I had a similar problem. Basically I was loosing amplitude of the
signal through the capacitor at < 5 Hz. Eventually, it would fall
below the threshold of the transistor. There is plenty of signal to
clock the 4024, it's just at the wrong level. I replaced that circuit
with a two resistor and diode clamp to clock the 4024 directly.
Details are at
http://modularsynthesis.com/cgs/cgs.htm
Yours sounds similar, but different in that it stops at a higher
frequency.
Later, Richard Brewster posted a message for a similar problem: "I am
finishing mine, finally. I found an error in the clock coupling
circuit etch. The diode that is supposed to clamp the voltage on the
transistor base is not connected to the base of the transistor, but
rather to the opposite end of the 100K series input resistor. I fixed
this (cut the connection to the non-grounded end of the diode and put
a jumper to the correct spot). I also DC-coupled (omitted the 100nf
cap) that delivers the ramp out of the VCO."
That might have fixed mine but I never tried it. Richard also posted
another message about an error on the damping potentiometer wiring
diagram.
Dave
--- In cgs_synth@yahoogroups.com, Anthony Rolando <goldenechos@...>
wrote:
connected to the CD4024).
was a good signal at pin 6 of the 3140. The collect of the BC547 was
just setting at 7V when the frequency was set to (or beyond) this low
point.
entire range of the Freqency Panel control. The filter sonds really
cool.
circit design in order to get it to work.
signal through the capacitor at < 5 Hz. Eventually, it would fall
below the threshold of the transistor. There is plenty of signal to
clock the 4024, it's just at the wrong level. I replaced that circuit
with a two resistor and diode clamp to clock the 4024 directly.
Details are at
http://modularsynthesis.com/cgs/cgs.htm
Yours sounds similar, but different in that it stops at a higher
frequency.
Later, Richard Brewster posted a message for a similar problem: "I am
finishing mine, finally. I found an error in the clock coupling
circuit etch. The diode that is supposed to clamp the voltage on the
transistor base is not connected to the base of the transistor, but
rather to the opposite end of the 100K series input resistor. I fixed
this (cut the connection to the non-grounded end of the diode and put
a jumper to the correct spot). I also DC-coupled (omitted the 100nf
cap) that delivers the ramp out of the VCO."
That might have fixed mine but I never tried it. Richard also posted
another message about an error on the damping potentiometer wiring
diagram.
Dave
--- In cgs_synth@yahoogroups.com, Anthony Rolando <goldenechos@...>
wrote:
>couple of questions.
>
> Hello, just finished building the Bi N Tic filter/ osc. and I have a
>basically only worked from about 12:00 on...
> I was getting quite a bit of slop on the Frequency panel control. It
>100k that is connected to the base of the BC547`(of the collector is
> I traced this down to the 100n cap between pin 6 of the 3140 and the
connected to the CD4024).
>frequency, the Saw wave would all but disappear AFTER the 100n cap. It
> What was happening is that once the VCO went below a certain
was a good signal at pin 6 of the 3140. The collect of the BC547 was
just setting at 7V when the frequency was set to (or beyond) this low
point.
>With the 100n out of circuit I get good strong oscillations for the
> I was able to rectify the situation (I think) by bridging the 100n.
entire range of the Freqency Panel control. The filter sonds really
cool.
>appreciate. I do not like the idea of removing something from the
> Any insight as to what might be happening would be greatly
circit design in order to get it to work.
>Stop by today.
> Thanx,
>
> Tony
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