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 Forum index » DIY Hardware and Software » MusicFromOuterSpace.com designs by Ray Wilson
MFOS VCO Scale Calibration
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keanenk



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

PostPosted: Thu Jan 14, 2010 12:03 am    Post subject: MFOS VCO Scale Calibration
Subject description: Noob needs help
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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
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keanenk



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

PostPosted: Fri Jan 22, 2010 3:40 pm    Post subject: Reply with quote  Mark this post and the followings unread

Anybody have any ideas?

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



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

PostPosted: Sun Jan 24, 2010 6:37 am    Post subject: Reply with quote  Mark this post and the followings unread

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.
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keanenk



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

PostPosted: Sun Jan 24, 2010 2:19 pm    Post subject: Reply with quote  Mark this post and the followings unread

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.
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haxster



Joined: Feb 01, 2006
Posts: 246
Location: MONTEREY PARK, CA 91754
G2 patch files: 2

PostPosted: Mon Jan 25, 2010 2:32 am    Post subject: Reply with quote  Mark this post and the followings unread

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


VCO TUNNING.TXT
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 Filename:  VCO TUNNING.TXT
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keanenk



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

PostPosted: Thu Jan 28, 2010 1:35 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for the link.

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

Anybody want to buy a half working VCO??
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RF



Joined: Mar 23, 2007
Posts: 1502
Location: Northern Minnesota, USA
Audio files: 28

PostPosted: Thu Jan 28, 2010 8:09 am    Post subject: Reply with quote  Mark this post and the followings unread

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

bruce

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"I want to make these sounds that go wooo-wooo-ah-woo-woo.”
(Herb Deutsch to Bob Moog ~1963)
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haxster



Joined: Feb 01, 2006
Posts: 246
Location: MONTEREY PARK, CA 91754
G2 patch files: 2

PostPosted: Thu Jan 28, 2010 10:33 am    Post subject: Reply with quote  Mark this post and the followings unread

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.
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jordroid



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

PostPosted: Sun Jan 31, 2010 9:06 am    Post subject: Reply with quote  Mark this post and the followings unread

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.
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hudsonnc



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

PostPosted: Wed Feb 07, 2018 9:17 am    Post subject: Reply with quote  Mark this post and the followings unread

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



Joined: Oct 03, 2017
Posts: 11
Location: Switzerland

PostPosted: Wed Jan 20, 2021 5:00 pm    Post subject: Reply with quote  Mark this post and the followings unread

I'm happy I found this post.
Believe me or not, but I did 3 of these VCO's and never properly calibrated them. Mostly because I was looking to do analog FM modulated noise rather than looking for good pitch tracking.
Things have changed now and I wanted them properly calibrated and I'm just doing the process now.

Had a few problems to calibrate the upper octaves, the second process of the calibration with R11. Basically I'd be always out of range. Also in my design back then R11 appeared to be 1M trim pot.

Replaced R9 as suggested, but here with 1.2k, and R11 by 100k... working well !
I also have to say that don't forget to let the circuit powered for some time before doing accurate adjustments. It takes about 10 minutes here for the values to adjust.

Thanks for this tool also for the frequency counter.. still valid in 2021 !
http://techmind.org/audio/

Another little calibration trick if you have a step sequencer.
Adjust 3 steps at the desired voltage and switch when needed.
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MFOSser



Joined: Feb 26, 2011
Posts: 25
Location: Ireland

PostPosted: Fri Feb 12, 2021 3:13 am    Post subject: Reply with quote  Mark this post and the followings unread

My first module was the VCO and it never worked until recently. I made other VCOs and left the original in a box. Recently, I needed another VCO so I methodically went through the first one.

The problem was that the sound was intermittent and the frequency range was poor. The frequency meter didn't show variation but I could hear it. I tracked it down to a faulty SSM2210, which I replaced with a matched pair (not so hard after all) of 2N3904. Other faults were sub-standard trim pots. Changing them allowed for better wave shaping and calibration.

As far as calibrating is concerned, all you need is a keyboard (unless you are only going to make bleeps and buzzes like the EuroCrack addicts) so get an Arturia keyboard with CV outs. Press bottom C, set Coarse to 200Hz (as measured by any multimeter with Hz setting) then press the next C up. If it isn't 400Hz then start twiddling. Go from one C to the other until done. Use the octave button to go up to higher values of 800, 1600, 3200 Hz to get the higher frequency tracking. (Yes, I know middle C is not 400Hz but you can change the pitch after calibration.)

All you need to build MFOS is a soldering iron, a multimeter with ohms, farads, continuity test, volts (mv and V) and Hz, and a second hand ANALOGUE oscilloscope. The whole lot will cost you about £80. You'll also need a sack of fuses for your power supply as shorts will work your way though them.

I have found that my common error on a board is a bad chip. I recently had a faulty VCF with no resonance. The LM13700 had fried. Probably another short. I am pretty clumsy with arthritis and poor eyesight. Once you get a board that works you can use it to check chips on other boards that you have suspicions about.
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