Compressor with side chain / ducking – recommendations & convert layout to 9v

[AROLB]

hello there! hope you're all well and enjoying the summer.

2 parts to this hopefully fairly straight-forward query. firstly is it possible to add a side-chain/ducking trigger input to some of the diy classic compressor circuits out there, like the orange squeezer or mictester's really cheap compressor, or even the dyna comp or Toadworks mr. squishy. Just looking for it to perform a pretty basic function.

i've seen it being done with the engineer's thumb, but curious if it's achievable with something way simpler.

part 2 – otherwise i was planning to build the moritz klein compressor that does that, but realised it runs on modular 12v. what would one change to make it workable with standard 9v?

schematic page 57 here https://www.ericasynths.lv/media/COMPRESSOR_MANUAL.pdf

and any tips on reducing the height of the layout – haven't got perfboard as tall as that!

many thanks,
rai

[PRR]

really cheap compressor, or even the dyna comp or Toadworks mr. squishy. .

It is too much brain-pain to trace non-trivial circuits from layouts. The schematic is far easier to reason from.

...the moritz klein compressor that does that, but realised it runs on modular 12v.

That uses +/-12V, two supplies. It can of course be re-imagined as single supply but that is tedious and error prone. (I made that mistake on my first limiter and the hack was never totally satisfactory.)

[AROLB]

thanks for the reply paul. here's the schematic for mr squishy (Link)

built it last night, does a good pumping compression and been messing with it to see if i can affect compression with an external source. it's sort of possible but seems to require sine/square signals. interested to hear how you think it can work. thanks!

[Eddododo]

thanks for the reply paul. here's the schematic for mr squishy (Link)

built it last night, does a good pumping compression and been messing with it to see if i can affect compression with an external source. it's sort of possible but seems to require sine/square signals. interested to hear how you think it can work. thanks!

Edit: Merlin makes a good point that adds a little context- if you want to mod this particular compressor because you like the feel, It's worth considering that the particular squishiness is partly a result of the feedback topology, and the response may change When triggered by a source that is not beholden to the feedback aspect
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The simplicity of that one makes it tougher; if you like that one and don't mind the parts count to mod it being a high percentage of the circuit, then I'd personally do something like this:

Take the output at the node with the 4u7 cap and the 2k1 resistor, and run that into its own buffer- to be the 'dry buffer.' Then from an added input jack, run the external source/trigger into another buffer, preferably one with variable gain (I guess that's an amplifier, not a buffer), the 'side chain buffer.' The side chain buffer and the dry buffer will both output into the resistor-> diode - the 'rectifier'

How you mix them  depends on what you want- you can have a switch that chooses between the dry signal or the external signal; if you do the switch method, then you only really need one buffer, mostly just to isolate the Dry output itself from the incoming signal.

You could instead use a blend/pan of some sort to mix the normal guitar-triggered compression trigger with the external source compression trigger. You may find you want another op amp to blend the two, or you may find that you're happy with the results of passive resistive mixing, with the blend controlled by volume pots for each signal, or some sort of blending pot scenario... the thing to watch for here is the relationship between the signal levels, the series resistance from what was originally the 2k1 resistor, and what the diode wants to see to turn it on. Mixing the two signals is probably easiest done into an op amp, taking the output to trigger the peak follower etc


It's a lot to throw into that circuit, but so what? If you like that particular feel, then what's a couple of op amps between friends?! There's almost certainly a more elegant way to do it; because the squishy is so simple, it's hard to say when we enter a 'ship of Theseus' scenario, but if you just want to kludge it into that circuit, this will work, with a little effort to tweak the resistor(s) before the diode


And then if you want to get crazy, adding some high-pass capabilities on the sidechain and/or dry signal is always neat.. for bassists, it's VERY helpful to get the compressor to react less to high energy low frequencies, but in practice it usually *feels* like you're just adding a secondary threshold/compression/ratio control. In this case, it's probably helpful as a means of catering the external signal into something that works how you'd like.. even with the gain control, some signals may just be more wieldy if you can ease some of the low end content- like if you're using idk an external recording of a song to create weird effects

[merlinb]

is it possible to add a side-chain/ducking trigger input to some of the diy classic compressor circuits out there, like the orange squeezer or mictester's really cheap compressor, or even the dyna comp or Toadworks mr. squishy. Just looking for it to perform a pretty basic function.

It's tricky with those circuits because they're feedback compressors. They rely on the side chain receiving the 'corrected' output signal to produce the right amount of compression.

[AROLB]

hey ed and merlin big love for going to town explaining this – much appreciated.

gonna spend some time over the weekend on this. im still quite new to circuits, so if it's not too annoying do you mind confirming these in relation to the perfboard layout i built..

Take the output at the node with the 4u7 cap and the 2k1 resistor

take this output from rail 2, between 4u7 and 2k1?

The side chain buffer and the dry buffer will both output into the resistor-> diode - the 'rectifier'

perhaps then output back to the spot right of the 2k1, or somewhere else?

my application of this is in a mixer setup, mostly for the sidechain function and less for it to doing general compression. so a switch will do nicely i reckon, keeping it simple.

if you do the switch method, then you only really need one buffer, mostly just to isolate the Dry output itself from the incoming signal

do u mind explaining this quickly – so i'll put the external source through a small amp circuit and into the rectifier – this external source won't be audible in the final output, just triggering the ducking – correct? or i'd need this other buffer as you mentioned to isolate it. thought the switch would do the job of isolating the 2?

if you want to mod this particular compressor because you like the feel, It's worth considering that the particular squishiness is partly a result of the feedback topology

ah yeah it's sounding good, but tbh im trying to figure out the simplest and most effective way to make a sidechain compressor using 9v pedal circuits, to be used at the same time as several fx chains so it can be very basic without that much control over the parameters. most things im finding are for modular setups with +-12v whereas i've been building all guitar circuits!

many thanks guys