Cinemag CMMI-10C input transformer voltage gain problem

Hello,

I chose Cinemag CMMI-10C input for a MILA-1 build. It sounds great.

http://cinemag.biz/mic_input/CMMI-10C.pdf
http://musiciansgig.com/mila/MILA1-Updated.pdf

But now I started wondering about the voltage gain mentioned on the Cinemag spec sheet. It says 19.75 / 39.5 dB. Impedance ratio is written as 37.5/150:15K, and 1:20/10.

I have connected the transformer using the wiring of "Test Circuit 1" and "Test Circuit 2". But I don't hear a 19.75dB gain difference between the two, more like 2-3dB more gain on "Test Circuit 2". Why not?

Could someone please enlighten me a bit on what real implications the spec sheet should have on my build? What am I doing wrong?

Thank you,
Mike

I'd never expect more than a few dB gain change switching 37 to 150 on the primary.  Also, I have found that, even with an unloaded secondary, putting a 150 source into a 37 ohm transformer input causes radical re-equalization of the sound, and probably also loading losses.   With the specified loading resistor, the 150 input is roughly 1K, and the 37.5 is about 250.  So, if you are using a 150-200 source into the 37.5 tap, you should be seeing about 6 dB of loading loss due to matching condition.   If you have a 30 ohm source, you should see somewhat different results.  

Thanks.

I didn't do the math, and was poking around in the dark with impedance and loads, still a bit gray area for me in general.

Guess I wasn't doing anything wrong after all and I'm glad to have that verified. It's indeed the "radical re-equalization" I wanted, but I expect far more gain based on the spec sheet. With a 50ohm source impedance (from DAC), I didn't measure change in bandwidth as I shouldn't, but I can certainly hear an audible change with dynamic mics (a quick test with sm57).