CS-80 Calibration Part 5: M-Boards
Calibrating the M-boards is the major part of the adjustment procedure: All in all 320 trimpots on 16 voice boards will have to be turned. The adjustments are split into 3 sections: Pitch, VCF and VCA Levels/Envelopes. A lot of crying, screaming and being puzzled happened here. ;-)
During calibration on one M-board all of a sudden the pitch went down while adjusting, resulting in a a slow crackle-beating. My frequency counter showed an oscillation of only 3 hz. It turned out in the end an OpAmp has gone bad. I have another post on that, including the equivalent which is easier and cheaper to source: TA7504M Substitute.
Somehow I haven't read this elsewhere, but the easiest way to know if the current M-board is active is to just use the Trigger Terminal (TR). Connect TR to your Oscilloscope or DVM and you will always know when the board is triggered.
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| M-Board adjustment sections |
During calibration on one M-board all of a sudden the pitch went down while adjusting, resulting in a a slow crackle-beating. My frequency counter showed an oscillation of only 3 hz. It turned out in the end an OpAmp has gone bad. I have another post on that, including the equivalent which is easier and cheaper to source: TA7504M Substitute.
Board Locations
This can be a little puzzling as the board numbers printed on the label inside the CS-80 are counting from right to left, whereas the voice board numbers are actually counting from left to right. Also, the adjustment manual talks about R51/R52 boards, which is just labeled R.
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| Board Position Label |
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| R51/R52 and M-Boards Location |
Which M-board is sounding?
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| TR Terminal on M-board |
Of course this only works when the board has been taken out from the rail and the TR terminal is easily accessible (it's on the left lower side). If the board is sitting in the rail, terminal TP1 can be used as an alternative. It's the one I use when the boards are in the rack. If the board is triggered, the meter will show 0V at TP1, otherwise it will be somewhere in the negative voltage.
Pitch Tuning
For pitch tuning I highly recommend using a Strobe Tuner. Pitch tuning is one of the quicker tasks and done in no time. Although, the trimpots are sometimes a little sticky and jumpy. I tuned the pitch one more time after I had completed the whole calibration process, with all boards sitting in the rack. Unfortunately pitch tuning cannot be skipped until the end, because tuned VCOs are required as a reference for a few other adjustments.
The very first step to adjust is actually the transposition gate zeroing, The trimpot case has this sticky glue paint on it. Be cautious, I almost ripped the case off of one when it was very resistant and I wanted to give it a lecture who's the boss. I then used my soldering iron with caution on the paint, and when it finally melted I was able to move it. I could not skip it, because of course it had to be one of the few that were out of specs. On most m-boards the original reading was within tolerance, though.
Just in case: when turning VR19 and the attack time is longer than 125ms, lengthen the attack time by adding the difference between the 125ms mark and the current end of the attack curve; if it is shorter, do the same by shortening the attack time.
Besides that, it's just a simple ping pong between the two trimpots - sometimes an annoying one due to jumpy trimpots, though.
After some further research I found a fellow CS-80 owner with the exact same question. I got in touch with him and and we experimented over a span of a few days to make sense of it. Our outcome is: The VCF level alignment chapter is erroneous!
One of the hints came from the CS-60 adjustment procedure, for it uses a different terminal (CP2) and instructs to adjust to 7.6Vpp.
For LPF resonance he came up with 1.6Vpp (manual instructs for 2.2Vpp). I agree to that, as both of our factory color markings on the trimpots are also around that 1.6Vpp range. If I try to adjust to 2.2Vpp then I have to move VR10 almost out of the range, which does not seem right anyway. Terminal for LPF alignment is either CP8 or CP3. (CP3 is on the same bus).
Caution: Be aware that both cutoff level trimpots VR7 and VR9 interfere with each other. I have realized that only after I thought I finally am done. You should have seen my face when I cycled through the notes for a final VCF level check, just to listen once again to different VCF colors. I think this was the first time I just silently switched the CS-80 off and left the room without returning until next day. Otherwise my skin would have turned green to be powerful enough to throw the whole thing out the window.
The interference acts like this: If I turn VR9 to its minimum position and measure at VR7 while I turn VR9 to its maximum position, it will have added 1Vpp (!) to the original reading. It's no wonder that I struggled with the VCF levels.
All the other steps are the same as written in the VCF Envelope generator chapter above (VR19 would be VR20).
