12 January 2010

Yusynth (Part 22)

This evening I started calibrating and tuning the Yusynth VCO I build today. The calibration part consists of two parts. First you have to center the Saw wave around the zero Volts with a 25 Turn trim potmeter and prevent it from clipping either on the positive or negative part. You can only do this with an oscilloscope. Then you have to fine tune the shape of the Sine wave and Triangle wave with another trim potmeter. Again you can only do this with an oscilloscope. You can see what it looks like in the picture. This part is quite easy actually and I have done it before with LFO's.

The tuning part is a lot more complicated. First you need a trusted CV source. You could use a tested and tuned midi to CV interface for example, but I decided to use the CV keyboard from my Roland System 100m set. The only problem with that one is that there is a tune button on that as well. So I used a Volt meter first to make sure that its output was exactly 1V/Oct and I was quite confident that it was. Then I attached a frequency counter to meeasure the exact frequencies on the output. The calibration proces is very well explained on Yves website by the way.

Here you can see my test setup. On top in the middle is the Volt meter. You can see it reads 4.00 Volts and the frequency counter measures 440.1857 Hz. Then you drop an octave and the Volt meter should read 3.00 Volts then and the frequency should be half so 220 Hz. While doing this you change the V/Oct trim potmeter until it is correct. Then you repeat this over and over again until it is in tune over an octave or 5. That should be fine I guess. I also send the output to a pair of speakers so that I could tune a bit on hearing as well.

Here is another shot with 2.001 Volts on the CV input (close enough for me) and 109.9316 Hz in stead of 110. Well I've seen a lot of number like this. After about an hour or two fiddling around like this I was finally satisfied. Actually I don't even know if my frequency counter is that good. But it sounded quite OK :) I run it through some sound effects and played some melodies on the VCO. Well I'm quite happy with that sound and also how it tracks. So Yves did a very good job with this design. And I already decided that I'm going to build some more of his VCO's :) I can recommend it. You will have a very good oscillator for a very low price. And it doesn't get more analog :)


yusynth said...

Congratulation, Michel
you succeeded in building and trimming what is probably the most difficult module of the yusynth series.

Five octaves is OK but you may achieve up to seven/eight octaves of V/Hz tracking. When I build a new VCO it takes me about two hours (with a lot of breaks to let temperature stabilize) to achieve a perfect tracking over 7.5 octaves.

Thumbs up anyway !

Synth.nl said...

Thanks Yves :) The reason I didn't go beyond octaves by the way has more to do with my CV keyboard than the VCO :) I'm going to build a few more of your VCO's en soon also a Midi2CV module. Hopefully I can test a bit better than.

yusynth said...

Hi Michel

To go beyond the 5 octaves with your Roland keyboard is easy, you just have to tune up VCO to be two octaves higher using the main frequency potentiometer and then proceed to the trimming just as you did before for the lower octaves ;-)


Synth.nl said...

Ah :)