Ortofon ST-M25 Moving Coil transformer

ST-M25 moving coil transformer is designed exclusively for the SPU Mono CG 25 Di MkII and SPU Mono CG 65 Di MkII.

The voltage output of these cartridges is too low to connect to the Moving Magnet ( MM ) INPUT terminal of pre amplifiers or

MM Phono Stages  resulting in inadequate Gain or Sound volume. ST-M25 is specially designed to increase voltage by 12dB to match MM input of the Amplifiers or MM  phono Stages.

These cartridges supply the same monaural sound from both L/R channels, therefore L/R channels of the cartridges should be connected through ST-M25 and amplifier to the final output “speakers (L/R) ".

You can enjoy your Rich , Glorious & Robust sound of monaural sound coming from both L/R speakers.

Specifications
Frequency Response： 10 ～ 100 kHz (+0 dB -1 dB)
Gain： 12 dB (1 kHz)
Input impedance : 5 Ω ～ 50 Ω
Load Impedance： ＞47 kΩ
Recommended Cartridge： CA/CG 25D(i), CA/CG 65D(i)
Dimension： 65 W x 39 H x 98 D mm
Weight： 410 g

What do these do?

SUT    These transformers are used for connecting a moving coil cartridge MC (on a turntable) to a MM phono preamplifier, MM phono input of a receiver, or your systems MM preamp.to boost output  from a MC Moving Coil Cartridge

Step-Up Transformers (SUT) are a serious option for anyone who owns a Moving Coil (MC) cartridge, one that can significantly improve both the sound quality and sonic character.  Quite simply, a good transformer is the best way to audition an MC cartridge with the highest performance possible.

Since the output of MC cartridges is lower than that of a Moving Magnet (MM), higher gain is required to utilize them, such as that provided by SUTs or MC phono preamplifiers.  Although both devices provide this requirement, both are fundamentally different in function and in sonic character.  This is where SUTs are frequently seen as superior; they are completely passive and offer exceptional noise performance and sound quality.

This is due to the fact that the structure of harmonic and intermodulation distortion is fundamentally different between MC-preamps and SUTs. While an MC pre-amplifier has a constant resistive input impedance, an SUT has an input impedance that is frequency dependent. The harmonic distortion produced by SUTs is highest at the lowest frequencies and drops as the frequency rises, whereas in most MC preamps the distortion increases as the frequency rises.  Combined with significantly lower Intermodulation Distortion (IMD), the sound produced with an SUT will be much more open, dynamic, spacious, and natural.

Stereophile April 2015 Listening by Art Dudley

"...This is among the hallowed few cartridges that really communicate everything that's special about 1950s and '60s mono LPs from the likes of Verve, Prestige, Clef, Columbia, and other labels, not to mention the best contemporary mono records.After receiving from Ortofon a sample of their CG 25 DI Mk.II mono pickup head ($902) for review, I was so impressed with its sound that I asked if I could buy the review sample