AWA Low Distortion Oscillator G232 - Teardown

[sean0118]

Just some teardown photos 





edit: Pretty sure this is the main oscillator? or at least part of it? It's potted so can't see much:


Frequency counter:


Level control:


Oscillator:


Power amp:


Output attenuator:


Power supply:


Front panel connections:

[Kleinstein]

The big gray box may be a kind auf audio transformer for the output. At least it looks like it is connected near the power amplifier output.
The actual oscillator is very likely a Wien bridge of similar RC oscillators with pairs of capacitors near the switches for the rages. So likely the osciallator with the discrete transistors near the capacitors.

It is quite some time since I saw a 4 digit frequency counter.  I would have expect the frequency to be a bit more stable, at least for a short time.

[trobbins]

The oscillator is a two RC phase-shift type around two stages, with one of the stage gains controlled via an LDR-LED, and was all BC550.

I have the previous G231 oscillator from 16 years earlier (1970), which does use a Wien bridge format.  I am about to get that on the bench again to see what distortion benefit can be gained from better matching of the bridge parts (even though AWA matched their capacitors pretty well).

The G232 has significantly lower harmonic distortion specs than the G231, and at the time AWA relied on their vintage F240 noise and distortion meter to confirm those specs.  The F240 (which uses an active twin-T notch filter) can't really measure down to such a low distortion level, so they had to use an additional custom passive twin-T notch filter jig to confirm spec.

[Gyro]

The manual, including schematics is readily available on the web. Just search AWA G232.