Two matched transistors of the same polarity can be arranged to supply opposite halves of each cycle without the need for an output transformer, although in doing so the driver circuit often is asymmetric and one transistor will be used in a common-emitter configuration while the other is used as an emitter follower. This arrangement is less used today than during the 1970's; it can be implemented with few transistors (not so important today) but is relatively difficult to balance and to keep a low distortion.