Harmonic Percolator - make one!

[Mark Hammer]

As I noted on the "crowdsourcing" thread I started, I put together a clone of an Interfax Harmonic Percolator last night, and fell in love instantly.  VERY nice pedal, and so simple to make.  Must have taken me less than an hour, start to finish, on perfboard.

I won't provide any samples because mine sounds exactly like the one Steve Albini demos on the Youtube video.  Eerily so, right down to the false octave-down that comes in now and then.  I used a 2N3565 (hfe around 150) and a 2SB172 (hfe 52-54), and some unmarked germanium diodes.   I don't mention this because you MUST use these values.  Rather that's what I used, and if have something similar, it won't NOT work.  I had socketed the transistors in preparation for swapping different ones in and out.  But the first pair I stuck in nailed it.  Lucky, I guess.

I've made and owned somany different distortions, it takes something truly different to capture my imagination/fancy.  This does it.  Pinkjimi, this is your next stupid pedal trick. 

[midwayfair]

+1 on this! However, I'll add:

Adding a switch for to go to a pair of silicon diodes (or my favorite "silicon range" diode, OA126) in a symmetric arrangement also gives you a fan-bloody-tastic low-medium gain OD in the same box.

[electrosonic]

Can you link to the schematic used? I seem to remember their being some differences among the published versions out there.

Thanks,
Andrew.

[Mark Hammer]

I used the 2007 George Giblet drawing that was posted here.  If you do an image search for the pedal, you'll find it in the first dozen hits.

[midwayfair]

Can you link to the schematic used? I seem to remember their being some differences among the published versions out there.

Thanks,
Andrew.

Madbean also has the "concensus" schematic values and the "Albini" schematic values in his Pepperspray document:
http://www.madbeanpedals.com/projects/PepperSpray/docs/PepperSpray.pdf

[Electron Tornado]

Tim Escobedo has a schematic in his circuit snippets collection for his take on this, calling it the Harmonic Jerkulator. Anyone know how it compares? 

[Jazznoise]

I actually have this sitting on my breadboard at the moment, just waiting on the chance to get to pick the college's techs stock to see if they've anything that might do it. They did have AC128's when I needed em, so you never know..

Actually? Would a low hfe AC128 do the trick? I'll have to try it myself obviously but I'm just wondering has anyone done it!

[Mark Hammer]

Madbean also has the "concensus" schematic values and the "Albini" schematic values in his Pepperspray document:
http://www.madbeanpedals.com/projects/PepperSpray/docs/PepperSpray.pdf

There are differences between what I made, using the Giblet drawing, and what Bean shows in the Pepperspray.
1) he shows R1=51k, I used 220k
2) he shows R2=91k, I used 20k
3) he shows R3=3M9, I used 750k
4) He shows C4=2u2, I used 100nf
5) He shows C5, I did not use C5

That doesn't make the Pepperspray erroneous or uninteresting, but those values are not required to make for an interesting tone, or may simply be needed in the event of the specific transistors used.  A low hfe AC128 is also likely not required.  However, we often associate distortion with higher gain devices, and can have a trickier time finding germanium devices in the parts bin with hfe >70.  I can happily say this is not required for aural success.

[midwayfair]

Madbean also has the "concensus" schematic values and the "Albini" schematic values in his Pepperspray document:
http://www.madbeanpedals.com/projects/PepperSpray/docs/PepperSpray.pdf

There are differences between what I made, using the Giblet drawing, and what Bean shows in the Pepperspray.
1) he shows R1=51k, I used 220k
2) he shows R2=91k, I used 20k
3) he shows R3=3M9, I used 750k
4) He shows C4=2u2, I used 100nf
5) He shows C5, I did not use C5

That doesn't make the Pepperspray erroneous or uninteresting, but those values are not required to make for an interesting tone, or may simply be needed in the event of the specific transistors used.  A low hfe AC128 is also likely not required.  However, we often associate distortion with higher gain devices, and can have a trickier time finding germanium devices in the parts bin with hfe >70.  I can happily say this is not required for aural success.

I didn't mean to suggest that any particular values are required. Mine deviated from all specs.

However, he gives two BOMs: One is the "Albini" version with the values shown in his schematic, and the other is the "Stock" (concensus) version, which matches most of the values you give, including the option to omit C5.

[DougH]

Hey Mark, Do you have a direct link for the schematic? I can't find George's anymore.

[Mark Hammer]

Go here: http://topopiccione.atspace.com/PJ24HarmonicPercolator.html

[LucifersTrip]

I had this one bookmarked:
http://www.diystompboxes.com/pedals/Percolator.gif

...I would like to see the schematic that Mark used that correlated to his changes in R's and C's

...and Mark, please at least post test voltages if you're going to ask us to "make one" !!!!

thanx

[davent]

Looks like George's schematic drawing was hosted on Geocities.

[newperson]

lets see some images of your layout work!

[Mark Hammer]

The layout is immaterial, plus there are some "video issues" to be attended to on my machine that preclude pics.

The voltages, however, are as follows (battery = 9.7V):

Q2:  C-3.24  B-2.12  E-1.58

Q1: E-1.58  B-1.49  C-1.39

Weird, huh?  I quickly stuck an OC70 (hfe 43) in place of Q1 and got very similar readings withn a few millivolts.

I mistakenly reported Q1 as a 2SB172.  It is in fact a 2SB33 (I keep them in the same parts drawer).  I made a 3-knob Tonebender with a set of 2SB33s, and it sounded pretty damn fine.

[Mark Hammer]

Okay, video card problem solved.  1=Orpheum, 2=Bosstone, 3=Octavia, 4=Dist+, 5= Percolator, 6=almost a Controfuzz

[Quackzed]

 
you could use a 2p6t rotary on that thing!

[newperson]

Thank you for the image.  I love to see other people's work and since you post so much I was particularly interested in yours.  It was six times as nice to see.

[LucifersTrip]

The layout is immaterial, plus there are some "video issues" to be attended to on my machine that preclude pics.
The voltages, however, are as follows (battery = 9.7V):

Q2:  C-3.24  B-2.12  E-1.58

Q1: E-1.58  B-1.49  C-1.39

Excellent...thank you very much!

that is one of the few oddballs I still haven't built, since I never was able to find a conclusive, "complete" schematic with voltages.

edit:
looking over my bookmarks, I now realize why I never built one. the built reports and voltages from everyone are all over the place. here're a few of the links I saved that I thought might help:

http://www.diystompboxes.com/smfforum/index.php?topic=68649.msg550551#msg550551

http://www.diystompboxes.com/smfforum/index.php?topic=55987.msg434050#msg434050

http://www.diystompboxes.com/smfforum/index.php?topic=55987.msg432770#msg432770

[glops]

Yea, I etched the madbean board and did the albini specs. More of an overdrive but has its own unique character but I just feel lIke there's something more magical that's not quite being released from it. Gonna mod it to Marks specs as that seems to be the way to go.