Here is how you can improve the sweep ratio of the EM3207 Electric Mistress if it is poor (this is quite likely as I explain below !!!).
Here's the modification: Replace R24 (30k) and R26 (10k) by a single 100k multi-turn (precision) trim-pot.
Pins 1 and 2 of the trim-pot should replace R24, and pins 2 and 3 should replace R26.
This effectively gives us the ability to trim the ratio of R24 to R26.
Question for DrAlx:
I'm working on a "version 5" build using an original R5106 that I came across.
I would like to implement your increased sweep mod, but I'm having a bit of trouble interpreting your description as to the placement of the 100K trimmer.
I worked on a drawing to replace the 30K and the 10K (version 5 = 11K) resistors with the 100K trimmer as described, (Pins 1 and 2 of the trim-pot should replace R24, and pins 2 and 3 should replace R26.) but this configuration makes a direct connection between the two op amp outputs with no resistance between them.
Looking at this schematic below from the Electric Mistress Mystery Page, the mod would involve removing the fixed 30k and the 11k resistors and using a 100k pot as follows.
The left pin of the pot goes to pin1 of the LM324.
The right pin of the pot goes to pin 8 of the LM324.
The middle pin of the pot goes to pin 3 of the LM324
Your first LFO pic is almost right (but the middle pin of the pot should go to pin 3 only).
One thing to point out is that I would use an internal trim-pot for this mod rather than a pot.
The reason being that if you try and generate too big a triangle wave, then the comparator part of the circuit that generates the clock will stop at the top of the sweep.
This will give an audible pop and then silence at the top part of the sweep (a "drop-out").
If I were going to expose this mod as an extra control pot on the front of the effects box (called "RATIO" or something),
then instead of connecting the left pin of this new RATIO pot directly to pin 1 of the LM324, I would make that connection through an extra resistor.
That will stop the sweep from trying to go too high and causing a drop-out.
I couldn't tell you what resistor to use, and I would probably use an extra trim pot for it (adjustable from 0 to 100k say).
I'd set the trim pot at zero and gradually increase it until the SWEEP RATIO pot stopped giving "drop outs" at the top of the sweep.
