VCF-Issue with first Lower-Voice

[Rio]

Hi there,

I got an issue with the Filter of the first Lower Voice (Voice A). The filter seems to be open the whole time and can't be closed f.e. by changing the cutoff with the slider. Only if you open the filter completely all voices sounds identically.

After a cross check of the SSM2044 without any success I check the control pins on IC33 Pins 2,5 and 6 against a working voice ... unfortunately no difference. Then I look after the passiv resistor network that leads to the Cntl-Pin 13 on the SSM ... also no difference. At least I change the SSM capacitors 3 x 1000pF and 1 x 220pF ... no success at all.

I think it's a interresting problem ... did I overlook something ? Is there another mechanism to control the filter cutoff ... or did you have any idea what else cause such symptoms ?

I greatly appreciate your help or hints ...  
Rio

Update: I added a part of the filter schematic and a wav file as attachement. And one more question ... is it correct that the EMU1 Filter Cutoff is adjustable in only 8 steps ?   

[Rio]

I solved it ... nothing spooky with this problem. My "known good" Cross-Check SSM is now a "known bad" SSM !

After the replacement of the socket nothing else could be the cause of this problem, so I repeat all my steps during repair and found that my known good SSM shows the same behaviour as the one in the defective voice. It must be died really quiet ... without any notice from me )

Now all voices are working. I replaced all SSM-2044 Filter against SSI-2144 with little adapter boards. They sound really good in this Emulator 1 and first of all they all sound exactly equal.

For everyone who is interrested : The Emulator 1 has only 8 different VCF-Settings available corresponding to the 3 Bits from IC33 Pin 6,5, and 2. Depending on their switch-state (0 or 5V) they create the control voltage at pin 13 of the SSM Filter through the following passive resistor network. For the whole filter range from completly close to completely open you can measure a voltage from round about -35mV to +35mV at the Control Pin of the SSM. At my opinion these 8 steps are absolutely enough for a manual setting per Slider.

First thought about this was ... only eight steps ? Did they realize a form of PWM at these pins to get a higher resolution ? Look at the 100nF capacitor at the control pin ... it might be possible to realize it with todays computing power but not with these ancient Z-80.

As I read there was a hardware option available for expanding the Emulator 1 possibilities regarding Filter Cutoff ADSR and Q-Control. Does anyone has information about it ?   

Keep on repairing and sharing your results ...
Rio

Update : Added a picture of the SSI-2144 Filter with adapter board.

[Elmbeatz]

...
As I read there was a hardware option available for expanding the Emulator 1 possibilities regarding Filter Cutoff ADSR and Q-Control. Does anyone has information about it ?  
...

I think what you mean is the JL Cooper GenMod retrofit:

https://www.flickr.com/photos/34217597@N08/3693011856

[Rio]

Hi,

thank you for the reply. It's the first time I see a picture of this ... looks a little bit ugly 
Is it A,D,S,R, Env Amount and Q Controls separately for Upper/Lower Voice ?

I searched the Legacy section on JL Coopers Website but found nothing about this GenMod Retrofit.