Unwanted radio reception??

**Damon Rondeau** · #1 06-02-2009, 03:04 PM

Technically this is a guitar question but I don't know anybody up there -- please don't make me go!

Anyway, was using a amplified acoustic bass guitar on a job the other day -- slumming a little bit, yeah, but enjoying the hell out of playing in tune for once. The ABG is a Kramer Ferrington, but it's got a non-stock piezo pickup in the bridge. I ran the signal through a Fishman pre-amp and then into my Acoustic Image Clarus head.

I was getting radio reception like crazy on that job. Plugged in the guitar player's axe as a test and the radio B.S. was gone, strongly suggesting it's something about the Ferrington creating the problem. I've use the same rig twice before and had nothing like this effect.

I'm quite ignorant about an electronic issue like this. Anyone care to take a shot at educating me about what's going on with this unwanted radio reception?

jtlownds · #2 06-02-2009, 05:17 PM

Last year, I played a gig in Naples, using my series II AI Contra. Was playing thru a Full Circle, straight into the Contra. When I turned it on, I got a radio broadcast of a baseball game. Not very loud (the audience couldn't hear it). I had a friend sit in with his Underwood equipped bass, and the ball game was still on. In fact, it continued to play the game with nothing plugged in. It never happened before, and it hasn't happened since. I have no idea what caused it.

coreyfyfe · #3 06-02-2009, 05:29 PM

This thread may be of use to you, it focuses more on the amp picking up the signal, but the same could be said about the grounding/shielding on the electronics of your ABG.

Amp is picking up radio signal

**Damon Rondeau** · #4 06-02-2009, 07:02 PM

Very interesting... Thanks, guys, for the input.

I've done hundreds of jobs, in dozens of venues, with almost the same gear. Usually I'm playing my DB with an Underwood pickup straight into the Clarus. The Fishman pre-amp was necessary to make the ABG sound OK; it's not been part of the DB setup for ages now. I've never had anything but whisper-quiet performance. Only the noises I make.

Tried re-orienting the amp and guitar on that last job: no dice. Still had the radio going. Sounded like AM radio...

It's gotta be the Ferrington. I'm gonna have to call Grierson and see what the heck he put in there...

fdeck · #5 06-02-2009, 07:10 PM

It's been my experience over the years that AM reception is due to a dodgy ground connection somewhere in the signal path. How you pick up radio is that some nonlinear element (all are nonlinear at some level) acts as the "detector" that demodulates the AM.

Non stock piezo might indicate a DIY job by the previous owner. Can you peer in through the sound hole with mirror and light bulb, to see what's going on?

moles · #6 06-02-2009, 07:23 PM

I've had my wireless system pick up weird things before. Same deal - hundreds of uses cross the country, and Cranbrook was the only town that I had issues with - in the form of taxicab-dispatchers coming through my amp. A guitar player that I had been working with recently had am radio coming through his Soldano (KY58! Sweet.....)

The wireless system is it's own issue, obviously. As for the shoddy grounding causing AM radio reception - might a lousy ground on the infrastructure of the building cause the same thing? (Guess I'm directing that one largely to you, Francis...)

Damon, what happens when you plug in the rig at home?

Gearhead43 · #7 06-02-2009, 09:30 PM

What station were you picking up?

knigel · #8 06-02-2009, 09:40 PM

Maybe you could talk to the dudes in Spinal Tap.

**Damon Rondeau** · #9 06-03-2009, 08:34 AM

Don't forget Woodstock...

The building: it was the Hotel Fort Garry. It's a very old railway hotel -- despite its stately beauty and significant modernizations, it wouldn't surprise me if its electrical system was flakey.

Does it do it at home? Nope.

What station? Couldn't tell ya. It was loud and obnoxious, so I'm thinking AM.

Inside the axe, with mirror and light bulb? Dunno yet. Tomorrow I get some workbench time, so I'll check it out. It seems most likely to me that something about the bass and its new pickup is crapping out...

Thanks loads, guys!

robgrow · #10 06-03-2009, 11:01 AM

This does sound like it's related to the building's electrical wiring. In any building, the ground and neutral conductors are supposed to be at ground potential (zero volts), and the ground conductor should never have any current flowing through it. Unfortunately this is often not the case in many structures, especially in older buildings. There can be lots of stray current on these conductors. Throw in a nearby broadcast transmitter, and there can be quite a bit of RF floating on the electrical wiring. With the very high impedances involved with piezo pickups, many things can make a very effective RF detector (a cat's whisker). This is called audio rectification.