Moving Coil Phono Step Up w/ Beyerdynamic 1:15/1:30 Transformers MC SUT

Description

Here's a moving coil phono step up transformer using a pair of German made Beyerdynamic TR/BV 351 215 006 transformers. These transformers have a 1:15 winding ratio, with a split primary that can also be wired in parallel for a 1:30 ratio. The gain switch selects between series and parallel so both ratios are available. With standard 47k ohm input MM phono preamps, these will load your cartridge with about 200 ohms on "lo" gain or 50 ohms on "hi". These beyers have a really great accurate sound, but their small size does give them a little more insertion loss than larger transformers. Although the winding ratio is 1:15, depending on the source and load resistances the actual output will be something like 10-13 times the input level, or roughtly double that on hi gain.
The ground switch selects how the aluminum chassis is grounded and gives you a few options for wiring. In the middle position the two audio grounds and the box are all kept separate from each other. In this position you need to run a separate wire from the SUT's ground post to your phono preamp ground post to be sure that the box is grounded and provides shielding. For convenience you can also attach the box to the left audio ground (in the "L" position) or you can tie all three grounds together (in the "L+R" position). Usually you don't have to think too much about grounding, just wire the box up how you like, and then put the switch in whichever position gives the lowest noise.
If you have any questions, please feel free to ask. I'm always happy to help if I can. Thanks!