This is going to be rather long, but I will try to explain
the difference between using an external MC step-up transformer into a MM phono
stage, and using a self-contained phono preamp that does it all.
Disclaimer: I manufacture Step up transformers. I started doing it
as a hobbyist trying to improve the sound of my system. Over time, many
improvements have been made.
Background: Matching Moving coil Cartridges to phono stages is a
difficult process. For MM cartridges it is relatively easy since there is
a standard for MM cartridges at 5mV and 47k Ohms. With MC cartridges,
there is a wide spectrum of output voltages and internal impedances, as well as
a variety of inductances. For a Phono stage manufacturer, it is a
nightmare.
Basically, almost all MC phono stages have a MM mode. The designer in
most cases, builds a second stage to convert the signal from a MC cartridge to
the MM level. Most do this with an active stage designed and built with
FETs. Some use internal step up transformers. The challenge is accommodating
a wide variety of MC cartridges. This is typically accomplished using a
bunch of switches or jumpers on a circuit board. Many have adjustments
for impedance and output voltage (different gain settings). If you look
at the specs of each phono stages and compare them for MC cartridges vs. MM
cartridges, there is usually a significant different in signal to noise
ratio. The ratio is lower by about 8-10dB for MC cartridges vs. MM
cartridges. This results in a louder background noise floor for MC
cartridges. Additionally, adding switches to low output signals is very
difficult without degrading sound.
For those phono stages that use internal step up transformers, there is a
limited range for MC cartridges and typically, the internal step up
transformers are not as good as some of the best in the industry. One
step up transformer cannot be made to work properly with most MC cartridges.
A stand-alone step up transformer can be used to better match a cartridge to a
MM phono stage, instead of using the internal active stage or the internal step
up transformers. You can use a step up transformer ranging from 1:5 to
1:40. For those who say that using a stand-alone Step up transformer is
not a good idea because it adds an additional set of interconnects; well, the
active stage or internal step up transformers are connected by wires or printed
circuits inside the phono preamp. Perhaps you would also say that a
console stereo is better than separates since no interconnects are
required. There are lots of excellent interconnects that are as good, if
not better, than the internal wiring.
