Problems with my cab. Help please!

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by The Rocket, Oct 6, 2004.

  1. The Rocket

    The Rocket Member

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    Hello guys,
    I really could use some help with my rig (Aiken head + 2x12 cab). When I hit the low E at high volumes I hear a very bad "scratch" noise coming from the speakers, even the pilot lamp of the amp flashes when the "scratch" noise occures and then the amp shut down...

    I tried the same amp with another cab and everything was fine, no problems there.

    I looked at the speakers' solderings and everything seems OK, but I'm not an expert.
    What do you think? Every input will be very appreciated, thanks in advance!
    Massimo
     
  2. spaceboy

    spaceboy Member

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    ..... phase...?

    ...

    :confused:
     
  3. The Rocket

    The Rocket Member

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    I really don't know...could be the speaker..maybe it is breaking down, but I don't understand the flashing of the pilot lamp...that's pretty weird!!!
    Thanks for your interest.
     
  4. fullerplast

    fullerplast Senior Member

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    Was the head sitting on top of the other cab you tried? If not, try that.

    Sounds like a vibration triggered bad connection from what you've described so far, probably somewhere around the AC input or PT secondary (since the pilot lamp is tapped off the PT heater output).
     
  5. John Phillips

    John Phillips Member

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    If the pilot light was flickering I'm almost certain the fault is in the amp - not even an intermittent short or open circuit in the cab should cause that, and that's the worst possible case.

    If the head doesn't do it with another cab, it must be just that the precise frequency that causes the amp to do it wasn't getting back into the amp for whatever reason.

    When you said the amp 'shut down', do you mean it blew the fuse? That would indicate a short somehere. If it just stopped working, but later came back on, probably a loose connection - if the pilot light was flickering, almost certainly in the supply circuit (power cord, switch, fuseholder, or power tansformer primary winding). My guess is this. If I had to place a bet (a small one :)) I'd say the power switch - they do sometimes do that.

    Have you tried calling Mr. Aiken?
     
  6. The Rocket

    The Rocket Member

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    Wow! Thanks a lot guys! This Forum is THE best source of info ever.
    Fullerplast: yeah, I tried, but the problem was there also when the amp wasn't sitting on top of the cab. Anyway I think you are right about the vibration..

    John: I will definetely write Mr. Aiken, great advice. So, do you think there's no way that the problem is the cab? I was very surprised to see the pilot lamp flickering and when the amp shut down the fuse didn't blow. I tried to switch it on 30 seconds later and the pilot lamp turned on...the amp had the same problem though...

    I will bring the head to a tech with all your great intuitions and see what happens. I really hope it's not something bad...

    Thanks a lot guys, I appreciate it
     
  7. fullerplast

    fullerplast Senior Member

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    I just took a look at an Invader power circuit. It looks he uses a 120v pilot lamp so that makes it even easier to trace. I'm assuming your fuses are not blowing since you probably would have mentioned that, so the AC connection is just opening and staying open. I'd agree with John that it is probably the power switch, or possibly the fuse connection. Your problem is somewhere here:

    [​IMG]
     
  8. The Rocket

    The Rocket Member

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    Thanks Fullerplast!
    Amazing...I don't know what to say.
    Thanks for the great help. You guys are great.
     
  9. fullerplast

    fullerplast Senior Member

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    You're welcome.

    I just noticed you are from Italy. If you talk to Randall, make sure you mention your voltage is 230. I don't know what his switches are rated at offhand. This may not be something he's seen too much as most of the amps are US operated...

    Aikens are one the the best built amps around. I'm sure your problem is a simple one.
     
  10. reaiken

    reaiken Member

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    That's a picture of the old MKI series Invader amps, so it wouldn't apply to this problem. The new amps are completely different inside, and the pilot lamp is a standard Fender style 6.3V jewelled lamp.

    Randall Aiken
     
  11. reaiken

    reaiken Member

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    That's a strange one. If the pilot light is flickering and no fuses are blowing and it is making noises, I would say it is almost certainly a problem with the mains input circuit (IEC connector/switch/fuse holder/PT primary winding), except for the fact that it would do it only when you hit a low E note, and that it would only do it with one cabinet. When the amp shut down, did the pilot light stay off? Did the fuse blow?

    Try another power cord and mains fuse (or check to make sure they aren't loose). Also check to make sure the rear panel voltage selector switch is firmly set to 230V (or whatever your voltage is) - you might want to turn it one click and back to make sure it is set properly.

    If you feel comfortable looking inside the amp, check all the solder joints and wiring from the AC mains connector to the power switch. and fuse holder.

    Does it do it every time on that cabinet, or did it only do this once? If it doesn't repeat itself, you may have just had a loose mains cable.

    If it continues and you would like to send it back for warranty repair, let us know. I'm sorry you are having trouble with the amp.

    Randall Aiken
     
  12. The Rocket

    The Rocket Member

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    Dear Randall,
    thanks for your reply. I will try all your suggestions and see if the problem continues. By the way when the amp shut down the pilot lamp went off and the fuse didn't blow, infact I was able to turn the amp on after 30 seconds.
    Let me say that the Intruder is a FANTASTIC amp and I'm really happy with it. I also have an original '68 Marshall Plexi 50W head and the Intruder sounds as good as the "mystic" Plexi!
     
  13. reaiken

    reaiken Member

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    If the amp shut completely off, the pilot light went out, and the mains fuse didn't blow, and no smoke came out, there can't be a short anywhere.

    There could be an open or intermittent connection in the filament wiring coming from the power transformer to the pilot light (which then goes and feeds all the tubes). These are the big green wires coming from the transformer going up to the pilot light. The filament wires are the black/red twisted pair that goes from the pilot light to all the tube sockets.

    It is likely either this or an intermittent in the mains wiring as previously mentioned.

    Randall Aiken
     

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