Harmonic Percolator - make one!

[pinkjimiphoton]

i can't "SHOW" it yet,  but i can let ya hear the mod i mentioned earlier in the thread.

AND i took this thing out and rocked the bejesus out of it live last nite, and it stood up real well in the live situation, better than i expected and much better than the other percs i've used. i was surprised. sadly, the sh!tty video quality doesn't let you catch all the nuance you can hear live with the percolation/focus mod done, but i think enough will get thru to show the difference the modification makes. let me know what you guys think..

[inductor]

I've listened to a few of the demos and my first thought is that it sounds a lot like Neil Young "Rust Never Sleeps" or other Crazy Horse stuff where it sounds like his rig is constantly about to explode.  Anyone know if Neil uses one of these, or is his rig really about to explode?

Neil uses a a rinky dink tweed deluxe. So yeah his amp is about to explode.

[garcho]

trace PDF

[vitopower1]

I've been really trying to get that sub octave, sounds like you got it with this? 

Do I understand correctly that you went 91k after the PNP collector to the volume knob 3, wiper to 47r then back to the junction before the 47uf tant?

really digging the sounds in the vids

i think it's soft clipping the signal with the transistors, and using some kinda SCARY PHASEING MAGIC i totally DON'T UNDERSTAND to make it do all this!

seriously, i think something about the circuit seems to  cancel dissonant harmonics.

i can get octaves out of it now...easily. up. down. both. it's insane.  no idea how/why it works. also discovered adding power supply filtering seems to affect it adversely!!

the latest is the best sounding one... if you make that 91k resistor a 47k from the collector of the pnp to the top lug of a 50k pot, and tie the wiper of that to a 47r resistor, you will get ALL the sh*t in albini's video. seriously.

it's bizzarre. you can make feedback come out in harmonic chords some times.

it's crazy man, like really crazy how ccrazy this crazy thing really is..

once my girl gets up, i will try and shoot some video. that 91k is the main key to percolation. the other is the 1m feedback resistor on the npn.

[pinkjimiphoton]

beats me, been a while since i did it, but yeah, there's  only the one 91k resistor. you need to make the pot "float" so you can get above or below the value.
the idea was to be able to adjust each transistor individually.

the two pots are MADDENING. they do completely different things depending on where and how the other knobs are set.

i don't have this anymore, it's been released into the wild, so whatever i did should be in this thread, but sorry, can't look at the original to see what i did.

[Chaloney]

Vitopower1 thanks for reviving this thread! Jimi, thanks for the demo videos. Now I gotta order some junk transistors!  Love the sound of this pedal. Anyone know if tayda has any transistors that will work?  I have an order waiting for the next discount code...

[pinkjimiphoton]

chaloney, check your pm's

[kgstewar]

Wasn't sure which Harmonic Percolator thread to post to but this seemed as good as any. First just wanted to say thanks for all the fantastic information on this thread. I decided to build a straight-up HP with no diode switch, and put together a little PCB that uses surface-mount resistors and ceramic caps (0.1uF). It's a tiny PCB that just hangs off the pots and fits vertically into a 1590B. Put it together, plugged it in and it sounds GREAT. I've included a couple of pics of the PCB with just the SMD parts mounted. From the silkscreen you can see where the through-hole parts go.

[pinkjimiphoton]

that is freakin' awesome!

[kgstewar]

Thanks Jimi, your great posts and videos were super helpful!

[pinkjimiphoton]

just standing on the shoulders of giants bro.

would love to hear some clips!!

[Addy Bart]

Sorry for digging out an old thread but I just made one of these using the Albini values with transistors and diodes from Small Bear, and the results sound quite disappointing. It's more like a polite overdrive. I'm not getting much bloom or octave. Quite sure there's nothing wrong with the build.

I tested the 2n404 and the hfe was around 160. It's not very leaky though, and I'm wondering if that's where the magic lies. So if someone has a couple of leaky 2n404 they could post to me (I'm in Norway) that would be sweet. Will gladly PayPal for them plus postage.

