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 Forum index » DIY Hardware and Software » MusicFromOuterSpace.com designs by Ray Wilson
Original Soundlab, LFO CV mod?
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elmegil



Joined: Mar 20, 2012
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PostPosted: Fri Oct 12, 2012 8:07 am    Post subject: Original Soundlab, LFO CV mod? Reply with quote  Mark this post and the followings unread

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



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PostPosted: Sat Oct 13, 2012 12:31 pm    Post subject: Reply with quote  Mark this post and the followings unread

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



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PostPosted: Sat Oct 13, 2012 1:33 pm    Post subject: Reply with quote  Mark this post and the followings unread

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



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PostPosted: Sat Oct 13, 2012 3:29 pm    Post subject: Reply with quote  Mark this post and the followings unread

of course it would be non-linear Embarassed

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



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PostPosted: Sat Oct 13, 2012 4:06 pm    Post subject: Reply with quote  Mark this post and the followings unread

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



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PostPosted: Sat Oct 13, 2012 9:35 pm    Post subject: Reply with quote  Mark this post and the followings unread

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



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PostPosted: Sat Oct 13, 2012 10:32 pm    Post subject: Reply with quote  Mark this post and the followings unread

We should stop apologizing at each other Very Happy

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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