3340 Sync - E&MM Spectrum Synth

[Martin Czech]

The question was, how "real" hard sync could be obtained with an 3340 type vco.
Well, the E&MM schematic uses 2 NJFETs to discharge the timing cap at pin 11 to 
two different levels. The sync input is either differentiated (short spike)
for normal sync operation or dc-coupled, this will provide a kind of
hold feature, depending on the sync-waveform (pwm).
(Good idea).
The soft-sync pin is not used in this schematic (Pitty)
Nor is the hard sync pin #6. (Colin is this correct ? My crt has no good 
resolution for this tif).
This would be very interesting, because the tri wave would reset to some 
small positive voltage in case of sync, but the charging state would not 
necessarily change, rather stay where it is, thus the sawtooth and pulse 
phase would NOT reset to a determined value in case of sync.
This is not quite what a conventional sawtooth hard sync does.

Suggestion:
Also use hard sync pin with some proper voltage spike to force
charging state (rise or fall).
Use only one fet for reset, but with selectable voltage, thus
enabling discharge or charge to any level. Less leakage, more fun.


m.c.