Need electrical help - How many ohms cut what hz?

[joecool85]

I'm working on building some guitar pedals and they tell me in the schematics that you can switch out resistors for cutting out different frequencies, but it doesn't say what does what. IE - If I put in a higher ohm resistor, does it cut lower frequencies or higher?

 

[CanadaRAM]

I'm working on building some guitar pedals and they tell me in the schematics that you can switch out resistors for cutting out different frequencies, but it doesn't say what does what. IE - If I put in a higher ohm resistor, does it cut lower frequencies or higher?

It ain't resistors alone, it's them plus the capacitors. Resistors alone will only drop the signal level. So what resistance to change depends on the design of the circuit.

A filter is an inductance-capacitance network (also known as an LC Network)

Bunches of info here:

http://www-users.cs.york.ac.uk/~fisher/lcfilter/
http://www.geofex.com/Article_Folders/EQs/paramet.htm
http://www.pcs-electronics.com/en/guide.php?sub=NewSchematics#Filter

 

[joecool85]

Sorry, I meant capacitor...

Here is the schematic for the pedal I made.

Can you explain what putting a higher or lower cap in would do?

 

[Sedulous]

This is easily the most technical threat I have seen on MR. What kind of guitar pedal is this supposed to be?

 

[CanadaRAM]

It's been many, many years since high school electronics shop, however I think that the smaller the capacitor, the higher the frequency, and the larger the capacitor, the lower the frequency. This looks like a low-pass filter, that is, it rolls off more or less of the high frequencies.

This filter has no inductor, so it is not a LC network, it is a capacitive filter

In a simple capacitive low-pass filter (one resistor, one capacitor), the cutoff frequency is: f(cutoff) = 1 / 2piRC where R is the resistance and C is the capacitance.

So the larger the capacitance C, the lower the cutoff frequency.

http://www.ibiblio.org/obp/electricCircuits/AC/AC_8.html

Edit; ah. I might be reading this wrong - you're describing a high-pass, not a low pass. It's been way too long. Anyway, it's the same formula. To get the values, you have to know the load as well - that is the resistance provided by the amplifier.

 

[joecool85]

Thanks CanadaRam, thats what I gathered. Can anyone find a list of what caps cut what frequencies?

And Sedulus, this is basically a volume control pedal so you can cut the vol, hence cut the overdrive on your amp with the kick of a pedal, instead of making a really hard to make overdrive pedal. It has a cap in it that lets the high frequencies through and stay crisp and clear.

 

[superbovine]

Thanks CanadaRam, thats what I gathered. Can anyone find a list of what caps cut what frequencies?

And Sedulus, this is basically a volume control pedal so you can cut the vol, hence cut the overdrive on your amp with the kick of a pedal, instead of making a really hard to make overdrive pedal. It has a cap in it that lets the high frequencies through and stay crisp and clear.

http://www.mouser.com/

 

[joecool85]

Got it figured out. The bigger the cap, the more low frequencies go through it. I'm going to stick with my 100pF cap for now, maybe up it to 220 or 300 later. Who knows? But it works/sounds great right now, so thats how its staying for a little while. No to get the box itself finished...I waiting on a seller from eBay to ship my damn DPDT switch! I should have just got it off from smallbearelec, but I didn't know better, now I do.