Doepfer

hi group,

been having lots of fun with the a113 subharmonic generator in the last few days, and i've been wondering how the rectangle to sawtooth conversion works.

any tips?

cheers,

stu

> hi group,
>
> been having lots of fun with the a113 subharmonic generator in
> the last few days, and i've been wondering how the rectangle to
> sawtooth conversion works.
>
> any tips?
>
> cheers,
>
> stu

A capacitor is charged by a voltage controlled current source (VCCS) and
reset by the falling edge of the rectangle. The control voltage of the VCCS
is generated by a simple frequency-to-voltage converter (nothing but a
one-shot multivibrator triggered by the rectangle and a passive low pass
filter). Far away from beeing a perfect sawtooth (same as the original
Trautonium) but the right choice for this application.

Best wishes
Dieter Doepfer

cheers dieter.

i'll have to do a little research to find out what some of that means, particularly the multivibrator, but that's part of the fun.

anyway, the a113 is a great module. the tones available by using the upside down harmonic series are really worth having.

is there somewhere on the pcb where one could tap the square waves before they get sawtoothed? i'm putting a rack together based around the a113 and the a107, and the extra waveform would be a useful extension. or so i assume, it's early days yet :)

thanks,

stu

> 
> A capacitor is charged by a voltage controlled current source (VCCS) and
> reset by the falling edge of the rectangle. The control voltage of the VCCS
> is generated by a simple frequency-to-voltage converter (nothing but a
> one-shot multivibrator triggered by the rectangle and a passive low pass
> filter). Far away from beeing a perfect sawtooth (same as the original
> Trautonium) but the right choice for this application.
> 
> Best wishes
> Dieter Doepfer
>

> cheers dieter.
>
> i'll have to do a little research to find out what some of that
> means, particularly the multivibrator, but that's part of the fun.
>
> anyway, the a113 is a great module. the tones available by using
> the upside down harmonic series are really worth having.
>
> is there somewhere on the pcb where one could tap the square
> waves before they get sawtoothed? i'm putting a rack together
> based around the a113 and the a107, and the extra waveform would
> be a useful extension. or so i assume, it's early days yet :)
>
> thanks,
>
> stu

The rectangles are available as the port outputs RB1...RB4 (pins 22...25) of
the microcontroller. If you want to use these at outputs you have to insert
protection resistors (~1k) between the corresponding pin and the sockets.
Otherwise the microcontroller may be damaged when a plug is inserted into
the socket (because of the short circuit that is generated for a short time
when the plug is inserted).

Best wishes
Dieter Doepfer

great, thanks for the reply.

stu

> The rectangles are available as the port outputs RB1...RB4 (pins 22...25) of
> the microcontroller. If you want to use these at outputs you have to insert
> protection resistors (~1k) between the corresponding pin and the sockets.
> Otherwise the microcontroller may be damaged when a plug is inserted into
> the socket (because of the short circuit that is generated for a short time
> when the plug is inserted).
> 
> Best wishes
> Dieter Doepfer
>