How to wire variable input cap?

Frequently asked questions on capacitor types, ratings, brands, use and abuse.
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nightendday
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Post by nightendday »

Hi all! I've done a few builds, a shin ei, bazz fuzz, electra, and a woolly mammoth.. So I decided to try maybe modding a familiar circuit to suit my tastes a little better... Here is what I have so far... Do I have everything hooked up ok?

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juanro
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Post by juanro »

Hi, if you're trying to mix between the 0.1u and 2.2u, yo have to swap them around... put the 0.1u fixed on the board, and the 2.2u over the potentiometer. With the current connection, you're adding 0.1u to the always connected 2.2u (turning it into a 2.3u total, not much difference). The other way you have a 0.1u input cap (the "standar" setting) and you mix in 2.2u ("fat" setting)

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Nocentelli
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Post by Nocentelli »

That layout appears to have a 100k resistance permanently connected direct from input to Q1's base, i.e.from lug 1 to lug 3. I'm not sure how this might affect things, but every cap blend I've seen has the pot wired as a simple variable resistor (i.e. using only two lugs) directly in series with the larger value cap.
modman wrote: Let's hope it's not a hit, because soldering up the same pedal everyday, is a sad life. It's that same ole devilish double bind again...

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nightendday
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Post by nightendday »

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It's actually the feedback resistor, and I was thinking about making that a pot as well...

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Post by Nocentelli »

No, I don't mean the onboard resistor (although a pot here can work really well - I'd suggest a 10k fixed resistor in series with a 100k pot using lugs 1 and 2 only, i.e. as a variable resistor ), I mean the pot itself: If you trace the input signal, it will go into lug 1 and through 100k resistance (the pot's entire track) then out of lug 3 and on to the Q1 base. Like I said, I don't know how this would affect the performance of the circuit, but a standard cap blend looks like this:

Image

The input goes to the small cap and straight to the transistor: it is also connected to lug2 and lug1 which are tied together. A parallel input signal encounters a series resistance set by the pot between lug2 and lug 3, where the signal is then sent through the larger cap to meet up with the direct "small cap signal".
modman wrote: Let's hope it's not a hit, because soldering up the same pedal everyday, is a sad life. It's that same ole devilish double bind again...

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nightendday
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Post by nightendday »

Nocentelli wrote:No, I don't mean the onboard resistor (although a pot here can work really well - I'd suggest a 10k fixed resistor in series with a 100k pot using lugs 1 and 2 only, i.e. as a variable resistor ), I mean the pot itself: If you trace the input signal, it will go into lug 1 and through 100k resistance (the pot's entire track) then out of lug 3 and on to the Q1 base. Like I said, I don't know how this would affect the performance of the circuit, but a standard cap blend looks like this:

Image

The input goes to the small cap and straight to the transistor: it is also connected to lug2 and lug1 which are tied together. A parallel input signal encounters a series resistance set by the pot between lug2 and lug 3, where the signal is then sent through the larger cap to meet up with the direct "small cap signal".

I did this and I'm only getting sound out of the .001 cap, turning the pot does nothing, is this because the other cap is an electro? I'm assuming that's there as filtering, so removing it could have some ill effects..

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Post by nightendday »

My mistake, got it working. THANK YOU SO MUCH!

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Post by Nocentelli »

Excellent: How does it sound?
modman wrote: Let's hope it's not a hit, because soldering up the same pedal everyday, is a sad life. It's that same ole devilish double bind again...

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nightendday
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Post by nightendday »

Nocentelli wrote:Excellent: How does it sound?
The input cap takes it from shin ei level nasaly snarl to doomy sludge goodness, thinking about raising the 2.2 to 4.7 and seeing what happens. :D
The "bias" knob I wired, just a 100k pot as a variable resistor, takes me from regular fuzz tones to distortion/overdrive sounds depending on where the input cap is set.

I did assume that with hfe of 260 and 280 I would have a lot more gain on tap..

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Post by Nocentelli »

nightendday wrote:I did assume that with hfe of 260 and 280 I would have a lot more gain on tap..
Sounds like it's working as it should: you could probably increase the bigger input cap to 10uF for even more sludge, but higher than that and you won't notice much increase. As for the gain, amount of gain is pretty subjective - 2N2222s are at the lower end of the hfe scale, I tend to use BC109c for my fuzz circuits, they are more like 400 and up.
modman wrote: Let's hope it's not a hit, because soldering up the same pedal everyday, is a sad life. It's that same ole devilish double bind again...

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