Okay it was wrong…

I admit it… the mic pre was almost right and the idea for a compressor was just plain silly!
But I published them at DIYstompboxes and was told, by PRR, how to do it properly.
mic pre comp
As you can see the pot has been moved to the emitter and therefore sets gain. Big signals wre just hitting the rails because the amplification was at 100 which is too much. This way the gain can be set anywhere between 8 and 100 which is a much better way to do things.

PRR at DIYstomboxes then kindly threw together an LED driver and put the LDR in a place where it’d work. Then I, always a twiddler and asker of questions, have published the above with the addition of pots and a trimmer to be able to tailor the compression somewhat.

Hopefully the 10k across the diode kinda allows turn on to occur when you want it to so would be attack I suppose. Lower resistances to ground would allow the smaller signals to go to ground and keep the LED from lighting until higher signal crossed that threshold… so maybe it’s a threshold control…
Then the 100k would allow the overall resistance to ground, and therefore the voltage divider between the 5.1k resistor and the resistance of the LDR leg to be set and therefore the amount of compression. The LDR thats gonna work has a dark resistance of about 1M and will go to about 5k at full light. Adding 100k means the overall resistance to ground would only go up 10% but the resistance at full light could be 5k to 105k, against the 5.1k resistor and so set compression from 50% to about 5%. The trimmer allows one to tailor the resistance curve accross the LDR somewhat while also making the dark resistance of 1M somewhat insignificant as a high impedance.

It’s still mostly untried yet though so maybe the resistances of the pots and trimmers could be better at other resistances. The trimmer might be better at 100k or even 250k while the 100k could be a 50k pot over a 50k resistor.

Good Golly… does this mean I have to breadboard something?

First though, I’m gonna change the mic pre I’ve already built and take the 100k pot off the end and relace the emitter resistor with a pot and a bigger cap of 100uf.

Right now though, I’m going to go accross town to pick up a broken stylophone beatbox. I’ll try and fix it but mainly I want to have a good look inside and get the schematic… hopefully it’s not SMD and digital in any way but as simple and straight forward as the original stylophone.

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