[sdiy] Help needed! - EFM VCO4d

[Jay Schwichtenberg]

james,

The outputs of this are not normalized (all the same). Their output level
and offset varies.

Put ~3K-5K pull up between the output of the pulse comparator and ground.
That will square up the edges. The comparator is open collector and needs a
pull up if it is going to work with a load. Also I've added a trim pot in
series with R23 (22K) in the sine circuit to adjust the amplitude of the
signal going into the CA3080 for a better sine.

Jay S.

*> -----Original Message-----
*> From: owner-synth-diy at dropmix.xs4all.nl
*> [mailto:owner-synth-diy at dropmix.xs4all.nl]On Behalf Of James Dunn
*> Sent: Monday, May 22, 2006 7:48 AM
*> To: synth diy
*> Subject: [sdiy] Help needed! - EFM VCO4d
*>
*>
*> Hi all,
*>
*> I've had this board for awhile, but just working on it again now - the
*> problem I have is with the pulse output. When I plug a jack in, it
*> disappears! There are some pictures of the waveforms here:
*>
*> http://www.4thharmonic.com/images/VCO4d/Pulse.gif
*> http://www.4thharmonic.com/images/VCO4d/Saw.gif
*> http://www.4thharmonic.com/images/VCO4d/Triangle.gif
*> http://www.4thharmonic.com/images/VCO4d/Sine.gif
*>
*> As you can see, the pulse output doesn't look right anyway, and there
*> seems to be a large offset in it. I gone over the whole board many
*> times, and can't seem to find any faults - I'm assuming it must be
*> something to do with the pulse waveshaping section - any ideas?
*>
*> yours hopefully
*>
*> James
*>
*> PS, there appears to be a small glitch in the sine wave too, more
*> noticeable at higher frequencies.
*>