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	Unless a push-pull power amplifier has a balanced input, at some point the unbalanced signal must be converted into a balanced signal, a push-pull signal. In a tube amplifier, this task is accomplished by a phase splitter, usually a Split-Load or a Long Tail phase splitter. Each circuit has it advantages and disadvantages. These two circuits, however, are not the only possibilities. Transformers have long been used to split the phase of a signal and even a center-tapped choke can be used.


	Split-Load Phase Splitter This single triode phase splitter has the best voltage balance, but has dissimilar output impedances per output phase leg.

Negatives
- No gain.
- Limited voltage swing.
- Dissimilar Zo's.
- Dissimilar PSRR's.

Positives

+ Single triode.


	Review of Tube Phase Splitters

Long Tail Phase Splitter

This two triode phase splitter has the advantage of high gain and large voltage swings, but must be tweaked to provide balanced voltage outputs.

Cross-Coupled Phase Splitter

This two triode phase splitter has the advantage of high gain and large voltage swings, but must be tweaked to provide balanced voltage outputs.


	Negatives - Requires tweaking. - Poor balance. - Dissimilar PSRR's. Positives + Gain. + Large voltage swing. + Similar Zo's.

Paraphrase Phase Splitter

This two triode phase splitter has the advantage of high gain and large voltage swings, but must be tweaked to provide balanced voltage outputs.


	Negatives - Four triodes. - Low input overload voltage. - Sub-optimal use of Cathode Followers.


	Positives + Gain. + Very low input capacitance. + Identical Zo's. + Identical PSRR's.


	Negatives - Requires tweaking. - Poor high frequency response. - Uses Feedback. Positives + Gain. + Large voltage


	Continued Next Month In the April issue, we will describe a low gain line stage amplifier that uses a phase splitter to convert single-ended input signals into a buffered balanced output. //J Broskie 99


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