Friday, May 19, 2006

Calibrating at the dining table

Two nights ago, I dragged my Motm to the diningroom table, got my manuals together, and set about calibrating some of the modules.
MOTM 300, MOTM 420 and MOTM 190. VCO, VCF VCA (in case you wondered).
Now that I have some patch cables I was able to get some of the calibration done, although I still need to calibrate the V/Oct signals.
I am fortunate enough to be in the possesion of a very good DVM (digital volt meter, although it should be able to measure more than that, so multimeter is a better description) , namely the FLUKE 867B graphical multimeter. It's a DVM with a large screen, that can also function as a simple oscilloscope. This proved helpful in tweaking the sine wave shape of the VCO, although it was near perfect to start with.
I also had a look at the other waveforms the MOTM 300 produces, and they are all very well shaped, no artifacts etc, just clean stable signals.
The filter and vca were also easy to do, provided you have the right tools of course. The calibration is very straight forward, but no rush job. Just as when building a module, you should take care and be patient when calibrating, it will pay of in sonic pleasure later! A good DVM is a basic requierment in my opinion, and get a proper calibration screwdriver/trimmer (usually made out of non conductive, antistatic plastic) from your electronics supplier.(Newark , Farnell , RS etc) . Any small watch maker screwdriver set works too, but a dedicated calibration tool is better.
Also I advise you to calibrate the modules seperated from your cabinet or rack, lay it flat on the table, (such so that the power supply cable can reach (it is sometimes easier to take out the power supply for that reason too, but be carefull for the mains voltages present on that module!!!) . You then have a stable surface for the module, and can calibrate more acurately.

I was done in about 30 minutes with all 3 modules. Tried out a few patches (the VCO outputs a signal when no CV signal is present too, and frequency is fully adjustable with the course and fine pots, and wow, the MOTM 300 does have quite a range, I was just tweaking and noticed the DVM indicate a frequency of more than 14kHz, and it could go higher still, one hell of a VCO, it can even create synth music for bats! :-)


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