| previous by date | index | next by date |
| previous in topic | topic list | next in topic |
On 12/3/2014 9:10 AM, backshall1@bellsouth.net [PolySix] wrote:
Yes, those old CMOS chips do seem to have a definite shelf life. I’ve seen a few dead 4051 chips in Polysix synths over the past few years. For that first problem, it sounds like it could be either on the mux side or the demux side and there are a couple of 4051 chips on each side. For such a similar sounding problem on both PW and Cutoff, I would expect it to be caused by a component that is common to both settings though, and PW goes through KLM-369 IC2 on the multiplexer side and KLM-367 IC19 on the demultiplexer side , while Cutoff goes through KLM-370 IC1 on the multiplexer side and KLM-367 IC18 on the demultiplexer side. Nothing common there. Are there other knobs affected? It might be a problem with the chip select logic, like an old 4011 getting slow.Don BackshallSent: Wednesday, December 3, 2014 11:12 AMSubject: Re: [PolySix] fully recapping a vintage synthHigh pitched whine could be old 4000 series logic chips. Similar sound ie. 4-5KHz whine arises on Yamaha CS50-80s, and is usually down to the logic chips on the CPU card.
A recap (when done well) is never a bad thing. At least it will improve the sonic characteristics, at best it will yeild improvements in all aspects of operations. It's never a bad place to start...especially if the synth has spent a long time switched off, and forgotten.
On Wednesday, December 3, 2014, jim@saltlands.com [PolySix] <PolySix@yahoogroups.com> wrote:
Understandable concern. This is a general question with the assumption that we're all knowing what we're doing, and with a curiosity specifically toward analog synths 30+ years old or so.
I myself have done a lot of recapping doing tape machine restoration, so am comfortable doing full scale recap overhauls of units.My polysix has a couple minor sonic issues that creep up now and again, and sometimes i have the urge to just put all new caps in and go from there. Sometimes this ends up solving problems, and at worst it just spends a handful of hours of my own time and a few bucks on caps and you get a freshly capped machine.One of the issues is I've got some strange grounding issue related to a multiplexer, i believe. It may be a faulty multiplexer or it may be a component connected to said multiplexer. The symptom is.. on a handful of pots, when i turn them they emit a sound like a square wave if turned at the right pace/quick enough. Sounds exactly like each digital point in the pots signal sent is somehow making this noise. So if you turn it slow, you can not hear it at all because the rate of it happening is low. https://soundcloud.com/circuitsynth/polysix-knob-sound
My other issue is more strange.. a high pitched sustained frequency arises sometimes in certain conditions unknown, and only goes away when you press either A, another note far away from the range of the previous note (ie up high or up low) or B, you hit the Chord Memory or Hold switch, sometimes one or the other. This pitch arrives once or twice every hour of playing. But it goes away fast if you hit the right thing.
This second problem is much more vague to me and perhaps a recap will address it. Could it be a decoupling cap somewhere failing? The pitch is the same exact every time. it's like 4kHz or 5kHz, around there.
I also like synths to be as least noisy as possible, so this is another case for recapping. I've already bypassed the effects section with a direct output and it's a huge improvement, but i still hear a need for it to be even better.