Light Speed Compressor - another experiment in optical compression

[samhay]

Thanks Febri

[287m]

Thanks Febri

youre welcome Sam
but the thanks is to you, the designer and for valuable share (y)

[Ice-9]

Nice design Sam, I will put that on breadboard as soon as I get some free time.

[samhay]

Cool - thanks Mick.

I also have a theoretical version with a combined ratio and threshold-ish pot for those that want to squash it into a 1590A. I will post a schematic when I have the chance, but it works much the same was as my old AOK compressor.

[samhay]

And here's the 2-knob version:


(click for larger version)

This is untested, but it should work ok-ish. A good place to start for a value of R8 is maybe 10k.

Edit - a cap between comp pot lug 3 and R8 may be needed if the output DC offset on the first op-amp is significant. If so, this will form a HPF with R8, so choose a suitable value with this in mind.

[samhay]

It's now built using this vero layout, which should be a comfortable fit in a 1590B:


(click for larger version)

You will note the mission creep - 12P1T rotary switch in place on on-off-on toggle for attack/release cap selection. I have caps from 22n - 100u. At 100u you get a noticeable dip as the compression kicks in when the ratio is turned up. This may be desirable, so audition your caps.
The rotary switch was more of a hassle than I anticipated as there wasn't enough depth in the enclosure to put the electrolytic caps above the switch pins - hence the squashed mess. In retrospect, I expect that an on-off-on toggle switch will give plenty of control over attack/release times, so I am not sure I would recommend the rotary switch option.

 

Nathan/vigilante - sorry, could fit the '-ish' on the end of threshold.

[deadastronaut]

cool build...

yep that rotary looks a nightmare...

[samhay]

Thanks Rob.
I've built rotary switches into guitars before - Varitone style - but these use smaller value caps (no electro's), which obviously (in retrospect) aren't as tall. Live and learn.

[Kipper4]

Necro post.
I breadboareded this tonight and found it to have a good amount of compression.
Yes it is somewhat interactive with the settings of the pots. and without probing with the ozziescope.
I cant hear what the threshold pot is doing. Might be my ears, might be a breadboard mistake, miswire.
Nice neat little design Sam. Thanks and as you say it can get into near limiter settings.
I breadboarded it with nsl32 opto, TL072 op amp, bat 41 rectifier, No Feedback leds.
I didnt notice any pumping. breathing.
It seemed there was sometimes a delay in the compression but i think this may be the breadboard. or rather the way I breadboard. Compnants shorting.
I didnt rig up the 1u 10uf switch I kept it simple for the breadboard with just the one 1uf cap across the led.
I subbed the input cap to a 20nf cause thats what came out of the box first.
It's late and time for bed.
I'm gonna mess with the vactrol next and see what i can do with a 3mm red and gl5539 roll my own.
PS what are the two feedback leds doing anyway? Limiting the output voltage? Clipping?
Both?
Thanks Sam

[Kipper4]

[Kipper4]

And here's the 2-knob version:


(click for larger version)



I like the simple 2 knob version. It's on the breadboard now.
all parts as in my previous post except my 24k (just what was close enough to 22k, it came out of the breadboard parts box first)
I tried 10k and 47k but like the ~22k.

Suggested parts change for a 3mm red led and gl5539 and 5516 please.
Thanks

[Kipper4]

Wait shouldnt i be able to just use a red/orange led with a gl5516 as a direct drop in for the nsl32

specs
http://akizukidenshi.com/download/ds/senba/GL55%20Series%20Photoresistor.pdf

[Kipper4]

Roll my own report
(Still not ozziescoped it)
I tried a 5mm super bright with gl4437 the attack time seemed a little slower to my ears on the intial attack but once compressing it did a good squshy job.
I tried a 5mm super bright red with a waitrony ke107 ldr (500k dark) and it seemed a little closer to the nsl32
basically i'd try any combination of vactrol and see how you like it. cobber........
"You get me?"

[Kipper4]

Sounds good with a nice brass or thick glass slide too.

[samhay]

Hi Rich,

If you don't find the threshold control very useful, then the 2 knob version makes sense - and you seem to have found it. Thanks for verifying it works! I assume your 22k is for R8?

> It seemed there was sometimes a delay in the compression but i think this may be the breadboard. or rather the way I breadboard. Compnants shorting.
I didnt rig up the 1u 10uf switch I kept it simple for the breadboard with just the one 1uf cap across the led.

The larger the cap and/or the slower the LDR, the longer the attack will be. I am guessing that is what the delay is. Making the cap variable makes it a bit more versatile and you should try 10+ u as it lets the initial attack through nicely (so it sounds a bit more natural) while still giving some sustain.

>I'm gonna mess with the vactrol next and see what i can do with a 3mm red and gl5539 roll my own.

I never tried it will a home-rolled vactrol. This usually seems to have a slower attack, which probably isn't a big deal here. It might not quite get to light speed, but close enough for rock and roll.

>PS what are the two feedback leds doing anyway? Limiting the output voltage? Clipping?

They stop the op-amp clipping when you turn the ratio up and turn the threshold down and/or use a large C8-C10 cap. With the 2 knob version, these may not be necessarily unless you go for a large value of C10 and/or have really hot pickups.

[Kipper4]

Thanks Sam. I'll rig the electros with a switch on the breadboard later tonight and I'll put the feedback Leds in too. Is it worth scoping it?

[samhay]

I can't imagine a scenario where scoping a circuit would be a bad idea.
However, I added the LEDs after I noticed (heard) objectionable clipping, so if you don't hear anything you don't like, then I see no harm in leaving them out.

p.s. The impedance around the vactrol LED is really high, so if you go looking there, use x10 scope probes if you have them.

[duck_arse]

I get you, cobber, it's the right "sam hay", but the wrong "optical compressor". thanks for the vid (I prolly should listen to it agin, listen for the kazoo). and if I have to plug swap for audio, you have to osc-ope, cause sam said.

[samhay]

I can answer to cobber too if it helps - I have a piece of paper somewhere with a picture of a kangaroo and an emu next to my name.

In other news, I had a recollection that I ripped the envelope/compression indicator out of my build as it was contributing some noise - probably LED conduction causing spikes on the power supply. Rich - did you add the indicator?

[Kipper4]

No I left it off mate