Messages

you can always make a passive volume control with a pot by making a voltage divider. there are a couple ways you could implement this. I would probably put a pot in series with the output of the effect and use the wiper as the output (with the third lug going to ground). you don't get a boost with this configuration, however.

I wouldn't use R18, although fundamentally it would probably work. the difference is the fact that C7 and R18 forms a high pass filter, so changing the resistance changes the corner frequency of the filter (changing frequency response at different gain is usually the sign of poor design).

if you're up for doing some testing, R17 seems to be the feedback resistor for the IC1B. if you make it bigger, the gain of the circuit will increase (thus more volume). if you replace it with a pot, you could have an output gain control. there is a problem, because R17 also forms a filter with C6, so the frequency response of the circuit will change somewhat. I would try something like reducing R17 to something like maybe 30k and putting a 50k log pot in series. this way, the resistance doesn't change _too_ much but probably enough to give you a little gain boost (or drop).

From Wikipedia:

"The 2N7000 is nearly identical to the BS170, except that the leads are arranged differently."
http://en.wikipedia.org/wiki/2N7000

do you let them air dry? i often put my spray painted enclosures in an old toaster over on low heat for about 20 mins. it really speeds up the drying process.

oh man, i love that paint. i need to get out to a hobby store pick some of that stuff up.

SHO is a great circuit to put in series with distortion/overdrive/fuzz circuits. i've done it with a few pedals now and it always works great. it's also small so you can stick it in almost any enclosure.

seems like the gain of the circuit would go way down if you remove C3, no? I think it's probably better to use a really big value... it's connected to ground, so it's really easy to orient a big electrolytic, something like 1uF or more maybe.

Does the circuit do the same thing no matter what setting the knobs have (in particular the fuzz and bite knobs)? The bite knob can be somewhat finicky so try playing around with it, turn it fully clockwise when it will be noisy and oscillate, and slowly turning it CCW until it stops.

otherwise, it's likely a mistake in the soldering somewhere. check your biasing so you'll have reasonable values (probably something like 1V at the collector of Q1 and maybe 2v at the collector of Q2, as rough estimations).

Actually, looking at it again, i think it's a low pass filter... it's a fairly complicated design so it's not particularly obvious what everything is to me...

in any case, looking at the formula for the cut-off frequency of a filter (formula is actually the same for low pass and high pass):

f = 1 / (2pi)RC

where R is the resistance and C is the capacitance. the topology of this filter is kind of complicated so it's harder to get R (it's actually the R that leads signal to ground or virtual ground), but the idea is that higher the value of C will make the cut-off frequency lower (because they're inversely related), so you'll get more upper-mids/high with the 22n. the value is pretty small so it will allow some pretty large frequencies to go through, probably on the order of 1.5kHz or so, it might be something like 1.2kHz for the 33n (which isn't really that different, you usually need to talk about orders of magnitude with capacitors to make much of a difference). these are just guesses without doing any analysis at all.

but there are so many filters in that thing. i really doubt changing one is going to make much of an audible difference anyway. i think the effect of C13 is diminished because it has R17 across it, too.

on second thought it's probably actually a high pass filter. but again it won't make much of a difference.

Either of those will work no problem.

C13 seems to be a low pass filter, so a bigger value will filter off slightly high frequencies.

the difference between those values is so small, though, you probably can't tell the difference.

i haven't been doing it so much lately, but if you've got the time, it may be worth drilling the extra holes. it makes your pots super-stable in the enclosure. just make sure your knobs are large enough that they'll cover the hole.

The reason people typically run pedals at higher voltage is for greater headroom. In other words, the voltage swing of the signal can be higher before it reaches the supply voltage and starts to distort.

If you're building a distortion or fuzz, (depending on the design of the circuit) you're taking advantage of the fact that voltage swing can never exceed supply, and that's what's changing the waveform of the signal.

So running distortion or fuzz circuits at higher voltage may give you some cruddy results, but again it depends on the circuit. (off the top of my head, some designs that use clipping diodes may actually distort more since they rely on the voltage drop across a diode to shave off the top of a sine wave. this assumes that more supply voltage means more gain, which isn't always true for many circuits).

conversely, running fuzz and distortion pedals at lower voltage often makes them crazy distorted by the same explanation above.

it's usually called enhancement-mode. it deals with the physical fabrication of the device. most mosfets we deal with (bs170, 2n7000, etc) are enhancement-mode. i as far as i know, they're more common in industry as well. i never really seen depletion-mode devices, the compliment to enhancement-mode, in my studies.

the difference has to do with the switching voltage of the gate, as i understand it. i think the gate has to be brought high to cut off the channel.

i don't know how it would sound in a circuit, but they're not drop-in replacements for enhancement-mode devices. you'd have to design a circuits specifically for them.

That is nice , I see that the starwars font is you trademark
clean build as always
I really should build a multi-FX box , but i'm having trouble getting a big box like that in Canada

kinda funny, hammond builds a lot of their boxes in canada.

Strange problem, but I don't think it's possible to figure out what's wrong without opening it up and tracing through the signal path.