VCS rise/fall time issue...

[jonkull]

I finished building my VCS last week and rise didn't work. After some troubleshooting I realized I needed to swap a transistor. Now rise works but I don't seem to have a full range of rise and fall times.

Rise goes from audio rate to about 1 minute with most variation in the 0 to about 9 o'clock area.

Fall goes from audio rate to about 2 seconds with most variation in the final quarter turn of the knob from around 3 o'clock to 5 o'clock.

Does anyone have any suggestions for getting the entire knob range to work and for getting a longer decay time? What could cause this?

[Sound]

Hi Jon.

Some DIY VCS are in my next plans

I would start checking the values of the two resistors in the fall section, they are not labeled in the schematics, the ones from the transistor to the potentiometer. They are 82K and 2k2.

Check if you have shorted the trace from the base of the transistor to the potentiometer with anything.

Check these things with the CV in linear mode.

Regards.

[andrewF]

I notice Ken spec'd log pots for Rise & Fall.
haven't tried, but would it work to swap the outer wires on these pots to get more control of the region where the action is?

[jonkull]

Thanks for the replies. I'll check the resistor values but I'm pretty sure I'm using 82k and 2k2. I'll also have a look at the trace from the pot to the transistor.

[jonkull]

Resistors look correct. No short between the pot/transistors.

[Sound]

Hi Jon.

Edited:
With the decay pot full CW, and linear mode could you measure with a multimeter what voltage do you have at the node within the trhee resistors and the Base of the transistor?

In the decay section of the circuit I mean, sorry but the schematics I have are not labeled.

[jonkull]

If I'm at the spot I think you mean I get 12.17v.