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Thread: Fender Twin Reverb Problem or Not

  1. #1

    Fender Twin Reverb Problem or Not

    I have a 1972 Fender Twin Reverb with AA270 circuit and no MV. I just discovered that the "MIDRANGE" tone control has to be turned up past 1 just a tad or the amp will not produce sound. Once the midrange tone control is turned past 1 it will produce sound and the Volume control works as it should. This is the way it is on "both channels". I have several AA270 schematics and Layout diagrams and all the wiring, resistors, caps, optic reverb module , etc are wired according to the schematic. Is this normal for the Twin ?

  2. #2
    Forum Member Don's Avatar
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    Re: Fender Twin Reverb Problem or Not

    Is this with the treble and bass controls set normally or all the way down?

  3. #3

    Re: Fender Twin Reverb Problem or Not

    Quote Originally Posted by Don View Post
    Is this with the treble and bass controls set normally or all the way down?
    Yes with the bass and treble controls all the way down. And even if I turn up the treble and or bass
    controls there is no sound until the mid is turned up past 1. I discovered this the other day wanting to see what it sounded like with the all 3 tone controls all the way down. I turn the bass and treble up with the mid all the way down and there is no sound. Is this normal ?

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    Re: Fender Twin Reverb Problem or Not

    I would have never thought to try that! Next time I have my "Twin" out, I'll have to see what it does.
    Looking at the AA270 schematic, there is a 100K ohm resistor in line to the tone stack that feeds the mid, (10K ohm, and treble-bass,250K ohm each). If the mid is at 0 ohms, wouldn't that send the signal to ground?

  5. #5

    Re: Fender Twin Reverb Problem or Not

    Quote Originally Posted by Bill Moore View Post
    I would have never thought to try that! Next time I have my "Twin" out, I'll have to see what it does.
    Looking at the AA270 schematic, there is a 100K ohm resistor in line to the tone stack that feeds the mid, (10K ohm, and treble-bass,250K ohm each). If the mid is at 0 ohms, wouldn't that send the signal to ground?
    Let me know what happens. I would hate to spend $75.00 at the amp shop just to have the guy tell me my amp is working as it should.

  6. #6
    Forum Member Don's Avatar
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    Re: Fender Twin Reverb Problem or Not

    Quote Originally Posted by supershifter2 View Post
    Yes with the bass and treble controls all the way down. And even if I turn up the treble and or bass
    controls there is no sound until the mid is turned up past 1. I discovered this the other day wanting to see what it sounded like with the all 3 tone controls all the way down. I turn the bass and treble up with the mid all the way down and there is no sound. Is this normal ?
    If you turn the treble, middle and bass all the way down the amp will be silent. I'll check my amp to see what happens if I turn the mids all the way down with the treble and bass up.

  7. #7

    Re: Fender Twin Reverb Problem or Not

    Quote Originally Posted by Don View Post
    If you turn the treble, middle and bass all the way down the amp will be silent. I'll check my amp to see what happens if I turn the mids all the way down with the treble and bass up.
    Also check if your amp has a hum with the reverb and vibrato switched on at the same time. Mine hums with both switched on.

  8. #8
    Forum Member Don's Avatar
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    Re: Fender Twin Reverb Problem or Not

    Quote Originally Posted by supershifter2 View Post
    Also check if your amp has a hum with the reverb and vibrato switched on at the same time. Mine hums with both switched on.
    Unfortunately, my amp's not a Twin Reverb. It's a PR with the tone stack modified to be like a Twin Reverb's. As long as the treble and bass are up some, turning the mods down all the way does not cause the sound to cut out completely.

  9. #9

    Re: Fender Twin Reverb Problem or Not

    After much searching and a few fone calls I was told this is normal on these fender twins. The fender tone control circuit is very strange. With the bass and treble on 1 the mid acts as a 2nd volume control. And I cant imagine anyone playing with the bass and treble on 1. I turn the mid and treble all the way up and the bass all the way down like Johnny Winter did. This thing is quiet and if the light wasnt on you would think it's turned off. I have a mod pot coming for the vibrato circuit to make the vibrato louder. And then we will need to make everything louder than everything else.

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