Build Your Own Clone Message Board

Hey just wondering.
In this schematic there is a 47UF cap Electrolytic running from E of the trans to Ground. Whats the purpose? I could understand if there was a gain control instead of fixed resistor, that cap would prevent "Scratchy Pot" but in this case there isn't a gain control so whats it do? LOL

Looks like a "bootstrap" or bypass capacitor. It will allow more gain at the frequency decided by the RC network it forms with the emitter resistor, as well as (probably) increase impedance of the circuit. Basically, the cap will allow frequencies above a certain freq to bypass the emitter resistor. The best way to see what it does would probably just be to breadboard this little guy real quick, then swap the cap in and out of the circuit.

I'd have to dust off my math skills to give you real info, but my hunch is you'll notice a boost in gain over a certain frequency range. This range will change as you adjust the value of the cap.

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I see. Im guessing this is increasing the gain on lower frequencies since larger caps filter out high frequencies.

the bigger the capacitance value, the lower the frequencies that will be able to pass. In this case, they're passing to ground. So the result might in fact be that only the frequencies ABOVE the RC network's threshold will be amplified. That would certainly make sense in a guitar effect, where too much low-end gain will make it too muddy. You could test this by breadboarding, then swapping the 47uF cap for something smaller, like a 47pF, to hear the difference. It will probably be very noticeable!

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I could be talking out of my ass, though... it's been a long time since I did this in school

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here's an article with a similar BJT circuit. Paragraph at the end explains what the cap's doing better than I did

https://casper.berkeley.edu/astrobaki/i ... r_Circuits

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Yeah, but you did pretty well for a guy talking out of his ass....

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“My favorite programming language is SOLDER” - Bob Pease (RIP)

My Website * My Musical Gear * My DIY Pedals: Pg.1 - Pg.2

Here's a bit more that will teach you something about using bypass caps for AC filtering as well as reactance of capacitors: http://www.learningaboutelectronics.com ... citor.html

It doesn't apply 1:1 to how we use them in guitar pedals but it's a good foundation (in guitar pedals we like to create distortion not minimize it!)

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RIP madbean v.1

This makes sense. Ive seen this done one other time in a pedal where a 22uf cap was used and increased the gain significantly in a Selmer Buzztone Clone. If I can find my breadboard i'll poke around and try a few different cap values and see what happens.

My ass just wants to help!

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