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Filter Resonance Not Working

Filter Resonance Not Working

2015-12-02 by voltagegrove@yahoo.com

Hey guys, delighted to tell you that my Mono/Poly is full healthy! For the time being that is... All voices are stable and in tune.


I had it powered on all day today, twiddling about to check over the parameters and what not.  I had let it sit powered on for a few hours only to come back to it with the filter resonance not working.  It only just increases the output level, basically just makes it louder. Regardless of settings, unison, poly, etc.


It was working great and then all of a sudden, no resonance, but it just increases the output level. The rest of the filter works fine. Very strange... 


Does anyone have any thoughts or ideas of what this could be caused from? 


I was so happy to have it back after its three month stay with my tech, only now to have another issue...


Any thoughts, hints, tips or tricks would be much appreciated...

Re: Filter Resonance Not Working

2015-12-02 by voltagegrove@yahoo.com

Can I assume correctly that if the 2044 was bad then the rest of the filter would not be working correctly?

Re: [korg_mono-poly] Re: Filter Resonance Not Working

2015-12-02 by Florian Anwander

Hello

On 02.12.15 07:37 , voltagegrove@yahoo.com [korg_mono-poly] wrote:
> It was working great and then all of a sudden, no resonance, but it just
> increases the output level. The rest of the filter works fine. Very
> strange...
The resonance potentiometer sends out a voltage, which controls the
internal resonance circuit in the 2044 via VR3.
But this voltage controls also the first VCA (double transistro Q10
after the VCF). This is, why the output level increases.

The question now is: does the resonance control voltage reach pin 2 of
the 2044. If no then check the voltages at VR3 and R2. I could imagine a
cold solder joint.
If the cv reaches the pin2 of the 2044, then the resonance VCA in the
2044 is dead. Then you have to replace the 2044.

Florian

Re: [korg_mono-poly] Re: Filter Resonance Not Working

2015-12-02 by Niklas Ehrlin

I have nothing to add, more than to say; What an absolutely wonderful answer, Florian! Short, precise and easy to follow.
:)

Niklas

2015-12-02 13:48 GMT+01:00 Florian Anwander fanwander@mnet-online.de [korg_mono-poly] <korg_mono-poly@yahoogroups.com>:
 

Hello

On 02.12.15 07:37 , voltagegrove@yahoo.com [korg_mono-poly] wrote:
> It was working great and then all of a sudden, no resonance, but it just
> increases the output level. The rest of the filter works fine. Very
> strange...
The resonance potentiometer sends out a voltage, which controls the
internal resonance circuit in the 2044 via VR3.
But this voltage controls also the first VCA (double transistro Q10
after the VCF). This is, why the output level increases.

The question now is: does the resonance control voltage reach pin 2 of
the 2044. If no then check the voltages at VR3 and R2. I could imagine a
cold solder joint.
If the cv reaches the pin2 of the 2044, then the resonance VCA in the
2044 is dead. Then you have to replace the 2044.

Florian


Re: Filter Resonance Not Working

2015-12-03 by voltagegrove@yahoo.com

Thanks for your reply. Much appreciated as it now is making sense. 

I will hopefully be able to dig in there tomorrow and will post my feedback.

I decided to order a 2044 just in case, wouldn't hurt to have one around anyway.

This might be a silly question but what is the likelihood of a solder joint going cold? Could this result from the synth being moved around, or possibly having the ambient temperature of its environment change?

If you have any other tips or tricks I would love to know. Im working very hard to build my skills, but am still quite the amateur here.

One last question, when measuring the voltage in a circuit, should I also have the common lead connected to ground?

Would it make sense to measure continuity first?

Thanks again...

RE: [korg_mono-poly] Filter Resonance Not Working

2015-12-03 by <alanmdicker@yahoo.co.uk>

The pot for the filter res also control a VCA which counter acts the drop in audio level when the filters resonance increases.  Sounds like the VCA is working just fine but for some reason the feedback res for you filter is not.  Res CV control is pin 2 on the SSM 2044 filter chip.  It may be socketed and could need a little push to make sure it is seated correctly or the chip might be at fault.  Trimmer VR-3 adjusts the res and the only other component between that and the pin is R2 1.7k resistor.  Check these are still OK.  I’m pretty sure VR-2 Res pot is fine and VR-4 trimmer is all good as this is the trimmer for the VCA which we know is working.

As it’s something that happened from being in use of a while rather than it being worked on or moved around then I suspect your chip has gone bad but these can still be found at a reasonable price.  If it’s socketed I would remove it and check with a scope what voltage I could see at the pin 2 socket point when adjusting the res pot. If nothing then there’s a problem with the trimmer VR-3 or R2.  If there is a good CV there then it’s your chip.

 

Sent from Mail for Windows 10

 

 


From: voltagegrove@yahoo.com [korg_mono-poly]
Sent: 02 December 2015 05:57
To: korg_mono-poly@yahoogroups.com
Subject: [korg_mono-poly] Filter Resonance Not Working

 

 

 

Hey guys, delighted to tell you that my Mono/Poly is full healthy! For the time being that is... All voices are stable and in tune.

 

I had it powered on all day today, twiddling about to check over the parameters and what not.  I had let it sit powered on for a few hours only to come back to it with the filter resonance not working.  It only just increases the output level, basically just makes it louder. Regardless of settings, unison, poly, etc.

 

It was working great and then all of a sudden, no resonance, but it just increases the output level. The rest of the filter works fine. Very strange... 

