picking up radio

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ubertar
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picking up radio

Post by ubertar » Sat Oct 04, 2014 11:02 am

I made a polyphonic fuzz that I love the sound of... I'm using it on my movable fretted, five-stringed (two double courses, one single), bowed/plucked thingamabob.

The problem is, it picks up radio. Even worse, it's Disney radio. So I'll be playing some evil-sounding 13 equal metal, and in the pauses, it's "players gonna play play play play play... haters gonna hate hate hate hate hate...". Clearly this is untenable.

I've tried running the wires that go to the output jack through and around a ferrite cylinder a bunch of times to make a toroid, but that didn't help. I don't know what else to do.
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Post by DrummerMan » Sat Oct 04, 2014 1:13 pm

"Evil" and "Disney" go hand in hand. I don't see the problem...




Other than that I have nothing useful to add.
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ubertar
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Post by ubertar » Sat Oct 04, 2014 1:56 pm

The music is abstract, fictional "evil". Disney evil is real.
get a hammered sound from guitar or bass! http://www.stringhammer.com
hand-made version to raise money for manufacturing... kind of like kickstarter, but you get a fully functional item now

Album!
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Post by iC » Sat Oct 04, 2014 7:02 pm

i recently had a hawaiian slide guitar's pickup-pzm combo latch ontu what i believe was an 8.5k tone emitting from the building's alarm system three rooms away... maddening.....it was slightly mitigated by lifting the guitar over his head...not fair.. count me curious.
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ubertar
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Post by ubertar » Sun Oct 05, 2014 7:08 am

Each of the fuzz circuits has a cap across the output for low-pass; that seems to work to keep out radio in a mono fuzz using the same circuit. Maybe one of those caps has a bad solder joint... I'll have to check that out. If not, maybe adding a low pass on the combined output will help.
get a hammered sound from guitar or bass! http://www.stringhammer.com
hand-made version to raise money for manufacturing... kind of like kickstarter, but you get a fully functional item now

Album!
https://paulrubenstein.bandcamp.com/album/one-eye-awake

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Post by The Scum » Sun Oct 05, 2014 12:53 pm

Two things come to mind to check/try:

First, go through the shielding and grounding and verify everything is solid and well-connected, from the guitar to the pedal to the amp, and on through to the outlet, mains panel and ground rod. If the ground were questionable at some stage therein, then it's possible that RF can't find the proper path to ground, so it's using the signal lines rather than the ground.

Last time I was demodulating FM, it was a node in a preamp circuit that should have been grounded, but wasn't. Once I found it, it was an easy fix.

The other thing to consider would be mirroring the small output shunt cap at the input. RG Keen explains it fairly well here:
http://geofex.com/circuits/what_are_all ... ts_for.htm

Ideally, the resistor and cap would be physically close to the input jack. Any run of wire that hasn't been treated thusly can become an antenna that re-radiates within the enclosure...a version of Muncy's "pin 1 problem."

The heart of a fuzz is a super-high-gain amplifier. If even a trace of RF finds its way in, it can amplify it into the audible range. The best cure is to keep the RF out to begin with.

Where were you putting the toroids? In the fuzz or the instrument?
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Post by floid » Sun Oct 05, 2014 1:56 pm

i've used a ferrite bead (rather than donut) at input and output, tied to a small value cap to ground on the way to/from the circuit. works well in fuzz and boost pedals.
if i'm understanding right, you've got parallel fuzz stages, and a single stage doesn't do this? if so i'd suspect something in the split/sum schemes, and input before output.
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Post by Snarl 12/8 » Sun Oct 05, 2014 2:09 pm

Please post a sample.
Carl Keil

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Post by casey campbell » Tue Oct 07, 2014 7:56 am

sorry if this has been answered already, but is the box metal or is the box well shielded?

also, make sure you are using good cable connecting the fuzz to the thingamabob.

also, what are you powering your fuzz with?

another thought, could it be that your stringed thingamabob is the antenna? perhaps that is your source of RF?

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Post by The Scum » Tue Oct 07, 2014 9:33 am

Or to ask that in slightly different terms:

What's the smallest configuration that still exhibits the misbehavior?

Remove things until it's functional, then build back up...
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Post by ubertar » Tue Oct 07, 2014 9:57 am

The box is metal. It's powered by battery. The instrument doesn't pick up radio without the fuzz. The mono version of the fuzz picked up radio with other instruments until I added a low pass on the output. With different amps, the problem is the same. The cable is good quality and doesn't have this problem in other situations. It's the fuzz.

Adding a low pass on the summed output in addition to the low passes that were already there on each fuzz's output has helped some. I'll try adding one to the input and see if that helps. Ferrite beads around the low-pass caps sound like a good idea too.

I was putting the toroids in the fuzz, around the output wires of each fuzz circuit, before the output transformer.
get a hammered sound from guitar or bass! http://www.stringhammer.com
hand-made version to raise money for manufacturing... kind of like kickstarter, but you get a fully functional item now

Album!
https://paulrubenstein.bandcamp.com/album/one-eye-awake

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