Resonant Lopass Gate PCBs (Taking orders as of 4/29/12)

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jschussler
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Post by jschussler » Sun Feb 03, 2019 4:39 pm

Separate question: I don't see any documentation for what the trimmer on the PCB actually adjusts. Anybody know?

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Triglav
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Post by Triglav » Sun Feb 03, 2019 4:43 pm

jschussler wrote:Separate question: I don't see any documentation for what the trimmer on the PCB actually adjusts. Anybody know?
It adjusts the offset position slightly.

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jschussler
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Post by jschussler » Mon Feb 04, 2019 12:06 am

Triglav wrote:
jschussler wrote:Separate question: I don't see any documentation for what the trimmer on the PCB actually adjusts. Anybody know?
It adjusts the offset position slightly.
Cool, thanks for that.

intercorni
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resonance starts too early

Post by intercorni » Tue Mar 05, 2019 5:26 am

Does anyone have the problem that the resonance starts too early?
At about one third of the way I'm already in the self-oscillation :-(
Then the signal stops completely.
I use a linear potentiometer for the resonance.
And i try the mod from https://modularsynthesis.com/nrm/lopass/lopass.htm
But it is the same.
Maybe is a antilog pot better?

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j450nn014n
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Re: resonance starts too early

Post by j450nn014n » Tue Mar 05, 2019 6:57 am

intercorni wrote:Does anyone have the problem that the resonance starts too early?
At about one third of the way I'm already in the self-oscillation :-(
Then the signal stops completely.
I use a linear potentiometer for the resonance.
And i try the mod from https://modularsynthesis.com/nrm/lopass/lopass.htm
But it is the same.
Maybe is a antilog pot better?
No idea, but thanks for the link to the mod.
Autistic. I like making noises at my workplace. I usually end up breaking something.

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Triglav
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Re: resonance starts too early

Post by Triglav » Tue Mar 05, 2019 7:14 am

intercorni wrote:Does anyone have the problem that the resonance starts too early?
At about one third of the way I'm already in the self-oscillation :-(
Then the signal stops completely.
I use a linear potentiometer for the resonance.
And i try the mod from https://modularsynthesis.com/nrm/lopass/lopass.htm
But it is the same.
Maybe is a antilog pot better?
Experiment with different values of R18 (originally a 50k by the resonance pot) until you find a range that you like.

intercorni
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Re: resonance starts too early

Post by intercorni » Tue Mar 05, 2019 8:19 am

Triglav wrote:Experiment with different values of R18 (originally a 50k by the resonance pot) until you find a range that you like.
Many thanks. How do I reduce the resonance with R18? Bring low values a low resonance? Ore higher values for a lower reso?

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Triglav
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Re: resonance starts too early

Post by Triglav » Tue Mar 05, 2019 9:37 am

intercorni wrote:
Triglav wrote:Experiment with different values of R18 (originally a 50k by the resonance pot) until you find a range that you like.
Many thanks. How do I reduce the resonance with R18? Bring low values a low resonance? Ore higher values for a lower reso?
If I recall correctly, a higher value means less resonance.

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j450nn014n
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Re: resonance starts too early

Post by j450nn014n » Tue Mar 05, 2019 10:51 am

Triglav wrote:
intercorni wrote:
Triglav wrote:Experiment with different values of R18 (originally a 50k by the resonance pot) until you find a range that you like.
Many thanks. How do I reduce the resonance with R18? Bring low values a low resonance? Ore higher values for a lower reso?
If I recall correctly, a higher value means less resonance.
Would it be worth putting in a lot of trim pots for fiddling? Are there any key resistors that can should be focused on?
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Triglav
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Post by Triglav » Tue Mar 05, 2019 11:50 am

I was happy with 60k which is giving me self-oscillation around 2 o'clock but I didn't do too much testing as I rarely use the resonance.

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Post by j450nn014n » Tue Mar 05, 2019 11:54 am

Triglav wrote:I was happy with 60k which is giving me self-oscillation around 2 o'clock but I didn't do too much testing as I rarely use the resonance.
Cool. Thanks. I'll start with that. I'm having a horrible time getting this puppy running, because of all the diverse ways of putting it together. I love canonical build guides, but I'm going to have to get my hands dirty and just go with the schematic and my scope. Oh, the humanity of it all!
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Triglav
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Post by Triglav » Tue Mar 05, 2019 12:15 pm

j450nn014n wrote:
Triglav wrote:I was happy with 60k which is giving me self-oscillation around 2 o'clock but I didn't do too much testing as I rarely use the resonance.
Cool. Thanks. I'll start with that. I'm having a horrible time getting this puppy running, because of all the diverse ways of putting it together. I love canonical build guides, but I'm going to have to get my hands dirty and just go with the schematic and my scope. Oh, the humanity of it all!
The only changes I'd suggest from the values printed on the board are:
— Raising R18 to tame the resonance.
— 4.7k for R17 to fix the offset range
— If you're building it for Eurorack (or other 12V formats) R3 should be 120k and R5 should be 80k.

intercorni
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Post by intercorni » Thu Mar 14, 2019 3:19 am

The trimm-pot TP1 does nothing - any suggestions?
The Offset-Pot works fine.

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Post by Jumbuktu » Thu Mar 14, 2019 4:21 pm

intercorni wrote:The trimm-pot TP1 does nothing - any suggestions?
The Offset-Pot works fine.
I think the trimmer is supposed to adjust the offset range, but I couldn't get anything useful out of it.

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panfriedcharlie
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Post by panfriedcharlie » Sun Mar 24, 2019 12:05 pm

Okay I'm tackling the Quad kit. I needed some kind of full diagram (I'm a visual learner) so I stole Jumbuktu's awesome wiring diagram and added my planned approach. Anyone see any problems here? The plan, simply is to connect the mix output of board 4 to the mix input of board 2. Thanks all, this thread has been really helpful!

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Post by artilect99 » Sun Apr 28, 2019 7:42 pm

Triglav wrote: — 4.7k for R17 to fix the offset range
— If you're building it for Eurorack (or other 12V formats) R3 should be 120k and R5 should be 80k.
For anyone building this now, definitely do these mods!! Unfortunately I only found out about them long after I built mine, but they fixed the offset pot and CV range weirdness completely. 4k7 is indeed the value on the original Buchla schematics and the NLC lpg which is based on same.

Here is a graphic I made to make locating them simpler:
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