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Thread: Crate RFX 65 RetroFex Hum

  1. #1
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    Crate RFX 65 RetroFex Hum

    I have a 65 Watt Crate solid state amp with digital effects, which hums badly whenever I plug in a guitar. It has a muting circuit which quiets it down when nothing is plugged in.

    It affects all three channels, very visible on output trace, seems to modulate with the beat of the effects. Unplugging J10 disconnects the digital effects board and cures the problem.

    Ground continutity is good, and 12V power to the digital effects board is pretty clean, less than 20 mV of ripple on the scope.

    There is nothing loose on the effects board (almost everything is surface mount but some caps and the crystal.).

    Any suggestions other than try a new effects board?

    Thanks,
    Tom S

  2. #2
    Senior Member Enzo's Avatar
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    With the FX board disconnected, does the amp work? SOme amps route the signal through the FX board, so pulling it would kill the hum, but it would kill everything else too.

    I don;t have docs on that amp, but if the DC supply to it is clean - I don't know, about 10v maybe - then pretty much its a new card.
    Education is what you're left with after you have forgotten what you have learned.

  3. #3
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    The amp works without the board plugged in. The signal return from the FX board mixes in at the same point as the CD inputs.

    Thanks,
    Tom S

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    Schematic and No Solo output

    Would you happen to have a schematic or a fix? I am fighting with a no output when I set the switches to run the solo mode.
    Thanks
    Gilbert

  5. #5
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    Gilbert,

    I have attempted to attach a PDF of the schematic.

    Tom
    Attached Files Attached Files
    Tom S

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    Schematic and No Solo output

    Thanks Tom, that really helped. I was able to get my Solo channel back. Shorted Solo switch (solder piece).

    Now I am stuck with the AC Hum problem.

  7. #7
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    Crate RFX 65 Hum

    Tom, Did you ever get rid of your hum problem?

    Gilbert

  8. #8
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    The hum was caused by the digital effect sboard. After providing the serial number to Crate, they said the effects board was no longer available for that amp. Evidently the board was changed sometime in production.

    Fortunately, simply unplugging the jumper cable to the board takes it out of the circuit, leaving a basic amp with no effects.

    Tom
    Tom S

  9. #9
    Senior Member jasonguitar's Avatar
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    I know this is an old thread but I recently acquired one of these amps from a student and it was doing the same horrible hum thing which went away when the effect board connector was unplugged as you described. Seemed to me that the connector cable was behaving intermittently so I directly soldered the connections to the board and the hum was virtually eliminated. I believe these effects boards are inherently noisy (more hiss than hum) but the noise level is now totally acceptable and even studio worthy.

  10. #10
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    Ok I know this is an old thread and like Jasonguitar (above) I too purchased one of these amps recently only to discover the loud hum/buzz. My solution was almost identical but instead of re-soldering, I disconnected the FX board... this is the red wire loom that goes to the circuit board at the back) and sprayed the contacts with WD40 (did this for both ends of the wire). This solved the problem reducing the noise to about 90-95% of what it was. Acceptable noise levels for on stage, rehearsals and maybe studio.
    I guess the area between the contacts has some sort of dissimilar metal corrosion going on and cleaning the contacts does the job. Hope this helps anyone.
    J M Fahey and g1 like this.

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