jph@ihlpe.ATT.COM (452is-Hayes) (01/23/88)
Does anyone have or can refer me to a simple RC oscillator circuit for audio or low-mid RF range? Need a "discrete" (straight transistor) type circuit (i.e., non-IC type circuit). Looking fro a Wein-bridge or Phase-Shift circuit that dosen't have too many components: don't want to use inductors. Is for home hobby project. J. Hayes ihlpe!jph IW, 1d-263
wtm@neoucom.UUCP (Bill Mayhew) (01/25/88)
My ancient copy of the ARRL handbook has simple little circuit for
a twin T single transistor circuit. It is quite stable. It
requires one transistor, 4 resistors and 4 capacitors. One of the
caps is used for coupling the output. Basically you use a low-pass
T circuit and a hig-pass T wired in parallel to feed back. The
circuit oscillates at the freqency where there is maximal feedback.
At that frequency, the phase shifts of both T sections is 180
degress, permitting oscillation.
You can approximate the output frequency by graphically overlaying
the responses of the T sections. Making the output fequency
adjustable is a hassle.
I'll give this a shot:
o (Vcc)
|
R-bais
|
+-------------+--------+
| |
| o (OUT) | c
| | b |
+----R1---+---R1--+----Q1
| | | |
| C1 | | e
| | | gnd
| gnd |
| |
+----C2---+---C2--+
|
R2
|
gnd
The output is taken at the R1-C1 junction. Harmonic distortion in
minimized at that point. To assure oscillation R2 ~= 0.1 * R1, and
C1 ~= 2 * C2. Rbias should be ~2700 - 4700 ohms.
I found this on pg. 522 of my 1974 ARRL handbook. I remember
building one with a 2N414 years ago. Definitely a circuit for Old
Farts. I never really did like the light bulb in a Wien bridge.
--Bill