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Help - I can hear another band

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by devbro, Oct 5, 2006.

  1. devbro

    devbro Member

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    So I'm rehearsing last night with my '63 Bassman in a rental studio and all of the sudden, I can hear the band in the adjacent studio next door coming through my amp. It was faint but loud enough to embarrass the sh*t out of me.

    The amp just had a cap job and new Tung-sol pre-amp tubes. I flicked the tubes thinking one had gone microphonic but no luck. It went away when I turned my guitar volume way down.

    I've read posts about RF and radio. Is this another issue? What's causing this and more importantly, is there a fix? :confused:
     
  2. pipedwho

    pipedwho Member

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    It is probably coming in through your guitar's pickups. If it happens again, unplug the cable from the guitar (not from the amp) and see if it still goes away. If it is still gone, then it isn't anything to do with the amp.

    Does it also happen in humbucker mode on the guitar (ie. positions 2 and 4 on a strat)? If so, then the electromagnetic noise is very strong, which means there is probably something like a hearing aid loop installed in the other auditorium. If it goes away, then it is probably more subtle, like an improperly connected building ground that is re-radiating the audio signal.

    It is difficult to fix these sorts of problems without looking at both setups (ie. yours and the other band's) and the building's installed wiring/sound system.
     
  3. devbro

    devbro Member

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    Thanks. My Guitar is a Suhr with silent single coil system so I doubt that's the problem. I suspect it's a bad ground. I'll try your suggestions next time I'm there.
     
  4. boobtoob

    boobtoob Member

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    Where you using a wireless setup?...the band in the other room might have a wireless mic on the same frequency.
     
  5. pipedwho

    pipedwho Member

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    The silent single coil system that is in the suhr needs to be tweaked to cancel the sound properly. It is also designed to cancel low frequency mains hum. Pickups aren't necessarily linear across a wide frequency range, so it is unlikely that the suhr silencer will work perfectly in this situation - in the same way that a humbucker will only cancel so much.

    A very small magnetic audio field can happen if there is a ground loop, but not usually something that will come through your amp - unless you're running a huge amount of gain.

    I've never heard an FM wireless system (which is what all the good ones are) interfere as an intelligible signal through a guitar/amp. It is possible for an AM system to do this, but I don't know of any AM wireless systems. (edit: actually, a poorly designed, or faulty FM transmitter that has a misaligned RF bandpass filter could possibly be at fault too. If you can hear the whole band it is probably stage wash into a vocal mike, since other transmitters will only carry a single loudly miked/direct instrument.)

    If the other band is running through the house system and there is a hearing aid induction loop installed in their auditorium, you will have exactly the symptoms that you're describing. It also may happen if you're standing directly behind a large unshielded speaker on the other side of the wall.

    A couple of questions: Did you try moving the guitar around to see if orientation had any effect on the level? Did you poke your head into the other room and see how the other band was wired up? Ideally, have a chat and see if they are using something unusual - ie. wireless system, unusual special effect, etc.
     
  6. pipedwho

    pipedwho Member

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    The hearing aid induction/current loops are audio frequency (baseband) magnetic field (induction) transmitters. Some (most?) hearing aids have what is called a Telecoil or T-switch that activates a small coil receiver in the hearing aid. This significantly improves aural clarity in highly reverberant rooms that also have a lot of background noise (ie. people coughing, shuffling, etc), where the hearing aid's microphones otherwise are unable to distinguish which sounds to amplify and which to 'ignore'.

    As you can imagine, to cover a whole room it takes quite a bit of power, much more than the string/magnet field in a guitar coil! And most installations aren't too careful about spill

    The reason I bring up hearing aid loops, is because it took me a while to work out what was going on when I could hear the announcer's voice coming out of my guitar amp - loud and VERY clearly! :eek: I kicked on the humbuckers, and it reduced the volume coming out of the amp by about 10 to 20dB, but was none-the-less still very present (it also sounded more muffled and distorted). I finally worked out what was happening when I brought in another guitar with a piezo bridge that completely removed the problem as soon as I disengaged the magnetics and went piezo only.

    BTW, the biggest problem in the above environment is feedback. It doesn't take much for the guitar amp's output to get into an open microphone and start the system screaming!

    The whole hearing aid thing is normally only a problem in venues that rarely host bands with electric guitars. I'd guess that a venue dedicated to rock'n'roll or blues bands would have long since removed the loops and put in an infrared or other type of system to cater for hearing impared patrons. But some clubs that also host a lot of daytime events for senior citizens still have these loops, but have the ability to turn the systems on/off during evening gigs for the younger crowd.

    Actually, just thinking about it, it is unlikely that this is really the problem for the O/P, since the other band would have been having serious feedback problems at the same time (unless they had piezo based guitars).
     

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