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Re: Balanced Differential or Push-Pull?

Posted by Dave Davenport (M) on June 13, 2004 at 20:29:05

In Reply to: Balanced Differential or Push-Pull? posted by Horn Jockey on June 13, 2004 at 19:59:40:

Hi Brian,

Push-pull is one implementation of a differential circuit. There are others, for example, the bridged differential circuit that I use in the Mood Indigo preamplifier. This scheme is really two single-ended-triode class-A amplifiers with their (out of phase) outputs bridged by a transformer and capacitor in a parafeed configuration. See the schematic at http://www.raleighaudio.com/ls_schematic.htm As the name implies, with the push-pull circuit one side "pushes" the signal through one-half of a transformer primary winding while the other side "pulls" the signal through the other half of that same transformer. The center of the primary winding is connected to B+. With the other circuit, the two sides are pushing and pulling against each other because the whole primary of the transformer is connected between the two plates with no connection to B+. Or, you could say that the transformer is measuring the difference between the two plates.

The term "balanced" is properly used for a signal, for example on the input of an amplifier, where the impedance of one side to ground is the same as the impedance of the other side to ground. The signal is referenced between the two inputs and not ground. In an "unbalanced signal one side is usually connected to ground and the signal is referenced between the non-grounded input and ground.

Dave

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