[sdiy] Gapped vs. Ungapped Transformers?

[Tom May]

Tim Curtis <sexsymbol at execpc.com> writes:

> Hi Everyone -
> 
> I've got a transformer question...
> 
> What does it mean when transformers are "gapped" or "ungapped"?  I'm
> wondering about an audio output transformer.  There are two of them
> listed at exactly the same specs but one is marked "gapped" and the
> other marked "ungapped - no d.c."
> 
> Anybody care to share their insights?  I'm not a transformer person.

"gapped": for single-ended systems, where there is a DC current, which
  will magnetize and saturate an ungapped core.  The gap increases the
  reluctance (magnetic "resistance") of the core and makes it harder to
  magnetize/saturate.  The gap can be optimized for a specific DC
  current to put the core in the desired part of its magenetization
  curve.
  
"ungapped - no d.c.": for push-pull systems, where the DC currents
  from each side cancel.

Tom.