Moving Coil Phono Step Up Transformer Cinemag 1254 4 Ratios 1:10 - 1:40 MC SUT

Description

Here's a moving coil step up transformer box using a pair of Cinemag 1254 transformers. This box will boost the signal from low output moving coil phono cartridges to a level similar to a standard moving magnet cartridge so that the cartridge can be used with normal phono preamps that wouldn't otherwise have enough gain for MC carts. This box will work with most moving coil phono cartridges with rated outputs below about 0.5mV.
The Cinemag 1254's have 4 possible winding ratios, 1:10, 1:13.3, 1:20 and 1:40, any of which can be selected on this box using two switches per channel. These switches put the two main primary coils either in series or parallel, and then select to use either the top tap or the first center tap. This is in contrast to a simpler form of tap selection that just puts the coils in series, and then selects the appropriate tap. Allowing the primaries to be paralleled for the higher ratios insures that current is flowing in as much of the primary copper as possible for each ratio, reducing leakage inductance and DC resistance to the lowest possible values, and maximizing fidelity and efficiency of the transformers.
The bottom of the box has an engraved table showing the position of each switch to get the desired ratio. The primary load impedances shown on the table assume your phono preamp has standard 47k ohm input resistance. The impedance value will scale linearly with the preamp input resistance, so, for example, if your preamp has a 100k ohm input resistance, the load provided by the transformer to the cartridge will be roughly double the value shown. I wouldn't recommend that these transformers be loaded with less than about 20k ohms on the secondary.
Please note that load "matching" for moving coil cartridge impedance is a little bit of a misnomer, as you generally do not want the transformer load impedance to exactly match the internal impedance of the cartridge. In general, the transformer load should be at least a few times higher than the cart's internal impedance, and many manufacturers suggest a minimum load impedance of around 10 times the cart's source impedance. If in doubt about compatibility with your cartridge, please feel free to contact me with any questions.
This box also has a 3 position ground switch that allows you to isolate the aluminum box from the audio channel grounds in the center position (in which case you need to run a separate grounding wire from the box back to your phono preamp ground post), or to ground the box to one (the left) or both of the audio grounds (L+R). In general you can just wire the box into your system in whatever way is convenient, and then put the switch in whichever position gives you the lowest noise.
This box is new, using new transformers from Cinemag. The Cinemag transformers are great sounding and very consistent, however I do check the transformers and verify matching for gain and frequency response before starting to wire each box.
Please feel free to ask if you have any questions. Thanks!