Smooshy face - and Afterlife on +-9V and a clean blend/boost

[midwayfair]

This is an optical comp with blend. Based on the John Hollis Flatline for the compressor side. The other side is just an op amp clean boost and clean blend using FET buffers. It takes up to 12V input and uses a charge pump for split rail operation to +-12V for some really high headroom. The compression and clean outputs have completely independent volume controls, so they can both be at, above, or below unity.

I'm building a small acoustic pedalboard for a Celtic project me and a friend are starting, and I needed something that would really leave the initial attack unmolested but would also give me a bit more sustain sometimes for airs and stuff (without just washing the whole thing out with reverb). I thought a bit about it and the afterlife had a lot of the characteristics I wanted, plus it was small enough that I could add the clean blend.

Unfortunately, as you can see from the guts, some things ended up going a little less smoothly than I anticipated. I was originally planning on just using the two extra op amp stages for summing, but I couldn't for the life of me get connecting two pin 1s together. Either output was good but if I connected them it distorted like crazy. I know I'm doing something wrong but while I anticipated it to work the same as tying the drains or sources of a transistor together, that wasn't the case at all.



The schematic is a bit of a work in progress. I used an A pot for both volumes, but I think a B pot might be correct for the clean blend, particularly if it ends up being just a 2x boost.
The vactrol is an NSL-32SR3, which is pretty fast for an optical device (5mS) and has really really high dark resistance, so it's a great choice in this circuit.

Some other options I considered:
1. I considered just adding the clean blend to the Diamond, but I've already got an EQ for the board (Source Audio EQ2! Amazing pedal, it's even a tuner and limiter).
2. I believe that it works to put a very large value pot in parallel with C1 to work as a decay control. With a limiting resistor of course. It's hard to figure out what the actual decay time is, though.
3. I'm not completely certain but I think a pot in series with a cap in parallel with R4 is a workable attack control. The other place to put it would be to ground between R4 and R3.

I chose to forgo the extra controls in part because the clean blend makes the attack control kind of unnecessary -- and you can't really get an instantaneous attack anyway, since it's optical -- and in part because I wanted a simple pedal. But also in part because the enclosure was a pre-drilled (for two pots) gift from a friend, and I wouldn't have really had room for the fourth knob.

There's an unused op amp and I'm not certain what to do with it, it seems a real shame to waste it, but since I wanted the boost (and not just unity) for the clean blend, I needed the extra op amp stage.

Charge pump not shown, it's just the normal LT1054 +- voltage circuit. I wanted the extra headroom for safety, and I also just like that everything's biased to ground to minimize switch pops (which the afterlife seems to have a problem with, though it's not completely cured here) and that it becomes really easy to just DC couple everything to avoid capacitors.

oh -- also, I think the two transistors tied together could maybe be BJTs with no change in parts otherwise but I didn't test it.

[jimilee]

Smooshy face!!! Very cool Job. Your awesome builds are missed around here.


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[karter2000]

Dou you have a layout available?  I have an afterlife that I love, but would love to build this.

[midwayfair]

Dou you have a layout available?  I have an afterlife that I love, but would love to build this.

Are you okay with perfboard? I can add it to the perfboard library when I get a chance.