[sdiy] [AH] SEM LFO square wave mod...

[James Coplin]

Exactly what I needed!  Thank-you for taking the time to do some hand
holding.  I wasn't familiar with a voltage divider and I've found some
good references since you mentioned it.  The output is working fine now.
Thanks!

James R. Coplin

> -----Original Message-----
> From: Stewart Pye [mailto:stewpye at optusnet.com.au]
> Sent: Saturday, May 28, 2011 3:20 PM
> To: James Coplin
> Cc: synth-diy at dropmix.xs4all.nl
> Subject: Re: [sdiy] [AH] SEM LFO square wave mod...
>
> Hi James,
>
> The positive and negative excursions should be roughly equal. It seems
> like you don't have a good ground reference for your measurements.
> There's no way it could be -19V when running from a -15V supply.
>
> The 27V p-p value seems reasonable as the op amp is running from +/-15V
> (30 total) and the op amp can't quite swing to the rails. You just need
> a voltage divider. We'll make the resistors low in value for a lowish
> output impedance but high enough that the LM741 can drive them. A 1.8 k
> for the top resistor (to the op amp output) and 1k for the bottom
> resistor (to ground) should get you close to 10V p-p. The junction of
> the resistors is the square wave output.
>
> This may help;
> http://www.raltron.com/cust/tools/voltage_divider.asp
>
> Stew.
>
>
> James Coplin wrote:
> > So, I found the square wave in the LFO.  Now, I am having trouble
> padding
> > it down to standard CV ranges.  Mine is swinging from ~8v to ~-19v.
> I
> > can't get the voltage down to match the internal triangle or sin wave.
> I
> > put a 1.5M ohm resistor on it and it only knocked a couple volts off.
> > What would be the best way to knock this down to a usable range?
> > Alternately, would I just be better off making a comparator and using
> the
> > triangle to generate a square wave in the proper range?
> >
> > James R. Coplin
> >
> >