Solving AC Noise in Fuzz Box Bass Guitar Circuit

In summary, when fuzz is on, an AC hum is present that is timed to the peaks of the signal. When fuzz is off, the AC hum is not present. It is possible that this is related to feedback from the clipping diodes.
  • #1
rolerbe
103
3
I'm working on a 'Fuzz box' for a bass guitar, ckt diagram below. With fuzz on and gains up, I'm getting a strange (to me) AC artifact -- Oscope images below (AC waveform from isolation xfmr at 10V/div, signal out at 2V/div).

With fuzz on, and the input shorted to ground, the artifact is timed to the AC peaks, and these peaks are flattened. With fuzz off, the AC peaks are 'normal'. The artifact is present (tho much smaller) at the input to the first amp stage, but I think it is somehow related to feedback from the clipping diodes (which make the fuzz).

Any thoughts? Thanks in advance.

Ckt diagram:
http://www.postimage.org/image.php?v=Pq2hSu_S

Fuzz On:
http://www.postimage.org/image.php?v=Pq2hSHtA

Fuzz Off:
http://www.postimage.org/image.php?v=Pq2hUDHA
 
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  • #2
AC hum usually is introduced by 1) a poor power supply, 2) improper shielding or 3) improper grounding. Check the supply for your circuit, or use a battery, to address #1. (Using a grounded supply can introduce ground loops, see #3). Are there any long wires, and if so are they twisted? Is your device in a tight grounded metal box? These steps will largely take care of #2. #3, proper grounding and eliminating ground loops, can be more difficult. I can't offer specific advice since this involves cable routing, the other equipment you are using, Earth grounds, and even things that are non-obvious. Try to learn about grounds and ground loops--there are many books on this topic (Ott's "Noise Reduction Techniques in Electronic Systems" is a good one), and it looks like a Google search has dozens of helpful online sites--then apply them to your system. Good luck!
 
  • #3
I am coming to the conclusion that it is #2 and/or #3 as you describe. Currently, its a raw pcb sitting on my bench. The gain controls are pots on long leads, not twisted. Flourescent lights overhead. So I guess I'll have to test it shielded.

But one curious thing is that there is no noise when S1 (the fuzz on/off switch) is open. So I don't think its the power supply.

Thanks for the input!
 

What is AC noise in a fuzz box bass guitar circuit?

AC noise, also known as alternating current noise, is unwanted electrical interference that can occur in a fuzz box bass guitar circuit. It can manifest as a buzzing or humming sound in the audio signal.

What causes AC noise in a fuzz box bass guitar circuit?

AC noise can be caused by a variety of factors, including poor grounding, faulty wiring, or electromagnetic interference from other electronic devices.

How can I solve AC noise in my fuzz box bass guitar circuit?

There are several steps you can take to solve AC noise in your fuzz box bass guitar circuit. These include: checking your grounding, using shielded cables, adding a noise gate pedal, and shielding the inside of your fuzz box.

Will solving AC noise affect the tone of my bass guitar?

It is possible that solving AC noise in your fuzz box bass guitar circuit may affect the tone, as any changes to the circuit can alter the sound. However, with proper troubleshooting and solutions, the impact on tone should be minimal.

Do I need any special tools or equipment to solve AC noise in my fuzz box bass guitar circuit?

Some of the solutions for AC noise may require specific tools or equipment, such as a multimeter or soldering iron. However, there are also simple solutions, such as using shielded cables, that do not require any special tools.

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