Arp Pro-Soloist

Synth Repair
1

Hi folks,

I have an Arp Pro-Soloist that I got serviced about 12 years ago. The shop I used to go to has stopped doing repairs. It’s been “dead” a few years and I’m looking to get it back up and running (very late on that; life gets in the way).

It worked great until a few years ago until some of the voices stopped working, then they all stopped working. I do have the repair manual / schematics, but I’m short on time, so I’m wondering if any experts out there might have some ideas to get me in the ballpark. I suspect the issue is in the voice selection/activation circuitry vs. the audio signal path itself, based on the way it degraded as described.

I hope it is a simple fix, like some single IC died. I will go dig out my schematics but wanted to ask preemptively in case anyone out there has an “aha”.

Thanks,
Chuck

2

Any idea if the tantalum capacitors have been replaced? Those significantly degrade over the years and eventually cause a lot of the issues that happen with Arp synths. Usually the first thing we do when working on an Arp is replace all of them with electrolytic capacitors.

It can be pretty hard to tell whether it’s the audio circuitry or the voice selection circuitry on these synths causing problems. The Pro Soloist has a sort of modular design where the oscillator gets routed through different available circuits for processing. For example, some voices like Tuba make use of the high-pass filter whereas Oboe doesn’t. In a synth where the high-pass filter circuit has failed then all of the voices using that circuitry will drop out but others will work fine.

Since you lost all voices there’s a good chance there’s a problem on the waveform generator board or something else all voices have in common. If you have access to an oscilloscope it will greatly help narrow down where the problem is because you can see where the signal drops out.

However, it could be the voice selection circuitry but I haven’t seen a problem there for one that I’ve worked on. But I’ve only worked on a few. Page 8 of the service manual has truth tables to help with verifying that circuitry is working correctly. Hope this helps, sorry it’s not a very short solution!