Cables - noise rejection - coax V shielded Quad

[Laudanum]

This is related to a turntable re-wire but Im interested in the cable properties, not the procedure so I think it's best posted here.  Hang with me on the introduction please.

I've wired several arms but this one is for a Technics SL1200 MK2.  The stock external cabling is coax.  Most re-wiring turtorials on the net replaces the coax with a another coax.
My understanding is that Quad has better noise rejection and that's what Ive used in several re-wires, all wood base, Rega like tables.  This one is a bit different because it's not a wood base table.
The stock external cable is a sistered coax.  Coax Center conductors connect to L+ and R+ from the cartridge.  The coax shields connect to L- and R- from the cartridge.  Then an external ground wire connects with the arm base, arm tube ground and chassis ground at a small PCB inside the arm base.

Hope you are still with me.  I would prefer to use my trusty Canare quad shield for external cable.  I would connect  L+ and L-  from cartridge to one pair of the quad and R+ and R- from cartridge to the other pair.  Then connect the Quad cables shield with all grounds (arm base, arm tube and chassis).   Along with the shield I would also connect an external ground wire with ALL the grounds inside the arm base.  This seperate, external ground would be for connection at the phono stage. The shield itself would NOT be connected at the RCA plugs.  If Im thinking right, this is the same thing "we" do with a twisted pair or quad, grounding the shield at the source but not at the component.

How I prepare the Quad for two channels ...  I split the jacket at the RCA plug end about 6" then break out the wires into two pairs.  I then wrap each of the pairs with some teflon tape and place a length of braided shield over each pair.  I tuck these two shields under the main braided shield that covers the quad and solder at that point so that the shielding continues all the way to the plugs.  I DONT solder the shield at the RCA plugs.  I use heat shrink over each pair and over the break out point to insulate everything (kinda like those cable "pants").

If you are still with me ... the main question is, given the above, should the Quad cable provide better rejection of "noise" than a coax?  
If so, would I be better off still if I didnt run the seperate external ground wire all the way from the arm base but instead, soldered the ground wire to the main shield of the Quad cable at the breakout where I split the quad to two twisted pairs?

Thanks in advance for input from anyone who I didnt lose.    

 

[Grainger49]

To be fair you need to compare a double shielded coax with the Quad.  But since you didn't say that, yes, the Quad should have lower noise impressed on to the audio wiring.  The dedicated shield in the Quad, grounded at the source, is the key. 

In a single shielded coax the shield is a signal carrier and grounded at both ends.  So it is shielded but not like the Quad.

 

[Laudanum]

To be fair you need to compare a double shielded coax with the Quad.  But since you didn't say that, yes, the Quad should have lower noise impressed on to the audio wiring.  The dedicated shield in the Quad, grounded at the source, is the key.  

In a single shielded coax the shield is a signal carrier and grounded at both ends.  So it is shielded but not like the Quad.

When you say "double shielded coax" do you mean that two shields are electrically insulated/isolated from each other?   Because the dual shield (braid and foil) or quad shield coax (two braids, two foils) that I am familiar with through CATV or satellite work are just stacked shields,  they arent insulated from each other at all.

Also, I think it was PJ who suggested that instead of running that seperate ground from the arm base, it might be better to connect the ground wire to the quad cables braid where the pairs are broken out. Something about the proximity of the ground and geometry of the quad shield cable, or something ???    It's easy to do and electrically doesnt change things because that shield and seperate ground wire would both be connected together with the table grounds inside the arm base anyway.  Do you think there is any advantage in terms of noise by eliminating that external ground wire for the entire run and just connecting/soldering it to the quads shield where I split it to the two channel pairs?  Or keep it a seperate run?

Thanks Grainger.

 

[Grainger49]

Desmond,

Yes a center conductor, insulator, shield, insulator, shield and outer jacket.  That gives 2 conductors for signal and a shield that can be grounded at the source.  It is done by several cable manufacturers.  The Quad is a nice way to get around the two stiff shields.

