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Re: My experience with current sensing MC phono pre's

Posted by jcarr (M) on December 5, 2002 at 12:16:48

In Reply to: Re: My experience with current sensing MC phono pre's posted by Jon Risch on December 5, 2002 at 10:36:30:

Hi Jon:

> I did in fact, implement a balanced (double) virtual ground input, both with, and without a frozen MC cart coil in the feedback loop. <

Whew! If you had developed your psuedo-balanced design exclusively for use with an MC cartridge hardwired into the NFB loop, I would have to say that you've got bigger balls than I do! (grin)

BTW, wasn't there a commercial product that also integrated an MC cartridge into the amplification circuit (was it from Kinergistics Research?)

> for the non-frozen cart version, the balanced version is the way to go. <

My personal feeling is that the choice depends largely on the complexity, cost and scale of the amplifier circuitry that needs to be doubled up. For integrated circuit implementations, I completely agree with you, as the cost, labor and extra board are required for another 8-pin DIP package are not much, and there is always the easy-out option of using a dual opamp. But if the amplifier circuit is a relatively complex discrete design, rather than doubling up the main amplifier circuits, it may be more cost-effective in the context of the overall design to allocate that effort elsewhere. I would look at better EQ components, lower Dk circuit-board materials or point-to-point wiring, or perhaps a regenerative power supply coupled with flying-cap (charge-pump) regulation.

Oh well, Jon, at least you have opened up some new options for how we cartridge manufacturers can deal with the dead cartridges that are returned to us all of the time ;-)

regards, jonathan carr

PS. The Japanese DIY audio magazine "Radio Gijutsu" has published a couple of articles discussing precisely this type of balanced virtual ground phono equalizer circuit (IC opamp-based).

PPS. From memory, the type of resistor used for the initial series input resistor has a _big_ effect on the overall sound.

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