[pinkjimiphoton]

hey bro,
did ya try turning the ge q 180 degrees?
sometimes with ge, you can reverse beta them from what ya expect, and they will work better.
i know this to be true with this circuit.
leaky ge q's may not be the answer.. they got tone, but the noise they produce can be astoundingly bad.
with a HP, if the transistor is backwards, yep, you'll get a mildish transistor overdrive instead of nasty obscene gobs of percolation
if that don't work, we'll figure out the next move.
can ya post your voltages, please?

[hellwood]

This circuit tortured me for about a year. extremely low gain / high leakage for Q1 worked nice, but was a bit noisy. I settled for a healthy 60hfe 2n404. I have switches for Ge / Si diodes as well as a 5-way rotary switch that changes both input and output caps simultaneously. I also put Q2 on a switch for germanium or silicon, and to make things more complicated, I have a bias knob for Q1. The germanium Q2 was high gain and leaky, and has a really nice grinding sound with the bias knob maxed but no octave. the silicon Q2 combined with higher value input/output caps, in addition to the diode switch on Si, as well as having my Q1 bias knob almost off really help the octave weirdness happen.

[Addy Bart]

hey bro,
did ya try turning the ge q 180 degrees?
sometimes with ge, you can reverse beta them from what ya expect, and they will work better.
i know this to be true with this circuit.
leaky ge q's may not be the answer.. they got tone, but the noise they produce can be astoundingly bad.
with a HP, if the transistor is backwards, yep, you'll get a mildish transistor overdrive instead of nasty obscene gobs of percolation
if that don't work, we'll figure out the next move.
can ya post your voltages, please?

Thanks Jimi. I flipped the germanium and it sounds more like a fuzz, which is pretty cool. I'm using a pcb from Stomptown which fits in a 1590a, so I'm not sure if the orientation is correct or not... It's good to know you can flip the transistor anyhow.

Here are my voltages:

Q1: 2n404a.
C: 3.38
B: 3.45
E: 3.46

Q1: flipped 180 degrees.
C: 4.10
B: 3.52
E: 3.27

Q2: 2n3565.
C: 5.02
B: 1.46
E: 3.61

Diodes are 1n695.

With Q1 flipped, it's shelving the attack with the harmonics knob dimed, but I've got some more 2n404 coming from Newark, so hopefully there'll be one with lower gain I can try. I had an extra pcb so I populated that with values for the stock HP. It'll be fun to see how they differ, although I wish I'd been more patient and maybe used some trimpots for the collector resistors. Oh well, guess I can always try it on vero again. Would be great to make one that sings!

[Addy Bart]

This circuit tortured me for about a year. extremely low gain / high leakage for Q1 worked nice, but was a bit noisy. I settled for a healthy 60hfe 2n404. I have switches for Ge / Si diodes as well as a 5-way rotary switch that changes both input and output caps simultaneously. I also put Q2 on a switch for germanium or silicon, and to make things more complicated, I have a bias knob for Q1. The germanium Q2 was high gain and leaky, and has a really nice grinding sound with the bias knob maxed but no octave. the silicon Q2 combined with higher value input/output caps, in addition to the diode switch on Si, as well as having my Q1 bias knob almost off really help the octave weirdness happen.

Sounds like the ultimate HP! If I can't get mine to sound any better, I'll follow the mods mentioned here. 

[pinkjimiphoton]

the 404 was definitely backwards i'd say.
its been a while, but the e's are tied together and should be reading the same, no?
i'd try a different silicon one.

to quote myriad guys way smarter than me,  don't worry about part values/names. try whatever works. a pnp is a pnp, an npn is an npn ultimately, and their gain ranges can be vastly different.

i would try a higher gain q2 first, and see if it comes to life. if higher doesn't work, go lower. eventually you will find the proper balance and it will come to life and sing.

ge transistors are a pain in the ass!! the gain never stays consistent... if you touch it, or even BREATHE on it FFS, it can completely change!!
that said, in some applications, they just plain sound better.

try a silicon in q1 too, unless you're 100% more concerned with "mojo"... escobedo's jerkulator sounds to my ears every bit as good as the hp does.

as for albini...
in them videos, he's using a significant amount of amp distortion (and i suspect a fuzz before the perc, too) so don't expect it to sound like his demo. the hp is a weird beast, and can be pretty unpredictable in some cases.

