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Preamp tube grind warmup delay

Discussion in 'Amps and Cabs [BG]' started by Jonathan Starr, Aug 24, 2003.

  1. Lately I've started to push my Demeter 201 (original tubes) a lot harder than I used to, to get more grit on the tone. I use the passive input with the input gain almost maxxed and I use the controls on the power amp to adjust volume. With my active basses cranked I get a nice gritty tone, and if I back off the bass output or play softly it smoothes out. I use a Raven Labs box to equalize my fretted and fretless bass outputs.

    I find that when I start playing, the tone is pretty clean, and after about 10 minutes the grit starts to increase, and it keeps increasing for a while and then it levels out for the rest the set. The volume doesn't change, just the amount of breakup, and it's pretty subtle. If I start playing in the perfect "slightly gritty" range, I have to turn down the bass or preamp after a while when it get's too dirty.

    I haven't noticed this with my other pres, but then I don't play them the same way.

    Is this a normal function of the tubes? Or a sign that I should change the tubes? Does anyone else notice this?


  2. What you're hearing is the effect of the passive components that feed volatge to the tubes (mostly resistors) heating and settling into tolerance. When the unit is first turned on, they're at value so the tones is clean but as they heat, their impedance rises slightly until their temp stabilizes and they operate normally. Some new metal film plate and bias resistors would clear it up right away; what you describe is normal with aging resistors.

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