monkboughtlunch
Super Member
I installed a Shure SC35C in an 1961 Zenith idler/belt hybrid drive turntable that was originally equipped with a Euphonics U2 ceramic cartridge. This version of the Zenith turntable predates the MicroTouch 2G tonearm. Instead it has Cobra arm apparently designed to track at about 3.5 - 7 grams.
The Euphonics U2 was reportedly good in its day, but even when I installed a NOS replacement stylus, the cart still performed poorly. I think it's due to rotted rubber yokes.
So I installed a moving magnet Shure SC35C, which tracks at 4-5 grams. This cart sounds amazing! But there is a problem.
While the sound quality, tracking, sibilance and IGD performance is far superior with the Shure MM cart, there is a constant motor hum being picked up by the SC35C that wasn't present with the ceramic Euphonics cart.
If I lift the tonearm as high as it will go, the hum decreases dramatically. When I bring the tonearm back down to the rest position, the hum increases dramatically.
And the hum is only present when the motor is turned on.
I'm thinking it might be the Alliance motor which appears to be unshielded. I suppose this is a two pole motor. But it also has two permanent magnets, making it a synchronous induction hybrid motor.
The underside of the Cobra tonearm is open (i.e. not in an enclosed arm tube) so the wires are exposed underneath. I wonder if that is part of the problem, as it was mentioned the cart itself may be well shielded.
Any ideas on how to eliminate the hum without pulling out the Shure SC35C and installing a low quality ceramic cartridge?
The Euphonics U2 was reportedly good in its day, but even when I installed a NOS replacement stylus, the cart still performed poorly. I think it's due to rotted rubber yokes.
So I installed a moving magnet Shure SC35C, which tracks at 4-5 grams. This cart sounds amazing! But there is a problem.
While the sound quality, tracking, sibilance and IGD performance is far superior with the Shure MM cart, there is a constant motor hum being picked up by the SC35C that wasn't present with the ceramic Euphonics cart.
If I lift the tonearm as high as it will go, the hum decreases dramatically. When I bring the tonearm back down to the rest position, the hum increases dramatically.
And the hum is only present when the motor is turned on.
I'm thinking it might be the Alliance motor which appears to be unshielded. I suppose this is a two pole motor. But it also has two permanent magnets, making it a synchronous induction hybrid motor.
The underside of the Cobra tonearm is open (i.e. not in an enclosed arm tube) so the wires are exposed underneath. I wonder if that is part of the problem, as it was mentioned the cart itself may be well shielded.
Any ideas on how to eliminate the hum without pulling out the Shure SC35C and installing a low quality ceramic cartridge?
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