Telephone-like feedback squeel on Tubeamp

[mh001]

Hi,

Not too long ago I had a gig with my band. The vocals were using a wireless in-ear system for the first time.
That same morning at home I tried my amp because I had cable-issues some weeks before. I bought some new cables and everything worked fine, no strange noises.

However, when we were setting up I got a strange kind of feedback. Stangely enough mostly when our female vocalist was singing or when her mic was triggered otherwise. The feedback is best describes as when a radiostation receives a call from a listener and the listener has the radio on way too loud. Some kind of echo-ish metally sound. It occured when I used my amp's overdrive channel. At one time the male-vocalist had a solo-song. He had his own microphone but he was walking and passed by the female-singer's mic while singing. The same thing happenend.

Several options came too mind : Microphonic tubes, interference from the wireless in-ear system or PA-speaker cables that ran too close to my own signal cables.

I don;t think I have ever had this same problem.

Kind regards, Merijn

[Jazz P Bass]

The problem sounds like it's the chick's wireless mic.

[mh001]

Why didn't our other guitarplayer suffer from the same problem? I plug my guitar straight into my amp and use the effects-loop for my effect-pedals. Sop I have 3 cables running To/from my amp. I have done so for years and with several amps. Never a problem.

[eschertron]

You mentioned it occurred when the OD channel was in use. High-gain amps (& high-gain channels) are more susceptible to RF interference simply because of the amplification factors involved.

My theory: The girl singer's mic was producing RF sidebands that 'just happened' to create intermodulation distortion in one of your amp's gain stages. The triodes in a guitar amp are called receiving tubes for a reason. unless the signal in your amp is band-limited well, it will amplify RF interference and give you AM products. I've never seen it happen with a signal source other than a pirate CB station, though!