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Thread: Basic questions about capacitors, resistors, and diodes

  1. #1
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    Basic questions about capacitors, resistors, and diodes

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    Hey, I recently built a DIY pedal from a kit and I'm happy with it but I feel like I don't understand enough of what's actually going on electronically.

    Could someone give me a little outline on exactly WHAT all of these pieces are doing? I know that I used various resistors and capacitors of different values, plus a silicon diode and transistor, but I don't exactly understand how these shape the sound. The kit I built (along with parts list) is here:

    Anyone wanna help me out a little?

    Much appreciated!

  2. #2
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    Signal comes in to the switch; if it's on, goes to C1. This is a coupling cap; it blocks DC and thus allows different DC level on either side of the cap (more later). Signal goes to Q1, a transistor. Transistors amplify. How much? This is a kinda complicated setup. Let's ignore the diode for a moment. AC gain is set by R5+R6 and the current gain of the transistor. It's also frequency-dependent because of R5/C6-->less gain at high frequencies. DC gain is affected by R5, R6, and R4. Thus AC gain is higher than DC gain. We don't really care about DC gain per se, only that if you don't have the DC levels set correctly, your transistor doesn't work too well.

    R1, R2, and C4 serve to set DC bias at the transistor input (B, for base). Again, just keeping the transistor happy here. D1, D2, R3, and C3 are a feedback loop with clipping diodes. That causes distortion, dependent upon the setting of R3 (a pot) and of course the amplitude of the input signal.

    C7 is another coupling cap, so you don't have DC going out your output. R7 is another pot, it is an attenuator and thus output level control.

    Lastly, C2 is a high frequency filter cap, intend to keep RF gunk out of your signal path.

    Mods? I would remove one diode, I think asymmetrical clipping sound better.

    One thing I noted: they say schematics are the same everywhere. That's not true; the European symbol for a resistor is different than the American symbol shown here (Euros use a rectangle, pretty boring). More importantly, "mfd" is NOT the standard for capacitors, unless you are an HVAC technician. It should be μF, for microfarad, or uF if you are lazy (I am lazy). mF is millifarad, which is 1000 times as large as microfarad. "mfd" is archaic.

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