OT orientation?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Leonc, Feb 15, 2012.

  1. donnyjaguar

    donnyjaguar Member

    Nov 4, 2005
    The Dynaco ST70 has the power transformer nestled between two output transformers and it doesn't hum. I think the only reason some guitar amplifiers have them separated is to balance the weight. :)
  2. Keyser Soze

    Keyser Soze Member

    Dec 14, 2008
    Johnson city, TN
    If the transformers are constructed in such a way that the laminations are orthogonal then proximity may not be a big issue.

    But I also wonder if having the OT and PT so close that the flux density is effectively constant through the entire OT there might be less noise as compared to a situation where they were slightly further away, but with the OT in a zone where the interfering field was more variable.
  3. Leonc

    Leonc Wild Gear Hearder Gold Supporting Member

    Jan 4, 2002
    Upstairs, L.A.
    I'm re-building another amp and am dealing with this issue again; using the headphone techqnique. On this amp, even at 90 deg (or some other angle), I can't really eliminate the hum until I move the OT clearly into the preamp section.

    Anyone have any thoughts on the desirability of completely eliminating this hum vs. mitigating it a bit? I'm just curious as to others' experience with the degree to hum produced with this headphone technique in indicative of a future problem.

    If other's have generally found that completely eliminating the hum is really quite important, than I guess one thing I'd consider doing is mounting the OT inside the cabinet, rather than on the chassis. (I'm inclined to think completely eliminating hum in this headphone technique isn't that serious or OT would probably be oriented differently lot of amps.)
  4. zzmoore

    zzmoore Member

    Sep 22, 2006
    USA, California, 94585
    The "typical" T.W. Express always made me worry.
    PT and OT living right next to each other.....
  5. VacuumVoodoo

    VacuumVoodoo Member

    Jan 9, 2005
    Gothenburg, Sweden
    OT & PT at opposite ends of the chassis puts the OT near to input circuits.
    This can cause instability and oscillation that can be difficult, if not impossible, to tame.
    Here is a remedy:
    shielding sleeves on both primary and secondary flying leads, grounded at the far end.
    This together with a shield on at least V1.


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