SIDE CHAIN MODULE (Ducking)

Yes! I did make a few minor modifications to get it running with a stompbox 9v DC supply and to accommodate a microphone signal for the sidechain.

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Very nice pedal :slight_smile:

What did you have to change to make it work with microphone level?

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Thank you! A very minor modification but I had to change the resistor values in the first op-amp stage to boost the signal enough to drive the vactrol - thatā€™s the preset pot in the top left of the second image. I used a rail splitter chip then to split the 9v supply in to +4.5 and -4.5

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Yes that makes sense, microphone level would be quite low compared to synth level.

Thanks for explaining :slight_smile:

My finish build

a little patch :slight_smile:

And the verified stripboard here

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Hey hey jackb!

Great looking build!
Could you send the layout for this? I donĀ“t know how to convert this to pedal format from the rack layout :confused:

Thank you so much! <3

I have gerbers for the circuit board I had made - would that help?

Yes that would be great :slight_smile:

Hi,
I noticed that the circuit puts out an inverted signal.
I was wondering whether it would be possible to get a non-inverted signal.
As a beginner in electronics i started puzzling and readingā€¦
Would this be a correct change to the circuit?
Or am I seeing things too simplistic?

link

Thanks for getting me on the road!

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This is precisely the principle of the Side chain, otherwise a simple VCA does the trick.
but itā€™s surely possible ā€¦

I assume you mean the audio is phase inverted, not the inverted change in amplitude. I think your linked solution would work, although I would omit the voltage divider / pot and just use a fixed input resistor ā€” I donā€™t like output voltage dividers, I prefer keeping the output signal high and doing attenuation on the downstream inputs. Or if you want that pot, why not just one fixed resistor and one pot in series on the inverting input? What you have would behave nonlinearly, almost all the change happening in the first 20% of the pot rotation, since itā€™s a large pot with a small resistance to virtual ground on the wiper:

Iā€™d also use 10k instead of 100k for the feedback and input resistances (including the pot), for a lower noise floor, and I think 220R is too small for the output resistor, Iā€™d use 1k.

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what is this ā€œrail splitter chipā€ named?

I did a PCB in Kosmo format with components on the panel in case someone is interested:

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Hey jackb, I also really want to adapt this circuit for guitar, but Iā€™m pretty new to circuitry, so I was hoping you would have a layout you could share.

Great adaptation