Ampdog
R.I.P. 23 June 2022
It would be prudent to first explain what I understand under the three magnetic types of record pick-up.
Moving magnet (MM): The stylus-carrying 'shank' has a small magnet (or magnets) rigidly attached to it at the coil end(s), which by virtue of its movement relative to fixed coil-carrying 'shafts', induces the signal voltage therein.
Moving coil (MC): The stylus-carrying 'shank' has (for stereo) two small coils rigidly attached to it at the mounting end, causing the signal to be generated by the motion of the coils in a constant magnetic field provided by a fixed magnet in the cartridge.
Variable reluctance (VR): Both the magnet(s) and the coil(s) are rigidly mounted in the cartridge body, and the shaft has nothing on it but a rear-end of magnetic conductive material, so as to 'complete' (obviously with air gaps somewhere) a variable magnetic path in the magnet-coil system and thus generating a signal there-in.
I must admit ignorance regarding the modern MM cartridges as to its exact operation. I have never had one spare to destroy by opening it in order to examine the precise internal construction. I must confess that I find some descriptions rather confusing as to whether some cartridges are stricly (MM) or in fact VR (i.e. fixed magnet).
If MM is indeed moving magnet and not VR, I find some difficulty in justifying its existance at all, because even preliminary calculations show that the VR principle can indeed have lower moving mass than MM, and possibly even than MC, and for a higher output than MC because a heavier coil of hundreds of windings may be utilised. This apart from the disadvantage of MC units, of vibration in the coil(s) leads to the (fixed) outside world causing failure through metal fatigue.
Will those in the know here kindly broaden my horizons as well as those of others, to whom LPs and cartridges are relatively new?
[Yes. I did Google! Wading through the now expected sales talk, I could not find a detailed modern discussion of the above matter. RDH does not give sufficient info either, because the last edition was printed in 1955 - long before some of the significant latter-day refinements. I would imagine Morgan Jones would have said a few things; I do not have one at my disposal.]
Let us see where this goes.
Moving magnet (MM): The stylus-carrying 'shank' has a small magnet (or magnets) rigidly attached to it at the coil end(s), which by virtue of its movement relative to fixed coil-carrying 'shafts', induces the signal voltage therein.
Moving coil (MC): The stylus-carrying 'shank' has (for stereo) two small coils rigidly attached to it at the mounting end, causing the signal to be generated by the motion of the coils in a constant magnetic field provided by a fixed magnet in the cartridge.
Variable reluctance (VR): Both the magnet(s) and the coil(s) are rigidly mounted in the cartridge body, and the shaft has nothing on it but a rear-end of magnetic conductive material, so as to 'complete' (obviously with air gaps somewhere) a variable magnetic path in the magnet-coil system and thus generating a signal there-in.
I must admit ignorance regarding the modern MM cartridges as to its exact operation. I have never had one spare to destroy by opening it in order to examine the precise internal construction. I must confess that I find some descriptions rather confusing as to whether some cartridges are stricly (MM) or in fact VR (i.e. fixed magnet).
If MM is indeed moving magnet and not VR, I find some difficulty in justifying its existance at all, because even preliminary calculations show that the VR principle can indeed have lower moving mass than MM, and possibly even than MC, and for a higher output than MC because a heavier coil of hundreds of windings may be utilised. This apart from the disadvantage of MC units, of vibration in the coil(s) leads to the (fixed) outside world causing failure through metal fatigue.
Will those in the know here kindly broaden my horizons as well as those of others, to whom LPs and cartridges are relatively new?
[Yes. I did Google! Wading through the now expected sales talk, I could not find a detailed modern discussion of the above matter. RDH does not give sufficient info either, because the last edition was printed in 1955 - long before some of the significant latter-day refinements. I would imagine Morgan Jones would have said a few things; I do not have one at my disposal.]
Let us see where this goes.
