Analog synth tuning...

CalvaryBand · 20th September 2008

So up until yesterday I haven't REALLY had to tune any of my analog gear. But I got something new in the mail, a Korg Polysix. And he is totally out of tune and I really don't know what I'm doing. There are trim pots inside for each of the voices, I hold down the middle A key and tune it to A440 on my tuner and all of the 6 voices tune right, all the way up to the top of the keyboard the thing plays fine, but below that octave it's detuned. Vice versa as well, if I tune below the middle the bottom is in tune but the top is not. Any help would be massively appreciated as this is fairly annoying and not much information is out there about how to manually tune these things by hand.

triez · 20th September 2008

If all of the voices are out then it is not likely that the voices are the problem, it is more likely that the power supply has drifted off spec. or there is an issue with keyboard scaling. Best to download the full calibration procedure and start at the top with making sure the power supply is properly adjusted. You will need a tuner and a digital multimeter.

CalvaryBand · 20th September 2008

Well I followed the service manual and got the thing in tune just fine across the scale but there is another problem that I think could be attributed to that PSU you are talking about... Two voices don't work through the envelope generator. The work when I bypass it but not with the ADSR on. Kind of strange.

Yeah I do need multimeter, I used a guitar tuner set to 440 and that worked fine, but these dropped voices, not sure what that could be.

vespiz · 20th September 2008

Sounds like my P6! (Well, nearly anyways).

I can't get it tuned anymore, I've tried tuning it several times, but it won't scale right. I get one end of the keyboard right, and the other end sounds like modern music...

CalvaryBand · 20th September 2008

Still can't get those voices to work in poly mode through the EG. Eh. I'll get it fixed one day. The ****er sounds incredible in unison mode though; all 6 voices work in that. I am quite impressed with this synth and have to say even though it only 90% of works (bought it off eBay, the guy put a new battery in and replaced all the keys, etc) it was worth my money. Opening it up and messing with the trim pots is very fun as well; Maxing the resonance and gain out eats my ears alive.

revstate · 21st September 2008

i have had my polysix in for a complete retuning and calibration. the tech replaced all of the bad chips, added midi, and repaired the entire main cpu board. and after i got it back, it still drifts... why you ask? because it has ssm vco chips... they drift. they drifted when it came out, and they drift to this day. either don't worry, because it's supposed to sound like that, or older vco synths are not for you. i keep a tuner plugin armed in my daw (logic) on all of my inputs that have a vco synth plugged into them (and all of my synths are vco ^_^).

CalvaryBand · 21st September 2008

I don't mind the drift. I followed the manual and it's in tune now (well, tuned enough to sound good).

The dropped voices in poly mode are whats bothering me. Without the EG poly mode isn't very useful.

sizzlemeister · 21st September 2008

The P6 doesn't have SSM VCOs, just the filters and VCAs are SSM ICs.

The OP probably has two bad SSM 2056s I imagine. If you look at the voice section while you have it open and play notes you'll notice little red LEDs cycling through the voices as you play them. Identify which voices are the ones that drop. Swap the SSM 2056s ICs in those voices with two voices that work. If the latter drop now after switching, then those ICs are bad.

If not, then you work backwards; there may a problem with the opamp that generates the CVs from the DAC. I can't remember how the P6 handles CVs for each voice, but if they're split up from the DAC then there may be a multiplying IC in there that is bad.

If the SSM is bad, you may want to replace the cap that protects it after you find some new 2056s (and let me know where you get your 2056s from, please, thanks).

Forgot to mention that if your Polysix drifts, you need to replace the mysterious PC1 part on the voice board. IIRC it's an optoisolator. Works like a charm on the tuning.

revstate · 1st October 2008

Quote:

Originally Posted by sizzlemeister

The P6 doesn't have SSM VCOs, just the filters and VCAs are SSM ICs.

it doesn't have the SSM2033 VCO chips like the mono/poly??

what does it have for VCO then?

zenguru · 2nd October 2008

Ooohhh, lots of useful information here, thank you all! Especially this I found very interesting:

Quote:

Originally Posted by sizzlemeister

Forgot to mention that if your Polysix drifts, you need to replace the mysterious PC1 part on the voice board. IIRC it's an optoisolator. Works like a charm on the tuning.

