John Linsley Hood phono stage

This was first introduced in an article in Electronics Today magazine (April 1992) as part of an integrated preamplifier project. JLH includes an informative discussion on the benefits of shunt rather than series implementations of the RIAA equalisation. The circuit is fully discrete, and uses a pair of medium power transistors in the input stage to reduce noise when a low-output cartridge is used. The input circuit is shown here (though the transistor codes show on this schematic only apply to the input devices). The gain and input load are selectable to allow a range of MM and MC cartridges to be used.

A slightly modified version of the circuit is available through Williams Hart Electronics as a kit. Here is a review of the kit by Richard Black.

The kit does not include a power supply, as it is primarily intended to be used within a preamplifier, but one is easily added. I used a simple dual-mono supply with 10,000uF of reservoir capacitors per channel and a single stage of regulation.

I built a hybrid of the RIAA stage from this circuit and the input stage described in another of JLH's articles on ETI. This latter uses matched pairs of low-noise transistors in cascode configuration to improve its noise figure with low-impedance cartridges. Once I'd sorted out a problem with RF demodulation (with the kind help of JLH himself), this circuit proved to be very satisfying in use, although the layout in the preamp box led to a certain amount of hum induced from a nearby mains transformer. I had been using a high-quality valve preamplifier (the Croft Super Micro A IV PP), with a high-output moving coil cartridge (a Milltek Olympia), and the JLH stage proved slightly more detailed and firmer in the bass, although I did miss the richness and ease of the Croft.

After several years of enjoyment, I upgraded to the ADEQ from Audio Synthesis, which was a definite improvement in openness and detail.

Links

Discussion on VinylEngine of the JLH design.

... and another on DIYAudio

Alex Megann, May 2001

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