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euphonic audio iamp picking up radio???

Discussion in 'Amps and Cabs [BG]' started by Kevinlee, Jan 13, 2004.


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  1. Kevinlee

    Kevinlee

    May 15, 2001
    Phx, AZ..USA
    I have a iamp 600 which sounds GREAT, but from time to time I pick up a radio station. It's only when a cable is pluged in to the input. And it happens even when the instrument is not pluged into the other end of the cable. So I'm guessing the cable is acting as an antenna. I use good quality cables, and it's more apperant when I have the power cranked up. I like to turn up the power section and keep the preamp section low.
    It lessons if I cut the higher frequencies, and it does not do it all the time. But I'd rather it not happen at all.
    Any ideas how to remedy this interferance?

    Thanks
    Kevinlee
     
  2. arizonabass

    arizonabass

    Feb 6, 2002
    Tucson, AZ
    Is it a commercial broadcast station or a local ham or CB radio operator? If it's commercial, and doesn't happen all the time, you may be picking it up with certain orientations of the cable. Try using a different length cable. Did this ever happen with a different amp? Maybe it's the electronics (if any) in the bass. Different settings on the bass may help "tune in" the station. Do you live near a broadcast station antenna?
     
  3. Kevinlee

    Kevinlee

    May 15, 2001
    Phx, AZ..USA
    I've never had it happen with any other amps using this same bass. It's an upright bass but I do have some electroincs involved a.i. pickups/preamp. I get's different stations. The station I heard at a rehersal studio the other night sounded like some christian gospel station. Then another time on the other side of town it was a top 40 kind of station. I will try swapping out all the cables, ac cord, speaker cable & instrument cable and see if this helps.

    Thanks
    Kevinlee
     
  4. KONG

    KONG Supporting Member

    Feb 14, 2000
    NY
    have you tried asking EA?
     
  5. A really high input impedance will make RF noise more evident because the preamp section will be much more senstive to small voltages. My G&L L2500 picks up radio stations in "active" mode, but you can only hear them through my Traynor and Wizard. My Ampegs are immune, and I've not tried it through my Trace tube heads.

    I would check your bass's electronics first. My Ibanez Musician is dead quiet in active mode through my earlier mentioned Wizard and Traynor.

    The location changes the station by your relative proximity to them. My guess is that there's something in your preamp acting as a demodulator probably due to grounding. You may need to have tech install one or more small disc capacitors in series with your ground plane to act as an RF filter.

    None of these should make any difference.

    That may change things; a higher capacitance cable will act as its own filter, but that would require a cable of decidely LOWER quality and would negatively impact your tone.
     
  6. Personaly I doubt that the RF will be picked up by the cable. Normally when no cable is plugged into an amp, the input is connected to ground. That is probably the only reason why you do not hear it when the cable is disconnected from the amp. To find out you could insert a spare jackplug (so without a cable) only.

    More lickely is that certain components pickup the RF. Components like coils and tubes are quite sensitive for that. If the amp is not well EM shielded this could be a problem.

    Try to find out if moving the amp makes any difference. And connect the mains to one with a protective earth (if not done so)
     
  7. pkr2

    pkr2

    Apr 28, 2000
    coastal N.C.
    "You may need to have tech install one or more small disc capacitors in series with your ground plane to act as an RF filter."

    I consider the term "ground plane" to be associated with antenna terminology. I have to admit that the term sounds highly technical and shrouded in mystery when used in amplfier discussion.

    In case someone may be searching for the "ground plane" in thier amp, don't ask me.

    Simply soldering a very small value capacitor across the input(ground terminal to hot terminal on the input jack) will sometimes reduce or even elimenate the prob. Keep the leads on the cap as short as possible.

    Harrell S.
     
  8. I used the term "ground plane" only because it may be necessary to use RF filters at more than just the input in which case, you need to find the ground plane of the entire circuit. The antenna anology is perfectly applicable because that's exactly what's going on; some part of the preamp is acting as an antenna.
     