Can you recommend a suitable replacement part?

I tried to tune my P6 with a tuning fork. That's right, a TUNING FORK. The result was quite shitty. Ok, I'm going to use a real tuner, I just didn't have anything better at my hands at the moment.

About the calibration procedure... I found some parts of it a little bit confusing. Maybe I just wasn't paying too much attention or I misunderstood something. Anyway, some of the tweaking didn't really do anything... VR1 for example. What's the "circuit board slide swich"? I assume it's the "SW1" on the KLM-366 board, but which position is "away from VR1"? What's the function of it, anyway?

Sorry if I'm stupid or something, I'm just an electronic engineer, forgive me :D

Mike6581 · 2nd October 2008

Depending on how the voice allocation goes on that synth, try playing the same note (an octave down) six times. I'm not sure if it's the case with Korgs but the voice allocation mode found in Roland synths (Junos and Jupiters) and the Prophet 08 works with each voice taking turns to play so if you press a key over and over, a different voice is playing it. If the "level of out of tuneness" stays the same with each key press then the that's probably not a dodgy oscillator chip.

CalvaryBand · 4th October 2008

Horray, I got my Jupiter 8 in the mail and it's completely in tune and stays in tune!

But alas, just like my Polysix one voice is bad. At least the JP8 has a usable mode with one voice gone bad.

Mike6581 · 6th October 2008

Oh eck! You don't have much luck with synthesizers do you? How is the dead voice manifesting itself? Is it missing out every eight note you play or every eight key on the keyboard? If it's the former you've probably got a dead voice. If it's the latter there might be a problem with the keyboard scanner (not sure of the correct lingo). My Jupiter 8 has a dry joint somewhere in the keyboard scanning hardware and did this a while back after being in transport (even thought it was in a flight case). After much cursing and swearing I gave it a smack (on the bottom in the middle) and it started working again. I don't suggest you try this as it'll probably do more harm than good, but at the time for me the red mist was running the show.

There are people out there who can fix Jupiters still, though it'll probably cost you a fair bit. You could try fixing it yourself and sourcing the parts, but Jupiter 8s are very, very complicated beasts. There's quite a large number of PCBs, all interconnected, under it's charcoal grey case. I'd suggest you do get it repaired as Unison mode does get a bit intense after a while and you'll be missing out on the lovely pads that the Jupiter is so famous for.

20th September 2008	#1
CalvaryBand Gear maniac Join Date: Sep 2008 Posts: 218 Thread Starter	Analog synth tuning... So up until yesterday I haven't REALLY had to tune any of my analog gear. But I got something new in the mail, a Korg Polysix. And he is totally out of tune and I really don't know what I'm doing. There are trim pots inside for each of the voices, I hold down the middle A key and tune it to A440 on my tuner and all of the 6 voices tune right, all the way up to the top of the keyboard the thing plays fine, but below that octave it's detuned. Vice versa as well, if I tune below the middle the bottom is in tune but the top is not. Any help would be massively appreciated as this is fairly annoying and not much information is out there about how to manually tune these things by hand.

