Does it improve the sound of a MM or MI cartridge by playing it through a phono stage?

Dear Raul, While I yield to your generally superior experience to mine, I must say that all the information at my disposal would indicate that the 300 series of Acutex cartridges were induced magnet types.  However, the 400 series are conventional MMs.  I do see that on the Bluz Bros website, they say that BOTH series are MM, which we both know for sure is incorrect with respect to the 300 series, which makes me all the more ready to disregard anything they have to say on Acutex, especially since they have none to sell.  On the other hand, I will grant you that the 400 series LOOK a lot like the 300 series in terms of shape, which would fit the idea that the 400s are also IM types.  However, I also found this quote from a website much like this one, and surely not the last word any more than this one is the last word.  Nevertheless, "while the 420 (full name 420 STR) is a very good cartridge, it's not in the same league as the 320 (full name M320III STR). The STR refers to the "Special Tri-Radial" stylus tip, a line contact type developed by Toshiba, so the 320 and 420 have that in common but that's about it.The 420STR and M320III STR were the top of the line in their respective series but the 300 Series had things going for it that were dispensed with when the 400 Series came along. Whereas the 300 Series were an induced magnet design, the 400 Series were of the more typical moving magnet type. They also abandoned the tri-pole design which is where the magic is in these cartridges and also in the boxy "Brick" types. The stereo chain responsible for the Acutex brand of cartridges, speakers and headphones (interestingly, all transducers) was Atlantis Sound in Falls Church, VA in suburban DC."

Chakster, What you say may be true for you and me, but the OP is in need of some basic understanding before getting into the nuances of a 100K ohm load vs a 47K ohm load for MM cartridges.  Right now he is fine with 47K as standard.  And I must disagree with your statement that external loading plugs are very useful for MM cartridges.  First of all because external loading plugs which in effect parallel a second resistance with whatever is the input resistance of the stage, can only lower the net resistance seen by the cartridge.  Thus, you cannot achieve 100K ohms or any value higher than 47K ohms by paralleling any value of second resistor with the standard 47K ohm load.  True, there are some who like to REDUCE the load resistance below 47K for some very particular cartridges, and this can be done by paralleling, but that is advanced thinking not needed here.  In my opinion, the capacity to add an external load resistor in parallel with the primary resistance is by far more relevant to MC phono stages than MM ones.

Look for "elliottbnewcombjr"For example, the thread titled "What SUT?...."
You asked, "why does a cartridge have a recommended load impedence from a phono stage and so many phono stages have adjustments for that?"  Because each manufacturer wants his cartridge to perform at its best.  So he selects a range of phono input resistances that ought to work well with his cartridge and publishes that information.  The rule of thumb is that the input resistance of the phono stage should be not less than 10X the internal resistance of the cartridge (which is another published specification that you should be able to find easily).  Most manufacturers do not stipulate one value; they usually will stipulate a minimum value which allows for higher values of input resistance to be used.  The 10-fold rule is not cast in stone.  You can get away with lesser ratios, but usually you don't want to go far below 10.  The reason for this is that as the input resistance of the phono stage approaches the output resistance of the cartridge, more and more energy in the form of signal voltage is lost to ground.  Also, the high frequency response starts to roll off.  This whole issue mostly pertains to MC cartridges which are often run at phono input resistances much less than 47K ohms.  For MM cartridges, you can forget about it and use the standard 47K ohms, to be found in nearly all MM phono stages.

Soko, Please re-read my post.  I am afraid you missed the main points.
"You need to match the output of the cartridge with the resistance/impedence [sic] of the phono stage." 

No, you need to match the output of the cartridge with the gain of the phono stage.  The input impedance is also important but only tangentially related to voltage output, in that very low output cartridges tend to be MC types which tend to have very low intenal resistance and can therefore be used with any input impedance, so long as the input impedance is at least 10X the internal resistance of the cartridge.  (Now I opened up another can of worms, not mentioned above. Read the thread about MC cartridges where Elliot is the OP.)  So, it is more correct to say you need to match the internal resistance of the cartridge with the input resistance/impedance of the phono stage.  Gain of the phono stage can never be "assumed to be adequate"; you need to know the value in db in order to decide whether a particular phono stage will work well with your particular cartridge.  For example, a stage designed for MM cartridges (producing about 5mV output) will typically add about 40db of gain in the process of equalizing the signal from the cartridge.  Such a stage would be wholly inadequate for use with an LOMC cartridge producing 0.2 to 0.5mV output.

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.