  9. arizonabass

    arizonabass

    Feb 6, 2002
    Tucson, AZ
    This thread is going to be a good one for "Stump the Chumps!"

    vdbroek81 wrote:

    "Personaly I doubt that the RF will be picked up by the cable."

    Everything picks up RF. The cable acts as an antenna for the electronic components inside the bass and inside the amp. Without the "antenna" the components have nothing with which to receive signals. Unless the amp's electronics are overloaded by an extremely strong signal from the radio station(s), the "antenna" is required for reception. I'm really curious how this all turns out!
     
  10. pkr2

    pkr2

    Apr 28, 2000
    coastal N.C.
    Actually, as you said earlier, some part of the circuit is acting as a demodulator or RF detector. any electrical conductor that is coupled to the input can act as an antenna.

    Exactly how does one go about locating the "ground plane" of an amplifier and what exactly do you put the cap in series with? I would have expected a cap that is being used as an RF shunt to be in paralel with the offending signal and ground.
     
  11. Ground plane= the physical ground line of the circuit:

    You find the ground and put the cap between it and earth in series if you've got a 'floating' earth reference acting as an antenna. It's common in preamps for traces to flake or break internally and float their reference. If it doesn't hum like crazy, it acts as an antenna.

    If the RF is brought in from outside via the cable, then you shunt the input signal through the cap.
     
  12. Well a shielded cable is a very bad antenna... but we'll see...
     
  13. pkr2

    pkr2

    Apr 28, 2000
    coastal N.C.
    A shielded conductor can be a very good antenna. It's called a colinear antenna. The degree of shielding determines the impedence of it.
     
  14. pkr2

    pkr2

    Apr 28, 2000
    coastal N.C.
    "It's common in preamps for traces to flake or break internally and float their reference."

    :) :) :)! Go back and read what you just said. You just keep getting in deeper and deeper.
     
  15. I don't like chasing RF problems and I like explaining my methodology to someone whose only intent is to harass me even less. Why don't you fix it for him? Aside from semantics, I've not seen you post ANYTHING to the contrary of what I've put up or even anything constructive for that matter.
     
  16. pkr2

    pkr2

    Apr 28, 2000
    coastal N.C.
    :)
     
  17. pkr2

    pkr2

    Apr 28, 2000
    coastal N.C.
    I know that you're angry and confused ,PBG, and I don't want to add to your problems but I missed the part where you stated your credentials. Your engineering degree came from where, again? :)

    Just to make it clear that I am trying to contribute, I'll repeat myself:"Simply soldering a very small value capacitor across the input(ground terminal to hot terminal on the input jack) will sometimes reduce or even elimenate the prob".

    Do you see the difference? One need not figure out what is meant by "the ground plane". When one makes up terminology to fit the application it tends to be confusing. Understand? Or should I type it once more except slower?

    :) :)
     
  18. Or supposing the RF is being picked BY the preamp itself and its not being carried in on the cable, you put a cap in series with the "earth" of the preamp to filter it out, just like Silverface Fender amps.

    I didn't use the term ground plane(which you yourself have admitted applies to antennae - what's probably going on here) and I've provided my credentials. What are yours? As I said before, if you have a problem with them, too bad. Maybe you should learn to read. Is that slow enough for you?
     
  19. Kevinlee

    Kevinlee

    May 15, 2001
    Phx, AZ..USA
    "Just to make it clear that I am trying to contribute, I'll repeat myself:"Simply soldering a very small value capacitor across the input(ground terminal to hot terminal on the input jack) will sometimes reduce or even elimenate the prob".

    This I understand.

    As far as finding the "ground plane"?
    I'm a little confused by all that. If I mention this to a repair guy will he know what I'm talking about?

    I played a show tonignt about 30 miles outside the city, using the same cables and the amp was as quiet as good be.

    I appreciate all the input on this anyway. Some of it is over my head,(I'm a player and not much of a technician) but I have a couple freinds that can probably understand it. They love all this tech stuff. I just like things to work when I hit the switch.

    Kevinlee
     



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