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keanenk
Joined: Jan 13, 2010 Posts: 4 Location: Hoboken, NJ
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Posted: 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?? |
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keanenk
Joined: Jan 13, 2010 Posts: 4 Location: Hoboken, NJ
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Posted: Fri Jan 22, 2010 3:40 pm Post subject:
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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
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Posted: Sun Jan 24, 2010 6:37 am Post subject:
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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
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Posted: Sun Jan 24, 2010 2:19 pm Post subject:
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Thanks! I appreciate the moral support in these tough times
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
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keanenk
Joined: Jan 13, 2010 Posts: 4 Location: Hoboken, NJ
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Posted: Thu Jan 28, 2010 1:35 am Post subject:
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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
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Posted: Thu Jan 28, 2010 8:09 am Post subject:
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Check and double check your cap and resistor values.
You CAN get this working...
bruce _________________ www.sdiy.org/rfeng
"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
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Posted: Thu Jan 28, 2010 10:33 am Post subject:
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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
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hudsonnc
Joined: Feb 07, 2018 Posts: 1 Location: California
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Posted: Wed Feb 07, 2018 9:17 am Post subject:
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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: 14 Location: Switzerland
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Posted: Wed Jan 20, 2021 5:00 pm Post subject:
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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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