Interfax - Harmonic Percolator  [schematic]

Discussion regarding early stompbox technology: 1960-1975 Please keep discussion focused and contribute what info you have...
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SPeter
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Post by SPeter »

:applause:
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echo
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Post by echo »

I've built several of these.. a few Collins and a couple of Sardonic Albinators and they've all turned out great, the Albinators seem a touch darker and less hairy which surprised me, I expected the opposite.

my issue is that all of the clones I've built hit unity at around 1-2 o'clock and when full up they're not nearly as loud as a Collins HP I have here for some work.. I'd say there's about 25% more output on the CC. This is with diodes in.. bypassed, it's very loud but loses it's great sizzle

I tried raising the 4.7k resistor to 10k as someone mentioned earlier in the thread but it made no audible difference... is there anything else I could try that would squeeze more output out of these without messing with the tone?

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Post by Hides-His-Eyes »

Anything that makes the output larger will clip more, so I think you're going to have to stick a booster on the end.
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Post by RnFR »

echo wrote:I've built several of these.. a few Collins and a couple of Sardonic Albinators and they've all turned out great, the Albinators seem a touch darker and less hairy which surprised me, I expected the opposite.

my issue is that all of the clones I've built hit unity at around 1-2 o'clock and when full up they're not nearly as loud as a Collins HP I have here for some work.. I'd say there's about 25% more output on the CC. This is with diodes in.. bypassed, it's very loud but loses it's great sizzle

I tried raising the 4.7k resistor to 10k as someone mentioned earlier in the thread but it made no audible difference... is there anything else I could try that would squeeze more output out of these without messing with the tone?
did you use the proper diodes? I understand they make a difference.
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echo
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Post by echo »

yes 1N695's from Smallbear

I'm just wondering why these aren't getting quite as loud as the CC version which also seems to get a bit nastier :scratch:

I've done these builds on tagboard if that should make any difference..

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Post by RnFR »

I think the circuit is also rather dependent on Hfe, so that could be the difference as well.
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Post by Whoismarykelly »

Has anyone run into issues where the output level is extremely low with the diodes in the circuit? I built one of these up over the weekend with a switch to disconnect the ground connection for both diodes and when the connection is lifted I get great output but when the diodes are connected to ground I get barely any volume at all. I replaced the diodes and reflowed the joints on the switch. Checked all continuity with a meter. Doesn't seem to make sense at all...

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Post by RnFR »

well, hard clipping Ge diodes will limit volume severely. it's just the nature of the beast.
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Post by Whoismarykelly »

Its not like that though. Its getting whisper levels at max volume through a loud amp. Ge diodes aren't that bad :lol:

Its just one of those mysterious cases where everything is wired perfectly and somehow this one little thing is causing a failure of some sort. Everything works fine with the diodes lifted and those diodes just kill everything. Even after replacement. Weird...

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Post by phibes »

What transistors did you use and what gains?
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Post by John Lyons »

Did you check the reverse voltage drop of the diodes? Maybe it's something like .1v or something
really low. That's the only think I can think of. If it's super low then you'd get an almost shorted to ground signal.

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Post by mictester »

Whoismarykelly wrote:Its not like that though. Its getting whisper levels at max volume through a loud amp. Ge diodes aren't that bad :lol:

Its just one of those mysterious cases where everything is wired perfectly and somehow this one little thing is causing a failure of some sort. Everything works fine with the diodes lifted and those diodes just kill everything. Even after replacement. Weird...
Your germanium diodes will limit the signal to about 200mV peak-to-peak. Without the diodes, the circuit will easily deliver several Volts of audio! The difference will be huge!
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Post by Alex Frias »

With the Harmonics and Volume pots full on, even with the severely clipping diodes action, the output volume is very healthy, even louder than my Dean Deceiver equiped with 81&89 EMG active pickups! :hmmm:

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Post by Kregg »

Post some pics. :hmmm:
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Post by Whoismarykelly »

I ended up figuring this out pretty soon after I last posted. Random late night error :slap:

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Post by phibes »

What was the error in case someone else runs into it?
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Post by hewie »

Having built a few of these over the past year or so, I can't help but think about what we can do to improve/modernize the circuit? (patiently awaits flamewar) Any thoughts on what can be done to achieve a similar sonic result? There are a few things, which some might consider to be important to this circuit, that seem like they could be implemented better. A quick example being that the harmonics/gain control at the input doesn't seem to be the most practical use. But who am I to judge, I'm a novice at best. Just wondering if anyone had a similar thought. Regardless, the Harmonic Percolator is a unique effect in a sea saturated with "boutique" tube screamers and big muffs tweaks.

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Post by Alex Frias »

I love this circuit! I am addicted to it!

But anythimg to improve or turn it less specific components dependent could be excellent.

One thing I really don't use in this box in my own set is the Harmonics Control, as I prefer to leave the dirty work for the guitar volume pot. But some people are not interested in some sort of fuzziness or octave down side effect at the highest setings of Harmonicas Control, so I think for them it's usefull.

Integrating some sort of good noise gate with it could be an improvement in my opinion. I started to use a BOSS NS-2 with it. The final timbre changed but to honest, I liked the way it changed and that's the I'm using it right now. I put the HP-1 into the NS-2 loop. And important: I didn't loose the easy acoustic feedback possibilities just setting the NS-2 correctly!

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Post by skumberg »

I just breadborded this thing using the sardonic albinator schem. I'm using 2n404 and 2n3565(hfe 260) but AA119 diodes(Vf around 0.3). It's got a healthy output but I don't get any crazy fuzziness like on this one . More of a smooth distortion. It's similar to the YT sound clips I've heard from fredriceffects so I guess it's correct. I found good use of the bass control on my g&l legacy strat. I think a similar filter in place of the harmonics control would be better as I control the input with the guitar anyways. The filter consist of a 2.2nf in parallell with a 1M pot just before the 250k volume control. So just a hipass filter. This way it would work better with humbucker guitars.

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Post by Alex Frias »

A highpass input filter... Very interesting idea, as employed in some Fuzz Face alike circuits I saw around the web. One of the things this BOSS NS-2 does is boosting a bit of the high frequencies, I liked a lot the results, specially on humbuckers and P-90 pups.

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