Use 2204 as a preamp

Discussion in 'The Workbench' started by JM5010, Mar 5, 2021.

  1. JM5010

    JM5010 Active Member

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    Stupid topic lol, messing around with recording setups.

    Was wondering if using my 2204 without power tubes and with no speaker connected would damage anything. Simple yes/no would help.
    I’ve powered on the amp without power tubes before, and nothing went wrong. Not sure if having no speaker connected in addition would kill the OT or anything.

    I plan on just running the preamp section into my recording interface to see how it sounds.
     
  2. Old Punker

    Old Punker Well-Known Member

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    I'm not a technician but I would never run a tube amp without a speaker cab connected. Hell, I don't even plug them in w/o a cab connected. My :2c:
     
  3. Gene Ballzz

    Gene Ballzz Well-Known Member

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    It would likely be just fine with the power tubes pulled, but certainly wouldn't hurt a darned thing to plug the speaker cabinet in also. No sound will come through it with no power tubes!

    Dose your 2204 happen to have an effects loop, to "send" the preamp signal from? If so, you should be good to go. Not sure how good it will sound, but.........? If no effects loop, you may want to look into installing or having one installed, as the D.I. out is notorious for not sounding very pleasing! The Metro Zero Loss Loop is highly regarded, although even a totally passive (no circuitry, just in/out jacks) would likely do just fine, for your purposes. I would however strongly recommend that you drill the holes for a passive loop on the same template as the Metro, just in case.

    Just Askin'
    Gene
     
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  4. wakjob

    wakjob Well-Known Member

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    Perfectly safe to run an amp without a load if the power tubes are pulled. The OT is de-coupled.
    Unfortunately, on a 2204 the DI output is daisy chained off of the speaker terminals, so no signal is gonna reach it.
    You'll need to tap the circuit somewhere else.

    Also, with the power tubes pulled, the preamp voltages are gonna increase thus changing the sound/feel of the preamp section.
     
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  5. KraftyBob

    KraftyBob Well-Known Member Gold Supporting Member

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    I repair amps as a hobby and when I first start up an amp I fixed I step through a specific procedure to make sure voltages are correct. I do not connect a load until I insert the power tubes. This is a well documented procedure. You’re amp will be fine.
     
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  6. JM5010

    JM5010 Active Member

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    Thanks ya’ll. Will probably tap the signal off of the master volume. Will it sound good or bad? I guess i’ll find out!
     
  7. Chris-in-LA

    Chris-in-LA Well-Known Member

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    I think that the master volume pot is before the tone stack and is between the first and second triode.
     
  8. Gene Ballzz

    Gene Ballzz Well-Known Member

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    Master Volume is just after the tone stack (off of the Treble pot, actually) and just prior to the phase inverter. Just prior to or after that Master Volume pot is the best place in the circuit to put an effects loop/preamp out! While the provided schematic is actually a Weber version of it but nearly identical enough to the original for these purposes, easier to read, etc. Also, even though the schematic is a 2203........:rolleyes: And FWIW, I'd go after the Master pot, for what I think are obvious reasons! I do have the original Marshall schematic also, if anyone wants to pick nits on and/or compare component values.
    Have Fun,
    Gene
    8cm100_schem copy.jpg
     
    Last edited: Mar 10, 2021
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  9. laycern8

    laycern8 Member

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    Cool idea, going into the circuit and surgically extracting the signal path from somewhere for recording
     
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