Mark has put together a phono preamplifier for moving magnet cartridges from an electronics kit. The kit comes complete with everything you need except for an enclosure and a power supply (AC walwart). The design uses LM833 opamps and the power supply section is regulated.
The design supports multiple compensations, including RIAA and DECCA. Mark reports that the kit is dead quiet, performs well and holds it’s own against a popular commercial phono preamp.
Phono Preamp Kit Construction
Mark started by installing the small parts, resistors and small capacitors. The kit comes with rectifiers (1N4004 diodes) 12V regulators (7812/7912) and a PCB shield. He inserted the two op-amp chips last and also added snubbing 0.1 uF polypropylene caps to the final filter capacitors to reduce diode and regulator noise and any induced RF. Also, he added a clip on ferrite bar to the end of the 15VAC walwart. The board can be fully populated in one or two hours. Be careful when installing the compensations components. You must align two charts in the instructions to select the correct components from many for the compensation networks
The case chosen is of ABS plastic. The plastic is tough to drill but does not shatter or splinter. He lined the case with sticky tar and heavy Aluminum foil tape on the base, lid and sides.The PCB stands on sticky computer stand-offs. The foil and stand-offs provide dampening and RF shielding. For further dampening he added large soft silicon feet.The gain control pokes through the front with the inputs/outputs (gold plated RCA jacks) and power socket on the rear. A LED was used for the power indicator.
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