Some of the stereo arms had four wires up to the cart, but one was cut short and folded back. Depending on how flexible after washing, i often replaced them as part of the conversion to magnetic.

It is best to avoid any ground loop especially in these high-gain such as with magnetic carts. A form of loop occurs with the cables that come from the arch where both grounds go to one pin and then come together again at the amp. This didn't matter with the high output from the ceramic cart, but does result in a slight hum when using a magnetic.

Ideally, the four pins should remain separate till they reach the amp itself.

RobNYC

On Saturday, August 5, 2023 at 10:06:17 PM GMT-5, Jay Hennigan via Jukebox-list jukebox-list@lists.netlojix.com wrote:

On 8/5/23 15:01, Shankar Singh via Jukebox-list wrote:

Should these models of tonearms have 4 wires, 1 for each terminal? Or can the 2 (-) close to the cartridge end be connected to each other, so that 3 wires are used in the tonearm?

Some of the earlier cartridges have a common ground terminal, hence three wires. By the time of the 3300 they probably used all four. If I recall correctly the grounds are connected together at the 4-pin Eby plug on the arch.

On Sunday, August 6, 2023 at 02:58:50 PM GMT-5, Nigel Pugh pughn@npsyssoft.force9.co.uk wrote:

Hi Rob, With magnetic would you join the 2 grounds at the preamp ? Or have a stereo preamp (even though mono jukebox) and join at the amp? I've always mounted the preamp at the rear of the right hand mechanism arch when looking from the front.. The the output from the preamp is one ground and one signal, but like you say there is an ever so slight hum. Never bothered with it as it's only me that's noticed it. Nige, Uk

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Well they do join grounds at the pre's input in any case. After that the signal is much higher and loops are not as much of an issue. FWIW: I run the channels discrete till they get to the pre, which i usually mount on the side inner cabinet wall, then a 'shortie" into the amp. Grounding the mech to the pre's ground post may, or may not help in reducing noise. If the cart is metal body the tiny grounding strap from one terminal to the body -must- be removed to reduce hum. We don't want the mech grounded through the signal ground.

In cases where the original cart was a Sonotone 8T the level from a modern cart and pre might be excessive to the amp input. In those machines i put a 100K-Ohm pot between pre and amp. I adjust level so the loudest record will just be slightly lower than the squelch as measured on the time constant caps. You need a fast meter since it will load a tube AGC. Note that all were done with Pickering DAT-NPAC carts and styli along with the Radio Shack pre, today's equipment may not need the pot.

I also mod the pre by reducing the NFB so as to give about a 7db rise at around 12KHz. That, plus a real tweeter really gets these machines out of the mud.

Rob