Interfax Harmonic Percolator question

[jmusser]

In Alfonzo's notes, he said that he traded out R4 100K fixed resistor, for a 100K pot. This schematic is on Aron's site. It must change the Q2 collector voltage to something more specific that's less than 9V. Anyway, I'm wanting to know how to wire that part. Do I put one end to +9V, One end to GND, and the wiper to the collector? I've had this box stuck in the closet for 3 years, and I'm guessing that it never worked, so I'm trying to see where I went wrong on the schematic. I used the bottom schematic, because it has componet values specified. Thanks

[aron]

When you substitute a pot for a resistor, take one lug and put it to where one leg of the resistor was, then put the middle (i.e. wiper) and put that where the other leg of the resistor was.

So, one outside leg to 9V (V+) and the middle(wiper) to the collector of Q2.

You can optionally tie the wiper to the "left over" or "other" outside lug.

Aron

[jmusser]

Thanks Aron. That makes sense. I was thinking about the old wire wound high wattage resistors that had the exposed winding in it that you used a band to "tap" with, in the wiper area. Then, the part of the resistor that's not tapped, is just not used. I just didn't know if there was a noise issue of some type if the all three legs weren't tied to something. I sure had this one screwed up! I had the emitter and collector swapped on both transistors. No wonder it never worked! I believe this may have been my first project, and then I abandoned it, and went on to the Bobtavia. I'll try to get it fixed after I get some sleep after this night shift.

[guitarhacknoise]

In Alfonzo's notes, he said that he traded out R4 100K fixed resistor, for a 100K pot. This schematic is on Aron's site. It must change the Q2 collector voltage to something more specific that's less than 9V..............Thanks

hello j ,
Where did you find A.H.'s notes? I would love to read them! I looked at his site but the diy section is "under construction".
I have never been able to "nail" this circuit, close but sounds different to me.
The one time I had it the closest (to my ear) I had jamed a 1n34a in the feedback of Q1, IIRC
-matthias

[aron]

I had the emitter and collector swapped on both transistors. No wonder it never worked!

Look how you can recognize the problem now!

VERY COOL!  

[Doug_H]

;lkj

[guitarhacknoise]

:oops:  actually it was Q2, and I tried it again, but It really does'nt change much as far as sound goes. sorry!
the jerkulator gets well past unity regardless of what transisters I use (of the ones I have tried!).
blah, blah, blah,...................................
-matthias

[jmusser]

Like I said, I had this thing in the closet for a long time. My notes say 5/23/01! What he said then, was that he used a 2N3906 for the first transistor, and a 2N5088 for the second. He changed the 100K fixed, to a 100k trimmer on the collector of Q2. He said to just turn the new R4 pot until the the circuit sounds good. He put in a .1uf cap, instead of the .01uf for the input cap. Now, having done this and fixing my problems, I put it through it's paces. If you crank up the input pot R3 about a 2/3 of the way, you get a real nice tube sounding overdrive. Once you crank it past the sweet spot, it distorts, but still sounds clean. It doesn't have a lot of sustain by itself, so I put an Arion SOC-1 compressor in front of it. That really brings this thing to life. I have a Fat Strat, and it really sounds good in the bridge/humbucker position with R3 2/3 of the way up in overdrive. The bass starts to come out once you pass that point with R3. When you go to the single coil neck pick up, you get a nice clean sounding distortion, which is headed towards fuzz, but never gets there. I believe this thing would probably make a decent blues box. The R4 pot should be turned until the circuit dies, and then back until you turn the circuit back on and it's as loud as it will go, before it dies again. I'm sure there's more technical ways to say that, but I'm a builder, and not a tech type.  It reminds me a lot of The Rocket box I built once upon a time.

[Doug_H]

;lkj

[jmusser]

It would be interesting to hear the difference between the Jerkulator, Speculator and Percolator. Si and Ge transistors along with the different Ge diodes in your Speculator would have to sound quite a bit different from mine. I used 1N34s in mine and 2Si transistors, and it never gets fuzzy at all. It's like you said, more of an overdrive. I'm not sure why I wanted to build it back then, except that maybe there wasn't a sound sample, and I wanted to hear it, since it was a vintage effect. Thanks for posting the schematic. unless someone wants an overdrive, I would suggest they build your circuit instead of this one. Thanks to Aron for the "atta boy". One of the hardest thing on perf boarding this stuff, is not to get things disoriented while you're switching from bottom to top. Your mind tends to want to orient things the same way they were on top, and once you turn it over to solder it, it's reversed.

[Doug_H]

;lkj

[guitarhacknoise]

here is a little tid bit from the guy famous for using this little number:

Q:

In particular at about the 5 minute mark of 'Mama Gina' a very unusual sounding distortion gets kicked in. How's that being done?


--------------------------------------------------------------------------------

A:

That's the Harmonic Percolator being turned on. It has a unique sound, but I haven't found it to be as extreme feeding other amplifiers or with other guitars. I think there is something about the particular combination of low-impedance noisegate acting as the source and the relatively low load impedance of the two amplifiers in parallel that makes the percolator sound so weird.


--------------------------------------------------------------------------------

for whatever it's worth....
-matthias