CEM3340 sync results

[Fraser, Colin J]

> -----Original Message-----
> From: Haible Juergen [mailto:Juergen.Haible at nbgm.siemens.de]
> Sent: 19 January 1999 11:36
> To: DIY
> Subject: CEM3340 sync results
> 
> last night I have finally made an A / B comparison between
> the CEM3340 + external transistor sync and "normal" sync
> of a saw VCO.

Weird, I did a very similar thing last night too - I compared the normal
3340 sync with the data sheet external transistor method and also with the
E&MM Spectrum method that uses a 2N3819 FET to discharge the 3340 timing cap
directly.
The Spectrum has two sync modes. The first is a normal reset to 0, the
second resets the wave to the halfway point - so it continues in the same
direction. I only implemented the reset to 0 method, but I will try out the
halfway option to see if it adds anything worthwhile.
A nice possibilty here is to have a reset level input, to allow 1 vco to
sync another vco to the instantaneous position of yet another vco.
Don't know how this would sound...
BTW from the Spectrum article I found that the timing cap on the 3340 sits
at about 1.6v at its lowest level - this voltage is dropped by the buffer
stage. 

The end results of my tests were much the same as Juergens.
The internal 'hard' and 'soft' sync modes of the 3340 are pretty awful for
'sync' effects - they are really only of use for locking two oscillators
together.
The external transistor methods both produce very similar results - so close
as to be identical, and they sound very much like the sync effects on the
Prodigy which I used for comparison. In normal use I wouldn't expect there
to be any advantage to either oscillator type.
I still prefer sync effect sounds on my Prodigy, but I guess this is not
because of any audible difference in the output of the oscillators, but more
probably the effect of distortion and filtering.

Colin f