Shure SPS Cartridge

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gvl_guy

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I have the M24H, an original from back in the day. I ordered a replacement cartridge from LP Tunes, one of those generic ones. Although it sounds fine, the channels seem mixed up on playback. o_O Front is rear. Things don't seem right. I sent it back and they sent me another. Same thing. Then I found a NOS replacement and it works perfectly! My best/favorite sounding cartridge.
 

jaybird100

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Did your original M24H cartridge go bad or was it just the N24H stylus that needed to be replaced?
Cartridges themselves rarely go bad. I haven't heard of the front and rear channels getting swapped, just because of the stylus. That would usually be within the cartridge, and Shure cartridges, except for the M24H, tended to do that. If you're using an external demodulator, the problem could be rectified by just swapping the channels on the back of the unit. I also noticed this with Grado cartridges from the 70's that claimed they were designed for CD-4.
 

MidiMagic

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I have the M24H, an original from back in the day. I ordered a replacement cartridge from LP Tunes, one of those generic ones. Although it sounds fine, the channels seem mixed up on playback. o_O Front is rear. Things don't seem right. I sent it back and they sent me another. Same thing. Then I found a NOS replacement and it works perfectly! My best/favorite sounding cartridge.
A replacement CD-4 stylus with the magnet installed backwards will cause the front and back channels to swap places in the demodulator outputs.

Reversing the magnet reverses the phase of the baseband signal. But it does not change the phase of the CD-4 demodulated signal. The signals are then wrongly combined in the matrix,

Baseband + carrier is supposed to be front. Reversing the baseband phase makes it back.
Baseband - carrier is supposed to be back. Reversing the baseband phase makes it front.

Reversing the magnet causes no perceptible change on stereo output.
 

gvl_guy

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A replacement CD-4 stylus with the magnet installed backwards will cause the front and back channels to swap places in the demodulator outputs.

Reversing the magnet reverses the phase of the baseband signal. But it does not change the phase of the CD-4 demodulated signal. The signals are then wrongly combined in the matrix,

Baseband + carrier is supposed to be front. Reversing the baseband phase makes it back.
Baseband - carrier is supposed to be back. Reversing the baseband phase makes it front.

Reversing the magnet causes no perceptible change on stereo output.
That's exactly what happened! Stereo was fine. CD-4..... o_O
 

par4ken

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There are a couple of other threads on this same topic. It seems that manufactures of replacement styli don't care (or even know about) about magnetic polarity. A customer would never be the wiser unless he uses CD-4 or if he can discern absolute phase (unlikely). When I built a moving coil pre-preamp using a single tube (inverts phase) and used it with a CD-4 demodulator the same thing happened. The FM subcarrier doesn't care about phase the demodulated output phase and amplitude depends only on the frequency change of the carrier. So as Midi already pointed out the main or baseband signal being reversed in phase causes the front to rear swap.
 
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