Need electrical help - How many ohms cut what hz?

Discussion in 'Community Discussion' started by joecool85, Nov 16, 2005.

  1. joecool85 macrumors 65816

    joecool85

    Joined:
    Mar 9, 2005
    Location:
    Maine
    #1
    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?
     
  2. CanadaRAM macrumors G5

    CanadaRAM

    Joined:
    Oct 11, 2004
    Location:
    On the Left Coast - Victoria BC Canada
    #2
    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
     
  3. joecool85 thread starter macrumors 65816

    joecool85

    Joined:
    Mar 9, 2005
    Location:
    Maine
    #3
    Sorry, I meant capacitor...

    Here is the schematic for the pedal I made.

    [​IMG]

    Can you explain what putting a higher or lower cap in would do?
     
  4. Sedulous macrumors 68000

    Sedulous

    Joined:
    Dec 10, 2002
    #4
    This is easily the most technical threat I have seen on MR. What kind of guitar pedal is this supposed to be?
     
  5. CanadaRAM macrumors G5

    CanadaRAM

    Joined:
    Oct 11, 2004
    Location:
    On the Left Coast - Victoria BC Canada
    #5
    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.
     
  6. joecool85 thread starter macrumors 65816

    joecool85

    Joined:
    Mar 9, 2005
    Location:
    Maine
    #6
    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.
     
  7. superbovine macrumors 68030

    superbovine

    Joined:
    Nov 7, 2003
    #7
    http://www.mouser.com/
     
  8. joecool85 thread starter macrumors 65816

    joecool85

    Joined:
    Mar 9, 2005
    Location:
    Maine
    #8
    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.
     

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