DIY Modular Compressor ?

[funkyfarm]

Hi !

is there any use in a modular COMPRESSOR/EXPANDER, a signal range processing module ?

I've understood BugBrand got an opto-compressor but i've found nothing else.


CRAIG ANDERTON COMPRESSOR is based around VTL5C3...
http://www.fortunecity.com/tinpan/humperdinck/223/effect.htm

Is this adapted to 10V p-p would be great ?


Or do you know this ? forselltech...


Is this a way to simulate compressor/expender with standard module (vca, env follower...)

hmm, hmm, quite a bit of questions ; answer ONE and ...you win !

[bugbrand]

Yeah I used that Craig Anderton design - its out of Electronic Projects for Musicians (good book). I think I built it pretty much straight and don't remember doing too much modification -- I like it already -- but I'm sure there'd be some good tweaks to improve it.

[funkyfarm]

Of course YOU answer and win !

maybe tweaks for time constant ?

Is stock OUTPUT potentiometer real use ?

And for the winner, the subsidiary question...

Will you describe it as :

a - "hard knee"

b - "soft-knee"

c - "i'm afraid you can't see it as having knees at all"

[bugbrand]

Yeah the output dial is very important --- its the output gain setting, so vital for bringing the signal back up to a decent level after being squished.

I dunno about knees really
(though oughta!)

[State Machine]

You might find this compressor / limitor design APP NOTE useful ....

http://www.thatcorp.com/datashts/dn115.pdf

There are many others like it

Bill

[para]

wel it is opto- so more then likely its more of a soft knee. you never know until you try.


steven

[funkyfarm]

[para]

the knee is the character of either its aggression or smoothness used to clamp down on anything above the threshold. the attack is just the speed it responds as you know.

this design is actually meant for guitar use so there may need to be some changes to get it to react to louder signals better but it should be fine ( i think in this case the 220k might also represent the impedance with the 1M in the feedback path ? i'm still learning but it could be changed to 100k if you want to try it ). but because its designed for guitar this is why you see the featured name "sustain" instead of ratio. i'd personally mess with the feedback resistor on the first 072 changing the1M resistor with a 1M pot might give you a threshold adjustment. ??? maybe. there doesn't seem to be release option? just the natural fall of the vactrol perhaps

but again take all that with a grain of salt. they are just wild guess's until i get a sec to build it myself.


the CLM6000 might be another vactrol brand's model number ? i don't know

[piedwagtail]

Optos are soft knee but the main point is the non linear lamp/led response which is dearly loved by the ear for some obscure reason.
Anyrate,haven't been here for at least a year....

I built four valve (modular!) opto compressors this spring.
The design is a mash-up of a too complicated and overly vactrolled
http://www.hamptone.com/tapeop2005.htm
not feeling like paying up UPS customs/shipping on vactrols from Newark thru Farnell,i hacked ahead with standard LDRs and yellow leds and that cable stuff you melt with a match....

here's the hack..just three transistors....get rid of the fussy opamp...15V supply no problem...i had a 12 V spare.The last jfet changes the varying DC voltage into a current for the 2N3904.I can't remember the precise emitter resistor but it was empirical for the led brightness.
{MISTAKES on back on envelope...2N3904 of course and i put a 10k in series with the release pot to stop it from interferring with some charge up at least}
After the LDR potential divider,the out goes to some sort of make up gain....mine is a 100k pot into the fascinating Broskie Variable UL pentode Aikido circuit


The double pot moves the input pentode(mine EF86) from triode to pentode operation...one can dial in distortion as well as compression.The ear is very alert to even (triode) and odd (pentode distortion).Odd works great on hardening toms and even is good on softening cymbals.
My build is modular in that the psu is outboard and the opto and makeup are separate...
four modules...each section can be used alone.
I don't bother with balanced polarity after the mic preamp it's completely overrated.
For anyone considering tube work,make life very easy for yourself and buy a tube regulated power supply.Costly perhaps,the Heathkit 2717 is super by the looks of it up to 400V at 100mA and plenty of LT,,,,,but it takes away so much bother.
I've built a few supplies and it is generally the hardest part.I'm using a Fluke 407.

I'm slow to finish the mechanical racking/decalling but in operation these are super.
Made my snare drum playing sound like Billy Cobham!
Buttery Fat.
The side chain is so simple and yet it works fine,plenty of leeway for adaption.
The A R controls allow plenty of sculpturing and the slow knee is great at missing the initial transients.
Just follow with a X10 opamp to avoid the HT.
For 10V p-p,you'll have to attenuate in and vamp up the make up opamp.Not sure any of these mentioned compressors will handle swings like that.Forsell and co is studio +4 dbU at most and guitar compressors are mV.But you could splash out $2500 on a fifties Collins/Gates/RCA broadcast compressor,they'd handle big swings.
But voltage is cheap in a modular so just attenuate heavily,pass the compression and then blast it back up.

For your modular stick a Thomas Henry 3080 VCA before or after the opto and add and subtract a parallel compression feed.
I will certainly be messing with that when i stop building,hence the modular build so i can stick the hacked Hampton into the modular brain.

