The unexplainable things that happen

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Gringo Starr
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The unexplainable things that happen

Post by Gringo Starr » Mon Jan 11, 2021 2:57 am

I have a Befaco ADSR. It’s always worked as expected. But whenever I send the Befaco ADSR output to the CV input of one specific filter then the ADSR stops working. The Befaco stops responding to the trigger-in and it stays dormant until I unplug it from the CV input of the filter. Then it starts responding to the trigger-in again.

Any other ADSR works as expected going into the CV input of this filter and the filter responds as expected.

Any idea why the Befaco ADSR stops working in this situation but works flawlessly with every other module?

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born_a_kid
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Re: The unexplainable things that happen

Post by born_a_kid » Mon Jan 11, 2021 3:32 am

A similar thing happens to my Befaco VC ADSR when I plug it into a CV input of an Intellijel Quad VCA. Then the ADSR gets stuck in the attack phase.

Rampage sometimes does something similar due to inconsistent impedance matching (viewtopic.php?t=141127&start=225). You could ask Befaco, they might give instructions like replacing some resistor. For a workaround, I patch the ADSR first through an attenuator or buffered mult when I need it on the Quad VCA.

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Re: The unexplainable things that happen

Post by Agawell » Mon Jan 11, 2021 6:28 am

I have a similar thing with Maths - I think it's expecting a buffered input - so I just patch through a buffered mult - works fine

it's one of those things with eurorack - no standards = workarounds - c'est la vie
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Gringo Starr
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Re: The unexplainable things that happen

Post by Gringo Starr » Mon Jan 11, 2021 6:28 pm

Thanks for chiming in. That’s the first time in all my years with modulars that something like that happened. Maybe I’m lucky? Anyways it’s not a big deal. I can use other ADSR’s and send the Befaco elsewhere. But I’ll try the Mult suggestion.

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Re: The unexplainable things that happen

Post by Pelsea » Tue Jan 12, 2021 1:11 pm

Did you build the Befaco from a kit? If so, double check resistor R101 (1k). If it got mixed up with R102 (100k) you might get the behavior you describe.
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Gringo Starr
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Re: The unexplainable things that happen

Post by Gringo Starr » Tue Jan 12, 2021 4:30 pm

Pelsea wrote:
Tue Jan 12, 2021 1:11 pm
Did you build the Befaco from a kit? If so, double check resistor R101 (1k). If it got mixed up with R102 (100k) you might get the behavior you describe.
No I have zero skills building modules or anything else for that matter. I bought it brand new factory assembled.

The mult-trick worked btw. Good enough. 🤷‍♂️

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Re: The unexplainable things that happen

Post by pugix » Wed Jan 13, 2021 3:47 pm

I took a look-see at my Befaco Rampage. If you have one, you can notice that if you patch to one of the Outs and touch the tip of the other end of the patch cord to a ground (like the sleeve of another jack on the panel), you see oscillation stop, in rising (Rise LED is on). Oscillation resumes when you open the ground connection.

The schematic shows a 1K series resistor on each output. But the op amp driving this output is also the integrator, and that output drives a lot of internal circuitry. Apparently, a high load on the output interferes with the internals. The Serge VCS module from Ken Stone has a similar issue. If a buffer had been added between the integrator output and the external out, there would be no problem. Using a buffered mult has the same effect.

So, explainable.
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