Thanks a lot Tom,

I've overseen the difference of the multimode lowpass vs. SVF.
Good read on the crossover circuit and the phase shifting! I read several times that the caps seem to cause phase issues but with an inverting stage at either the HP or LP it seems fine.

Thank you too for the explanation of the simplified SVF circuit earlier.

How about using a quad VCA like the AS2164 or is it wise to rather take two seperate AS3360s? Two VCAs for the SVF frequency control and the other two for the L/R panning?
Interesting would be if the AS2164 / AS3360 works fine with microcontrollers like PIC, Attiny85, Raspberry Pico.
Would be cool to use something different than LDRs.

I don't like the idea of using the LM13700 due to the buffers that can't substitue a proper TL72 buffer for each side.

A fast switching VCA trem is probably close enough for me to ditch ring modulation.

The new set of voltages is helpful. It clearly shows that the suspect JFET is not being completely allowed to turn on. In fact, it shows that when it's supposed to be on (that is, its gate allowed to float near the channel voltage) it in fact runs right in the middle of the range between on and off. The datasheet for the J113 shows a Vgsoff of -0.5 to -3V.
With -1.3-ish volts between the gate and channel, it's riding between on and off, which would account for the buzzy distortion too, as the signal voltage itself wobbled it across the on/off line.
Now for finding the cause.
The JFET switching relies on the source and drain being held up in the middle of the supply, at roughly the voltage your schematic marks as "+4V".  The gate in question is driven by the G1 signal (if I'm reading the schemo correctly) with a diode, a capacitor to ground, and a 1M resistor to the not-Q  signal of the 4013. Just to be sure, put your meter on the not-Q pin of the 4013 and toggle the bypass switch. Does it go to 8.7 and ground? (your schemo says yes, but I put this step in just to be sure)
Now put your meter on the junction of the 1M, the cap to ground, and the diode. Toggle the bypass switch again. Does it still go up to 8.7 and down to ground?
This point has to rise above the nominal +4V, and  down to nearly 0V. If it doesn't rise above the +4V a good amount, some component or solder joint is faulty and keeping it from rising. If it doesn't go nearly to 0V, something is keeping it from doing so. A prime suspect in this case would be the diode being faulty or some current leakage into the junction of the diode anode and JFET gate. This could be a faulty JFET, or maybe leakage or solder short on the board.

For now i put the 3pdt back

Found the problem. I traced out the cvircuit and found everything was dying at pin 7 on IC1, so I swapped out the 4558 (Socketed) and everything started working like a champ. I had a feeling that was going to be the issue. Just wish I had gone with my gut and started there.

I have read they are very suspectable to static esd damage.

Quote from: PRR on Today at 12:29:52 PMI think it is actually a CHOICE of transistor and pin-out.

Thanks Paul..!!

Didn't notice 3904 pins numeration corresponding to IC transistor array..

I can relate to your skepticism.
In a pinch, I'd just check the complimentary darlington pair to ensure that they are there. Going further, I'd check on the opamp portion to see if it's in-line with a couple of the "Typical Applications" examples in the datasheets.
Even more simple, make it a unitity gain buffer and see if the output voltage matches the input voltage.

Consider the 3094 a pimitive single channel LM13600, where many applications can be interchangeable with the proper rework and minimal value changes if any at all.
-That one is if you'd rather tinker and not run the math.

Quote from: antonis on Today at 05:11:32 AMFunny parallel BJTs of different h_FEs and V_BEs configuration..

I think it is actually a CHOICE of transistor and pin-out.

Quote from: GGBB on Today at 10:33:00 AMSecond - I recommend you breadboard one of the test circuits provided in the datasheet and use that to test your chips.

THanks for your answer, i don't know which one of the test circuits will be enough to check. Can you recomend me one of them?

thanks again

Quote from: mozz on Today at 10:12:15 AMWhere are you located at?

hello, I live in the city of Linares, Chile