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  • MM Vs MC Cartridges

    Here is something I have always wanted to know...
    Why were moving coil cartridges invented?
    Do they have some sort of benefit or superior sound kinetics to the moving magnet cartridge? What makes them superior or is it just an uneducated Galo opinion? I just don't understand the reasoning behind something so complex and cumbersome compared to the MM.

    Any knowledge/comments I'd love to hear (esp Craig/Rick)
    Last edited by Doug; 05-21-2005, 06:36 AM.
    At work I may look like I'm doing nothing, but at the cellular level I'm actually quite busy

  • #2
    My opinion? Well, I think that it is a gimmick allowing manufacturers to charge a lot more money for the cartridge. They are more difficult to manufacture than Moving Magnet types. Additionally, when the stylus fails, you need to send it back to the manufacturer to have it changed. That means even still more money for the manufacturer. Another thing; if you want one that plays LP's and 78's, you will need two, not one, since the stylus can not be removed. That means even still more money again for the manufacturer of these since x2 is better than x1 if you are selling these things. Lastly, you need an expensive impedance matching transformer or a special pre-pre amplifier to bring the signal level up to a reasonable level. That means more money again for the manufacturer. It also means more distortion since transformers and/or pre-pre amplifiers produce that. I have never seen a transformer or amplifier of any type which reduces distortion. As a matter of fact, they elevate the noise and distortion content of a signal.

    So - there you have my humble opinion on the matter. Summarized: moving coil cartridges are absolutely great for the manufacturers of same.
    Last edited by Craig Maier; 05-20-2005, 08:18 AM.
    "Who put orange juice in my orange juice?" - - - William Claude Dukenfield

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    • #3
      Hi all,
      Back in the early to mid 80's, I purchased (approx. $150) a hand calibrated B&O moving coil cartridge that at the time was the best sounding cartridge I had ever heard. My system sounded better than any of my friends who also had somewhat expensive systems at the time. (Even they reluctantly agreed)

      If I remember correctly, the common thinking back then was that MC stylus movement was less restrictive, and tracked the record groove much easier as the coil assembly attached to the stylus had less mass & weight than MM cartridges of the day, which had to swing around a solid magnet. This also led to the belief that the records that were played with a MC cartridge would have less wear, and thus would last longer. Technology in magnet materials that we have now, such as the introduction of neodymium and other materials in modern audio products, have of course outdated such thinking. I believe I have an article somewhere on that very subject if you would like to see it. It could make for some interresting reading, even if just for the sake of history!

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      • #4
        Hmmm, so I'm not a cynical old bastard? (that, or we both are Craig!)
        I just couldn't understand moving from a format with an already limited S/N ratio to something even worse for more money! As far as I have seen, the un-weighted S/N figures are >10db worse for MC pre-amps compared to a MC pre-amp. I also can't/wont believe that a stylus anchored to the cartridge via coils moves more freely than the stylus in an MM cartridge - it may have, but I find it difficult to believe...the finest copper wire would still enforce some resistance to movement, I'm certain of it.

        I guess DJ that you have the upper hand here, as I have never seen or heard a MC cartridge...I'm just going on the theory/pre-amp circuit problems behind it.
        At work I may look like I'm doing nothing, but at the cellular level I'm actually quite busy

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        • #5
          Quoting Doug:

          "- - - the finest copper wire would still enforce some resistance to movement, I'm certain of it."
          -------------------------------

          I am not so suspicious of the resistance term in the equation. I am much more suspicious regarding the Mass term which affects inertia (the reactive term in the energy transfer portion of equation). Certainly, a moving coil has mass just like a moving magnet, and a lot of turns of copper wire would have a lot of mass. I know that it would take quite a large number of turns to create a moving coil that produces a reasonable electrical energy conversion efficiency given that it is an air core system. This fact is probably why these things produce such poor electrical output signal levels. Using rare earth magnets in a moving magnet design should completely make comparable the inertia value of a MM stylus assembly compared to a MC one without all of the disadvantages of a MC design.
          Last edited by Craig Maier; 05-21-2005, 10:54 AM.
          "Who put orange juice in my orange juice?" - - - William Claude Dukenfield

          Comment


          • #6
            Not all MC Cartridges are the same...

