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Erica Synth Black Varishape VCO2 issue
MUFF WIGGLER Forum Index -> Modular Synth General Discussion  
Author Erica Synth Black Varishape VCO2 issue
AudioCycles
Hi Guys,

I'm new in modular world but have a pretty good experience with synths.
So, i bought a Moog mother 32 a few months ago and now i'm extending it. I bought a second hand Black Varishape VCO2 but i can't get it properly tracking. When i tune it on a certain note with the frequency knob it's ok. But when i play other notes they goes more and more out of tune. The 1voct is connected to the moog "kbd" issue that provides the pitch. I made some test with a microbrute and ha no problem with it. I also made a test using a Kilpatrick K1600 controlling the VCO pitch directly and had the same problem...

Would you any idea about what could happen?

Thanks for your help.
Dave Peck
Since the mother 32 doesn't have a way to adjust / calibrate the 1V/oct output that would be used for controlling external oscs, and you plan to use the new osc with the mother 32, you should calibrate the new osc so that it tracks properly when connected to the mother 32.

First, are you sure you are connecting the mother 32's 1v/octave keyboard output to the correct "1V/OCT" input on the Black VCO2? If yes, and it still does not track correctly to the mother 32, you need to calibrate the Black VCO2.

There should be one or more small trim pots on the back of the Black VCO2 for adjusting the 1 volt-per-octave tracking, no?

Do you have experience calibrating the 1v/octave pitch tracking of analog oscillators?
AudioCycles
Thanks for your reply Dave.

Yes it is properly connected: input 1v/oct to kbd output. What i did is to tune Black VCO using the frequency button. Until here, no problem. If i play notes close to the current tuned note it's ok. If i jump one octave lower, the Black VCO goes a bit of a tune, 2 octaves higher, the Black VCO is even more detuned, and so on.

I received a calibration information from Erica in the meantime. I tried to follow the procedure but i didn't success. Indeed i don't have experience in VCO calibration. smile
Dave Peck
If you post the calibration info here, someone may be able to walk you through it.
AudioCycles
Hi,

here is the procedure i received from ERICA:

1) Remove the VCO from the rack but leave it connected to the PSU. Let it "heat up" for ~15mins. Set Saw wave to max, other waves to 12 o’clock, suboscillator full CCW, set octave switch to 0
2) Connect a tuner to the output of the VCO
3) Connect ka keyboard/midi-CV interface that generates 1V/oct CV to the input
4) Play C4 on the keyboard and use FREQUECY potentiometer to adjust tuning so that tuner shows C4
5) Play C5 on the keyboard and see the tuner reading
6) If the tuner shows something higher that C5 use SCALE tripmot to INCREASE the frequency of the VCO slightly. If the tuner shows something lower than C5, use SCALE trimpot to DECREASE frequency slightly
7) Play C4 again and use FREQUECY potentiometer to adjust tuning so tuner shows C4 again.
8) Play C5 and see, what you get. The tuning should be more precize. If it’s not exactly C5, go back to step 6
9) Once you are happy with C5, check what you get on C6, C7 and C3. You may need to adjust it little bit more as described on step 6.

I followed it carefully but i didn't succeed. C4 id ok but C5 is out of tune and C6 = G, C7 = F...
Dave Peck
So when C5 is out of tune, did you adjust the tiny SCALE TRIM POT on the PCB? (NOT the large frequency knob on the front).

If so, what happened? How did adjusting the SCALE TRIM POT affect the tracking?
AudioCycles
If i use the scale trim to tune C5, then C4 goes out of tune. It seems impossible to play the full octave range but only one octave to stay in tune. I'm sure that is is due to my lack of experience confused
Dave Peck
Yes, that's normal, yo just need to turn the trim pot the right amount and then RE-TUNE using the front panel FREQUENCY KNOB and repeat the process until the octave scaling is correct across multiple octaves.

Here's a hint:

1. Tune C4 using the front panel knob.

2. Play C5, which will be out of tune, and turn the SCALE TRIM POT in the direction which gets it closer to 'in tune', but not all the way there, just somewhat closer. Make a note of whether you had to adjust the trim pot clockwise or counter clockwise to get it closer to being 'in tune'.

3. Now play C4 again and re-tune the osc using the front panel knob again, and make a note of whether you had to tune it UP or DOWN to get it back in tune.

4. Now you repeat the process, and pay attention to whether you needed to turn the trim pot in the same direction as before, or the opposite direction as before, to get it closer to 'in tune'.

5. Now play C4 again and re-tune the osc using the front panel knob again, and note whther you needed to turn the panel knob in the same direction as before, or the opposite direction as before, to get it closer to 'in tune'.

6. If you notice that you continue to turn the trim pot in the same direction each time when playing C5 to get it closer to 'in tune', and you continue to turn the front panel knob in the same direction each time when re-tuning the osc at C4, just keep repeating these steps until the tracking is right.

7. If you notice that you keep having to turn the trim pot and front panel knobs in the OPPOSITE direction from the previous time, it means you are turning the trim pot TOO FAR on each attempt and you are repeatedly overshooting the correct position that you need for correct octave tracking. Try turning the trim pot just a small amount each time.
AudioCycles
Dave,

Many thanks for your patience smile Indeed there are some complementary information that seems useful. I think i begin to understand my mistakes. I'll get back later to let you know.

Thanks, again
EpicAxe
Did you ever get the erica vco to calibrate properly? I own the classic black system and the vco's are constantly out. I've tried calibrating and 30 minutes later they are out again.
witchbutter
I am having the same problem. I have the Varishape VCO 1 & 2 and the #1 seems to track most of the time but the #2 is way way off and I can't seem to get it to work at all even with these instructions
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