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In Reply to: Re: Atma-Sphere MP3 phono input posted by Rushton on June 14, 2005 at 16:35:56:
Thanks Rush,
I should have known you'ld have an answer.
Why does Ralph build the phono using XLR if the cable needs to be modified anyway?
Thanks, Adam
Follow Ups:
Ralph is firmly of the view that it's sonically preferable to wire from the cartridge pins on in a balanced configuration. He would be converting from RCA to XLR, he'd connect the arm tube wiring that way all the way through the system. It can be debated endlessly. ;-)
FWIW (2 pennys?) any signal source that only inverts phase when you reverse the connections is a balanced source (that is to say, it does not hum and buzz like the dickens). Phono cartridges, tape heads, microphone elements and anything with a transformer coupled output are all examples of balanced sources.This is why if you run a phono cartridge single-ended, you have that funny little ground wire that no other single-ended source seems to need. If you run any balanced source as single-ended you have to do something like this.
The MP-1 and the MP-3 really don't care if you run the phono single-ended or balanced, it will work about the same, but *you* should care, because running the phono signal balanced all the way sounds a bit better. Why not do it if you can?
There are real benefits related to wiring your phono cartridge in balanced configuration, and it is a very simple matter to do so. If your tonearm has male RCA plugs directly wired to it, then you can use or make an RCA to XLR adapter that connects the hot lead from the RCA jack (the center pin) to female input #2 on the XLR input on the MP3 and the ground lead from the RCA jack to female input #3 on the XLR input. Ground in the XLR is pin #1 and usually you don't have to worry about it at all. If there is some hum, then wire the shield from the tonearm cable to pin 1 on the XLR. A better approach is to cut off the RCA jacks completely and solder an XLR male plug directly to the cable, connecting it as described above. I highly recommend the latter approach, since the phono signal wants to see as few cable connections as possible for maximum fidelity.
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