worst case, if ya get stuck, if you can pay the shipping i can send ya some really crummy low gain ge's to play with. may be cheaper to just buy them tho.

i'll send ya a linky via pm to some surplus ge's

[Addy Bart]

the 404 was definitely backwards i'd say.
its been a while, but the e's are tied together and should be reading the same, no?
i'd try a different silicon one.

to quote myriad guys way smarter than me,  don't worry about part values/names. try whatever works. a pnp is a pnp, an npn is an npn ultimately, and their gain ranges can be vastly different.

i would try a higher gain q2 first, and see if it comes to life. if higher doesn't work, go lower. eventually you will find the proper balance and it will come to life and sing.

ge transistors are a pain in the ass!! the gain never stays consistent... if you touch it, or even BREATHE on it FFS, it can completely change!!
that said, in some applications, they just plain sound better.

try a silicon in q1 too, unless you're 100% more concerned with "mojo"... escobedo's jerkulator sounds to my ears every bit as good as the hp does.

as for albini...
in them videos, he's using a significant amount of amp distortion (and i suspect a fuzz before the perc, too) so don't expect it to sound like his demo. the hp is a weird beast, and can be pretty unpredictable in some cases.

worst case, if ya get stuck, if you can pay the shipping i can send ya some really crummy low gain ge's to play with. may be cheaper to just buy them tho.

i'll send ya a linky via pm to some surplus ge's

Nice one Jimi. I tried a couple of silicon PNPs for Q1 (2n2907A and 2n3906) and they sounded even more shelved than the 2n404a (not a bad sound in my book either... Almost like a tremolo). But flipping the 2n404a has done wonders, so thanks for the advice. I'm sure you're right about it being the wrong way round on the board. It's way more textured now and less polite. Actually sounds really good on the gain channel on my little Kustom amp - with a louder amp it'll start to sing I'm sure.

I've ordered twenty 2n404As (they were just a couple of dollars each from Newark) so hopefully I'll find the perfect match. If not, I'll PM ya. Thanks man!

[pinkjimiphoton]

awesome, rock on bro!

[digi2t]

Quick question for all the HP noodlers here...

Has anyone tried an all germanium version? I've been snooping through the net on this, and I don't seem to see anything along those lines.

Why I ask is because Phil and I have been planning a board for the HP, but using lead spacing more suited to older NOS parts. In the meantime, I've gone back to noodling with this circuit on the breadboard. I know, I know.... after all the work I did on it a few years back, you'd think I would have built this damn thing already, right? Nope. It's been sitting on the back burner, just simmering away. Anyway, where was I... oh yeah...

All germanium HP. OK, here's a schematic I drew up way back. Based on the original mixed si and ge version, using what I found to work well at the time. It's got some minor mods to the original, just to keep things quiet;



While I really liked the flat out roar of this circuit, there was always a hint of trailing fizz that.... I dunno... just bugged me. Didn't matter if Q2 was high gain, or low gain, it was always there. Perhaps that's what kept putting me off building this. Anyway, with nothing but time on my hands, and with a bunch of GT404's kicking about, I thought to myself, "What would it sound like with a germ in Q2?". I measured one up, and threw it in there. It seemed to be way less fizzy than the silicon Q2 circuit. I swapped out the 91K collector resistor for a 100K trimmer, and started messing with the bias. This is what I have on the board now;



I retweaked the Q1 and Q2 voltage to what's stated in the drawing, and wow... it sounds prrrreeeeeeettty darned good! Actually, much better than the mixed version. With the Harmonics pot dialed back to 50%, the roar is quite acceptable, but allows for very nice clean up when the guitar volume is rolled back. With Harmonics at 100%, well, the roar is moar, but guitar roll back gives a nice soft overdrive chunk. Really sweet!

I also found that C3 and C5 could be tweaked to suit single coil or humbucker equipped guitars quite nicely. 10n for really fat buckers, or up to 47n for thinner single coils. I find that 22n is a nice all rounder. YMMV

So, has anyone tried this angle before? If anyone has any PNP and NPN germs kicking around, can you try this, and give me your thoughts?