Korg Mono/Poly

Hi,

My name is Nick, from Australia and I have owned a Mono/Poly for about
one week! Up until yesterday, it worked 100% but I fear it's dying now...

Triangles now sound distored, unless the resonance is up full, then
they sound normal! And in poly mode, chords sound badly distorted
unless res is up full...

I don't think there's anything I can do for it, but anyway, I look
forward to learning as much as I can from you guys.

Cheers,

Nick.

Hi

The higher the Resonance the lower the level of the signal. This
explains why the distortion is gone. May be you simply switched the
output level to "high" (aside the Master volume), and now your following
audiostage (mixer, computer, whatever...) is distorting.

Florian

nickeax wrote:

> Hi,
>
> My name is Nick, from Australia and I have owned a Mono/Poly for about
> one week! Up until yesterday, it worked 100% but I fear it's dying now...
>
> Triangles now sound distored, unless the resonance is up full, then
> they sound normal! And in poly mode, chords sound badly distorted
> unless res is up full...
>
> I don't think there's anything I can do for it, but anyway, I look
> forward to learning as much as I can from you guys.
>

Hi Florian,

Thanks for the reply! I don't think that's it, as there is no change in this even with headphones directly plugged into the Korg. I have also noticed that with the OSC levels really low, everything seems to be OK.

The 'distortion' is not like an overdriven circuit sound, it's a lot more bubbly. Almost like a high speed LFO is garbling up the signal.

I think I'll just have to send it in to a professional. I can't find any other references to this problem online.

Have you checked that the Arppeggiator isn't set to latch. with MG2 at a high speed this can make thigs sound like you discribed.  I often have moments when its on and I don't realise.

--- On Sat, 17/5/08, Nick Fletcher <nickeax@gmail.com> wrote:

From: Nick Fletcher <nickeax@gmail.com>
Subject: Re: [korg_mono-poly] Hello, I am a new member.
To: korg_mono-poly@yahoogroups.com
Date: Saturday, 17 May, 2008, 1:02 PM

Hi Florian,

Thanks for the reply! I don't think that's it, as there is no change in this even with headphones directly plugged into the Korg. I have also noticed that with the OSC levels really low, everything seems to be OK.

The 'distortion' is not like an overdriven circuit sound, it's a lot more bubbly. Almost like a high speed LFO is garbling up the signal.

I think I'll just have to send it in to a professional. I can't find any other references to this problem online.

Sent from Yahoo! Mail.
A Smarter Email.

Hi Alan,

It's not that either, but thanks for the suggestion mate.

Nick.

And is it only tri waves that are sounding bad?

--- On Sat, 17/5/08, Nick Fletcher <nickeax@gmail.com> wrote:

From: Nick Fletcher <nickeax@gmail.com>
Subject: Re: [korg_mono-poly] Hello, I am a new member.
To: korg_mono-poly@yahoogroups.com
Date: Saturday, 17 May, 2008, 1:34 PM

Hi Alan,

It's not that either, but thanks for the suggestion mate.

Nick.

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It's not as noticeable on the saw and pulses, but they're being affected too. It's odd, everything was working fine when I first got it home. :-(

Hi Nick

> The 'distortion' is not like an overdriven circuit sound, it's a lot
> more bubbly. Almost like a high speed LFO is garbling up the signal.

Can you put a sound example to the file-section of the yahoogroup?
http://launch.groups.yahoo.com/group/korg_mono-poly/files/

Florian

Wasn't sure if it might be the wave form symmetry.  had a quick look through the service manual but couldn't find any thing on adjusting this.  another cause might be the sync effect being locked on but then if you get the same distortion on VCO 1 that wouldn't be it.  A sound file as Florian suggested would help.

--- On Sat, 17/5/08, Nick Fletcher <nickeax@gmail.com> wrote:

From: Nick Fletcher <nickeax@gmail.com>
Subject: Re: [korg_mono-poly] Hello, I am a new member.
To: korg_mono-poly@yahoogroups.com
Date: Saturday, 17 May, 2008, 1:58 PM

It's not as noticeable on the saw and pulses, but they're being affected too. It's odd, everything was working fine when I first got it home. :-(

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Thanks a lot for all the help so far guys! I'll get a file up there tomorrow (+10hrs here).

