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Vintage Gramophones and Phonographs

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 HMV TA, TC and T9 gram chassis and magnetic cartridges
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 Return to top of page · Post #: 1 · Written at 9:13:58 PM on 7 January 2024.
Ian Robertson's Gravatar
 Location: Belrose, NSW
 Member since 31 December 2015
 Member #: 1844
 Postcount: 2370

This very common and long-running series has a very interesting (and seemingly undocumented) feature that I found when I was looking to fit a magnetic cartridge to my Y2-D3.

Even though units with these chassis were fitted with ceramic cartridges, it seems you can just drop a mag cart in with no changes. You don't need to add a preamp or modify the circuit in any way.

I wondered why the circuit is the way it is so I modelled it in LTSpice, using the Shure analogue model for the mag and the accepted ceramic model of a voltage source in series with 800pF.

It checks out! I get the same output for both types, flat from 100Hz to 5kHz at least.

It's a disarmingly simple circuit idea that just uses shunt current feedback in a novel way.

What gets me is why HMV didn't tell anyone about it!


 
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