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Tame 'Scale Control' high end

Discussion in 'Shock Brother's DIY Amps' started by Tom Kamphuys, Sep 1, 2019.

  1. Tom Kamphuys

    Tom Kamphuys Tele-Holic

    Sep 18, 2018
    The Netherlands
    In my JTM45 clone (https://www.tdpri.com/threads/jtm45-build.881258/), I've tried a 'Scale Control' (see attachement). One might think of it as a In-Phase-Inverter-Master-Volume: A variable bias allows the LTPPI to distort early ('at least vaguely similar to the distortion produced in a push-pull power output stage'*) and simultaneously limiting the output voltage.

    It limits the volume and introduces compression, doing what it is supposed to do. It doesn't make the amp quiet, though. I have to use it to the max to get it usable at home (sort of...). The problem I have with it is that when I use the scale control, by the time I get some preamp distortion (using the preamp volume), the LTPI is generating too much high frequency distortion (shrill, yelling, ...).

    What would you guys advice me to tame this high end (distortion)?

    I can think of 3 ways (Don't let these options limit your suggestions, though):
    - Use another speaker. I'm currently (mis?)using a Hot Rod Deluxe (1x12) as a cabinet. Any speaker suggestions (also for my jcm800 I'm contemplating to build)?
    - Use the Vox Cut Control as suggested by RobRob's on his website.
    - Switch/add a pre or post phase inverter master volume.

    Any advise on these?

    * 'Designing Tube Preamps for Guitar and Base' by Merlin Blencowe.

    Attached Files:

  2. dan40

    dan40 Friend of Leo's

    Aug 19, 2015
    Richmond Va
    The cut control works very well on my 18 watt style build. Takes the high end down without changing the core tone.
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