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elmegil
Joined: Mar 20, 2012 Posts: 2177 Location: Chicago
Audio files: 16
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Posted: Fri Oct 12, 2012 8:07 am Post subject:
Original Soundlab, LFO CV mod? |
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I'm building a soundlab for someone (assembling mostly, he already did the soldering), and we want to make it patchable. For all the stuff that's documented on Ray's site, that's pretty easy.
One thing we'd like to do as well though is provide a CV in for the LFO Would it be as simple as putting another 1M resistor in to pin 2 of IC7-A ? Obviously it wouldn't be V/Oct, but for the purpose at hand I think it would suffice.
Thoughts? |
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mrmrshoes
Joined: Feb 19, 2011 Posts: 73 Location: Newcastle Upon Tyne
Audio files: 4
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Posted: Sat Oct 13, 2012 12:31 pm Post subject:
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Alright man.
I don't know if that would work?
One tried and tested way is to add a 2n3904 (or any general purpose) NPN transistor in parallel with the freq pot. I've done this with CMOS oscillators and it works pretty well.
Have a look at the WSG schematic for reference.
hope that helps man
mrmrshoes |
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elmegil
Joined: Mar 20, 2012 Posts: 2177 Location: Chicago
Audio files: 16
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Posted: Sat Oct 13, 2012 1:33 pm Post subject:
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I will check with the guy I'm making this for and see if non-linear, non V/Oct is acceptable for what he had in mind. For an LFO I suspect it may not matter as long as it behaves with some kind of predictability.
Thanks!! |
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mrmrshoes
Joined: Feb 19, 2011 Posts: 73 Location: Newcastle Upon Tyne
Audio files: 4
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Posted: Sat Oct 13, 2012 3:29 pm Post subject:
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of course it would be non-linear
I was thinking in term of positive CV. I believe the soundlab work's with negative and positive CV values, (I know the LFO does) not the best solution to the problem seeing that you lose half of your resolution.
As you can probs guess i'm a bit out of my comfort zone here like. I would love to see what you figure out for this. |
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elmegil
Joined: Mar 20, 2012 Posts: 2177 Location: Chicago
Audio files: 16
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Posted: Sat Oct 13, 2012 4:06 pm Post subject:
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I didn't mean to sound like that was a negative. I honestly dont know whether he'd like it or not. For all I know, any variation will be fine....[/right] |
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mrmrshoes
Joined: Feb 19, 2011 Posts: 73 Location: Newcastle Upon Tyne
Audio files: 4
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Posted: Sat Oct 13, 2012 9:35 pm Post subject:
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I'm sorry man, i didn't mean any dis-respect.
I don't think i explained my self very, sorry about that dude.
I was trying to say that i didn't realize that mod would be non-linear. I didn't factor in the dual supply. I've worked more with single supply.
looking forward to see your solution to this problem
cheers
mrmrshoes |
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elmegil
Joined: Mar 20, 2012 Posts: 2177 Location: Chicago
Audio files: 16
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Posted: Sat Oct 13, 2012 10:32 pm Post subject:
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We should stop apologizing at each other
I was just noting that the transfer functions in the datasheet aren't linear. Not because of the supply voltages, but because of the behavior of the transistor.
Actually, looking at the diagrams more closely, I think what's relevant are the first graphs on page 3 of transconductance, and while they are definitely not linear, if they stay in the right range, they might not be too bad. I'll have to build it and see because I'm not sure from the circuit diagrams what kind of gate-source voltage range I'd be looking at. |
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