Wiggins Circlotron

[Bill Layer]

Hi Jorgen,

>Well, you always need dual power supplies to be able to DC-couple signals.
That is the basis for all normal op-amp designs. What is so special about
this? It sounds like some mumbo-jumbo designed to impress audiophiles that
know nothing about electronics design.

OK.

The Circlotron stage was invented in the mid 1950's, and today forms the
basis of design for Balanced Audio Technology, Sumo, Atma-Sphere and
others. It is a fully symmetrical balanced design, which requires only
*two* active devices, and is not an operational amplifier. It was first
conceived as a cost-saving approach to the problem of large, expensive
transformers required for increasingly powerful tube amplifiers.

Since the output has no DC, the transformer may be much smaller as bias
current saturation is a non-issue. It was later realized that the
transformer was not actually required, if the output impedance of the power
tubes could be made low enough to transfer usable power to a load. 

The point of this, is that the design works even better for solid state
devices, as they have naturally low output impedances. By substituting a
Circlotron section for an op-amp, the cost of the op-amp is saved and the
signal maintains better integrity as it passes through only a single
differential pair (which also has a very high degree of common-mode
cancellation), rather than the group of active devices in the op-amp.

A second consideration is the tremendous potential bandwidth, or speed of
the design.

Also, I tend to think of op-amp power supplies as bi-polar, rather than
dual. The supplies of the circlotron are not necessarily referenced to one
another, and may be thought of as two  simple batteries. In practice, the
_negative_ side of _both_ supplies are often referenced to ground, for the
practical purpose of controlling bias in the output devices. 

I'll make available a .gif of a circlotron section later today.

In the meantime, those interested should check out
<hrrp://www.condor-connection.org/asog>. There may be one posted already.


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