plbeard
Active Member
I have a Pioneer PL-50 that may have a ground loop; it isn't a simple ground issue. The ground wire takes care of 80% of the normal ground noise, but at 50% volume (with no music) one can hear a lingering 60 cycle buzz and some hum when the TT motor is engaged. Frankly, this isn't objectionable in casual music listening, but this is a puzzle I have to solve. All of my other vintage turntables are dead-quiet of ground noise.
I have tried just about everything intuitive, and most things scientific, including resoldering all the ground connections. The noise is equal in both channels. The RCA cables are original, but clean. The noise is independent of the headshell or cartridge, though the wiring in the tonearm could be at issue. Please limit advice to removing ground loops and, especially, how to get really scientific about finding the culprit location in the circuit. Is there a way to do this with an oscilloscope? Could someone direct me to some instructions for using a scope (or other foolproof way) to track down TT ground noise? For technical trivia, the motor is the one pictured here, and unlike most Pioneer TTs of this era (early 70s), the motor has a ground wire on the external chassis of the motor. Not included in the mechanical drawing here, this extra motor ground comes out of the right, lower corner of the motor below, attached with a screw; I have made sure this is well attached at both ends; taking it out of the circuit curiously does not change the noise.
I have tried just about everything intuitive, and most things scientific, including resoldering all the ground connections. The noise is equal in both channels. The RCA cables are original, but clean. The noise is independent of the headshell or cartridge, though the wiring in the tonearm could be at issue. Please limit advice to removing ground loops and, especially, how to get really scientific about finding the culprit location in the circuit. Is there a way to do this with an oscilloscope? Could someone direct me to some instructions for using a scope (or other foolproof way) to track down TT ground noise? For technical trivia, the motor is the one pictured here, and unlike most Pioneer TTs of this era (early 70s), the motor has a ground wire on the external chassis of the motor. Not included in the mechanical drawing here, this extra motor ground comes out of the right, lower corner of the motor below, attached with a screw; I have made sure this is well attached at both ends; taking it out of the circuit curiously does not change the noise.
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