MFOS VCO Scale Calibration

keanenk · Joined: Jan 13, 2010 Posts: 4 Location: Hoboken, NJ

This is the first VCO module I built and I am not sure how to properly adjust it. I couldn't get it to track properly using a tempco. The trim adjustments (R16) would max out with it in. I am assuming the tempco is somehow not working correctly. I had to use a 2k resistor for R24 instead and then finally I could set it to get the proper hertz... 100hz at 0v, 800hz at 3v and 3.2khz at 5v (my MIDI to CV doesn't go to 6v), but if I go through the notes, one will be sharp and the next will be flat and it sounds off. If I go from the note C1 (0v) to C4 (3v) it will be perfect, but C6 (5v) is like a B, but it reads 3.2khz on my meter. Any ideas?? Confused

keanenk · Joined: Jan 13, 2010 Posts: 4 Location: Hoboken, NJ

Anybody have any ideas?

Still not working correctly. It's very depressing.........

jordroid · Joined: Jan 17, 2010 Posts: 193 Location: ithaca, new york

I don't have much of any advice for you but i thought i would drop by for moral support. It sounds you are going by Rays' calibration instructions on the most recent VCO page, but it looks like a pretty tweaky and potentially frustrating experience. Sorry dude, i looked over the instructions and i've got nothin' for you. Good luck though and hopefully one of the smarty pants's will be along to help out. You will get it working eventually, but i feel your pain in the meantime.

keanenk · Joined: Jan 13, 2010 Posts: 4 Location: Hoboken, NJ

Thanks! I appreciate the moral support in these tough times Smile

I think it's possible I am not calibrating it right. Does anyone have any tips or did anyone do it differently than the process listed on the site?

Also, my sine and triangle waves sound very flat and lifeless. On my scope they look perfect though.

haxster · Posted: Mon Jan 25, 2010 2:32 am Post subject:

Maybe this txt file will help. It is similar to what your doing already.

VCO TUNNING.TXT

Description:

Download

Filename:

VCO TUNNING.TXT

Filesize:

2.14 KB

Downloaded:

318 Time(s)

keanenk · Joined: Jan 13, 2010 Posts: 4 Location: Hoboken, NJ

Thanks for the link.

I tried it out and I am still not scaling correctly...

Anybody want to buy a half working VCO??

RF · Posted: Thu Jan 28, 2010 8:09 am Post subject:

Check and double check your cap and resistor values.
You CAN get this working...

bruce

haxster · Posted: Thu Jan 28, 2010 10:33 am Post subject:

R24 has to be 2k
R16 has to be a 100ohm Multiturn Trimmer
R19 has to be 470R

R9 I use 470R instead of 4k7, this garantees you don't run out of trimmer for the higher section of tracking.
R11 I use 100k instead of 20k

These mods make the vco sometimes Vanish, you need to turn the 100k trimmer until it comes back to earth and you hear it again. Then you can start the calibration.

I use a cheapo 100ppm 2k Tempco and 2n2222A trannies and i have never got one not to track. Sure it drifts a little bit but It still lands on the note. It is only noticable with 2 vco's.

Yeah you can get this working. It's just frustrating at first.

jordroid · Joined: Jan 17, 2010 Posts: 193 Location: ithaca, new york

I don't know if you have seen this yet, i think it's pretty new-

http://www.musicfromouterspace.com/analogsynth/TRANSISTORMATCHER/TRANSISTORMATCHER.php

the three videos at the bottom detail oscillator tuning, what a guy that Ray is.

hudsonnc · Joined: Feb 07, 2018 Posts: 1 Location: California

I know it has been about 8 years, but did you ever get it working? I am in the same boat now...