The thing is, if the board is not triggered, the waveform amplitude differs, resulting in a wrong adjustment. In any case, it will be noticed the latest when O is to be set to 80mVpp. The waveform will show, but turning the trimpot does not change the amplitude at all as the waveform from another board is actually displaying.
After doing some of those mistakes over and over again it got on my nerves at some point and I was going for an alternative way: DVM to AC mode, took a reference reading of all four adjusted VCA gain levels on one board and applied this to all the other boards. I did some control readings in between and it turned out to work great. I will list my values, but those are only an example, as my DVM is no TrueRMS and I don't trust the tolerance:
The last step requires the O terminal to be unsoldered. There is no way of getting around that, as the noise of the other boards will interfere otherwise and don't give a reliable reading. All my DC offsets have been somehwat off. It showed especially when setting the oscilloscope to the lowest amplitude setting.
Continue to Part 6: Noise, PWM and Sub Osc
The very first step to adjust is actually the transposition gate zeroing, The trimpot case has this sticky glue paint on it. Be cautious, I almost ripped the case off of one when it was very resistant and I wanted to give it a lecture who's the boss. I then used my soldering iron with caution on the paint, and when it finally melted I was able to move it. I could not skip it, because of course it had to be one of the few that were out of specs. On most m-boards the original reading was within tolerance, though.
VCF Envelope Generator
This has caused some headache because I was misreading the instructions first and almost committed suicide after a few hours of desperation before reading it again properly.Just in case: when turning VR19 and the attack time is longer than 125ms, lengthen the attack time by adding the difference between the 125ms mark and the current end of the attack curve; if it is shorter, do the same by shortening the attack time.
Besides that, it's just a simple ping pong between the two trimpots - sometimes an annoying one due to jumpy trimpots, though.
Using MIDI for Envelope Triggering
Having a Midi Retrofit installed saves some triggering trouble. See here how to set up the host and use the two patterns labeled Envelope Sequence. The sequence will play a loop through all notes at 250bpm, taking into account that the desired voice is playing long enough to be able to build up the attack curve for 125ms.VCF Alignment
R Boards
The manual instructs to take measures from R board at terminal FH/FL for adjusting the HPF/LPF Cutoff levels. There was no illustration of the R board. Looking at the labels for the card positions there are two boards starting with an R: R51 and R52. The required terminals are on the left side of the board as marked in the picture below. I have added this board to the updated manual too.
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| R51/R52 Board |
Alignment
The VCF alignment was really the longest and most exhausting part of the whole calibration. After desperately trying to get the HPF resonance adjusted to specs I had to stop here and do some research. It is not possible to get the HPF resonance to 4.3Vpp measuring at terminal CP3. I have tried to reach out to a few CS80 repair guys, but unfortunately I never got any reply.After some further research I found a fellow CS-80 owner with the exact same question. I got in touch with him and and we experimented over a span of a few days to make sense of it. Our outcome is: The VCF level alignment chapter is erroneous!
One of the hints came from the CS-60 adjustment procedure, for it uses a different terminal (CP2) and instructs to adjust to 7.6Vpp.
Findings
We have different findings for the HPF resonance adjustment, his solution is 8.4Vpp. I wasn't able on two boards to adjust to 8.4Vpp properly - I somewhat got it adjusted to 8.4Vpp, but when I hit a note, I could watch and hear the curve amplitude building up in slow motion over 2-3 seconds on a few boards. So I decided to go for the adjustment instruction from the CS-60 adjustment procedure and set all boards to 7.6Vpp for HPF. The correct terminal for HPF alignment is CP2.For LPF resonance he came up with 1.6Vpp (manual instructs for 2.2Vpp). I agree to that, as both of our factory color markings on the trimpots are also around that 1.6Vpp range. If I try to adjust to 2.2Vpp then I have to move VR10 almost out of the range, which does not seem right anyway. Terminal for LPF alignment is either CP8 or CP3. (CP3 is on the same bus).
Caution: Be aware that both cutoff level trimpots VR7 and VR9 interfere with each other. I have realized that only after I thought I finally am done. You should have seen my face when I cycled through the notes for a final VCF level check, just to listen once again to different VCF colors. I think this was the first time I just silently switched the CS-80 off and left the room without returning until next day. Otherwise my skin would have turned green to be powerful enough to throw the whole thing out the window.
