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Tube Mic Fried DIGI 001 Mic Pre?

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  • Tube Mic Fried DIGI 001 Mic Pre?

    Recently, I plugged a tube mic into one of the DIGI 001 mic pres. The mic/power supply cable that came with the mic had been wired improperly (perhaps applying 250V where it should not be). Ever since doing this, the following problem has appeared:

    - The gain of the DIGI 001 mic preamp has been reduced 50%
    - Turning the phantom power on or off produces a terrible crackling/hiss noise that dies down over a minute or two.

    Initial troubleshooting notes:
    - The phantom power crackle is happening before the gain pot
    - The DIGI 001 uses combo jacks--balanced & 1/4"--and I believe it has separate gain stages for each. The 1/4" high-impedance preamp has no loss of gain
    - The other mic pre (Input 2) is fine. It shares phantom power with Input 1, and does not have the crackle/hiss noise.


    Without a schematic, my intuition says that I should start replacing components--all electrolytics and ICs in that first gain stage. My intuition gets me in trouble sometimes, and I'll be needing a magnifying lens to work on that PCB, so I thought I'd run it by some other minds first. Any "input" is appreciated.

  • #2
    The symptoms sound very like a leaky capacitor. So I'd start by replacing the two large DC block electrolytics and see if that fixes it.

    (the ones in series with the mic inputs that block the 48V from going into the preamp, and would have got 250V across them if your cable was miswired like you thought)
    "Enzo, I see that you replied parasitic oscillations. Is that a hypothesis? Or is that your amazing metal band I should check out?"

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