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Thread: Bedrock 1400 head tone stack not working

  1. #1
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    Bedrock 1400 head tone stack not working

    It's been a really bad amp week for me this week. First my Mesa breaks down and now the tone stack is not responding on my old Bedrock 1400. Help!!!!

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    Did I stump the Amp Gurus of this forum? I know I'm stumped. I checked every component. Everything checked out fine. IDK

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    Schematic? Gut shots? Anything?

    Justin
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    Senior Member Enzo's Avatar
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    It isn't about the parts, it is about the circuit. A 10k resistor might be fine, but if one end does not make the connection to the rest of the circuit, it might as well be an open part. Dead tone stacks are often a missing link to ground at the bottom.

    Responses are often better if you include or link to a schematic.
    Justin Thomas likes this.
    Education is what you're left with after you have forgotten what you have learned.

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    I cannot find a decent schematic. I found one for a later model with the pull clean(mine doesn't have that) but it's really blurry. I contacted one of former owners, who now owns Jetter pedals. He doesn't have one either. I'll post some gut shots.
    Justin Thomas likes this.

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    Is it an FMV tonestack, and do any of the tone controls have any effect at all?

  7. #7
    "Thermionic Apocalypse" -JT nickb's Avatar
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    Quote Originally Posted by Redline View Post
    Did I stump the Amp Gurus of this forum? I know I'm stumped. I checked every component. Everything checked out fine. IDK
    The Bedrock 600 used a conventional Marshall style TMB tone stack. If the ground connection to the middle pot goes open then the whole thing will stop working.
    Experience is something you get, just after you really needed it.

  8. #8
    Supporting Member The Dude's Avatar
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    If you can't find a schematic, it shouldn't be too difficult to sketch out the tone stack. Or, just download the Duncan tone stack calculator and take some screen shots. Tone stack circuits don't vary that much.
    “Yeah, well, you know, that’s just, like, your opinion, man.”

  9. #9
    "Thermionic Apocalypse" -JT nickb's Avatar
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    This should help a little. A bit blurry and no component values. It would great if you could annotate it with some values off what you have in front of you. The tone stack, though drawn a little differently is a Marshall style, as mentioned elsewhere.

    bedrock-1400_2k.jpg
    Experience is something you get, just after you really needed it.

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    Quote Originally Posted by Enzo View Post
    It isn't about the parts, it is about the circuit. A 10k resistor might be fine, but if one end does not make the connection to the rest of the circuit, it might as well be an open part. Dead tone stacks are often a missing link to ground at the bottom.

    Responses are often better if you include or link to a schematic.
    No schematics exist for this amp.

  11. #11
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    If you've lost the ground connection to the tonestack you should experience a large volume increase over what it was like before.

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