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BMC43 4x Decay [new PCB]
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author BMC43 4x Decay [new PCB]
Hi everyone, I have a simple new PCB available. It is the decay circuit from my analog drum module produced 4 times on a single PCB, so each channel is just input, output and decay knob. There is a pulse shortening circuit so it treats all gate/trigger/oscillators as if they were the same length and it makes for an easy to build/use way to help make percussive sounds from your modular instead of using integrated percussion modules.

Here is the page on my site for this design.

woohoo another awesome BMC circuit. looking forward to this build. your PCbs got me started in this game and to date are still my favorite. my next order will be considerably larger then my first one. I love your circuits!
Great! I had nearly the same idea ot design something like this. Only i wanted to incorporate 4 hardwired vca's also.
Really handy for drums.
You could of course just stick 4 vactrols on it Guinness ftw!
Finished mine last weekend. I decided to add some switches to slip in a longer decay without needing to redial

Here's a thing. I'm trying to use this to control an exponential VCA, but I'm finding the output just too low to be of any use. If I'm seeing about 7.5V at the output of the TL074 (say pin 7) then I'm only seeing just under 2V at the output jack

Ideally I want to see 5V. I wanted to ask what was the thinking behind the voltage divider on the output ? I'm operating at +/-15V so the divider is set as per the BOM - 6K2/2K2. Before I start mucking around with stuff I wanted to check if there's anything I've overlooked.

My thinking is that I can change the 2K2 on the divider to 1K (because it's at the edge of the board so easier) to get the 5V output

(or piggyback 1K8 or 2K over the 2K2)

Anyone got any wise words ?
unrecordings wrote:

Anyone got any wise words ?

not really.

But if zou change the 2.2K to 1K, the voltage should be even lower, right. You better put a resistor parallel to the 6.2K (for testing). Or replace the 2.2K with a larger resistance.

That said, however, you may also check why there is only 7V on the output of the TL074. Does it see the full +/-15V or something close on the power inputs (4&11)? Is the input resistor really 10R?
Ah yes, guess who forgot to reset the values on the potential divider calculator

10R is, I believe part of the power supply filtering, in place of a ferrite
Well power rails were fine. Voltage coming out of the diode was +7.5V

So I just decided to swap out the 6k2 for a 1K to give a nice 5.1V ish output
If I find that 2V is useful then I'll just use attenuators

But for now I've got some white noise hooked up to a bunch of fixed filters, the voltage to rhythm converter is doing it's thing and the quad decay is firing a bunch of exponential VCAs and everyone is happy (save maybe the neighbours)
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