Audio Osc Nuts & Volts Magazine Project - osc.jpg (0/1)

Hi, I'm an electronics hobbyist with the following problem (actually,
I have more problems than this, but they're for other news groups)

I built an audio oscillator project from the Nov 1993 issue of Nuts &
Volts magazine. It didn't work, so after carefully checking the
connections and component values, I decided to breadboard
a version of it (attach.). While playing around with the circuit, I
removed the 2N3819, and got it to produce a distorted sine wave; more
like a square wave, but it was oscillating. I checked the 2N3819 both
by sustitution and transistor checker and it appears to be OK. I'm
beginning to suspect that the circuit in the article contains an
error, but then again, I'm not claiming to be an electrical enginear
(sic). The 2N3819 is being used as a variable resistor according to
the article, and i guess that when I remove it, the gain of the stage
goes way up to the point that the resulting sine wave is clipped.

Can anyone out there tell me why this sucka, sheet don't wanna woyk?

Thanks,
Ron

 

"a version of it (attach.)"

Ron -

Send post with attached schematic to: alt.binaries.schematics.electronic

 

Connect a variable resistor in place of the transistor that is supposed to
act like a variable resistor and see if you can adjust for a sine wave. At
least this will be a starting point in your troubleshooting odyssey.

 

Hi Ron
Looking at the schematic and reading your description leads me to believe
that the oscillator is not getting enough positive feedback to maintain oscillation.
In theory the 2N3819 acts as a AGC (automatic gain control) for the positive
feedback portion of the oscillator.This is to limit the positive feedback
so it dosn't overdrive the output into clipping.
Try decreasing the 47k feedback resistor
to the 2N3819 or increasing/eliminating the 10k resistor across it.
Good luck.

Colin G