Does it improve the sound of a MM or MI cartridge by playing it through a phono stage?
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Sorry Wolfie - I guess a better phono stage is a better phono stage, even if they are both ideally matched to a MM/MI cartridge and have a 47K ohm impedance. Maybe it doesn't make as big a difference as with a MC cartridge, or maybe it is assumed people who buy MMs don't want to spend $$ for a phono stage. |
Wolfie is misinformed. The 400 series of Acutex cartridges are MM types and for all I know they do have some relationship to AT, which is nothing to be ashamed of, because AT made some of the great MMs. But Acutex also made a totally unique and more expensive line of cartridges, the 300 series, that employ the induced magnet principle and were among some of the best cartridges out there in their day. I rate the LPM320 among the top half dozen I have heard. Soko, I think you are confusing the phono input impedance with phono gain. Generally, cartridges are classified according to the way transduction of the signal in the grooves is achieved and according to gain. MC cartridges have a tiny coil of wire attached to the cantilever, on the other end from the stylus. The moving stylus makes the coil wiggle in between a pair of strong tiny magnets, which are stationary. this motion produces a signal voltage. The output of a cartridge is stated in millivolts (mV) for a standard stylus velocity, either 3.54 or 5.0 cm/sec. MC cartridges can have "high output" (HOMC), up to about 1-2 mV or low output (LOMC), in the range from about 0.2mV to less than 0.6mV. These latter require more gain in the phono stage and can be run with input resistances from 47K ohms on down to 100 ohms. MM cartridges place the actual magnet at the far end of the cantilever, and it moves in relation to stationary coils of wire. This gives much higher signal voltage output, like 3 to 6mV. The beauty of MM cartridges is that you can use them with much less gain needed from the phono stage. The phono stage has one other even more important job; it has to equalize the output of the cartridge. This is a very dense subject, but it is necessary because the voltage output of any MC or MM cartridge is proportional to stylus velocity, which means that bass frequencies are less amplified than treble frequencies by the transduction process taking place in the cartridge. Phono stages employ a filter which reverses this phenomenon to produce a flat response at the output of the phono stage. So, in no case can you use either an MM or an MC without this phono equalization. As it turns out, 47K ohms was adopted as a standard input resistance for MM phono stages many decades ago, and it remains a standard. Why MMs need a relatively high input resistance is yet another arcane subject. With LOMC, like I said, 47K and on down to 100 ohms typically "work". So, to summarize: Phono equalization is a must. After that, choose a phono stage with gain sufficient to work well with your chosen cartridge. An alternative to using a very high gain phono stage with a very low output MC cartridge is to use an MM stage with a Step-Up Transformer (SUT) between the tonearm wires and the input to the phono stage. Search these archives and Vinyl Asylum for more background. |
Thanks Lewm. I won't confused. You need to match the output of the cartridge with the resistance/impedence of the phono stage. I was thinking with a standard output MM cartridge, it wouldn't matter what phono stage you used as long as it operated or had a setting at 47K ohms. Gain of the phono stage is assumed to be adequate and not the issue (I don't think). I don't think that is the case anymore - phone stages matter - even at the same specs.. |
