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Marantz 1060 grounding

R

resoundpdx

New Member
I am working on a major rebuild/recap of a 1060 and have run into an area I don't recall seeing addressed in the the many past threads/postings on the 1060: grounding. The unit I am rebuilding has clearly been worked on by someone before, so it is not always clear what is original and what is not. And while I do have the repair manual and schematic, I have not found these to be 100% accurate/dependable.

What I am finding is the following: there are short straps connecting the circuit ground directly to chassis on the power supply board, the tone board, and the power amp board (but not the phono board). There is also a short strap connecting the negative side of the big 4700uF filter cap to chassis. And the shields of all of the input connectors are also tied directly to chassis. Since there are also wired ground connections between the various boards (and from the filter cap to the power amp board), isn't this a recipe for ground loops?

If I replace the main power cord with a three wire one (and tie the green wire to chassis inside the amp) will I make things worse (create more problems)?

Related question: all of the connections (including those from the filter cap) to the power amp board have been extended by 9-12 inches, presumably to make it easier to remove/access that board for troubleshooting. I am not too concerned about the outputs, as they will be driving long speaker wire runs eventually in any case. But this seems questionable for the power and ground. (Why upgrade to an ultra low ESR/ESL filter cap and then connect via a long thin wire?) At a minimum it seems like these power/ground wires should be beefed up in gauge if the runs are extended.

Am I worrying needlessly here?
 
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All a three conductor (three prong) cable will do is provide a connection from the chassis to ground. This ground will be no different than an external ground wire from a lug on the chassis to "earth ground". If you do convert connect the green ground wire to the grounding plug on the chassis. The grounding of the phono amp can be different and the turntable is usually grounded directly to the grounding lug found on most legacy HiFi equipment. The phono amp is designed to amplify the extremely low voltage output of the cartridge so any noise will be amplified to an unacceptable level if not grounded properly. The grounding of the turntable directly to earth ground before allowing it to get into the phono amp is a good practice. My experience with Marantz units is that they are very thoroughly grounded internally with straps to the chassis. Some other makes of legacy audio equipment run the grounds back to the power supply pcb which are then connected to ground by a lug or a screw holding a solder pad to the chassis. This arrangement can lead to noise issues if the main filter caps are grounded to close to the ground wires from other PCBs with audio signals. The only thing I don't like about the Marantz is that the ground straps are made as a stamping of some thin sheet metal in some models. A more flexible conductor would be nice but no big deal. The Marantz grounding is pretty well thought out. As far as the length/gauge of the ground wires goes 18-20 gauge should be fine.
 
I've restored two 1060's, and a 1030. I never had a ground issue with them. I kept one of the 1060's and gave the other to my son. Both have been working perfecy for about 10 years now without any ground issues or hum. I agree flexible ground straps would be better when it comes to working on them. But the metal straps do the job. These amps are well thought out and I like the separate boards and symmetrical layout.
 
Thanks to both of you for your replies. This all makes sense. The one thing about the design that I still think is a bit odd is running the negative speaker terminals back to the negative lug on the big filter capacitor (grounded to chassis) instead of directly back to the power amp board. But I guess that is pretty much equivalent, given the connection between the cap and the power amp. And I can't even swear that this is the original configuration since someone before me mucked around with things. I do agree that overall this is a very nicely designed and constructed amp.
 
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