Moving-Magnet Head Amp - without RIAA

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That sounds very ortofon.

Ray: I have a couple of silly low impedance MMs. One is 30 Ohms DC. I know it's in the realm when vinyl noise is so far above this it's not really worth worry about, but you know how it is :)
Thanks to eBay, I just scored a discontinued Ortofon MC with 3 Ω DC, no inductance listed. It's 0.09 mV at 1000 Hz, 5 cm/sec. I'll be fabricating a PCB for that cartridge using a different schematic.

As soon as I started focusing on my MM collection, I'm getting interested in MC. Oh, the dangers of audiophile hobbies and electronics design experience...
 
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Tell me about it. Two years ago I settled on the AT150MLx being my 'high end' MM and an Ortofon S120 for mono duties. I was going to pension off my old MC and run just MM for a few years. Then things started going horribly wrong :). Then I found a nice man in Russia who could fix almost anything and it got worse!



The ortofon MC is likely to be a few uH. Nothing worth worrying about for all but the strangest preamps.
 
I am also intrigued. I know that many MM show a dip around that region with a 47k||C load but I don't think its due to frequency selective behaviour.

An article in the JAES from 1986 for an MC cartridge, move around the parameters for a MM cartridge:
 

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Not sure that helps explain it. The dip is shown on many measurements but not on others (for the same cartridge) but the the only model that matches it is the van Raalte one from linear Audio (image courtesy of LA). But that model fails to explain the attached FR plot done with a transimpedance load on the cartridge which is flat to 100kHz or so. I would like to get to the bottom of it.
 

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I think you would have to look at the exact measurement set-up to decide where the mid-range dip came from. Tone arm resonance? Head shell resonance? Was the response measured using a reference disc? If so, was the EQ ok etc etc.


The HF resonance within reason is easy to understand (cart L, cable C, input amp C if discrete JFET un-cascaded for example. On single ended discrete EQ amps with feedback to the 1st transistor emitter, I would imagine the load moves around a bit as well.) Some of the plots however are pretty horrific - I struggle to see how the measurement could be accurate or well conducted.

:)
 
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Was the response measured using a reference disc? If so, was the EQ ok etc etc.

I measured it (IIRC I posted it here) with a CBS labs unequalized constant velocity 500-50kHz sweep and flat pre-amp. Some day I'll bring it over to Kevin's and try it with his strain gauge carts and fancy schmancy styli. It might help if we had more measurements on completely magnetics free cart systems.
 
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