frequency LC Oscillators for Dummies info?
>
> I'd like to build some, but it's been too long
> since I did that in school and that was probibly
> RF and with tubes and I didn't really pay enough
> attention anyway and my books are buried in the
> garage somewhere.
>
> The coils are on a rod core and maybe something
> like 10-100mH.  50mH and 2uF would res at about
> 500Hz, but I don't even know if that's a
> reasonable range.
>
> Interaction between oscillators with the coils
> near each other is a definite plus.
>
> Don't care about a clean waveform.
> Don't care if it's stable.
>
> Thanks,
> Toby Paddock
>
> PS- Unrelated, but does anyone use inductor
> saturation or hysteresis for distortion?
>
>