            I've got a couple of information updates as I've been going through some of my old publications. Craig, you were incorrect on a couple of points in your first post on this thread. There were several MC cartridges on the market over the years that did have a user replacable stylus. All of the Satin MC cartridges by Osawa had a user replacable stylus that could be changed in seconds. Even some of the better known brands, such as the Audio-Technica AT30E had a user replacable stylus, although theirs replaced the coil assembly with it! I bet if I kept digging throug my publications, I could find more...

            And as for the need of pre-preamps and/or transformers, I would like to quote a couple of ads. The first is on the Adcom Crosscoil MC cartridge.

            "In practice, the Adcom Crosscoil generates enough output to drive a standard phono input without the need fo an expensive transformer or pre-preamp. Thus, aside from the obvious cost savings, the Crosscoil eliminates a major source of noise and distortion. Not only does the Adcom Crosscoil provide more output, but its moving mass is extremely low permitting its use in a whole new generation of low mass, high performance tone arms." (The bandwidth of this cartridge extended out to 60,000Hz)

            A quote from a Satin MC ad:

            "...the high-output 117Z uses Satin's ultra-thin 10-micron aluminum ribbon coil and high energy magnet so you don't need an expensive noise-prone pre-preamplifier or transformer like most other moving coil cartridges. The 117Z connects directly to any quality preamp or receiver"

            I may have been somewhat incorrect on my Bang & Olufsen cartridge - It was referred to as a MMC cartridge - Moving Micro Cross. I believe the magnet & coils were both stationary while the cross varied the magnetic field within the cartridge. It was a wonderful cartridge though & tracked at only 1 gram!

            Prior to the digital audio revolution which only began in 1982, phono & cartridge competition was extremely fierce. There were many designs, both very wonderful, and/or extremely outragous. The digital era resulted in many (if not most) of these technologies to fade away. Too bad for us. We could sure use such competition today in our restoration endeavors. I guess we'll just have to settle for what's available now. I rest my case.

            Comment


            • #7
              DJBohn,


              I have to admit that I am certainly no expert in the field (no pun intended) of magnetic phono cartridges. I just understand the basics. I was unaware of removable stylii on MC designs. The MMC design that you describe that you had sounds to me like the old mid 50's General Electric "Variable Reluctance" approach. Both the magnet and coil were stationary in that design. The magnetic pathway was modulated by the stylus, thus creating a dynamic flux in the coil wound around the stator which was in series with a magnet. By varying the reluctance or magnetic resistance of the magnetic circuit, a variation in the flux density was produced. This resulted in an output signal from the coil which was wound around the stator structure by virtue of the concept that Voltage = Time Derivitive of Flux multiplied by the loop area formed by the copper wire.
              Last edited by Craig Maier; 05-21-2005, 06:13 PM.
              "Who put orange juice in my orange juice?" - - - William Claude Dukenfield

              Comment


              • #8
                Wasn't this good?

                I hope somewhere down the line others may add to the post...
                Anyway, I have seen a number of MC pre-amp designs (mainly DIY Hi-Fi) avoiding the use of matching transformers by using an LM394 (an "exceptional matched pair of bi-polar transistors") as the 1st stage of amplification...but then I see that the best theoretical S/N ratio for an MC cartridge with the best pre-amp is ~68dB anyway (20-20kHz un-weighted). That is poor compared to the typical MC cartridge (and equal to the worst MC RIAA pre-amps that I have seen using 741 op-amps!). That is why I queried the idea.
                Last edited by Doug; 05-21-2005, 11:03 PM.
                At work I may look like I'm doing nothing, but at the cellular level I'm actually quite busy

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                • #9
                  Quoting Doug:

                  "Wasn't this good?"
                  -------------

                  I certainly learned something! Thus, it was good.
                  "Who put orange juice in my orange juice?" - - - William Claude Dukenfield

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                  • #10
                    Ok Craig, just to send shivers down your spine (and possibly push you over the edge)...what is with the unduly surge in interest in valve based phono-preamps? Wouldn't these add to the thermal noise already inherent to the cartridge? what about the additional high-tension hum/RF interference? Some of them sell for up to $50K US (unfortunately for valve enthusiast, they also regularly contain solid-state components like, (and God forbid), TRANSISTORS, or worse still, Op-AMPS!
                    Am I alone in thinking phono-design has gone backward exponentially since it's peak in the 80s?
                    At work I may look like I'm doing nothing, but at the cellular level I'm actually quite busy

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                    • #11
                      That really does send shivers down my spine! Not only do "Fire Bottles" have all the problems that you describe, but they introduce a few percent harmonic and IM distortion. But, that is what some people like - - - -yup - - - harmonic distortion. So, that is fine, but here is the rub -

                      Why not transfer the recording with no distortion and noise with a good op-amp based preamplifier and then later add the distortion with something like the VVA? It is very easy to add distortion, but it is very hard to remove, thus it just does not make any sense.

