Marshall amp mod?

Discussion in 'General Electronics Chat' started by musicalavtech, Apr 30, 2014.

  1. musicalavtech

    Thread Starter Member

    Mar 23, 2012
    Does anyone know of a design to integrate into the clean channel of this amp for a "master volume"? The other channels have a master control, and if the clean channel did, it would serve me even better. I could achieve more gain without disintegrating my eardums.

    Schematic attachment:
  2. MrChips


    Oct 2, 2009
    Not sure what you mean. There is a VOLUME control on the Clean channel.
    Doesn't this do it for you?
  3. musicalavtech

    Thread Starter Member

    Mar 23, 2012
    So the volume of the clean channel is a "master" after going through the tube circuit? It can't dial in anymore gain towards driving the tube? Just making sure that's what you're saying.

    That's fine if it is that way. So it is technically "full gain" of a clean nature...correct?
  4. Veracohr

    Well-Known Member

    Jan 3, 2011
    Marshall's handbook for this amp says the 'Volume' control on the clean channel controls the gain, and can get crunchy at high levels. I can't tell which pot in the schematic is that control, but it must be before the tubes.

    I think if you were able to insert an attenuator pot after IC3 ("PREAMPOUT"), followed by a buffer, it might accomplish what you want.
  5. GopherT

    AAC Fanatic!

    Nov 23, 2012
    It is a clean nature up until it is not. I don't mean to sound sarcastic but, Marshall's clean channel even offers more gain than the amp can produce and that is why even the clean channels eventually become "crunchy" as volume is increased.

    Just so it is clear, no common audio amp design has volume control after the final power amplification stage. It is before so you control with common and cheap potentiometers. Otherwise your pots would be massive and they would generate a bunch of heat trying to attenuate the full power of the amp.
  6. musicalavtech

    Thread Starter Member

    Mar 23, 2012
    This is from the manual:

    2. Volume
    This controls the volume of the Clean Channel
    and is useful for balancing the level of the Overdrive
    and Clean Channels. Once turned past half way this
    channel will start to crunch up
    your guitar sound for
    semi-distorted chords and bluesy leads.
    style blues crunch. Increasing this will result in
    higher gain sounds ideal for classic rock tones.

    That makes me think the volume is more like a gain trim of sorts. Prior to turning up even halfway is super-loud. So not much crunch is happening as well. If there was another level control integrated in back end of the clean channel circuitry...(before the power amp, I could get a nice low level of crunch without bleeding ears.