[sdiy] 3340 FET sync

[Finlay Shakespeare]

Hi all!

Long time lurker here - I really haven't mailed in a long time - but wondering if anyone could shine a light on this...

I'm working on a 3340 circuit (using new-generation Curtis chips here) employing MOSFET sync rather than the standard hard/soft sync methods given in the datasheet. This allows for resetting of the waveform to a known(ish) point of the waveform, rather than just giving a sync-soundalike. Known-ish, however, because at certain frequency settings / ratios (between syncing and sync'd oscillator) the waveform will "overshoot" before stabilising on the next cycle.

I've attached both a schematic and a shot of the scope here - if anyone has any guidance for minimising (or even better, completely removing) this overshoot, that would be fantastic. On the scope, the blue trace is the pulse input to the sync circuit, and the pink trace is the waveform from the sync'd 3340's ramp output.

Please note that the resistor and capacitor values given in the sync network going to Q4 are not necessarily as they currently stand - I've managed to improve the situation by tweaking this network, but seemingly I can't remove the overshoot completely.

Cheers!
Finlay Shakespeare
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