Here is another simple project. With a little help from the people in this forum (thanks @illucynic), I managed to get a working layout on stripboard for the Korg MS-20 VCA. It follows closely the schematic of the MS-20 service manual for the VCA in the modular section of the synthesiser (labelled MVCA in the manual). The schematic calls for an 4558 op amp, but I changed that to an TL072 and I also changed the transistor to a commonly available 2N3904. Other than that I had to adjust the values of the resistors around the second op amp to fit the (low resistance) LDR I had available at the time. I tried a couple of different LEDs and a 5mm green LED gave the best response. You might need to play around with these components, but I found that there are several combinations that work. I also made the output AC coupled, but this is entirely optional and you can remove the resistor and capacitor without altering the layout on the board.
Now, I don’t have an MS-20 but there are a couple of videos of the MS-20 on youtube that sound similar… In any case, I found this VCA to be very usable, especially since it does not require any fancy or expensive parts.
