Picking up the radio?

[dmusic148]

Why is it, amp gurus, that certain amps just love to play the local radio station, with a bass plugged in? Not really loud, but loud enough to hear "You know you know you know you just ain't seen nothin yet!" during quiet moments, clearly?
My SWR amp loves to do this, with any bass. My GK amp does not, ever. Both amps are firmly grounded to the ground pin on the power cord, to the bass's shield. This happens at my home, mostly, where the electrical system is known to be solid and in compliance with codes. The grounds are connected to ground, not neutral, for example.
The SWR does NOT do this without a bass plugged in. Gains/Volumes etc. are irrelevant. Clearly, the bass is acting as some sort of antennae, providing signal(inductively?) to the preamp of the SWR.
ANY bass, passive or active. So?


UPDATE: I just tried a ground lift on the power cord. I know this is a bad idea but did it as a diagnostic tool. No difference. None.

[Supa Scoopa]

I wonder the same thing, my old superbass likes to pickup the radio every now and then.

[ezstep]

Many times, it is the cable acting as an antenna. Unplug the bass (or guitar) and leave the cable plugged into the amp. See if anything changes.

Other times, it actually IS the grounding of the particular electrical outlet. Many older houses were built (within code) using two wires, no ground. Later, when many appliances required a grounded, three-prong plug, homeowners simply replaced the receptacle without getting it grounded. Not grounded, but still within code (at that time).

[jelwood]

Bob Gallien is a f****** boss and his amps only do what they're told, that is, what you play in to them is what comes out. Radio stations don't dare mess.

[delta7fred]

It is due poor amp design. Old tube amps had no high frequency roll off built into them. The output transformer usually did that quite effectively but the earlier stages were good for some pretty high frequencies. The signal chord acts as an antenna and picks up any rf going. Under certain conditions one or more AM radio station signals can get demodulated.

Most solid state amps don't normally have this problem.

[Arthur Strand]

Radio can get picked up as long as something is acting as an arial and it is co-incidentally close to a frequency. I remember many occasions - mainly with valve amps - when taxis, aircraft, police, ambulance, fire brigade and radio stations butted in. Another occasion, I recall, when a leaner arrived foe guitar lessons once a week, his amp and guitar picked up the English-speaking station of Radio Moscow! The lad was a son of a fairly successful English pop-star, probably more Tory than Commie!
You need extra shielding from radio frequencies on guitars/basses leads, and amplification.

[coreyfyfe]

Use the search function. This comes up every so often and there are a few easy remedies you can try, one of which I believe involved soldering a cap onto the ground of the input jacks.

[mcbradley]

I have a 2000 Warwick Corvette Standard 5, and I pick up radio signals through it. It seems to happen regardless of which amp I'm playing through, whether an SWR Workingman, Mesa Boogie MPulse 600, or even if I'm plugged in direct at my church.

Is this an issue with the bass itself? I'm thinking of upgrading to a Warwick Thumb BO, used of course, but I'm wondering if I'll likely have the same issues. Any thoughts?

[fhm555]

We used to play a semi regular job in an old, old, old church converted to a private social club and every time we played there you could just barely hear this disembodied voice of a real fire and brimstone preacher when we took a break. Turns out my SWR basic 350 was picking up a 24/7 AM station who's only programming was recordings of fire and brimstone preachers.

[okcrum]

Bypass cap at the input. Ferrite choke on the instrument cable if necessary, since the shield is the antenna. Have you tried a better cable? That might be the only problem. 90% shielding or better is desirable on the cable.

If the above is confusing, take the amp to a tech.