That Forsell link...try the EQ LC circuit....it's the most impressive thing i've heard as a DIY......shows one what a pathetic compromise most eqs on mixing desks(at least that we can afford)are.I stuck a rotary switch with12 different caps on top of some dirt cheap inductors from Rapid,5 sections with 5532 as the opamp.Truly powerful and certainly worth putting in a modular.Simple again and hard to fuck up on.

Now back to a vari-mu comp....where's the weller?

Robert

[para]

Allied sells vactrols

http://www.alliedelec.com/Search/searchresults.asp?N=0&Ntt=vactrol&Ntk=Primary&sid=464CEC80107C617F&i=0

nice work, but working with tubes and voltages that high scares the F__K out of me.


steven

[Scott Stites]

Dang, Robert, where have you been?

Nice to see you back.

Good info, too!

Cheers,
Scott

Edit: OK, that was a stupid question. Tube synth - that's where you've been. All that would have taken me two years. Or more.

[zipzap]

A DIY Modular compressor
Great topic! Currently i´m working on my diploma for university. I was lucky to get a diy subject approved.
The work will be about the history of messed up sound in theory and will have the design of a "new" dynamic tool as practical part.
So right now i´m experimenting a lot and collecting information.
I´ll do some posts when i have some more to share, no shematics for now - till then:
Compressors always work by these pronciples:
Gain cell (=vca), cv generating and cv processing.
The way these components behave will give you different rersults.
What i have done till now is build different vca-designs (SSM2018, diode bridge, vactrol, pentode)
They all sound and respond very different...
btw, you normally want an vca with unity gain at 0v cv and that attenuates with pos cv. So that´s different from modularsynth designs, although cvs can always be inverted and shifted, so it doesn´t really make a difference.

Then you need a "precission full wave rectifierer"
That´s a standard opamp circuit. http://www.elektronik-kompendium.de/public/schaerer/syncrec.htm

Threashold can be applied here: The cv gets an offset (threshold pot) and passes an "ideal diode", another opamp-classic. THe offset will determine how much of the rectified signal will pass. Everything at min threshold, only peaks at high threshold.

This will give you a cv that has to be smoothed. Here a lag circuit comes in, to give you atack and release controll. This is the coolest, most interesting part. If you want pumping drumbeats you need these controlls!

The ratio is nothing but a pot that sets how much of the cv will reach the vca.

Lots of theings for us to interact.
It makes a huge difference where the audio for the cv is taken from.
Ahead of the vca is called feedforward. With this methode its possible to get very drastic results, eg "negative" ratio. You´ll find out...

[zipzap]

some reading:
http://www.tonmeister.ca/main/textbook/node407.html

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[bugbrand]

On the subject of THAT chips - there's the THAT2180 - I used a couple of these in an SSL buss compressor clone. Sure there must be ways to get 'em right in a modular setup.

CLM6000 -- yes, that's the optocoupler C.Anderton uses for all the designs in Electronic Projects for Musicians. Never seen mention of it anywhere else...

[funkyfarm]

really thank you all !

We're reaching high voltages here....as well as high points !

[zipzap]

the link above explained it pretty good to me.
Threshold is not just ofset.
It´s (neg) offset followed by an ideal diode that will let only voltages above 0v pass.
So as long as the cv from the envelope follower is below the offset (threshold) level, nothing will get to the output.
Ratio is the amount that reaches the vca.
Timing is a cab with independant charge/recharge (via diodes+pots)

If it sounds right it is...you know

[mediatechnology]

You might be interested in this one:

www.picocompressor.com

In the interest of full disclosure this is the website Roger Foote and I share. They've turned out to be pretty popular over at Prodigy-Pro and make a really good stereo program compressor (two units) when connected in "true power summing" mode.

Schematics are here:

http://www.picocompressor.com/picocomp/Image_Index.htm

[elektro80]

[synth_ollie]

Ive heard the the picocompressor is good

a vc compressor in a modular can be useful sometimes, I built my cv compressor from an old boss cs-3 compressorpedal,
it was very easy to modify it for cv control

[funkyfarm]

oh yeah ?



with a vactrol around sustain pot or with transistor ?

[synth_ollie]

yep, thats the one

if I remember it right (I have the schemo somewhere...) the sustain pot
sets a voltage to the input of an op amp, so you just have to add a jack and a resistor at the sus. pot and there you are

also there are some simple mods for the cs-3 to make it perform much better than original, just by changing some resistors and caps, I have info on how to do that somewhere too....

[bugbrand]

Hey, going back to the orig Anderton project mentioned at the start --- I'm building a new one for my special custom mixer so I've been looking again......

On that posted schematic, the 1M eedback resistor on the 1st half of the TL072 --->> in the orig documentation its recommended that that is 220k for line-level operation.

I'll try some tweaks out and see how things work-out.. I'm aiming to have it as a complete mix compressor (maybe lofi! -- will, obviously, be bypass-able)

[para]

but isn't modular level actually higher then line level ?


+4 dBu is 1.228 V
−10 dBV is 0.3162 V

[funkyfarm]

[funkyfarm]

I'd like to test this design around C3 but I need something like a option-switch to get fully decided !
it could be circuit-bending, body sensor

No way to tweak response ? harder knee (different faster cell ?)