DSE mini-synth rants

[harry]

Hi Marjan (and all)...

If the PLLs are in track mode... then an offset is almost impossible
because
the VCO will correct for any difference you try to inject.  Better might
be to
introduce different loop delays so the two VCO have different settling
times.
Or possibly making some kind of digital phase shifter or delay to the
other
output.

H^)  harry

">>>marjan<<<" wrote:

> Hi all,
>
> I suppose you're all in holiday mood, but when you get back,
> take a look at this very interesting project:
>
> articele:   vinyl.plattsburgh.edu/minisynth.html
> samples :   http://members.optusnet.com.au/~shudder/minisynth.htm
>
> Right now, I have too many projects started but maybe I'll
> consider this one sooner or later.
>
> Anyway, the schematic has some errors. Here's what I've found:
>
> R41 mic input level pot shouold have lower pin to gnd but
> all other components on the same rail should be at V/2 (R2/3
> divider) so dot on R41 gnd connection is wrong - others
> (I think) are OK at V/2.
>
> C6 at V/2 divider should be C2
>
> IC3 pin 14 should be connected to IC1 pin 8 output (schmitt)
> according to text but theres dot connection missing (otherwise
> there's no sense to it), but cathode of D4 is connected to IC4
> pin 12 which is wrong, I guess it's also dot on the wrong place
> (pin 12 should go to IC2,3 input pins 14 and scmitt out.)
>
> R39 is missing from PCB overlay.
>
> Also, if you install separate pll input for IC2, shared R11 pull
> down resistor will stay only with IC4 pin 13, so you'll need
> another pulldown at pin 12.
>
> I don't like LFO sharing IC with amps and schmitt. I'd consider
> making two LFOs in separate 324. LFO wave is square RC filtered
> which's strange, I'd use triangle from cap, maybe use remaining
> opamps from another 324 for bufferig. Tri/square switch.
> Level pot for each LFO (before 4M7 resistors). Range sw for LFOs.
> Mix both sections into one output. Maybe simple RM (XOR)?
>
> Now, anybody have idea how to add detune pot to one of the oscs,
> just add CV to pin 12 via res or variable res at pin 11?
>
> If you find some more errors, or have some nice mod, please
> share...
>
> Cheers,
>
> marjan