Radio interference with guitar volume down when using DIY fuzz pedals

[rosscocean]

I seem to get radio interference with my guitar volume down when using DIY fuzz pedals. How do I stop this?

I've noticed it on a few pedals I've made: Bazz fuss, fuzz factory and fuzz face.

Cheers
Ross

[Pigyboy]

I would start here
http://www.guitarnuts.com/wiring/shielding/shield3.php
Then question the pedals.

[Davelectro]

I seem to get radio interference with my guitar volume down when using DIY fuzz pedals. How do I stop this?

I've noticed it on a few pedals I've made: Bazz fuss, fuzz factory and fuzz face.

Cheers
Ross

I'd appreciate any help too.

My diy fuzz face is properly grounded and inside a metal enclosure. Shielded wire was used everywhere, also 100pf cap from input to ground and 10k resistor in series with input. Any ideas?

[Pigyboy]

Is this happening with production pedals too? Could be ground loop problems. Need to see pictures of the builds to tell more.

[rosscocean]

No just with DIY pedals. I tried fuzz face on breadboard through my main amp (switched from a sound city sc10 to a twin amp) and a different guitar (switch from a mim strat to a lite ash tele) earlier and it was fine.

[Pigyboy]

Post some pictures

[Gurner]

Does it pick any radio signal with no guitar plugged into the pedal?

What happens if you short the signal lug on the stompbox input jack socket to ground? (do you still get radio pickup)

What happens when you get a known good solid ground connection & touch it to the stompbox chassis? (ie where there's no paint & you can get a good electrical connection)

[rosscocean]

Does it pick any radio signal with no guitar plugged into the pedal?

What happens if you short the signal lug on the stompbox input jack socket to ground? (do you still get radio pickup)

What happens when you get a known good solid ground connection & touch it to the stompbox chassis? (ie where there's no paint & you can get a good electrical connection)

I'll try these tonight and let you know. I don't think I can hear radio with the guitar unplugged but I'll double check.

Cheers
Ross

[rosscocean]

I tried you're suggestions on a bazz fuss circuit I've got on my breadboard. The circuit did have radio interference with my MIM start's vol down. It did stop with the guitar unplugged and when I shorted the signal lug to ground.

Ross

[Gurner]

I tried you're suggestions on a bazz fuss circuit I've got on my breadboard. The circuit did have radio interference with my MIM start's vol down. It did stop with the guitar unplugged and when I shorted the signal lug to ground.

Ross

I thought we were troubleshooting a radio signal through a circuit in a pedal? (it's what's your opening post suggested). A breadboard enviroment has no shielding whatsoever.....what's more the grounding on breadboard is generally sub par at best....better to talk about a specific pedal (& try the good known ground wire temporarily touched to a bare part of the pedal chassis like I mentioned)

[rosscocean]

I've tried your sugestions on my fuzz factory clone. No radio interference with the guitar unplugged and ground the input dims the radio but doesn't get rid of it completley.

I'm not using shielded wire for in and out, would that make a lot of difference? 

[Gurner]

I've tried your sugestions on my fuzz factory clone. No radio interference with the guitar unplugged and ground the input dims the radio but doesn't get rid of it completley.

I'm not using shielded wire for in and out, would that make a lot of difference?  

I'm not sure I'm foillowing you here - you're feeeding a guitar into a stompbox - but you're not using shielded cable?

If not, then I think you'rve just found your problem - without using shieding you're essentially plugging an antenna into your signal chain.

[rosscocean]

No, I mean the input wire inside the pedal isn't shielded. I'm using a shielded instrument cables from my guitar to the pedal and from the pedal to my amp. 

[deadastronaut]

theres ya problem...shield hi gain stuff!..always..

what was on the radio btw?...

[Gurner]

No, I mean the input wire inside the pedal isn't shielded. I'm using a shielded instrument cables from my guitar to the pedal and from the pedal to my amp.  

Inside the box should be ok (the metal stompbox chassis should be providing the RF shielding inside the stompbox - but only if it in itself has a good connection to ground)

Ok, let's recap...

You say that this same guitar/cable into a commercial stompbox has no radio interference - therefore not the guitar or the external guitar cables

You *do* hoewever get radio, on the same setup into your diystompbox....but only with the guitar volume rolled down.

IMHO it's likely to be poor grounding inside your stompbox - get yourself a known good earth external cable/point & touch it to the stompbox chassis to see if the radio reception goes.

Have you got star ground arrangement?

You certain there's a good ground at the jacksockets?

(another quick test is to solder a short wire  from the output socket ground lug to the input socket ground lug - this may improve things (or at least give you an indication if it's in this general area - but once again, check your grounding of the input/output sockets)

this is quite urgent - I know how bad Radio Hallam can be

[Jaicen_solo]

No, I mean the input wire inside the pedal isn't shielded. I'm using a shielded instrument cables from my guitar to the pedal and from the pedal to my amp.  

this is quite urgent - I know how bad Radio Hallam can be

Agreed. I think if I ever heard Big John coming out of my amp, I might go Pete Townshend on it's ass!

Anyway, back on topic. In my experience, if you have RF getting into your pedal, there's not a great deal you can do. I've found that Ge trannies, particularly metal can's, are just plain old succeptible to interference, depending on the circuit. Fuzz Factories seem to be particularly troublesome for some reason. I know that some people have used ferrite beads on the wires right where they join the PCB with good results, likewise a small 22pf cap to ground on the input helps.

[rosscocean]

I did have a wire directly connecting the in and out sockets ground lugs and it had the Ri.

The lead is a high quality planet waves cable but it is quite old and fairly long. I've brought a short, brand newcable back from the practice room so I can test it tomorrow.

What is star grounding?

I'll try the cap on the way in and see if that helps.

Cheers for all your responses!

Ps it wasn't big john... Thank god!

[rosscocean]

I tried the new lead with the guitar vol down and it got rid of the RI on my modified Bazz Fuzz pedal. It didn't quite get rid of all the RI on my fuzz factory (with it turned up LOUD! And the drive up full) but you can only just make out the RI amonst the natural pedal/amp noise and I can gate it out.

So to conclude... I'm an idiot for not checking the lead first!

Thank for your help.   

[earthtonesaudio]

Anyway, back on topic. In my experience, if you have RF getting into your pedal, there's not a great deal you can do. I've found that Ge trannies, particularly metal can's, are just plain old succeptible to interference, depending on the circuit. Fuzz Factories seem to be particularly troublesome for some reason. I know that some people have used ferrite beads on the wires right where they join the PCB with good results, likewise a small 22pf cap to ground on the input helps.

Most fuzzes that have this issue employ a common emitter gain stage, which is a really good way of making a simple radio receiver.  If you want it to not be a radio, you have to either stop the stage from rectifying the incoming signal, or reduce the gain at radio frequencies.  Since the rectification is often part of the desired sound, the only remaining option is reducing the gain at RF.

One way that does NOT work reliably is to put a capacitor from the input to ground.  In fact, when the OP turns his volume down, that's exactly what he has done.  The guitar lead becomes a capacitor to ground at the input, and the result is he tunes in a radio station.  The cap does shunt frequencies for some stations (which is why this is often suggested as a fix), but for other frequencies it may tune them in stronger.  So it works for some people, some of the time, but it is not a cure.

Several things you can do to cut down generalized RFI:  Adding a small input resistor and relying on the Miller effect can form enough of an integrator to bring the radio sound below annoying levels.  If the resistor alone is not enough, consider adding a small cap from collector to base, i.e. making a more purposeful integrator.

[yeeshkul]

Interesting thread. I used to have the same troubles with my Si FF. Thank you Alex for the explanation.