20th September 2008	#4
vespiz Gear addict Join Date: Feb 2005 Location: Tampere, Finland Posts: 416	Sounds like my P6! (Well, nearly anyways). I can't get it tuned anymore, I've tried tuning it several times, but it won't scale right. I get one end of the keyboard right, and the other end sounds like modern music... __________________ Cheers, Jussi Kulomaa www.masterstroke.info jussi.kulomaa(at)gmail.com

21st September 2008	#8
sizzlemeister Gear maniac Join Date: Jun 2005 Posts: 209	The P6 doesn't have SSM VCOs, just the filters and VCAs are SSM ICs. The OP probably has two bad SSM 2056s I imagine. If you look at the voice section while you have it open and play notes you'll notice little red LEDs cycling through the voices as you play them. Identify which voices are the ones that drop. Swap the SSM 2056s ICs in those voices with two voices that work. If the latter drop now after switching, then those ICs are bad. If not, then you work backwards; there may a problem with the opamp that generates the CVs from the DAC. I can't remember how the P6 handles CVs for each voice, but if they're split up from the DAC then there may be a multiplying IC in there that is bad. If the SSM is bad, you may want to replace the cap that protects it after you find some new 2056s (and let me know where you get your 2056s from, please, thanks). Forgot to mention that if your Polysix drifts, you need to replace the mysterious PC1 part on the voice board. IIRC it's an optoisolator. Works like a charm on the tuning. __________________ Nothing new right now, but pretty soon. Stay tuned to this sig!

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20th September 2008	#2
triez Lives for gear Join Date: Apr 2003 Location: Australia Posts: 1,315	If all of the voices are out then it is not likely that the voices are the problem, it is more likely that the power supply has drifted off spec. or there is an issue with keyboard scaling. Best to download the full calibration procedure and start at the top with making sure the power supply is properly adjusted. You will need a tuner and a digital multimeter.

21st September 2008	#6
revstate 3 + infractions, forum membership suspended. Join Date: Mar 2008 Posts: 619	i have had my polysix in for a complete retuning and calibration. the tech replaced all of the bad chips, added midi, and repaired the entire main cpu board. and after i got it back, it still drifts... why you ask? because it has ssm vco chips... they drift. they drifted when it came out, and they drift to this day. either don't worry, because it's supposed to sound like that, or older vco synths are not for you. i keep a tuner plugin armed in my daw (logic) on all of my inputs that have a vco synth plugged into them (and all of my synths are vco ^_^).

2nd October 2008	#11
Mike6581 Lives for gear Join Date: Jun 2008 Location: Manchester, UK Posts: 643	Depending on how the voice allocation goes on that synth, try playing the same note (an octave down) six times. I'm not sure if it's the case with Korgs but the voice allocation mode found in Roland synths (Junos and Jupiters) and the Prophet 08 works with each voice taking turns to play so if you press a key over and over, a different voice is playing it. If the "level of out of tuneness" stays the same with each key press then the that's probably not a dodgy oscillator chip.

4th October 2008	#12
CalvaryBand Gear maniac Join Date: Sep 2008 Posts: 218 Thread Starter	Horray, I got my Jupiter 8 in the mail and it's completely in tune and stays in tune! But alas, just like my Polysix one voice is bad. At least the JP8 has a usable mode with one voice gone bad.

6th October 2008	#13
Mike6581 Lives for gear Join Date: Jun 2008 Location: Manchester, UK Posts: 643	Oh eck! You don't have much luck with synthesizers do you? How is the dead voice manifesting itself? Is it missing out every eight note you play or every eight key on the keyboard? If it's the former you've probably got a dead voice. If it's the latter there might be a problem with the keyboard scanner (not sure of the correct lingo). My Jupiter 8 has a dry joint somewhere in the keyboard scanning hardware and did this a while back after being in transport (even thought it was in a flight case). After much cursing and swearing I gave it a smack (on the bottom in the middle) and it started working again. I don't suggest you try this as it'll probably do more harm than good, but at the time for me the red mist was running the show. There are people out there who can fix Jupiters still, though it'll probably cost you a fair bit. You could try fixing it yourself and sourcing the parts, but Jupiter 8s are very, very complicated beasts. There's quite a large number of PCBs, all interconnected, under it's charcoal grey case. I'd suggest you do get it repaired as Unison mode does get a bit intense after a while and you'll be missing out on the lovely pads that the Jupiter is so famous for.