I've managed to successfully build a number of effects now, and after years of making cables and on site fixes I'm pretty confident in my ability to wield a soldering iron. The next step is to modify and create so I need to learn, a lot.

To this end I've gone back to the start and begun breadboarding circuits starting with the May Queen treble boost. Some prodding and several attempts at a coupe of sections I now have a working circuit sitting on my breadboard. So far I've had a fiddle with the effects of increasing the capacitor which forms, what I assume is, a low pass filter with the bias trim. However as far as I'm aware this is the wrong format for a low pass filter, or is the capacitor operating with another resistor?

Admittedly this is working backwards somewhat so I'd like to work forward from the start.

The 10n capacitor and 47k resistor forms a high pass filter around 340Hz

Up to the 10n decoupling capacitor it appears to be a buffer as the input to the capacitor seems to closely match the input signal, but with a slightly reduced voltage. Is there an associated drop in resistance to produce an increased current? Again I'm  little confused as the layout seems to match what I can find as a common emitter which I thought would invert the signal.

At this point on my ignorance comes to the fore and I'm now clueless as to how the second section of the circuit operates (not a massive change from the first section). The scope shows the output from the 2n3904 has about a tenfold increase in voltage along with a number of harmonics, although I wonder if the harmonics I see are already present and just become more obvious due to the increase in voltage.

I appreciate this is a long post and I'm looking for what is most likely basic information but I'm at the point of staring up at a huge mountain of information and looking for a way to start picking at the pile. Any  information you can share with regards to the operation of this circuit, and any suggestions as to which areas I should look at first or suggest similar circuits for the breadboard which employ similar techniques and variants that will help understand whats going on.

Thank you in advance.

1) for readers who can't memorize 997 different pedals in 3,456 different variations, give picture or link to the version YOU are looking at.

2) Any audio amp with _SIX_ significant capacitors is a bit much to swallow, especially for starters. Pick something simpler.

3) "Up to the 10n decoupling capacitor" I would say there is no 10nFd DE-coupling cap. Perhaps a wrong term. If you want to discuss a circuit, and we are not at the same chalkboard, you'd best find one with component numbers (not just values) or it gets hopelessly tangled.

4) "the capacitor which forms, what I assume is, a low pass filter with the bias trim. However as far as I'm aware this is the wrong format for a low pass filter" - The electrons don't care what network forms are "conventional", whatever works. However this IS a low-pass. What looks wrong is that most basic filter essays assume Voltage Sources. Here the JFET is a Current Source. Read-up on Thevenin-Norton equivalencies.

5) "10n capacitor and 47k resistor forms a high pass filter around 340Hz" --- not that simple. I applaud you knowing 10n+47K, but there is also the 470K. If it went to ground, that would be 10% higher F and I would overlook it. But it goes to the amplified and anti-phase signal. In fact the effect of 470K is multiplied by Q1 gain to act like a smaller resistor. What is Q1 gain? Depends on Q1 current, and if Q2's base (after the 33K) acts like low or high impedance. I'll dartboard Q1 gain as 40, which means the 470K acts-like less than 10K, the input cap is loaded in much less than 10K, the input bass-cut is higher than 1KHz. However the 2.2uFd under the JFET is marginal, may bleed-back through the 220K and reduce Q1's gain in the bass.... this is NOT a simple circuit. Don't try to analyze it.

6) "about a tenfold increase in voltage along with a number of harmonics" Clue: mostly, nonlinear products are related to signal level as a fraction of supply voltage. A 0.001V signal in a 9V circuit is usually very-clean. A 9V signal out of a 9V circuit will be more distortion than signal. You can NOT judge non-linearity except at various signal levels.

7) "I'm at the point of staring up at a huge mountain of information" Start with a mole-hill of information, a small spoon, and chip away slowly.

Or just get a pile of caps and breadboard it.

1: the circuit I'm using is the one in the runoff groove collection

2: as I spent more time last night looking at the circuit and looking up transistor theory and methods of circuit analysis this became more and more apparent. I think I may take your advice and try starting with the rangemaster from ggg. Am I right and this is going to be a better starting point. I have no shortage of bread boards so the may queen can wait until further down the line. At the least it's another milestone to work toasted. I'm still very much at the unconscious incompetence stage of learning.

3: duly noted. I suspect what your implying in this specific instance is that I meant coupling capacitor. However I'll hold off quoting specific part numbers until I have a circuit that I may successfully analyse.

4: at the very least you've already pointed me in the direction of another topology. As soon as I started to search for current sources filters this arrangement popped up very quickly. I'm a little confused as to how I include the effect of the jfet in an equivalence analysis. Do I need to look at it as a number of discrete states in order to replace it with an equivalent resistance or current or is there some further technique that will come to light as I get further in.

5: I thought it seemed a little high for a filter as it would be acting over the whole lower two octaves of the guitar. I think I shall leave this point for now as there is a lot more work to go until I can properly comprehend the reasons for the behaviour here.

Thankyou for taking the time to point me in the right direction and I hope I can at least demonstrate some progress without you needing to spoon feed me the whole mole hill.

I've got a few gigs over the next couple of days but as soon as I can get back in the workshop I'll get a fresh board and start looking at a circuit I may be able to successfully dissect. If you have any suggestions I'd be grateful, otherwise I'll start on the rangemaster

> it would be acting over the whole lower two octaves of the guitar.

If you strum a "wide" chord (long interval between low note and high note) and then fuzz it, you get a MESS of intermodulation, with harmonics of strong bass notes covering-up the musically important higher notes. The resulting hash is complex and not generally musical. Many-many fuzz designs dump all the bass and some of the highs before fuzzing.

Obviously you should try it yourself. Make coupling caps many times larger. Play. Single notes may play well with musically useful fuzz. Multi-tone (chord) inputs tend to be less happy. "Optimum" is a matter of style and taste.... but the Well Known fuzzboxes are a good place to start.

QuoteI'm still very much at the unconscious incompetence stage of learning.

or maybe this is the problem:

Quote... to work toasted.

That should have been

Another milestone to work towards

Bloody iPhone spellcheck