                      But, I guess some people like to stare at the "warm, reassuring glow of an electron tube" while they are listening to their stereo. Maybe they do not have a fireplace! Scientifically, however, it makes no sense whatsoever. And that is not just an opinion, that is an engineering fact. I challenge anyone to present me data to the contrary. LOL!
                      "Who put orange juice in my orange juice?" - - - William Claude Dukenfield

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                      • #12
                        "Cartridge Impedence Interaction"

                        Ok, so Op-amp based phono-preamps represent one of the best methods to amplify phono signals to line levels (other than bulky discrete circuits!)...Even though most perform the RIAA Eq accurately, there is often an audible difference in the tonal qualities between preamps. I always assumed that this was due to distortion/intentional deviation from the RIAA curve. However, I recently read:

                        Originally posted by ETI, Sep 1981
                        Cartridge Impedence Interaction represents the most important signal reason for the difference in sound between preamplifiers. Most preamps suffer from some degree of cartridge impedence interaction and in many cases the effects are pronounced
                        I don't really understand what this effect is, how it originates and affects tonal quality/reproduction of a recording. Does it result from using a single stage preamp for both amplification and RIAA implementation?

                        Not sure, would like others input.
                        Last edited by Doug; 05-23-2005, 06:10 PM.
                        At work I may look like I'm doing nothing, but at the cellular level I'm actually quite busy

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                        • #13
                          I do not understand that statement regarding impedance interactions. If you connect a high performance, high gain x bandwidth product op amp in the appropriate configuration (use the non-inverting input connection to the signal input) to a phono cartridge, there should be virtually no interaction since the input impedance of the op amp circuit will be up there in the 10 Meg Ohm area or greater over the audio frequency spectrum (the output impedance of a phone cartridge is very low by comparison - - - somewhere in the few hundred ohms area). However, I do believe that there are differences in the EQ curves; that could be intentional or a result of component tolerances. That is one benefit to transferring to your computer with a flat pre-amplifier and then correcting it to the right curve later with the software.
                          Last edited by Craig Maier; 05-23-2005, 08:44 AM.
                          "Who put orange juice in my orange juice?" - - - William Claude Dukenfield

                          Comment


                          • #14
                            Hi guys!
                            I ran across another ad for the Empire EDR.9 cartridge ($200 US) that touches on this subject, all though there could be some marketing hype here as well. What they said was:

                            "Conventional cartridges exhibit radical changes in their frequency response when connected to different preamplifiers. This is because the load conditions - the amounts of capacitance and resistance provided by the preamp - very tremendously from one preamp to another, and from turntable to turntable. Consequently, most phono cartridges, even expensive ones, have their frequency response determined essentially by chance, depending on the system they are connected to. But the electrical elements of the EDR.9 have been designed to remain unaffected by any normal variations in load capacitance or resistance. Thus, the EDR.9 maintains its smooth frequency response and accurate transient reproduction ability in any music system, irrespective of load conditions."

                            Of course they threw in a couple of frequency response charts to show the variations. That was 1979 when DIY phono playback systems were not the norm. But you guys & others at this forum can easily work around these old loading problems. The impedence and capacitance loading necessary for different cartridges could more than likely be found somewhere on the Internet, if not in the literature that came with the cartridge. The Ortofon website is where I got those specs on my cartridge.

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                            • #15
                              Hi -

                              It is quite easy to control the loading resistance and capacitance with a modern Op Amp based pre-amplifier. The only wild card is the cable capacitance effect, which is not a practical issue unless you run more than about 5 feet of shielded cable (co-axial cable) between the tone arm and the pre-amplifier. But, again, the pre-amp itself is "out of the equation."
                              "Who put orange juice in my orange juice?" - - - William Claude Dukenfield

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