mosfet ect.

Discussion in 'Amps and Cabs [BG]' started by Willie_the_Pimp, May 2, 2005.

  1. Willie_the_Pimp


    Apr 19, 2005
    I'm looking at a carvin redline 600 and it says it has a tube emulator circuit and that it sounds better and less hassle. And then I look at new Ampeg svt pro and that it has a tube preamp driven Mosfet Amp or something like that... now my question is this: do these amps with the emulator circuits and mosfet saturate, and get warm and chunky at high volumes like a genuine tube amp?
  2. As i think is true with many things, it emulates it, so its close, but its just not the same
  3. There's no magic to mosfet transistors. Like tubes, they are voltage contolled devices, but there's where the similarity ends. Don't expect them to "saturate" like a tube does because they are at heart still a transistor.
  4. Willie_the_Pimp


    Apr 19, 2005
    how does the preamp with the 12ax7's work in an amp like that?
  5. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    In most of the "tube driven mosfet" type amps, including ours, the mosfets are "gain-of-one followers".

    All the voltage gain is tubes, the mosfets just take the signal and match it to the speaker, without any more gain or any attenuation.

    That way you DO get the tone and overload behavior of the tube, although it is an in-between type usage closer to "preamp tube tone" since there isn't any output transformer and push-pull tube stage.

    Still, the tube is used somewhat more as if it were in a poweramp, with large signal amplitude. And, the mosfets have the least effect on sound.

    In a "real" all-tube amplifier, the output tubes have some gain, different clipping and inherent distortion from the preamp, and the transformer is affecting the sound as well.

    With an SS poweramp after a tube preamp, whether the amp is mosfet or not, its different. There, the character of the SS poweramp also affects tone and overload characteristics.