Whistling amp...help!

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by saxdragon, Jan 23, 2012.

  1. saxdragon

    saxdragon Member

    Messages:
    1
    Joined:
    Jan 23, 2012
    Hey everyone.

    I have a Crate Palomino 32x12. It's all tube, with a clean channel and an overdrive channel activated by a footswitch and switches on the control panel. The controls looking down on the control panel are like this:

    [volume] [gain] [treble] [mid] [bass] [overdrive volume] [reverb]
    ^ ^ ^
    [overdrive] [boost] [presence]

    (The three on the bottom are push/push switches)

    When using the clean channel, the amp starts to make a shrill whistling sound at around 1/4 of a turn on the clean volume knob. The more you turn it up, the louder and shriller it gets, but it doesn't change pitch. This happens whether there is a guitar plugged in or not.

    I recently had to replace the input jack. It's a stereo jack that goes into a little broken-off chip of PCB with a couple resistors on it. It's possible I didn't wire the terminals on the jack correctly.

    I checked the tubes for microphonics and poked at the components with a chopstick. I didn't hear any farts or crackles. But a couple times when I pushed the wires that went from the input jack to the PCB chip, the whistling noise appeared and got louder or softer depending on where i pushed the wires.

    It also occasionally starts farting and crackling static. When it does, i smack it on the side with my hand and it stops. I started leaving the overdrive on all the time, but with the gain turned almost all the way down as a way to use the amp until i can get it fixed. I have no problem with that whistling noise if i have the overdrive switched on.

    Any ideas?

    Thanks,
    SaxD
     
  2. 900z1

    900z1 Member

    Messages:
    278
    Joined:
    Apr 26, 2011
    Location:
    ottawa,canada
    I don't have specific experience with that amp, nor have I had a whistling sound, but if I did, I would get a schematic and compare to the repair I did.

    I'm not sure of your experience, but it is not too difficult to find the input on the schematic and compare the signal path to the actual amp.

    also check for burnt / overheated components.
    check for shorts with an ohmmeter in the area you did your work

    when you did the work, did you remove the whole main board ?
     
  3. Blue Strat

    Blue Strat Member

    Messages:
    30,036
    Joined:
    Aug 2, 2002
    Location:
    Sterling, VA (not far from Washington DC)
    +1. When something bad happens immediately after you've made a change, the first thing to suspect is whatever you just changed.

    Short of that, you could have a microphonic preamp tube.
     
  4. guitarcapo

    guitarcapo Senior Member

    Messages:
    2,337
    Joined:
    Mar 16, 2010
    3 things it probably is:

    1. Bad tube.
    2. Poorly seated tube (one of the pins has a loose connection.
    3. The input jack isn't grounding itself. This is usually something to check if the whistle is only present when you don't have the cord plugged into the jack. But if you didn't wire the jack right maybe? Lots of amps require that jack to be grounded or referenced to ground with a high value resistor when the guitar is plugged in to avoid oscillations.
     

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