Circuit Salad's *Optical* Orange Squeezer -- layout and discussion

[midwayfair]

Ray Ring started a thread for his delay recently, but nothing for this particular circuit. I love compressors and the Orange Squeezer particularly, so when I saw this I pretty much had to build it. This is an outstanding sounding compressor. It sounds a lot like an Orange Squeezer, but involves no biasing (so you know yours is actually working as a compressor), and the compression knob can be run all the way down to work as more of a boost all the way up to a really hard squish.

Here's the schematic from his website for the simplified version (original version is here: http://circuitsaladdotcom.files.wordpress.com/2012/09/compressor3.gif):


This can also be built fairly cheaply -- although his original schematic calls for a fairly expensive OP amp, I found that an LM358 worked very well, too. The only other uncommon part is the H11F1, which can be picked up for a couple bucks from Mouser.

Here's a verified small perfboard layout for his "simplified" version. Keep in mind that the spacing may be a little tight for full sized electrolytics and 1uF box caps, but I did this layout to fit in a 1590A.


https://dl.dropbox.com/u/9878279/Jon%20Patton%27s%20layouts/opto-squeeze%201.2.pdf

[Sorry for the giant images, for some reason they won't resize.]

Edit: Replaced a corrupted picture file.

[midwayfair]

Ray noted some distortion on minimum comp settings, so I did some more testing and discovered that disconnecting the Comp pot from ground corrected the problem nicely. Among the benefits of this is that the circuit now seems to work with a polarized sustain cap (just like in the regular squeezer), and a separate resistor can be used (completely optional) if you wish to adjust the decay. My layout has been updated.

Edit 8:30pm: Ugh, nevermind. After boxing it, I found that this lowered the output way too much and killed a lot of the compression control (no boost anymore ). The better solution was a resistor between the Comp knob's Lug2 and IC1 pin 5. This constricts the compression range a little, but it doesn't distort on the lowest settings and can still get well above unity.

[rockhorst]

I have one of those opto chips to spare...maybe this is a good destination for it.

[John Lyons]

Cool stuff Jon. I need to try this as well.

[midwayfair]

the distortion seems to have been tied to the voltage (anything >200mA) across the opto-FET. Ray Ring just posted a solution to the distortion issue on his blog:
http://circuitsalad.com/2012/10/17/opto-fet-issue-solved-with-negative-feedback/

"By applying shunt feedback from the Drain to the Gate of the first JFET stage of my compressor, I reduce VDS across the optofet  by a factor of 5! So with a input of 1 volt, the the VDS of the optofet is about 200mV worst case. Now it performs beautifully. The feedback consists of a 470k ohm resistor in series with a .1uF cap from drain to gate. Now the source must be bypassed with a 10uF cap – where before it was optional. The gain of the stage with this feedback is now about 4. What happens is that the feedback subtracts from the input at the optofet drain node greatly reducing the VDS across the voltage controlled resistor – while still providing gain."

Hopefully there will be an updated schematic. I'll be updating my layout after I can get home and test/verify it. This looks like a MUCH better solution than my hack. Looks like I'll need to revisit it a little.

Hope he doesn't mind me posting this here, I'm just excited when I see innovation in compressors.

[Processaurus]

Thanks for pointing this out, I'd never seen his site before.  Looks like an interesting designer in the pedal world, as he is comfortable using modern parts and MOSFETs.

[midwayfair]

Thought I'd update this thread now that I've boxed up my build. I ended up even further simplifying his design: I simply grounded the FET sources and ended up saving a couple parts and getting a little more output.

Ray posted his new version in another thread recently. I ended up not using his shunt feedback fix because it lowered the output below unity on comp settings past noon; I figured it was easier to just not use the lowest compression setting on higher output pickups than to deal with the volume drop.

Alternatively, I could see applying the shunt feedback mod and then changing the output stage to a pretty standard MOSFET booster. This would give you a big gain boost on the output without contributing much in the way of noise. I'm kind of done messing with it, though -- I like how it sounds with the comp knob near noon, and my guitars don't distort it, so that's good enough for me.