 

Does anyone have any thoughts or ideas of what this could be caused from? 

 

I was so happy to have it back after its three month stay with my tech, only now to have another issue...

 

Any thoughts, hints, tips or tricks would be much appreciated...

 

 

Re: [korg_mono-poly] Re: Filter Resonance Not Working

2015-12-03 by florian anwander

Hello

Am 03.12.2015 um 03:34 schrieb voltagegrove@yahoo.com [korg_mono-poly]:
> This might be a silly question but what is the likelihood of a solder
> joint going cold? Could this result from the synth being moved around,
> or possibly having the ambient temperature of its environment change?
Yes one of these is the actual event, that causes the joint to break,
but the initial cause is some fault while soldering, when the synth has
been built. Unfortunately you don't see this.

Alans advice on the socket is good too.

Florian

Re: Filter Resonance Not Working

2015-12-03 by voltagegrove@yahoo.com

so far I have been able to reseat the 2044, which did not have any effect.  I have also tested the R2 resistor which is fine, although it seems to be a 4.7k instead of a 1.7k... I have also tested continuity between the Res pot, trimmer, resistor and 2044; which there is a full connection. I have ordered a new 2044, should be here early next week. I am just going to start there.

My next task will be to test voltages in the circuit, which I admit I am not completely comfortable in doing...

Would I just put the common lead (black) of my multimeter on a GND source and then the Red lead onto the source that I would like to measure?

Just by doing exactly what I have explained above. It seems as though a 11.82 volts does reach each component. If I am doing this incorrectly or if there is a better way to measure voltage could someone please point me in the right direction...

Yes... Unfortunately I am this much of an amateur.

I really appreciate the wisdom and advice!

Re: [korg_mono-poly] Re: Filter Resonance Not Working

2015-12-03 by Florian Anwander

On 03.12.15 20:53 , voltagegrove@yahoo.com [korg_mono-poly] wrote:
> Would I just put the common lead (black) of my multimeter on a GND
> source and then the Red lead onto the source that I would like to measure?
That is correct.


> Just by doing exactly what I have explained above. It seems as though a
> 11.82 volts does reach each component. If I am doing this incorrectly or
> if there is a better way to measure voltage could someone please point
> me in the right direction...
This sounds like your black lead is connected to the -12V supply. Not to
the Ground. An easy to find ground is the groundwire at the output sockets.

Florian

Re: [korg_mono-poly] Re: Filter Resonance Not Working

2015-12-03 by voltagegrove@yahoo.com

So I confirmed that it is indeed on the ground source.  I was getting 1.7 volts. Which seems much more plausible.  I measured each component and it does seem that its getting all the way around to pin 2 of the 2044.  When the replacement gets here I will pop it in and hope for the best.

Any other considerations?

Re: Filter Resonance Not Working

2015-12-04 by voltagegrove@yahoo.com

So it seems as though I can trace the voltage all the way to the chip. Question though... It does not seem as though VR3 nor VR4 has any effect whatsoever.  I am just basing this off the VCA level increasing, but any adjustment of the trimpots does not have any effect. Is this to be assumed? 

I am just trying to figure out more about this issue in case the new 2044 chip has no effect.

If you could be anymore specific as to what exactly I am looking for or testing, that would be much appreciated.  I apologize about my extreme amateur nature and/or ignorance; but I have a vast collection of synths and they are my prized possessions. If there is anything I can learn, the new knowledge is treated as golden eggs of opportunity.

I really appreciate what you have put forth so far Florian. You have no idea how grateful I am...

Re: Filter Resonance Not Working

2015-12-08 by voltagegrove@yahoo.com

Hey guys, just wanted to report that popping in the new SSM2044 was a complete success! What a relief! 

Only problem now is that I have to work through the filter calibrations. Because the resonance is way off.

If anyone has any tidbits of knowledge, tips, tricks or techniques. It would be greatly appreciated.  Especially because I have very limited knowledge in skill with electronics.

Thanks in advance.

PS - I bought four new SSM2044 chips. All brand new. If anyone ever is in need, I have three to spare. Wont charge you anything more than what I paid. 25 a piece.

Cheers!

Re: Filter Resonance Not Working

2015-12-08 by voltagegrove@yahoo.com

Just reviewed the calibration manual... I do not own an Oscilloscope.
Is there any chance that I could manage without one? 
By using my DVM and my ears? 
Is there any chance that I could calibrate the filter with just my ears?

I know what a proper VCF should sound like. I own almost two dozen analog synths, both vintage and modern...

Anything will help.

Re: [korg_mono-poly] Re: Filter Resonance Not Working

2015-12-08 by Florian Anwander

Hello

The VCF adjustment always can be done by ear. I think you will only have
to adjust VR19 with the voltmeter, like described in the adjustment
instructions topic 6.1.
Then adjust VR18 like described in the adjustment instructions topic
6.2., but simply use your ear. Set the trimmer so that you just do not
hear the ringing of the highfrequency resonance. A slight change of the
cutoff down, should make the ringing appear immediately.

Florian

m 08.12.2015 um 05:37 schrieb voltagegrove@yahoo.com [korg_mono-poly]:
>
>
> Just reviewed the calibration manual... I do not own an Oscilloscope.
> Is there any chance that I could manage without one?
> By using my DVM and my ears?
> Is there any chance that I could calibrate the filter with just my ears?
>
> I know what a proper VCF should sound like. I own almost two dozen
> analog synths, both vintage and modern...
>
> Anything will help.
>
>
>