Hoffman Amplifiers Tube Amplifier Forum
Other Stuff => Effects => Topic started by: hesamadman on November 06, 2014, 07:00:38 am
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I made a very simple overdrive pedal on my breadboard. This is the first one ive done. Once I plugged in guitar. It had an amazing overdrive tone but LOTS OF NOISE. Now I got rid of the noise two ways. One way got rid of all the noise except a very low volume high pitch scream. I put an electrolytic cap from positive to negative on my power supply. Like a filter cap. Like I mentioned....most noise gone....not all. Second way I added various values of resistors between the pedal and the 9 volt power supply. This eliminated the noise all together but also acted as a noise suppressor on steroids. If i plucked the strings hard it played the notes but if I barely hit the strings no noise came out.
My signal goes as follows.
input -> .047 cap -> pin 3 lm386 (in) -> out of pin 5 lm386 -> 220uf cap (ive used many values) -> output
LM386- pin 2 and 4 ground, pin 6 9v+
I do not have any diode clipping after pin 5 of lm386. I put them on and doesnt even seam to be altering sound. Nor do I have a resistor to ground after pin 5. Same scenario. No real change. My goal was to add more to this circuit once I get this cleaned up.
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hi; I have not seen the LM386 being used as an overdrive chip. They are generally used to run a speaker or a set of headphones. If you are plugging a guitar into the "custom od" and then running it into another guitar amp, you probably have too hot a guitar signal on the input of your amp. There are a wide variety of od pedal designs out there using the dual op amp chip. You might try a different chip on the breadboard and see if it cures the problem. An old standby chip would be the TL072.
:icon_biggrin:
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... got rid of all the noise except a very low volume high pitch scream. ...
Probably the IC oscillating. Place a 0.01uF to 0.1uF cap from 9v+ to ground, right at the chip's pins (that is, the cap is sitting right next to the IC).
Typically, solid-state needs a power supply bypass cap right at the chip to avoid oscillations. It's one of those "unwritten rules" of solid-state electronics.
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There's a lot of info w/ very little circuit information to go on to give definitive answers. Have you tried to simply use a 9v battery instead of a power supply to confirm if the noise is from that source? Remember that playing a circuit on a breadboard can be noisy simply because there's no shielding between your guitar and amp's input or when certain wires are close to others. Resistors between your supply voltage is causing a voltage drop to your circuit likely lowering gain and why the input sensitivity while lowering noise at the same time but you don't want this to correct an issue that is likely from something else.
Edit: sorry forgot to mention that this could need a regulated supply to stabilize it. Also, check your e-lytic caps to make sure their voltage ratings are sufficiently high, could've blown one if things got lost/farty.