PMC - Poor Man's Compressor

[11-90-an]

"Recovery" mod....
Scrapped R16 and replaced R17 with a 10k resistor and 100k pot with a 22uF cap in parallel to smooth out some volume loss... I have no oscilloscope so I can't measure the attack/release times...
Basically starting to look like more of a dynacomp...

EDIT: Putting a 10nF cap in parallel with the 1k output resistor works too...

[jonny.reckless]

And also, jonny.reckless, why did tou use a transistor configured as a diode rather than a diode itself? Diodes are cheaper...

To make the peak detector input impedance symmetrical. You can use a 1N4148 there and it will work, but the turn on voltage for negative and positive half cycles will be different which affects the sidechain slightly. I pay about a penny for a 1N4148 or a BC546 so there's no difference in cost for me. The total component cost of the poor man's compressor (neglecting the footswitch and case) is less than $2 hence the name.

[jonny.reckless]

Just wondering jonny.reckless, why didn't you put the peak detector at the input side like the engineer's thumb? It would probably give adjustable threshold, attack and ratio... and sustain... So adding volume/level to that, you have a 5-knob compressor!

This type of peak detector doesn't work well with a feedforward topology. The design was inspired by the simplicity and beauty of the Dynacomp, hence just 2 knobs for sustain and level. I've designed several feedforward circuits including both revisions of the Reckless diode compressor, but that wasn't my design intent here. The goals were low cost, simplicity and a nice squish. The engineer's thumb is a wonderful design, but it's a fundamentally different architecture. If you're interested, I did an engineer's thumb redux variant a few years ago, featuring lower noise and the inclusion of a flexible noise gate. That has 8 knobs and a switch
https://www.diystompboxes.com/smfforum/index.php?topic=97123.msg1129089#msg1129089

[11-90-an]

Ok.. Makes sense...
I tried swapping the transistor with a diode and there was a bit of a difference.  The transistor sounded better....   

the engineer's thumb redux that you did sounds amazing, thig is the lm13700 is pricey...

[Rob Strand]

An interesting variation to the dynacomp full-wave is the one used on the Eden WT400,
https://elektrotanya.com/eden_wt400_pre_sch.pdf/download.html#dl

See Q5 and Q6.  I did a slightly more balanced version at some point.  IIRC I added another transistor somewhere so only base currents flowed.  As it stands one polarity has base current and the other emitter.

[bartimaeus]

does anyone have an enclosure drill template for the rev B? since everything is PCB mounted, not much wiggle room so i'd like to play it safe.

[bartimaeus]

update, i threw the gerber files in a viewer and measured it out.

not sure if anyone else has the original PCB, but here's what i found:
the top edge is 53mm above center.
the pins for the pots are 8mm below the center, and 15mm to either side of the center. note that the actual pot drill holes are ~16.5mm above the pins.
the jacks are centered 23mm below the center.
the 3pdt is 43mm below the center.
the LED is at 16, -43.