Experimenting with output caps of Electra Distortion

[SpringbokUK]

Hey everyone

Wondering if you can help me out with my query.

I breadboarded the Electra Distortion using NO diodes. I used a 0.22uf input cap and for the output cap, instead of 0.1uf i used a 0.01uf which literally cut out all bass frequencies. I then added a 0.22uf in parallel to the 0.01uf and a potentiometer in between. I found that as i turn my pot more to the 0.22uf, it gets really beefy and has a lot more bass. Here's my confusion. I thought that to get a low pass filter, which im guessing is what i've got here, you had to have a resistor in series and then a cap going to ground. I tried that but it just cuts my signal. So does that method only work on the INPUT Caps? If so then what's the difference in that method and the one i've done. I knew that the smaller the cap, less bass. So I'm just unsure of the method i've used and what it's actually doing.

Cheers

Liam

[Mac Walker]

OK, I'll bite.....

A coupling cap acts as a high pass filter, whose cutoff frequency is determined by the capacitance (not a low pass, where high frequencies are shunted to ground).

Cutoff frequency being defined as the point at which the amplitude of the signal passed drops by around 3 dB, or the amplitude of the signal drops by 50%..... (3dB is a barely perceptible drop in volume)

(In this case if you had an audio oscillator sine wave, that swept from 20 hz to 20 khz you could quantify the peak to peak voltages measured on the output, in this manner)

Increasing the parallel capacitance (turning the pot towards the higher capacitance value) lowers the cutoff frequency, allows more of the lower frequencies to pass, I think around 2 uF is the point at which the filter becomes flat relative to audio frequencies, that is, all audible frequencies can pass equally....

[SpringbokUK]

Ahhh i get it.

Very much appreciated mate.

I connected the 0.01uf cap to ground but it just cut my signal. I'm guessing the low pass filter only works at the beginning of the circuit?

[wilrecar77]

You can use a low pass anywhere in a circuit.

Take a look at this page: http://www.beavisaudio.com/projects/TrotskyDrive/

Towards the end, there is a switch connected to a 22nf cap labeled "bright cut". With the switch engaged, the frequencies that can pass through the 22nf capacitor go to ground and do not show up at the output of the pedal (aka low-pass). You don't need the switch for it to work, it is just there to make it selectable. I guess the important thing to know is that caps are not intrinsically low-pass or high-pass, but that they will only pass certain frequencies. It is how you connect capacitors in a circuit that makes them high-pass or low-pass (or rather part of a high-pass or low-pass filter).

[Havaden]

2.2uF input cap, 5nF output cap metal film and removing the 680Ohm resistor sounds pretty neat, together with a good tube amp its tweed heaven.

[SpringbokUK]

Ah nice one man.

I recently got an oscilloscope like but i've yet to learn how to use it. With the oscope i hope to see what the different values of input caps does to the eq band. I've mainly been using simple colorsound circuits as a skeleton to build upon and develop.