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Toroidal Transformers

Discussion in 'Amps and Cabs [BG]' started by lesmarshall, May 12, 2011.

  1. lesmarshall


    Feb 26, 2011
    I noticed that ceratin solid state amps have "toroidal"" transformers in their power supplies ,which look like a donut of wire. For example, my ABN Evo II 500 has them and I think certain of the Mark Bass amps have them too. In their literature , Mark Bass credits the availability of high quality torroidal transformers as one of the items that has enabled these compact amps to handle the low frequencies better . They add some weight to the amp, but I was wondering if amps that have these types of transformers are superior in producing the lower frequencies and transient responses , etc. These transformers are used in different classes of amps , including for example Class AB ( Evo II) and Class D (MB F500) , but other Class D designs do not use them.
  2. Jeff Scott

    Jeff Scott Rickenbacker guru.......... Supporting Member

    Apr 11, 2006
    I thought they were, generally, lower in weight compared to equivalent EI transformers. :meh:
  3. Sneakypete


    Jul 22, 2009
    They are used in almost any mains-operated electronic equipment you could name but to the best of my (limited) knowledge these transformers are simply a part of the power supply. It is true that torodials are generally more efficient, have a smaller physical profile and are lighter than the equivalent VA-rated laminated 'boxy' type. They may even have a reduced external magnetic field so might be less susceptible to hum but I can't think of any reason why they would affect sound quality. If the power supply section is going to affect sound quality I would have expected it to be due to good regulation design and big, fat capacitors rather than just the AC/AC stepdown. Tube amps with output stage transformers are probably a different matter. I predict a number of contradictory posts will shortly follow!
  4. Mr. Foxen

    Mr. Foxen Commercial User

    Jul 24, 2009
    Bristol, UK
    Amp tinkerer at Ampstack
    Some modern valve amps have toroidal output transformers. They are lower noise that square ones too apparently, from there being less straight runs of wire to flex slightly and produce mechanical noise.
  5. nysbob


    Sep 14, 2003
    Cincinnati OH
    I believe the Marshall VBA400 uses one.

    No weak sister there. :cool:
  6. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    True. They also run cooler and have vastly lower EMI. And they're more expensive, so they're generally a sign of a high quality amp.
  7. lesmarshall


    Feb 26, 2011
    I am not sure how this applies to sold state amps , but the following describes how the power supply can affect the tone of a valve/tube amp:

    In Amps! The Other Half of Rock 'n' Roll Ritchie Fleigler wrote that "...old amps derive much of their sound from their (sometimes intentionally) under-engineered transformers and sagging voltage supplies."

    Voltage or power supply sag is a major contributor to an amp's organic sound. The heart of the amp, the power supply is the foundation where the amp's soul is born.

    When a traditional amp's power supply is cranked, the strings come along, technically producing a lot of voltage sag. A very slight delay and slight variation of volume cause notes to bloom or blossom at your touch.

    When a traditional amp is turned down, or deliberately designed to produce little or no sag, the guitar strings behave as if they are directly connected to the speaker; snappy and immediate. You can definitely have too much sag, but zero sag is crystally clean, tight and great for bass amps.
  8. impactwrench


    Feb 22, 2009
    Most of the GK RB amps have them afaik. Definitely the BL600, 400RB-III, and 700RB and 700RB-II as ive opened up all of those.
  9. emblymouse

    emblymouse exempt Supporting Member

    Jan 22, 2006
    My Mesa Boogie Walkabout has one, as it's bigger brothers do.
  10. I had a Ampeg SVT Pro-3 and a solid state B100R that both had toroidal transformers
  11. seamonkey


    Aug 6, 2004
    One of the best places to buy them Plitron

    You can get custom wound ones, surprisingly fast and fairly fast. Even if you by one.
    They have brackets to replace just about any transformer.

    New SMPS power supplies like those used in class-d mini amps also use them. They are just much smaller. They use the cores on the output filters also.
  12. Hi.

    While toroid transformers have their undisputed benefits, the main reason for using them in MI gear, 19" rack gear especially, is their low profile when comaring it with an EI transformer of the same rating.

    Over 100W from 1 RU for example would be impossible without special (or multiple) PT's if EI cores were used.

    As for the cores and the winding methods affect on the sound, that's just marketing BS with high hopes that the customers are uninformed ;).

    As the tooling and winding machines get slowly upgraded from EI- to toroid capable, all but the simplest/cheapest low power transformers available will be toroids.

    A toroid OT is something entirely different because of the totally different requirements and the choice between toroid and EI will be much debated for decades.
    I personally don't see that it could replace EI OT in MI amps.

  13. WingKL


    May 12, 2007
    Just FYI, some manufacturers (Thunderfunk) think that EI power transformers "sound" better than toroids. If I get a chance to swap the transformer in my TF for a toroid, I could find out for myself and post my findings here.
  14. keyboardguy

    keyboardguy Supporting Member

    May 11, 2005
    My carvin B1500 has one; great amp.

    From a BassPlayer Magazine review:

    "The B1500’s interior was clean and orderly. Unlike many amp manufacturers, Carvin winds its own toroid power transformers, and it chose a particularly massive one for the B1500."

  15. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    Thank you for some good, accurate information.

  16. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    Agree it's a decision based more on space than sound..... It's just a transformer............

    If the manufacturer knows their stuff, it *can* be lower in external magnetic field and so lower "hum nise", or EMI. That is no guarantee, some otherwise good makers apparently don't know how, or don't bother in general. (I had to teach a few what to do).

    They have problems too.

    They do not do well with multiple windings using different sized wire, mostly due to the typical mounting methods.

    The mounting of standard styles is a nuisance, the best is the epoxy-filled middle, the metal plates are mentioned only as a terrible idea.

    A badly wound toroid has a lot larger "hum field" than most E-I core types.

    They nearly always cost considerably more because they are harder to wind, even with proper winding equipment.

    Usually, the inrush current when the unit is turned on is quite a bit more with toroids, often requiring extra circuits to deal with it.

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