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Effect build not working

Discussion in 'Effects [BG]' started by MilkyMcMilkMilk, Dec 30, 2012.

  1. MilkyMcMilkMilk


    Dec 17, 2008
    I'm having trouble with a pedal build.
    I just finished building this pedal
    with this wiring diagram http://tagboardeffects.blogspot.com/2012/02/offboard-wiring.html

    I have built one pedal previously. It was a one knob no led, just battery fuzz pedal and it worked on the 1st try so i figured I'd try a 2 knob jobby.

    This pedal isn't working.
    I can hear my clean bass when bypassed but when I engage the effect the led comes on but no sound.
    Only thing I did different was add an extra ground wire onto the veroboard to run to the volume 1 lug.

    What would be the 1st thing to check?
    I have a volt meter I need to learn to use, i've only used it to find the resistor values.
  2. Skrogh


    Jan 28, 2010
  3. Crater


    Oct 12, 2011
    Dallas, TX area
    Make sure the input and output are wired to the correct places, I've gotten turned around working on pedals because things are "backwards" when the pedal is upside down when you're working on it, so the input jack is on the left instead of the right. Make sure the battery polarity (+ and -) is correct. Make sure there are no "solder bridges" connecting parts that aren't supposed to be connected.

    Get your voltmeter, and I'd also recommend a few "test jumpers" from your local Radioshack, it makes things easier. Set your voltmeter to read DC volts, connect the (-) test probe to GROUND. Now you can use the positive test probe of your meter to read the DC (bias) voltages of the transistors. The transistors Q1 and Q2 are biased the same, so you should get nearly the same voltage readings on the C and B of each transistor.

    You'll need to have a battery installed to make these tests, and a plug plugged into the input jack to turn on the battery. It doesn't matter if the effect is ON or in bypass, the circuitry is always powered when a cord is plugged into the input.

    I'm not familiar with the circuit, so I don't know the exact voltages you should be getting, but for the collector voltage (C terminal on the transistor) you should read "about" half the battery voltage, or about 4.5 volts, or at least somewhere between 3 and 6 volts, if it's a zero or almost nine volts there's a problem. Voltage on the base (B terminal of the transistor) should read about 1.5 volts, give or take. The E terminals of both transistors are connected to ground and should read exactly ZERO volts.

    If the DC bias voltages are wrong, you could have installed the wrong resistors, or maybe overheated a transistor. :meh: If the bias voltages are OK, then there's a problem with the AC signal passing through the circuit, double check your capacitors' values.
  4. MilkyMcMilkMilk


    Dec 17, 2008
    I don't have this wired for a battery.
    can I test with a volt meter with it plugged into the wall with power supply?
  5. bongomania

    bongomania Supporting Member Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
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    Primary TB Assistant

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