3340 Sync - E&MM Spectrum Synth

[Colin Fraser]

>----------
>From: 	Martin Czech[SMTP:martin.czech at itt-sc.de]
>Sent: 	30 July 1997 11:18am
>To: 	Colin Fraser; Juergen.Haible at nbgm.siemens.de; synth-diy at horus.sara.nl
>Subject: 	RE: 3340 Sync - E&MM Spectrum Synth
>
>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).

That's not what I thought - the pulse wave from the master oscillator is
differentiated, but the pulse wave from the slave is dc-coupled. This
means the slave will ignore the incoming sync pulses until its pulse
ends, so the PW control on the slave allows sync to variable intervals
above the master.

>The soft-sync pin is not used in this schematic (Pitty)

I'm sure you could add another input...

>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.

The voltage the cap is charged to is set to be low enough to ensure true
reset by the trimmer.

C