After modifying an old module, In the same case I had my first simple LFO which has always been a little strange . It works well with VCO pitches but not with other stuff like VCAs.
It was an opportunity to test it.
And I actually measured around -2V and + 2V max at the output !
I rechecked everything several times, the schem, the component values, the solder … everything looks fine. I don’t understand.
Here is the schematic I used (sorry i don’t know the source), I just changed a few resistance values next to the Range pot to adjust the speed like i want it, but I don’t think that’s the problem.
Could someone tell me what resistance values I could change to increase the output voltage please.
This appears to be identical to version 1.2 of David Haillant’s Simple LFO (he’s now on version 1.4, which I think only changes the LED driver). As noted R10 and R11 are changed to 22k and 100k from Haillant’s 2.2k and 10k. That shouldn’t affect the gain. Haillant says the output should be ±10 V and I’ve done a simulation that more or less reproduces that. The square wave is produced by a comparator that should give ±11 V or so at U1 pin 7, and then U1C is a gain stage with gain 1.22 so the only thing that should limit its amplitude is the pot R9. So there must be some error in your build. As you say, changing the resistances on the left side shouldn’t affect the amplitude.
Wait, was it the triangle or the square or both that was ±2 V? What were the resistor changes?
Also, I just noticed another significant difference: In Haillant’s version the LFO Square tag is on U1 pin 7. In your version it’s on the line at the top, which connects to pin 7 via a voltage divider which will reduce the amplitude to about ±8 V. Of course that doesn’t explain your ±2 V.
Ah — now I see your version corresponds exactly (? — except the noted resistor changes) to Version 1.1.
