Clean Squeeze Compressor 2020

[rankot]

I built this one long time ago, and always liked it. Based on Afterlife/Flatline, it was actually the only one opto compressor that I built that worked as expected. It is very nice, and has full wave rectifier, so almost any vactrol can be used. This is the original schematic:



After some time, I decided to try to mod it a little. DISCLAIMER:I still didn't try anything of this, just made a concept schematic, so I must ask you to take a look and give me your suggestions. This is the modified schematic:



And PDF: https://docdro.id/dN96skN

So, those are the changes:

• added JFET buffer in front
• added switch to choose between compressor or expander (it actually connects LDR in parallel with R1)
• switch to work as feedback / feed forward (not sure if this will work)
• "low pass" switch (when open, only highs pass to envelope detector)
• HP/0/LP switch (another variant, this one can pass full band, lows or highs to env. detector, will use either this one or previous one)
• Attack pot, I presume it will change the speed at which filter capacitors will charge
• Attck switch, to choose different filter caps
• Release pot, I presume it will change the speed at which filter capacitors will discharge
• Threshold pot, I presume it will change the LED current
• MOSFET based compression indicator (PRR shown something like this long ago)
• or simply parallel LED indicator
• and finally, another dual op amp to make Vref more stable and, if needed to make an output buffer / volume control at the output.

So, what do you think? Any obvious mistakes?

:EDIT: Please note that I used BJT opto symbol for LDR opto and I have three different JFETs in input buffer simply as a placeholder for different pinouts.

[garcho]

added JFET buffer in front

Why would a FET op amp need a FET transistor in front of it? Is it to buffer the feed forward option?

switch to work as feedback / feed forward (not sure if this will work)

I'm not either, and I'm not sure if it's needed What do you want out of the feed-forward option? That tends to be more of a studio compressor thing, not a guitar pedal thing. Obviously, a big generalization. The worth of a great "one-knob squeezer" like the original you showed (assuming it sounds good, I haven't heard it) cannot be overstated, especially for a guitar pedal.

if needed to make an output buffer / volume control at the output.

Not needed.

That BJT optocoupler in the schematic is an LDR in real life?

[11-90-an]

Cool ckt...

I don't have any germaniums or schottkys so i can't try it on the breadboard... yet

+1 on not needing an output buffer...

[rankot]

Why would a FET op amp need a FET transistor in front of it? Is it to buffer the feed forward option?

Exactly. Wasn't sure how it will behave when using feedback option, so I put this buffer. Will do no harm. 

I'm not either, and I'm not sure if it's needed What do you want out of the feed-forward option? That tends to be more of a studio compressor thing, not a guitar pedal thing. Obviously, a big generalization. The worth of a great "one-knob squeezer" like the original you showed (assuming it sounds good, I haven't heard it) cannot be overstated, especially for a guitar pedal.

That's the point. I wanted to promote it a little - so not only for guitar use. We have a small home studio and this could be handy. 

if needed to make an output buffer / volume control at the output.

Not needed.

That BJT optocoupler in the schematic is an LDR in real life?

Yes, LDR really, but had no symbol for that, so used this one. I'm planning to use few different models, until I find the one which works fine and IS obtainable. So maybe NSL-32, or even home brew, who knows?

[rankot]

OK folks, updated schematic:

https://docdro.id/CWIveBC