MC Pre-pre as Mono Phono stage for 78s! December 15 2013
Gavin McKenzie has built a very clever phono stage for 78 rpm records using the Boozhound Labs moving coil pre-preamp.
Many 78s were made before there was an accepted standard for the EQ curve applied to the cutting heads that creates the master record from which the rest are copied. Therefore, there is no standard for the playback phono stage like the RIAA curve for LPs.
Gavin found an old, passive, Master Record Compensator that provides a switched set of various EQ curves for 78s. The problem was that this is just the EQ, and needed external gain stages to turn it into a phono stage. Gavin originally was planning to use a BHL Phono stage and bypass the EQ section, but since he only needed 1 channel for mono, the MC pre-pre gave him 2 simple gain stages between which he could sandwich his EQ.
Basically this is the left channel of the pre-pre, then the EQ section, then the right channel. A nice simple design with a minimum of wasted parts. This could be built as a stereo unit using 2 of the pre-pre boards.
Thank you Gavin for the email and the clever phono stage!