Moving coil transformers are intended to mate low or mid output MC pickups with normal phono inputs on an amplifier or on RIAA pre-amplifiers that only support Moving Magnet or mid/high output moving coil pickups, most phono inputs on amplifiers and many phonostages do not have the capability to handle low output/impedance MC's so if you intend to use such a pickup either check if your amp/phono stage supports one before you buy that kind of a pickup, or budget for a transformer as well.
Another potential problem when adding a MC pickup to your turntable is that many RIAA preamps simply do not have wide enough variability of impedance or amplification to handle some pickups especially very low output models, but to be able to handle pickups of 0.1mV it needs a gain of 26 dB but many offer only 23 and many low output picks require loading of less than 50 ohms. This may simply mean that while in theory your pre-amp may support your pickup, the steps between gains and impedance characteristics are so coarse that it does not mate well in practice, in those cases it is an easier solution to simply add a low gain transformer in between and treat the output as a higher one at the phono stage.
Electronic MC pre-preamplifiers have never been as popular or plentiful on the market as transformers but there is a certain group of people that can't stand the sound of trannies and some of these electronic amps are rather good but please note that in general those electronic amps may require more than 10 times higher impedance loading than a transformer with the same gain, i.e. a pickup that works best with a 3 ohm loading on a transformer may need a 50 ohm loading on an electronic one. The correct name for a pre-preamp is actually Head Amplifier but it should not be confused with tape head amplifiers.
Audio Experience This company makes the only headamp driven by therminionc vales that I am avare of on the market today, namely the Solo, it actually has exellent audio specifications despite the glassware and the price is very reasonable all things considered but it has a fixed gain and impedance of only 20dB and 100 ohms respectivly.
Audio Note/Kondo Makes the AN-S6cz transformer, it's made out of a range of exotic materials and both input impedance and output load are variable, and you can switch between balanced and single ended operation.
Audio Note UK Ltd. Makes the AN-CD and the AN7D silver wired transformers (those are expensive BTW), those are based on older Audio Note/Kondo designs, the company also offers the more realistically priced ANS-1, ANS-2 and the ANS-3 transformers.
Bent Audio Makes the MU Step-up transormer, this is a mono unit that is shiped in pairs, gain is (optionally) switchable from 14 to 26dB and while loading is not configurable the company sells a resistor package for those who need more flexible loading, the unit is also available in kit form.
Denon Makes 2 transformers intended to mate with their own Denon Pickups, the AU-S1 is a high end model that is intended to mate with the company's high end, low output models such like the Denon DL-S1 and weighs in at a whopping 3,2 Kg and has a price tag to match, while the AU-300LC is a very keenly priced model that has a slightly lower gain and is intended to mate with their low/mid output MC models, neither of those designs appears to be distributed outside of Asia, but you can find more info here.
Docet-Lector This Italian maker has the MM70 Pre-pre which is basically their MM70 MC design with the RIAA preamplification section removed, the total gain is 23dB which means that while it will work with most MC designs it will not work with some very low output pickups, it also has a fixed impedance of 150 ohms. Going a bit more upmarket they have the valve based .
Dynavector Makes the PHA-100 head amp, impedance is switchable from the 4 to 7 ohm range to 30 to 40 ohm range. Use of a modern op-amp as the main active component means it's very quiet.
Graham Slee Projects Makes the Elevator EXP which is a high end electronic design that offers 24dB gain and switchable resistance and capacitance options, more info on that model can be found here, the company also has recently introduced a cheape version in the form of the Elevator Fanfare but when this was written there was no real information avalable on that model.
Hi-Fi Club Makes a Moving Coil amplifier that allows you to connect a low output MC to a phono input.
My Sonic Lab The company has a highe end transformer avaialable that they call Stage 202, it is obviously geared towards use with their own My Sonic Lab Eminent although it will work with other pickups of a similar output strenght. We have have not seen it for sale in the west but the price in Japan is approx 180.000 ¥.
Ortofon Makes 3 transformers, the high end T-3000 that has thorodial core wound with silver shielded permalloy wire and sports some serious specifications and accepts cartridges with 2 to 10 ohm impedance, the "budget" T20 MK II that also has is a thorodial but features a cheaper copper shielded wiring, and finally the company makes one transformer specially designed for the SPU line of MC's named SPU TG100.
Rothwell Makes the aptly named Moving Coil Transformer which has 24dB gain which the company says makes it best suitable for pickups with 0,3 to 0,6mV output.
Shelter Makest the 411 II, this is a high end unit that is very remisent of the old Fidelity Research MC transformers in particular since it uses a toroidal transformer which is very unusual these day's, but it is designed for use with Shelter Pickups and thus features less than 15 ohms impedance and a 33dB of attenuation which is only useable with a limited number of pickups, mainly Japanese high end models. Note that the company and it's distributors does usually not differentiate between the current MkII model and the earlier 411 MkI models in their advertising literature.
The company is best known for supplying transformers as components rather than as end-user modules, they make the TX103 series of transformer that are available wound from either copper or silver wire but it is expensive in copper form and seriously expensive in the silver wire version. They also make the TX1003 series that is more realistically priced for the average Joe at around 150 UKP ex VAT pr. pair, it is available with 5x, 10x or 20x gain and from time to time the company makes available a housed version of the 10x TX1003 transformer that retails for around 360 UKP including VAT.
SUN Audio Manufactures the SAT-1000 that is a high end tranformer based unit reminisent of old classic Japanese high end designs from Grace and Fidelity Research, it is unusual in that it is a 4 channel model, eg you can have 2 stereo pickups hooked up to the unit, one channel has input taps with a 3 Ohm impedance while the second has taps with 20 and 40 Ohm impedance, with a gain ratio of 34, 26 and 23db respectivly. The transformer is a custom made toroidal transfomer which meas that this tiny unit wheighs in at a whopping 3,5 kilograms.