Here's mine (the perf is a little different from the above layout because I changed it a little after it was done and had some standing resistors in a previous layout):

[rring]

Midwayfair did alot of work the tweaking this design and I have to thank him for figuring out that the LM358 will work in these ground referenced op amps designs. To extend this even further I have worked up a new design that uses 2N7000 or other generic enhancement mosfets for the gain stage and voltage controlled resistor. It uses the LM358 and any silicon diodes you please. I added an LED driver that gives a visual indication of compression level by changing the intensity of the LED.  There is lots of room to play with this thing - in terms of gain, attack, decay, etc. Many of my component values are non critical and I am still tweaking values myself  as I try different guitars, playing styles, etc. I hope someone will try building this and hopefully make some improvements as Midwayfair did with the opto version.

I have a board layout which is verified and is an expresspcb file that anyone can use as they please. Its available at www.circuitsalad.com.

here is a picture:


here is the schematic:


demo:

[midwayfair]

Cool -- I like the idea of the compression indicator! Some nice "pop" in sound on the demo, too. Thanks for sharing this one, and for sharing your PCB files.

[midwayfair]

Ray revised his Opto-FET comp design recently. So of course I built the new version. It's excellent. It has a lot of the attack characteristics from his MOSFET compressor, with a decay pretty much identical to the Orange Squeezer. The tone is a bit more transparent (not nearly as bright), it's quieter, and the threshold (compression) control is much, MUCH better than in the first version. It doesn't squash as hard as the MOSFET compressor, but now it really does sound like a better Orange Squeezer.

It's also fewer parts than either compressor now. Amazing job for how few components are involved.



New layout:

(I used 22K in place of the 100K on the input for a brighter sound.)

Current schematic:
http://circuitsalad.com/2013/03/02/the-opto-compressor-revisited-simple-and-works-well/


I might do a layout for this one in Eagle, single or double sided.

[Kipper4]

Chips and darlingtons ordered.
Thanks guys. i'm gonna try this compressor.

[Kipper4]

what is the H11F1M thing and where can i get one pls

[midwayfair]

what is the H11F1M thing and where can i get one pls

IT's an opto-FET, a chip-based type of optocoupler. You should be able to find it at mouser.

Tayda sells a bunch of chips like it. If you want, I can see if some work tomorrow morning (I have pretty much all the different kinds tayda sells). It's also possible to use a regular optocoupler, though you need really, really low light resistance and a fast response.

[Kipper4]

i got one on ebay thanks jon

[Kipper4]

i'm intrested to see the ones on Tayda if you have a link though.
thanks

[Kipper4]

i found some on Tayda, I am intrested to see if they work in the circuit though please Jon

[midwayfair]

i found some on Tayda, I am intrested to see if they work in the circuit though please Jon

I couldn't get any of the chips Tayda sells to work just by plugging them in, but there could be some way to make it happen. If I get them to work I'll post it here.

If you order a few of their generic photocells, you can use one that measures above 1M dark and below 2K light. I found a couple that worked, but they vary widely, so order more than just one or two. It's not as good as using the H11F1 (which has more predictable results and a better attack), but you can use a socket and plug in the chip later. I did sometimes get a little distortion, so there may be other issues that need solving if you go this route. It's not adequately tested and keep in mind that it won't function the way the pedal is meant to.

[Kipper4]

i ordered a couple of octocouplers H11f1 from china. i hope theyre ok
they have the fairchild F on them but they could be fakes so i wont know until i try them now.
i like making compressors too . Does it show?

[duck_arse]

It's also possible to use a regular optocoupler

jon, do you mean led - transistor/darlington, or led - ldr?

[midwayfair]

It's also possible to use a regular optocoupler

jon, do you mean led - transistor/darlington, or led - ldr?

It's *possible* to use LED+LDR. I don't think it sounds as good, mainly due to the light memory and the time it takes to fire up, though the VTL5C1 has similar turn on time to the chip. The H11F1 is also cheap ... part of the reason I was originally excited about this design, actually.

Incidentally, I talked to Ray a bit over e-mail about some other aspects of this particular design if anyone's wondering about a few parts:
1. R4 (the 470K base > ground) basically sets the maximum compression swing, linearizing the response some.
2. In my version, I built it with a 22K on the input, instead of 100K. Ray did the math, and the difference in volume attenuation (assuming the LED in the chip turns on fully) is negligible, so you can in some ways control the overall brightness of the effect by changing that resistor. I like my compressors to be slightly brighter.