[sdiy] MORE Russian synth schematic...

[mikas]

>> If the transmission gate IS a 4016... the polarity of thsi signal is
>> wrong IMHO.
>> The oscillator gives negative going pulses, which would make the switch
>> closed almost all the time.
> 
> That's right, it looks like a mistake in the schematics. DD4 pin 10 instead
> of pin 11 should drive the pins 13 and 12 of DD9.
> 

by the way, there is another mistake: DD2.3 and DD2.4 should be instead of
DD4.3 and DD4.4

thanks guys :)

>> Any experiences with this type of switched filter ??? I would have to
>> believe that dropping the modulation into the audio range would be heard.
> 
> I built such a VCF some twenty years ago. It was based on a schematics from
> the soviet "Radio" magazine, either... A "classical" variable-state filter
> with three
> op-amps (741 type); the integrator resistors were switched by analog
> switches
> (1/2 of 4016), both driven from a VCO (approx. 10kHz - 1MHz) with a
> constant-width pulse output (1µs).
> Unfortunately, I cannot recall if there was a crosstalk of the switching
> frequency
> on the output... As far as I recall - there was NONE. I think the switching
> frequency is being filtered out in the integrators. An alternative could be
> a
> constant-frequency clock (eg. 1MHz) with pulse-width modulation.
> Note: there are some other musical applications of "switched resistors", for
> example VCA's, voltage-/frequency-controlled mixers, phasers etc. They are
> all very simple! The only difficulty is to generate a high frequency clock
> with fine
> and precisely controlled duty cycle. A task for an FPGA?
> 
> Regards
> Jarek
> 
> 
> 
>