Serge PCO FM behavior?

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asymptote
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Serge PCO FM behavior?

Post by asymptote » Wed Oct 14, 2020 12:57 am

I've got a question about the FM behavior on the Serge PCOs. I'm specifically interested in the new R*S version, though I assume that the FM circuitry is the same (or at least similar to) other iterations of the PCO. If anyone out there has experience or knowledge on the subject, I'd be most appreciative. And apologies in advance if this has been discussed before--I tried a search but came up empty.

I see a 1v/o input (x2 on the upper PCO), both AC and DC coupled inputs for linear FM, and a DC input with attenuverter labeled 'VC F.' Does anyone know exactly how this 'VC F' functions? Is it an entirely separate FM input + attenuverter? If so, is it linear or exponential? Or is it a kind of indexing VCA that modulates the linear inputs to the right?

Here's a pic for reference:

Image

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dksynth
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Re: Serge PCO FM behavior?

Post by dksynth » Wed Oct 14, 2020 9:29 am

asymptote wrote:
Wed Oct 14, 2020 12:57 am
I've got a question about the FM behavior on the Serge PCOs. I'm specifically interested in the new R*S version, though I assume that the FM circuitry is the same (or at least similar to) other iterations of the PCO. If anyone out there has experience or knowledge on the subject, I'd be most appreciative. And apologies in advance if this has been discussed before--I tried a search but came up empty.

I see a 1v/o input (x2 on the upper PCO), both AC and DC coupled inputs for linear FM, and a DC input with attenuverter labeled 'VC F.' Does anyone know exactly how this 'VC F' functions? Is it an entirely separate FM input + attenuverter? If so, is it linear or exponential? Or is it a kind of indexing VCA that modulates the linear inputs to the right?
It's similar to SOME PCOs ;) I don't have a dual PCO but here are my guesses:

I'm not sure what is going on in the linear FM side.... the line connects the AC and DC inputs, so i assume that means an AC and DC linear FM input? Unless they added a VCA on the linear FM input that is always open unless you connect a jack? That's possible.

the VC F however is usually exponential FM.

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asymptote
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Re: Serge PCO FM behavior?

Post by asymptote » Wed Oct 14, 2020 11:26 am

Yeah, that’s how I’d assume the linear FM inputs work. And I also kinda suspected that the VC F control is exponential, but it’s nice to get confirmation. It’s a little disappointing for me, though, as I really like having control over the depth of linear FM.

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Re: Serge PCO FM behavior?

Post by Xomrys » Sat Oct 17, 2020 11:54 pm

Standard PCO has two 1V/Oct + variable. So the VCF is the variable. It's exponential. Perhaps the (white) control above the (black) linear FM input is for scaling the linear FM?

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batchas
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Re: Serge PCO FM behavior?

Post by batchas » Sun Oct 18, 2020 12:19 am

asymptote wrote:
Wed Oct 14, 2020 11:26 am
It’s a little disappointing for me, though, as I really like having control over the depth of linear FM.
Manual control makes indeed more sense IMHO.
You're sure it's not a pot in place of the black LIN FM IN? Seems strange to me.


EDIT: you're right. I checked the R*S pages, no pot :(
I guess they had to choose between CV IN and pot for space matter and decided CV IN makes more sense.
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Re: Serge PCO FM behavior?

Post by asymptote » Sun Oct 18, 2020 9:57 am

I’ve been watching the videos on cybernetics and analog AI by mfaraday, and I noticed that his Dual PCO has a potentiometer in place of the AC linear FM input. I wonder if R*S ended up opting for this arrangement in all of their production units or if it’s available as an option on the pcb. I sent an email asking about this to Patch Point. I’ll report back if/when I get a reply.

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Re: Serge PCO FM behavior?

Post by mfaraday » Sun Oct 18, 2020 10:03 am

yeah the AC coupled linear FM input is definitely a pot - you can see in the picture on the R*S page as opposed to the mockup

http://randomsource.net/serge_4x4?mod=RS_PCO4X4

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Re: Serge PCO FM behavior?

Post by asymptote » Sun Oct 18, 2020 10:48 am

mfaraday wrote:
Sun Oct 18, 2020 10:03 am
yeah the AC coupled linear FM input is definitely a pot - you can see in the picture on the R*S page as opposed to the mockup

http://randomsource.net/serge_4x4?mod=RS_PCO4X4
Ah, good to know. Thanks for the confirmation. And btw your videos are aces!

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Re: Serge PCO FM behavior?

Post by batchas » Sun Oct 18, 2020 12:31 pm

http://randomsource.net/serge_4x4?mod=RS_PCO4X4 = a bit confusing isn't it?

Anyway. Pot, no pot, the Serge PCO is a great oscillator.
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