Korg DW8000, Mono/Poly, MS-20...

I don't suppose anyone here knows how to retune the individual voices on a Poly61 do they?

Each of the 6 voices on my poly61 are slightly out of tune with each other which makes playing anything useful impossible as every note is tuned differently to the previous one. There are trimmers on the board for each voice but they are only for VCA, EG, FC (cutoff) and Resonance.

I can't believe there wouldn't be some method of retuning the voices to each other, unless of course its just so old that components have started to fail at different rates.

My Poly-61M has some serious battery corrosion issues on the main board (KLM-509A) and is currently out of commission until I repair that, but since I've already got it town apart, I can look at the analog board and tell you it's got several trim pots for each voice labeled: VCA ADJ, EG ADJ, FC ADJ, and RES ADJ. Unfortunately these are not responsible for adjusting the pitch.

It also is a good time to point out that the Poly-61 has DCOs, which implies that the tuning is digitally controlled, and probably compensated as well. This was a "feature" after a decade of completely analog synths that wouldn't stay intoned. So overall, I don't think they really intended for the oscillators to be trimmed.

I expect that your tuning problems might originate from some bad components -- resistors and/or capacitors which may have been faulty. It may be possible to inspect them closer to see if they are leaking, and you can use a multimeter to check the resistors while the power is off.

Check out my Poly-61 photos in the Photos section if anyone else wants a closer look! -pc

--- In DW8000@yahoogroups.com, "crustypaul" <crustypaul@...> wrote:
>
> I don't suppose anyone here knows how to retune the individual voices on a Poly61 do they?
>
> Each of the 6 voices on my poly61 are slightly out of tune with each other which makes playing anything useful impossible as every note is tuned differently to the previous one. There are trimmers on the board for each voice but they are only for VCA, EG, FC (cutoff) and Resonance.
>
> I can't believe there wouldn't be some method of retuning the voices to each other, unless of course its just so old that components have started to fail at different rates.

Dear friend,
I have a trusty DW8000 on wich I dared to put my unexperienced hands upon, in order to try and " customize" it a little, using the famous " D****ss" system... All began when I heard some little noises on some waveforms, probably digital low resolution ones, but I thougt it could be a need of trimmers setting... So I completely upset my machine, but at least I learned how good and close to analog it was engineered. So, since Your synth is so similar to mine with regarding to the single voice " strip channel" ,  is another good idea to purchase the service manual and follow the suggestions to retune and set correctly resonance, volume trimmers etc, since it seemed to me they heavily influence each other, with so many combinations You can't achieve a good result without it...There should be reported all the values You have to restore with a screwdriver and a tester, and so on.. If You, or a former owner, didn't put his hands on these trimmers, then it could really be the option the other kind member suggested.
Hope it could help You,
Regards,
Francesco Manduca.

--- Gio 17/9/09, crustypaul <crustypaul@...> ha scritto:

Da: crustypaul <crustypaul@...>
Oggetto: [DW8000] Tuing poly61 voices
A: DW8000@yahoogroups.com
Data: Giovedì 17 settembre 2009, 19:53

 

I don't suppose anyone here knows how to retune the individual voices on a Poly61 do they?

Each of the 6 voices on my poly61 are slightly out of tune with each other which makes playing anything useful impossible as every note is tuned differently to the previous one. There are trimmers on the board for each voice but they are only for VCA, EG, FC (cutoff) and Resonance.

I can't believe there wouldn't be some method of retuning the voices to each other, unless of course its just so old that components have started to fail at different rates.

Theres a few places around the net that state that DCO1 is in fact a VCO 'by the signal generation method', whatever they mean by that. I haven't checked it out yet but you are right, if they are 100% digital then its unlikely there would be any way to retune the voices as in theory there should be no way they could drift.

I've been through the service manual and adjusted the trimmers on each voice so that the filter, EG and VCA are as identical as i can get them but the tuning remains a problem.

There aren't any electrolytics in the area of the board that seems to control the pitch of each voice so that removes the obvious possibility of failing caps. I guess its time to get out the multimeter and test every voice for differences.

