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I get radio signals through my amp [message #13661]

Fri, 14 May 2010 21:09

XsSpeed
Messages: 9
Registered: September 2009

Junior Member

I just got done with a gig and while I was playing through my 200, I was getting serious radio traffic coming out of my Ampeg SVT 8x10. I've had that before in my basement during practice and blamed the old Mu-Tron Bi-phase or my basement wiring for it but it never happened during a gig. It was really loud too! I turned off the Mu-tron (even though I wasn't even running through it at the time) and unplugged from my effects pedal (overdrive ODB-3) and got no relief.

What is causing this and how do I stop it? thanks.

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Re: I get radio signals through my amp [message #13667 is a reply to message #13661]

Sat, 15 May 2010 12:14

pleat
Messages: 1452
Registered: June 2004
Location: Belding, Mi

Senior Member

My first thought is, are you using a coil guitar cord? Coil cords will pick up radio signals. I've had CB radio's bleed through the PA system. Winding the mic cord around the mic stand acts as an antenna even with Lo Z mics.
pleat

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Re: I get radio signals through my amp [message #13671 is a reply to message #13661]

Sat, 15 May 2010 17:19

stevem
Messages: 4733
Registered: June 2004
Location: NY

Senior Member

The first thing you need to confirm is that all of your cords you use have good shielding, as just one cords shielding going south will let radio signals in.
This was also a problem on some amps to the point that the factory put out a fix of adding a small value cap outo ground out the incoming radio signals.
If you PM me your email adress I will forward you a scan of the fix tomorrow.

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Re: I get radio signals through my amp [message #13737 is a reply to message #13661]

Sun, 23 May 2010 18:54

BrianBB
Messages: 46
Registered: November 2008
Location: Fayetteville, Ga.

Member

stevenm,

I'm having the same problem with my C-595 Frank head. Do you mean that using an unshielded cord once will infect your amp with radio signals that will remain with it even after switching cords? Yikes. Shocked

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Re: I get radio signals through my amp [message #13744 is a reply to message #13661]

Mon, 24 May 2010 02:38

Van
Messages: 134
Registered: April 2004

Senior Member

My old Kustom combo organ used to do the same thing.
Never found a cure for it.

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Re: I get radio signals through my amp [message #13746 is a reply to message #13661]

Mon, 24 May 2010 06:12

stevem
Messages: 4733
Registered: June 2004
Location: NY

Senior Member

kustom issued a cure/fix for this problem to dealers in a bulletin back in 69.
The fix is placing a .005 cap in serise with a 47k resistor to to ground off of the tip/hot connection of the input jack.
The cap comes first off of the jack followed by the resistor.
The cap be a cheap ceraimic type, and if it has even just a 50 volt rating thats plenty, the 47k resistor need olny be a 1/4 watter.
Be carefull installing this on amps that have the 5 watt resistor on the pilot lamp, as these gat vert hot and stay hot for a good couple of minutes after the amp has been turned off, and also much sure that the gear is unplugged from the ac power when working on it.
The two big power supply filters bleed down very fast voltage wise once the amp is off so if the gear is unplugged from the wall the shock factor is zero within two minutes.

[Updated on: Mon, 24 May 2010 06:15]

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