Korg Polysix synthesizer

[SteveNielsen]

Re: Korg Polysix synthesizer

Well, I'm gonna table this project. The PSU works fine and is within specs however there is a lot more wrong with this thing than I am capable of dealing with at this time without a scope, and I need to make room in my small work area for something else.

[SteveNielsen]

Re: Korg Polysix synthesizer

I did and it appears to work fine with and without loads on +15 & -15 outputs. I read 7~8mV AC ripple on all outputs either with or without a load. All voltages are within the tights specs. I believe it will all fit now but I'm gonna tack the caps down with some hot glue. They're a bit mobile and the trace pads on this old board don't take kindly movement of parts. Then I'll have to do some reassembling and see if the whole synth works now.

[stj]

Re: Korg Polysix synthesizer

go for it

[SteveNielsen]

Re: Korg Polysix synthesizer

Back to the Korg... I have some concern about the stacked caps I'm using for C13 fitting with the case closed. I do have another 6800uF 56v cap I could use in its place and save some space but I've already bumped C13 from 2200uF to 2700uF. Is using the 6800uF for C13 out of the question?

[stj]

Re: Korg Polysix synthesizer

some car stereo's and mini hifi's use them.

[SteveNielsen]

Re: Korg Polysix synthesizer

I see. I haven't got one that I know of but I've issued myself a BOLO for one.

[stj]

Re: Korg Polysix synthesizer

not exactly a rotary switch - not in the traditional sense.

it has 2 outputs, and lots - usually 10-50 clicks per revolution.
it switches the 2 outputs in sequence as you turn it - the sequence indicates the direction it's turning.
you sometimes find them used as digital volume controls or channel selectors.

[SteveNielsen]

Re: Korg Polysix synthesizer

Haha! I know, you want to get back to the tester! I do too! I have to wait and see if I can buy the chip and programmer for that, and that'll be a bit, I get $$ tomorrow, then ordering and waiting. You mean a rotary switch? I think I've got one somewhere. If not, please elaborate.

[stj]

Re: Korg Polysix synthesizer

anything wih a rotary control that just keeps turning.

i'm asking because you can add one to your component tester to use extra menu's / functions in the new software.

[SteveNielsen]

Re: Korg Polysix synthesizer

Yeah, and there's a metric butt-load of op-amps in this thing.

No, I'm afraid I don't have a rotary encoder unless there's one inside of something in my pile of junk I haven't operated on yet. What would have one?

[stj]

Re: Korg Polysix synthesizer

btw, do you have a rotary-encoder in your spares box?

[stj]

Re: Korg Polysix synthesizer

i suspect that the load will be all over the place once the cpu starts sequencing stuff through all those op-amps.

i dont know how much current those use, but they often run pretty warm!

[SteveNielsen]

Re: Korg Polysix synthesizer

Oh I'm not leaving it like that, it was just a test while I've got the board out and it got me wondering why they used such high cap values in the 1st place, most linear PSUs I've seen don't use anywhere near that high of capacitance in the rectifier filtering. I thought the capacitance was selected mostly based on the ripple frequency and the circuit impedance.

For checking out how the PSU does hooked up to the rest of the boards I will revert back to the stacked caps as you advise, but no they won't quite fit with the case closed unless I string them off to the side somehow. I will replace them with the proper parts once I obtain them (which will be a while unless I happen to salvage some good ones).

[Agent24]

Re: Korg Polysix synthesizer

Yeah you're better off staying with the same value or a little higher. It's not good practice to reduce capacitance unless you test and measure the system thoroughly and find it doesn't make a difference.

You don't want to go chasing another non-existent fault later on because you used capacitors that were too small. If the larger, paralleled ones fit, just use those.

[SteveNielsen]

Re: Korg Polysix synthesizer

I'll eventually get the right spec caps for it when I can afford to. I'm a poor retired man on a fixed income All I have to use are salvaged parts. In the meantime I'm experimenting

[stj]

Re: Korg Polysix synthesizer

it may not cope well with a varying load.

[SteveNielsen]

Re: Korg Polysix synthesizer

What would be the danger of significantly reducing the capacitance on C13 and C14?

I tried a 1200uF in place of the 2200uF (C13) and a 1500uF in place of the 4700uF (C14). The output is the same with or without dummy loads. I checked AC ripple at the outputs and it is below 5mV, same as using the stacked caps for higher capacitance.

[SteveNielsen]

Re: Korg Polysix synthesizer

Yeah, I already miss that little guy.

[stj]

Re: Korg Polysix synthesizer

yes, i was just thinking about that, all those op-amps and the logic boards.

lets switch to fixing your component tester - go link the red battery wire to the regulator input and see if it turns on when you connect the battery.

[SteveNielsen]

Re: Korg Polysix synthesizer

LOL! True. True. Well, we'll see how many more pages it gets to because the PSU of this thing is just the beginning of the project. There are like 9 or 10 other boards in this thing!