--- In DW8000@yahoogroups.com, "PC" <paul@...> wrote:
>
> My Poly-61M has some serious battery corrosion issues on the main board (KLM-509A) and is currently out of commission until I repair that, but since I've already got it town apart, I can look at the analog board and tell you it's got several trim pots for each voice labeled: VCA ADJ, EG ADJ, FC ADJ, and RES ADJ. Unfortunately these are not responsible for adjusting the pitch.
>
> It also is a good time to point out that the Poly-61 has DCOs, which implies that the tuning is digitally controlled, and probably compensated as well. This was a "feature" after a decade of completely analog synths that wouldn't stay intoned. So overall, I don't think they really intended for the oscillators to be trimmed.
>
> I expect that your tuning problems might originate from some bad components -- resistors and/or capacitors which may have been faulty. It may be possible to inspect them closer to see if they are leaking, and you can use a multimeter to check the resistors while the power is off.
>
> Check out my Poly-61 photos in the Photos section if anyone else wants a closer look! -pc

I've heard something similar -- From that guy who seriously modded his poly-61 on YouTube actually. He say DCO2 is completely digital.

But you can have VCOs generating a waveform, while using a D/A to control and automatically trim the voltage it receives based on a sampled frequency that is compared against a digital clock. Synthesizers like the Jupiter-8 and Sequential Max have VCOs that are digitally trimmed with a built-in auto-tune function.

The Poly-61 is probably similar in that respect, and I would suspect resistors and caps in the area of the A/D or divider circuit they are using to sample the VCO outputs. If these voltages are not correct, or the caps are discharging too soon, the CPU will interpret the frequency incorrectly. That's just my guess... I bet there's nothing at all wrong on the voice board.

Did you have to replace your battery? Did it possibly damage the main board at some point? Mine's completely hosed and it's difficult to tell which components are damaged and which only look bad. Even the traces are suspect. -pc

--- In DW8000@yahoogroups.com, "crustypaul" <crustypaul@...> wrote:
>
> Theres a few places around the net that state that DCO1 is in fact a VCO 'by the signal generation method', whatever they mean by that. I haven't checked it out yet but you are right, if they are 100% digital then its unlikely there would be any way to retune the voices as in theory there should be no way they could drift.

i was talking to the guy that wrote this incredibly useful guide on the poly61 about this.

http://www.mik-music.org/tiki-index.php?page=Korg%20Poly-61%20Repair&pagenum=1

Because DCO1 is a digitally controlled VCO theres no way to individually tune the voices but his idea was that i was just getting the raw VCO and it had lost its digital control. I was getting nothing on my scope where i was meant to be seeing the TTL signals that control the pitch for the DCO1 so i would say he was right.

I'm using the past tense here as i was just tracking down the source of the clock signals when i went to make a cup of tea, and when i came back and turned the Poly back on it was dead. Now when i turn it on all the button LED's come on at once, the numerical LED displays stay dark and it won't respond to any button or key presses.

I'm guessing this is going to be down to some crappy logic IC dying for no apparent reason but its a pain in the arse trying to track it down. Its been suggested to me that the 4051 IC's were causing the problem with the tuning in the first place. I'm certainly a little wary of these chips after rebuilding a Poly800 which had at least 5 dead 4000 series logic IC's

The battery appears to have been replaced on this poly61 some time fairly recently already. I can see that there was some very slight leakage at some point but its been cleaned up well.

> I've heard something similar -- From that guy who seriously modded his poly-61 on YouTube actually. He say DCO2 is completely digital.
>
> But you can have VCOs generating a waveform, while using a D/A to control and automatically trim the voltage it receives based on a sampled frequency that is compared against a digital clock. Synthesizers like the Jupiter-8 and Sequential Max have VCOs that are digitally trimmed with a built-in auto-tune function.
>
> The Poly-61 is probably similar in that respect, and I would suspect resistors and caps in the area of the A/D or divider circuit they are using to sample the VCO outputs. If these voltages are not correct, or the caps are discharging too soon, the CPU will interpret the frequency incorrectly. That's just my guess... I bet there's nothing at all wrong on the voice board.
>
> Did you have to replace your battery? Did it possibly damage the main board at some point? Mine's completely hosed and it's difficult to tell which components are damaged and which only look bad. Even the traces are suspect. -pc