Thursday, 6 March 2014

The Shunt Regulated Push-Pull (SRPP)

The SRPP is an elegantly simple circuit, and is really a small output transformerless (OTL) amplifier. It was widely used in TV circuits for delivering significant current into heavy capacitive loads. It was first patented in 1940 by Henry Clough of Marconi, and has returned in many designs since. Interestingly though, it was not referred to as the SRPP until quite recently and instead had a variety of other names like 'bootstrap follower', ‘mu follower’ and 'shunt regulated amplifier'.

Sennheiser HD450

I have used the SRPP principle in a stereo headphone amplifier. The circuit below was made twice (lefthand and righthand channel) and combined with a PSU it forms the amplifier. Allthough the output impedance of the SRPP amp does not exactly match the headphones impedance, the amplifier provides a nice and clear sound to my Sennheiser headphones.

The input comes from a digital source (CD-player, DVD-player or PC soundcard).

                                                       Circuit diagram, 1 channel

                                                     Building in progress, spring 2012

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