Carl, I didn’t know you had done this conversion.
First, you can NOT use the same RCA female or shielded tonearm cable on the arch after converting to a mag cart. The shell is electrically touching the arch and creates a ground loop. The cart must be “floating” and not touch ground till it reaches the preamp.
The stereo models use a multiprong connector that does not touch anything, so it can be used when converting those machines.
The preamp must be grounded to either the arch or the amp chassis, just as you would with any other turntable.
Finally, even after all this, those amps were never “broadcast silent” –there was always some alight hum. It is usually obscured by the turntable rumble J RobNYC
On Tuesday, February 7, 2023, 08:09:11 PM GMT-5, Carl Haines via Jukebox-list jukebox-list@lists.netlojix.com wrote:
Now that you bring this up, several years ago I converted the amp from Cobra to a magnetic cartridge + preamp. The input to the amp is basically line level now which makes it easier to test on the bench.
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