Phono cable build question


I’m replacing the phono cables on my Technics 1200 and have decided to use cable that has two conductors and is shielded. My question is what do I do with the shield?

When making regular interconnects with shielded cable, I normally solder the shield to the negative conductor and only on the source side of the cable. Do I do the same with phono cables? I thought maybe I might instead solder the ground wire to the shield, not to negative, and also have a separate traditional ground wire go to the preamp ground terminal.
kommanderkurt
kommanderkurt

When making regular interconnects with shielded cable, I normally solder the shield to the negative conductor and only on the source side of the cable. Do I do the same with phono cables?
It isn't clear what you mean here. Typically, you'd connect the shield at the preamp end, and leave the other end - be it to a source or an amplifier - unconnected. That's all part of the "star ground" concept, and how cable manufacturers mark their shielded cables for directionality.
Thanks cleeds- so I connect the shield of the phono cable to the negative at the preamp side, not the phono side?
Yes, only connect the shield at the preamp end, not at the Technics end. And if you intend to use moving magnet cartridges, the cable should be low capacitance.
Cleeds and Viridian, you are mistaken. The two conductors from each channel connect to the signal carrying twisted pair that is within the cable shield. One cable for right, one cable for left. The shield connects to the black tonearm ground wire at the turntable end and to the phono stage chassis ground at the other end. This gives you a properly shielded connection from cartridge to phono stage. 
I believe, in that configuration the shield will act as a second ground with a different resistance from the phono ground wire. This may increase the likelihood of hum.

Now if the shield was attached to the phono ground at only one end, presumably the phono stage end, that should work well.


Shield in this situation is the tonearm shield. The tonearm tube in this type of Technics turntable is electrically isolated from the turntable’s chassis. For purposes of rejecting RFI, the tonearm has a black ground lead, usually 20AWG terminated to a spade lug which is then connected to the chassis ground binding post of the phono stage.

By using a separate shielded twisted pair for each channel, the chassis ground of the phono stage is extended through the shield ground, which is greatly preferable to the convention of using one of the signal-bearing conductors on each channel as a makeshift shield. 

Since technically, only one source of ground should be used, the shield ground from either the left or the right channel should be used to ground the turntable tonearm and the other left unconnected at the turntable end. This ensures both channels have grounded shield provided via chassis ground at the phono stage and that the tonearm itself is also grounded. 
sleepwalker65
Cleeds and Viridian, you are mistaken. The two conductors from each channel connect to the signal carrying twisted pair that is within the cable shield. One cable for right, one cable for left. The shield connects to the black tonearm ground wire at the turntable end and to the phono stage chassis ground at the other end. This gives you a properly shielded connection from cartridge to phono stage.
That you would wire your pickup arm differently doesn’t mean Viridian or I are mistaken. Nor is it clear when you refer to your scheme as yielding "a properly shielded connection" just what you mean. As Viridian notes, your addition of a second ground may actually increase the chance of hum.

The loose, dangling, black ground wire common to many pickup arms is to help reduce ground loops; it can’t shield against RFI because it isn’t constructed as a shield - it’s just a dangling wire.

This is all moot in my system, because I keep the phono cartridge signal fully balanced. It’s wired into a balanced/differential phono stage - there's no need for a shield to reduce RFI.
The tonearm is the origin point of the signal, and in many cases it is metallic or made with conductive materials. In the OP case the Technics tonearm is designed to be an RFI shield. It is therefore a requirement to run a ground wire from said tonearm to the phono stage chassis to be effective. The use of twisted pair cable with a separate shield both provides continuity of shielding for both signal-bearing conductors of each channel, and phono stage chassis ground for the tonearm. Remember, the OP is using shielded twisted pair cable. 
Hi sleepwalker65- So I attach the black ground wire from the tt to the preamp chassis as normal.  Then, on the preamp end of the phono cables I cut the shield off and do not solder to anything.  But on the tt end, I twist and solder each shield together and run it to the origin of the black ground wire and solder it there. Is that correct? Thanks 🙏🏽 Kurt 
sleepwalker65
The use of twisted pair cable with a separate shield both provides continuity of shielding for both signal-bearing conductors of each channel, and phono stage chassis ground for the tonearm.
Whatever works for you is fine, of course, but I'd never wire a phono cable as you've suggested, and didn't even when I used a single-ended phono connection.
sleepwalker65 - what I’m asking is how exactly would you build them? I tried understanding what you’ve already written but, as I’m a novice, I’m a bit confused. Do you solder the shields of the interconnect cables to anything? If so, to what and where?
Kurt, you may use the method you described to ground the shield of each channel. 

Cleeds in my setup, I’ve retrofitted XLR jacks to my phono stage. This makes all connections simple via two plugs from the turntable. 
Thank you all for your input. I appreciate you taking your valuable time to do so. 🙏🏽