Guitar Buzzing

[jbord39]

Hey guys.  I built a few guitar pedals, and some of them seem to have a low buzz sound constantly in the circuit.  I am guessing this is gaussian white noise (My wires are not short and nice like they should be, lots of loops) caused by the 60Hz wall signal, and am wondering if there is an easy circuit to remove this? 

Would a simple RC high-pass filter work, with the cutoff frequency somewhere around 120-130 Hz? 

Thanks for any information,

John

[CynicalMan]

It's more likely a power supply or guitar issue. What power supply are you using? Does the noise disappear with batteries? What kind of pickups does your guitar have? Is your guitar shielded? Does the noise volume change when you move around the guitar or pedal?

[jbord39]

Turn's out that it's the circuit.  I just got back from a friends where I was testing it on a few amps/guitars.  It has true bypass switching so I can tell it's not the guitar.  I also hooked it up in loops with other guitar pedals.  Some reduced the buzzing but it is definitely still there.  It's being powered by 12V wall wart (I used a few to check if that was bad).

I am troubleshooting the circuit but does anyone know if a simple RC network high pass filter could work?

[Johnny Lemonhead]

It's being powered by 12V wall wart (I used a few to check if that was bad).

Do all the pedals work on 12V? Is the wall wart regulated?
Unregulated power supplies can introduce amounts of noise that can render a pedal useless. Like CynicalMan asked - does the noise disappear with batteries?

[jbord39]

Ah! it does.  Thank you guys both.  So a LM7812 should work to solve this, right?

[Skruffyhound]

LM7812

- not necessary

Search power filtering. A large cap from + to - on the power before it meets the circuit usually helps reduce the ripple in the supply, but there are lots of ideas documented in threads here. A PSU with better filtering might be worth checking out if this is happening with a few circuits because many designs include that big cap I'm talking about as a standard feature.
Good luck

[CynicalMan]

For PSU filtering: www.beavisaudio.com/projects/Huminator/index.htm
Or get a 1spot.

It has true bypass switching so I can tell it's not the guitar.

That doesn't mean much because many circuits, especially compression and distortion, amplify hum in the signal.

[Johnny Lemonhead]

IMO, getting a regulated PS is the first step in troubleshooting hum problems. You can deal with each pedal individually - filter and regulate, but if it can be solved at the stem then why not.

It's like calling tech support, when the first thing they ask you to do is restart the computer.

[petemoore]

So a LM7812 should work to solve this, right?
  It'll take ripple out of DC, requires 2volts to work.
  Whether 'this' is relevant to that [the regulator] depends on whether there's ripple in your DC.
  To get 'perfect DC' [as close to 'pure DC' as it ever seems to get] use a battery, if there's still noise 'this' isn't introduced by the power supply.
  The guitar pickup/noise antenna can simply be removed [unplugged] to compare with/without, another 'trick' is turn the guitar all the way down to ground the input.
  If 'this' is unwanted noise introduced by a ground loop, the ground loop will inject available noise [depends on setting etc.] for amplification. The grounds can be isolated at different points, the power supply transformer is a preferred point of eliminating ground connections...no ground = no ground loop !
  See Spyder power supply article at GEO.   

[jbord39]

Thanks a lot.  I am going to look into this.

[PRR]

> a low buzz sound constantly in the circuit.  I am guessing this is gaussian white noise

"Gaussian white noise" is hissss.

"Buzz" is harmonics of 60Hz power frequency.

> My wires are not short and nice

That usually does not cause hiss. It sure can catch all the buzz in the room.

> Would a simple RC high-pass filter work, with the cutoff frequency somewhere around 120-130 Hz?

No. A 120Hz high-pass will cut "hum", pure 60Hz, but not a lot.

However "buzz" is 120Hz and higher, usually to at least 360Hz. To get useful rejection with a simple high-pass, you'd have to hi-pass well above 700Hz, over 1,000Hz. That leaves a guitar's tone totally gut-less, no lows at all.

Run on a battery. Batteries don't hum or buzz.

If that is a complete fix, but battery is not acceptable, get a GOOD power supply. Most wall-warts make crummy "DC". You can clean it passively with a 100 ohm resistor and a 1,000uFd cap; as shown in many posts and plans. Watch how much the voltage drops: low-power pedals can use a larger resistor for better filtering, high-power pedals may sag too much which leads to a smaller resistor and larger capacitor.

For "no" sag with OK filtering, regulators work, but MUST start from a higher voltage than you need. To get regulated 9 Volts you should start from over 13 Volts.

If pure power does not fix your buzz, or if buzz changes depending where in the room you hold the pedal, then it is room-buzz leaking in via case, shields, ground paths. Low-level circuits must be shielded with attention to detail. It is like building a water-proof basement. If you put a perfect rubber membrane on 99% of the foundation you will still have a damp basement. Or if the cellar is 100% rubbered but the roof leaks a dribble inside the walls, you have damp.