Percolation Station -> Karma Suture (sort of)

Chuck D. Bones

Circuit Wizard
This is my attempt to replicate the Catalinbread Karma Suture using the Percolation Station (Harmonic Precolator) board. Catalinbread offers some tantalizing clues in their adverts as to what they did to create the Karma Suture from the Harmonic Percolator. I have not been able to find a Karma Suture schematic, and so far, I've been too cheap to buy a KS to trace myself. So this is my best guess. The KS adds two knobs: DIODES and DENSITY. I put my own spin on it and added a diode switch. With DIODES and DENSITY dimed and the DIODE switch set to GE, it's a stock HP.

The DENSITY control rolls back the bass at the input, which has a huge influence on the tone. I replaced C2 with a 3.3nF cap and then wired a C100K and 47nF cap in series and connected that in parallel with C2. I put the DENSITY pot, and two caps on a little Vero board.

The DIODES control is simply a C50K pot connected in series with the clipping diodes. When DIODES is turned down, the clipping diodes have less and less effect on the tone. Volume increases, distortion and compression decrease. For fun, I wired in a SPDT on-off-on switch to select between Ge diodes, LEDs or Si diodes. I also increased the BALANCE (Volume) pot from A50K to A100K so there's a little more signal available to push the diodes. I used red LEDs and 1N4743A zeners for the Si diodes. The zeners are wired in parallel, so they only conduct in the forward direction. Zeners tend to have a larger forward drop, that's why I chose them. Any Si diode will work, such as 1N4148. I left the diodes and R5 off of the PCB and put the diodes, R5 and DIODES pot on a little Vero board. It would have been neater, but the LEDs were thrown on as an afterthought. The LEDs are pretty subtle; you have to crank the HARMONICS, DENSITY and DIODES controls for the LEDs to do anything.

If you set DIODES and DENSITY to zero, BALANCE to max, and use HARMONICS as a Boost control, it makes a decent treble booster.

Here's the schematic and some pix. I went with side-mounted jacks so I'd have room for the Vero boards. Top-mounted jacks would probably have fit, but I wanted easy access to the two new pots and Vero boards. As you can see, it's a very snug fit between the jacks and the stomp switch. I had to grind the jacks down a bit and mount the stomp switch rotated 90 deg. I recommend socketing both transistors because this pedal's tone is very sensitive to the transistors. Lower hFE gives less compression and more headroom. I currently have a Russian P28 and 2N2222A installed. One day, I'll paint and label the box. The controls layout is the same as the KS.

Harmonic Penetrator front panel 06.jpg

Harmonic Penetrator innards 06.jpg

And here it is painted and labeled (finally!). I went with the KS control names.

Harmonic Penetrator 03.jpg
 

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Cant you add a small trim pot / bias control to adjust the sensitive of the transistors ?

I think i had one of those on the side of my Twin bender.....Very cool build btw !
 
Thanks! I'm planning to do an acrylic pour, but I'm also kinda digging the industrial bare metal look.

What do you mean by "sensitive"? There are a couple of resistors that could be tweaked to accommodate higher gain transistors. I usually avoid trimpots as much as possible because they don't stay put and are not all that reliable. I think you are better off trying different transistors than messing with trimpots. Just my opinion.
 
I thought those transistors are weather sensitive...like in Fl humidity ....if the pedal sounds bad adjust the bias to them. Thats pretty trick what you done...all in CDB fashion , great layout with the side jacks.

Only trick i done was stand up the broom yesterday ...lol...it worked !
 
Thanks, Mike.

Ge transistors are temperature sensitive. They should definitely NOT be sensitive to humidity. The transistor die is hermetically sealed inside the metal packages. Plastic package devices are not sealed quite so well. Believe me, if any moisture gets in there, the transistor is history.
 
I bought a set of transistors: 2N3565 & 2N404 from Small Bear. Also got the 1N695 diodes from Small Bear. I tried those transistors and some others I had, settled on 2N2222A (from my NOS stash) and P28 (bought on eBay from a guy in Ukraine). I don't recommend buying semiconductors on eBay unless a) you know how to test them and b) you are a gambler. Feel free to experiment with different transistors and Ge diodes. I found that medium HFE (60 to 100) transistors bias better in this circuit than high HFE. The Ge transistor needs to be low leakage. It's a cool dirt pedal and makes some bitchen tones. Have fun!
 
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Okie dokie, I'm working on sourcing parts for this percolator - this is the first project of mine that would use transistors like these.

Some noob questions for you all:

Sockets - in order to play around with transistors, you use sockets, right? If so, do you use a socket like this from Small Bear?

Transistor Experimenting - I like the idea of swapping transistors and hear different sounds, like @Chuck D. Bones did. I'll try the original transistor pairs ( 2N404A / 2N3565 ) and some other pairs... any suggestions on how to pair rando transistors would be greatly appreciated. Can you just swap NPN and PNP transistors to your heart's delight? I cruised through a few sources, and there are (duh) so many to choose from.
- For example, if I wanted to use a 2N2222A (NPN), could I pair it with just another medium Hfe PNP transistor?
- Any other pro tips or reading material or youtube vids would be appreciated, if that's easier.

Thanks, ya'll!
 
Those SB sockets are the ones to get.

As for pairing transistors, there are as many opinions on how to do that as there are transistors! Just get a few and try them. Don't be surprised if many of the combinations sound the same.

My goal with the Percolator was to get the highest collector voltage on the NPN for maximum headroom. Both transistors influence that.
 
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Another question on the Percolator: that 50 nF cap... can I use a 47 nF cap? As much as I want to attempt your sweet mods, I may opt to go an easier route prior to some next level wizardry...
 
Hey! I just picked up this same clone and I'm wondering how you were able to do everything. Going to be trying to use your photos and info to make one for myself!
 
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