Music Synthesis

As previously discussed here my key problem with my vintage ARP were random spikes and noises happening whenever I was playing. After one evening of work I am glad to say that this is finally fixed !

I correctly identified the CA3080 as the source of the problem and I was lucky enough to find a spare one in my old box of unused components from previous experiments I had done in the 80s !

Replacing the copmponent wasn’t the easiest activity especially with my simple tools. First I had to remove the old chip: unfortunately, at least in my Odyssey version, they come with round metal case (called TO-99 I think) with no socket. You have to be very careful when desoldering it as the legs are bent over the circuit board and you have to use a screwdriver to pull them one by one. Unfortunately a couple of pads in the printed circuit went away because of the heath and the pressure I had to put on legs.

Inserting  the new one it’s as difficult as removing it. You have 8 pins to insert at the same time and it’s very tricky to manage it. Also make sure you insert the right pin numbers. This is quite easy because pin 8 (the one with the marker on the lid) has to be inserted in a position that is near the center of the holes circle in the circuit board.  After 30 mins of attemps the chip was finally there and I was able to start soldering. This was fairly easy but I had to make sure that the legs were soldered to the circuit board tracks wherever a soldering pad was gone.

I remounted everything and my Odyssey is fine. Next step in the journey fixing the Sample and Hold…

After a while I made a resolution to move forward with my restoring activity on my ARP. After fixing the sliders I decided to analyse the intermittent noise problem: basically every time a note is playing you can hear a randomly coming noise (a bit like a wave). I tried lowering oscillators volumes but the noise was still there so it had to be originated in the following chain of modules: VCF and VCA. By googling I found that the CA3080 an Operational Transconductance Amplifier used as VCA core with time often has a tendency to become noisy. Before replacing the IC I decidede to do some testing with an audio probe that confirmed my diagnosis: noise is originating from the IC.

The next step now is finding a replacement component because I believe it is not in production anymore: should I look in eBay or find an alternative ? any suggestion from anybody ?