Help- Radio traffic through my amp!

[XsSpeed]

I just got done with an outdoor gig and while I was playing through my Kustom K200B, 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.

[craig.p]

Something in that amp or attached to that amp is acting as a rectifier, causing RF signals to be demodulated. Things that can cause that are corroded contacts/terminals in the amp, funky/old instrument cables, funky/old BG internal wiring including the jack itself, funky/dirty/corroded BG cavity shielding, bad tube in the amp, and get this -- even a crummy old corroded/deteriorating speaker cable. Yes, I actually saw the last case. The old, internally-corroded (green inside!) speaker wire was rectifying AM signals and injecting them into the amp via the amp's feedback loop.

When you troubleshoot this problem, change one and only one thing at a time.

[coreyfyfe]

A common fix for that is to solder a small cap across the input jack which should filter interference. There are also these things: http://www.radioshack.com/product/in...entPage=search I've never tried them, but supposedly they work. If the problem is with the amp itself or with the speaker cable, these products aren't likely going to help. I used to get a lot of interference at my old practice space (spanish and sports radio were the most common) but it was always solved by unplugging my bass, so I'm pretty sure it wasn't the amp. But, a few weeks ago I went to play my B15 and I was getting radio so loud I couldn't even play bass over the noise and nothing I did got rid of it (even with no instrument plugged in). I was doing a session the next day so I was going to be pissed if the amp didn't work. A few hours later the interference was gone and I haven't heard it since. Intermittent problems suck.

Good luck.

[ausf]

Nigel?

[IvanMike]

the other possibility is the shielding on your bass itself may be not that great allowing RF interference. Good chance it's the amp though. I would try using another bass thru the amp or even cranking the amp with nothing plugged in to see what else happens.

[KramerBassFan]

Tin foil around the amp. Ghetto fix.

[XsSpeed]

Corey - here's another radio shack idea... http://www.network54.com/Forum/13357...riod+chokes%2C

I need to check into all the advice a little better. I guess the vintage tone comes with some baggage!

[okcrum]

Clean all the input connectors, and use 90% shielded instrument cable. The cheap cables may only have a 30-50% shield coverage, making them excellent antennas.

[XsSpeed]

Thanks guys. I think if I clean all connectors, use shielded cables (pretty sure I am), put the ferrite chock core on my guitar cable and the toroid choke between the amp and the speaker cab - it should work..

[BassmanPaul]

At the impedances that speakers operate it's highly unlikely that your speaker cables are causing this. Don't bother with the chokes. A ferrite bead slipped over the input lead inside the amp might help as would a low value cap from the input to ground.

Paul

[Pilgrim]

Simple fix to experiment with - try changing to a different cable (and length) between guitar and amp. That solved a similar problem for me.