The interference acts like this: If I turn VR9 to its minimum position and measure at VR7 while I turn VR9 to its maximum position, it will have added 1Vpp (!) to the original reading. It's no wonder that I struggled with the VCF levels.
Doing it an alternative way
To cut the story short, following is my solution that finally worked for me after some long experimentations: Taking measurements on all alignment steps, writing them down and applying them on all the other M-boards. As the maximum HPF cutoff level amplitude on two M-boards didn't go up as high as the others and as I wanted to have all cutoffs even (avoiding the instruction setting them to max), I was choosing the one with the least amplitude as my new reference.Determining reference values
- Setting DVM to AC and connecting scope and DVM to terminal CP2
- Turning VR8 and VR10 out of their range (pointer direction straight down. The two pin trimpots have no stopping point, they can be dialed 360 degrees until end of days, so I just dialed them out of range)
- Turning VR9 to its minimum left position
- Adjusting HPF cutoff at VR7 to almost maximum (don't push it too hard to max), taking a reading from DVM, writing it down
- Adjusting HPF resonance level to 7.6Vpp -> turning VR8 slightly to the left to try to compensate the interference, taking a reading from DVM, writing it down
- Connecting DVM and Scope to terminal CP8
- Adjusting LPF cutoff at VR9 to almost maximum (don't push it too hard to max), taking a reading from DVM writing it down
- Adjusting LPF resonance level to 1.6Vpp, taking a reading from DVM, writing it down
- Connecting scope to CP8, moving levers into position for HPF adjustment and controlling the curve. If the reading does not look right, starting over from to step 1 and trying to turn VR8 a little more to the left on end of step 5.
Applying reference values
Eventually CP2 will show 7.6Vpp for HPF and 1.6Vpp for LPF. Then, finally, I applied those reference values from my notes to all the other voice boards:- Setting DVM to AC and connecting DVM to terminal CP2
- Turning VR8 and VR10 out of their range (Pointer direction straight down)
- Turning VR9 to its minimum left position
- Adjusting VR7, VR8 at terminal CP2 and VR9, VR10 at terminal CP8 one after the other
Done, finally my filter colors were sounding even (almost). If you have midi, use that to check and play the sequence Testing all voices with different velocity levels. Btw, don't use the factory programs for testing, your VCF levels may differ for each voice. The touch calibration will be done at a later step and will have a direct effect on the VCF . I fell into that pit first before I realized.
The values I used are (don't use them, only to testing or for inspiration):
- HPF Cutoff: 3.100Vrms
- HPF Resonance: 2.630Vrms
- LPF Cutoff: 0.600Vrms
- LPF Reso: 0.380Vrms
VCA Envelope Generator
Setting the initial level to -200ms was a little challenging, even micro turns jumped 20-30ms around. I would have preferred multi-turn pots there.All the other steps are the same as written in the VCF Envelope generator chapter above (VR19 would be VR20).
VCA Levels
When adjusting the VCA levels it is important to monitor the trigger signal to make sure the right board is currently sounding, because a waveform will be showing on all terminals, regardless if the current board is being triggered or not.The thing is, if the board is not triggered, the waveform amplitude differs, resulting in a wrong adjustment. In any case, it will be noticed the latest when O is to be set to 80mVpp. The waveform will show, but turning the trimpot does not change the amplitude at all as the waveform from another board is actually displaying.
After doing some of those mistakes over and over again it got on my nerves at some point and I was going for an alternative way: DVM to AC mode, took a reference reading of all four adjusted VCA gain levels on one board and applied this to all the other boards. I did some control readings in between and it turned out to work great. I will list my values, but those are only an example, as my DVM is no TrueRMS and I don't trust the tolerance:
- VCA gain #1: 0.380Vrms
- VCA gain #2: 0.344Vrms
- VCA gain #3: 0.152Vrms
- VCA gain #4: 0.300Vrms
The last step requires the O terminal to be unsoldered. There is no way of getting around that, as the noise of the other boards will interfere otherwise and don't give a reliable reading. All my DC offsets have been somehwat off. It showed especially when setting the oscilloscope to the lowest amplitude setting.
Continue to Part 6: Noise, PWM and Sub Osc
CS-80 Calibration Part 5: M-Boards
Reviewed by MFox
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Reviewed by MFox
on
5:00 PM
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