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

[Stewart Pye]

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
>
>