Cheers,

Nick.

I've made some recordings of the offender:

OSC1 triangle, beginning with it's level all the way down and gradually increasing:
http://www.guitaraustralia.com/MonoPoly/triangleOSC1.mp3 595KB

OSC1 saw , beginning with it's level all the way down and gradually increasing:
http://www.guitaraustralia.com/MonoPoly/sawOSC1.mp3 283KB

OSC1 PWM , beginning with it's level all the way down and gradually increasing:
http://www.guitaraustralia.com/MonoPoly/pwmOSC1.mp3 605KB

OSC1 PW , beginning with it's level all the way down and gradually increasing:
http://www.guitaraustralia.com/MonoPoly/pwOSC1.mp3 212KB

Polyphonic mode,  triangles with resonance fully off:
http://www.guitaraustralia.com/MonoPoly/trianglePOLY_resDown.mp3 126KB

Polyphonic mode,  triangles with resonance fully up:
http://www.guitaraustralia.com/MonoPoly/trianglePOLY_resUp.mp3 206KB

Polyphonic mode,  saw with resonance fully off, then increased to fully up:
http://www.guitaraustralia.com/MonoPoly/sawPOLY_resDownUp.mp3 591KB


I hope you guys can help, but thanks very much for trying so far!

Hello Nick,

I am sorry to tell you this, but this does not sound good. To me it
sounds like a broken filter chip. Appearently the filter dose nto work
as it sould do: The example

> Polyphonic mode, triangles with resonance fully up:
> http://www.guitaraustralia.com/MonoPoly/trianglePOLY_resUp.mp3 206KB

shows no resonance at all, but feeds through some portion of the input
signal to the output.

Does the filter basically work? What happens if you turn the cutoff
frequency potentiometer full counter clockwise?

You might check, whether the SSM 2044 on the filter board is socketed
and perhaps the chips got loose in the socket and needs to be reseated.
If the chip is soldered direct to the pcb I think it is broken at all.

Florian

"Does the filter basically work? What happens if you turn the cutoff
frequency potentiometer full counter clockwise?" - Florian

Yes, it does work, but seems to lack and beef. And the resonance does not
add the same type of squelch as you'd expect. I will check the ICs in the morning.

Thank you so much for all your help!

Luckely the SSM 2044 can still be got quite cheap. http://cgi.ebay.co.uk/SSM-2044-4-POLE-VCF-REMOVED-ORIGINAL_W0QQitemZ120261021597QQihZ002QQcategoryZ38071QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

count your self lucky you don't need a filter chip for a Prohpet 5 SSM 2040 £65 each. ouch http://cgi.ebay.co.uk/SSM2040-SSM-2040-VCF-CHIP-FOR-Rev2-PROPHET-5-NOS-RARE_W0QQitemZ170218509386QQihZ007QQcategoryZ38071QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

--- On Sun, 18/5/08, Nick Fletcher <nickeax@gmail.com> wrote:

From: Nick Fletcher <nickeax@gmail.com>
Subject: Re: [korg_mono-poly] Hello, I am a new member.
To: korg_mono-poly@yahoogroups.com
Date: Sunday, 18 May, 2008, 4:40 PM

"Does the filter basically work? What happens if you turn the cutoff
frequency potentiometer full counter clockwise?" - Florian

Yes, it does work, but seems to lack and beef. And the resonance does not
add the same type of squelch as you'd expect. I will check the ICs in the morning.

Thank you so much for all your help!

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A Smarter Email.

The chip is firmly in it's bracket, so I guess it just died with the excitement of being used again after 14 years. :-)

I owe you guys a lot, because I was about to take her up to the big smoke and hand her over to a white coat, along with substantial hard earned.

All I can offer is a heads up on a nice vintage synth going on eBay:
http://cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&rd=1&item=260241655166&ssPageName=STRK:MESE:IT&ih=016

Once again, a BIG thank you!