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An RIAA Preamplifier For Magnetic Cartridges

Many modern amplifiers lack phono inputs. This preamplifier solves that problem.

By Leo Simpson & Ross Tester

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The RIAA Preamplifier and ±15V power supply can be built as one board, as shown here, or divided in two for a separate power supply and preamplifer. The reasons for the "split" are explained in the text.
Seemingly, no sooner than the print was dry on the December 2001 issue which featured the second article on the Ultra-LD Amplifier, than we had several requests for a magnetic cartridge preamp to go with it.

What to do? This had not been part of the game plan: there is really not enough space inside the amplifier for a preamplifier. We were also concerned about being able to obtain a sufficiently good signal-to noise-`ratio, if it was somehow packed into the rear compartment of the amplifier.

Of course, one neat solution would be to build the LP Doctor featured in the January & February 2001 issues of SILICON CHIP. This not only features a good preamp but it also electronically removes the clicks and pops on vinyl records. Kits are still available from Dick Smith Electronics.

However, as good and effective as the LP Doctor is, many people want just a simple preamp - and that is what we are presenting here.

It comes on a single PC board together with its own power supply, including an encapsulated 20VA toroidal power transformer. It is intended to be mounted inside a standard turntable plinth, either on the underside of the turntable chassis or the Masonite (hardboard) cover underneath the plinth.

The beauty of having the preamp directly underneath the turntable is that the input signal leads are kept to an absolute minimum and that should mean minimum hum and noise. On the other hand, care has to be taken to ensure that any hum and noise from the turntable motor and mains wiring is minimised.

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