LMNC Simple VCO with Fine tune issue

Greetings comrades…

I have built the LMNC simple VCO with PWM and added 1V/oct, CV pot, sync, fm, and the Track, Centre and High track trimmers using the 1222 Performance oscillator schematic. It all works and it tracks 1V/oct over the whole keyboard. I found it difficult getting the course tune spot on so i’ve added the fine tune pot and now it won’t track 1V/oct. Not even close. It has messed up the scaling completely.
Can anyone explain why and what i can do to get it to track now?
Would i need to add the reference point so i could get the volts trimmed up and if so how can i do this without adding the rotary switch as i want to keep the variable course tune pot.

Thank you and live long and prosper.
Jo

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Welcome in the forum, If it’s tune without fine tune, add just this resistor and pot for fine tune, it work fine for me :slight_smile:

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I’ve added your fine tune and the range sounds like it might be ok but now my centre note trimmer doesn’t work so i can’t tune the oscillator. Any idea why the fine tune pot is affecting the centre note trimmer? I’d like to be able to tune the centre note and have an octave up and down on the fine tune.

Rgds.
Jo

you can’t have this, fine tune can change between 0 and 1 ton, not 12 half ton. For this you need to add the rotary switch circuit to have octave select.
have you a schem of your build ?

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Why not? It’s just a matter of gain. And what does the octave switch have to do with fine tuning? Octave switch and coarse tune pot are essentially the same thing, just discrete vs. continuous.

I used LMNC simple VCO with PWM as my core and used LMNC 1222 Performance VCO schematic to add 1v/octave, Fm, Sync, and the centre note and high track trimmers.

It all worked except for the fine tune which messed up the tracking so then i took out the fine tune section from the 1222 VCO schematic and added the above fine tune pot wired off the course tune with the 3m3 resistor. now my centre note trimmer doesn’t work.
Here is the 1222 VCO schematic that i used to add the centre note trimmer.

FINE TUNE and CENTRE NOTE just adds more CV to the same frequency control summing node input that handles all other CV, so if that messes with tracking make sure you connected things to the right place.

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if he added the fine tune pot as he said he did, with my schem, he will never have an octave .Or change the value

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I made exactely the same core + …
but i don’t add center note , and i calibrate it with Track trimpot for adjust all octave, and after tune it with the frequency pot in what you want (D,C …) and the fine tune to adjust.
Sorry i don’t understand really what the Center note do.

Center note just adds a constant offset to the CV. Whether 0 V should correspond to C0 or middle C or some other note is something there’s big disagreement on, the center note trim allows you to make that choice.

Presumably you could if you reduce the value of R.

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Same as coarse tune in the stripboard layout, except that it’s a trimmer:

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My centre note trimmer had a bad solder joint.

All working now and tracking across 4 octaves nicely.

The fine tune pot works great, thank you Dud!!

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