Every Harmonic Percolator I make dies ;(((

[diyDog]

The biggest problem is the 2-transistor amplifier.  It's not working well, and given the way the transistors are biased, that's no surprise.  The 3.9meg bias resistor used with the NPN transistor doesn't allow enough base current to turn the transistor on, for one thing.  The whole amplifier circuit is odd, and I"m not sure it will ever work well.  You might save yourself lots of grief by copying a more conventional 2-stage bipolar-transistor amp as can be found in many fuzz boxes.

[Gus]

i thought the main purpose of the 47u was to be a "neutral" ground point between the two transistors as a tsikli pair or whatever ya call it bro.
it goes to the common point of both transistors, and floats and isolates them above ground, doesn't it? and establishes leakage current to a point to introduce some feedback in the common emitter or collector or whatever , i don't have it in front of me and don't remember the exact circuit..
doesn't seem to be a lotta gain there the way it works, to my eye it's 2 transistors workin as one stage, but i am often wrong
i mean, a push/pull amp stage may have two whatever tubes/transistors as amps, but it's still one stage.
the perc does funny things when you play with it.
a starve control i don't think is gonna help much. i messed with it, made it blatty and not work.
messing with the resistors and turning 'em into pots was interesting, but i found i had to float the pots with resistors to get
reasonably useful ranges.
for a tone pot, i'd just use the guitar. but it really depends on how ya wanna tune 'em in most of all.. i never saw the need, or had the output for a tone pot other than on escobedo's variant.

Look at the way the transistor are biased.  They have a resistor from Collector to Base
Note a series circuit has the same current
The current "in"  the collector is the same as the C to B and emitter current "out" added together

The two gain stages are in series for power
Now when one stage "tries" to change the collector voltage when amplifying a signal this effects the other stage because they are powered in series, however if you stick a cap at the two stages middle power supply node you can adjust the amount if interaction from the caps value in uf and ESR (Al vs tant)

The two stages are in series for gain

Also the  C to B resistors set both the bias and feedback resistance,  Things to keep in mind the source resistance, transistor gain, feedback resistor and the loading

[induction]

The biggest problem is the 2-transistor amplifier.  It's not working well, and given the way the transistors are biased, that's no surprise.  The 3.9meg bias resistor used with the NPN transistor doesn't allow enough base current to turn the transistor on, for one thing.  The whole amplifier circuit is odd, and I"m not sure it will ever work well.  You might save yourself lots of grief by copying a more conventional 2-stage bipolar-transistor amp as can be found in many fuzz boxes.

I guess that depends on your definition of 'working well'. If you want a fuzz face, build a fuzz face. If you want heavy metal distortion, build something that gives you that. But if you want the unique sound of a harmonic percolator, accept no substitutes. It's my favorite dirt pedal by far, and will work great if you build it right. The lower-volume cleanup sound is fantastic. It is an unconventional topology, but it has been built by many, many people with great success.

[DelSpanisho]

I replaced C5 with a 330nF cap just for giggles, but when I place it on a row of the breadboard that's not connected to anything else (i.e. have it "going nowhere") and pinch the chicklet part of the cap itself, the pedal picks up several radio stations at once.

How can I build this function into the pedal as a, say, switch? I've tried linking each end of the cap with resistors of multiple values (the human body is one big resistor, right?), but that does nothing.

[PRR]

> human body is one big resistor

The key detail is "big", not "resistor".

Resistor is 2 inches. You are 70 inches. 35 times bigger; really more difference because 2 inches is really really small for radio.

Grab 10 feet (3 meters) of wire and stick one end in the circuit at that point. Radio reception may be a lot better.

> several radio stations at once.

Where I grew up it could only be ONE station (the one I could see out my window). Here it would be about none (even a good radio has trouble with local stations and some really bad power-line buzz). So don't expect the same effect at home, at Downtown Bar, and at Out-Back Shack.

[DelSpanisho]

Hmm, okay, so it's the length of the connection that matters. If it's really the length of the wire that does it then I'll probably skip the idea. I figured it wouldn't pick up many stations in different areas anyways.