I'm a fan of braided shields as they are more flexible and easy to solder to.

I'm at a loss trying to explain most of Paul Joppa's comments.  Sometimes I get it, many times I don't. 

What concerns me is having a central ground in your phono stage and another central ground on the table.  But this is a try it and see situation.  Grounding/hum/noise is often a try it and see thing.  Luckily we are hobbyists and the changes are pretty easy.  This applies to the external ground wire.  Try it with your meter set on the lowest AC range.  Just read with and without the external ground wire in place.  Keep everything connected (line stage, amps) and read the noise at the output of the phono stage.

 

[Laudanum]

With the wooden decks, like the Regas, there apparently isnt any reason to ground anything but the tone arm tube and the base.  The motor and main platter bearing are isolated because everything surrounding them is wood.  So the ground wire to the phonostage only connects to the arm tube and the arm base.  Well, actually Rega doesnt even use an external ground wire, they ground the arm to one of the RCA shields (single shielded coax).    Since the Technics SL1200 has a metal deck, I think they added the ground to the chassis (grounded at one of the pitch slider to base mounting screws)  along with the arm tube ground and the arm base ground.  Anyway, it works, they are generally nice and quiet.  But the tonearm wiring is pretty poor and it connects to the external cabling through a PCB in the arm base.  Stock internal tonearm wire is a stranded, tinned copper as well.  So, it's generally accepted that a tonearm re-wire with better quality wire is a worthwhile mod.

Seeing how it is quiet as it is, I would expect that it should remain quiet retaining the grounding scheme.  But I asked about the Quad in this case just to make sure that it should be better at noise rejection than the single shield coax.  Or atleast, not worse seeing how it is quiet in the stock configuration.  About Pauls idea for connecting the external ground wire to the quads shield instead of a run all the way from the arm base ... I didnt understand his explanation either.  But it seems counterintuitive from the perspective that the shield would actually be physically connecting at the pre-amp end doing it that way.  It's electrically the same from a strict sense, but as you mention, noise issues can be tricky and illogical.  So I may stick with what I know has worked in the past.

Thanks

 

[Laudanum]

Hey Grainger, just an update if you are still lurking.  Seems to have worked out fine.  Not any quieter as it was quiet before, but no added noise.  Notable sonic improvement too.  I think it's the tinned, stranded arm tube wires that are/were the biggest offender (harsh, tizzy treble).

 

[Grainger49]

Excellent! 

I have an old Souther SLT arm and rewired it with the Incognito/Cardas/Rega arm wire replacement.  A solder joint at the cartridge clip and a solder joint at the RCA plug that goes into my Eros.  A single strand of Cardas wire from cartridge to input.  It was a definite improvement.  IIRC, I did it a long time ago, it removed some hum I had because the Souther wire was unshielded.

 

[sl-15]

hi desmond,
i rewired my technics with a canare star quad as well. not sure if i fully understand how you did it, but correct me if i am wrong. you basically are having one cable coming out of the turntable and have both the left and right channel in it. so two from the 4 wires for each channel? i did it one cable per channel. i include a picture for better understanding. i stripped the pvc outer insulation but left the metal braid in place, put shrink tubing over it to insulate. then i connected the braided shield and the white pair to each channels minus and the two blue cables for each channels plus. i left the braided shield disconnected at the rca end. i am quite happy with the results. the problem is the size of the two cables but stripping the outer jacket and replacing with shrink tubing helped. i had to alter the plastic cable crimp that holds the cables in place to fit the wires through but it worked with some elbow grease.

 

[Laudanum]

Hi Stefan.
Yes, that's how I did/do it.  But I didnt retain the stock circuit board, I used a turret board that KAB sells.  It has screw holes that match up to the two holes in the arm base the hold the circuit board.

For anyone else who may be interested, this is a summary (that now probably should be in phono   ) ... In running the single Canare cable, I pair the white conductors for + and - of one channel and the blue conductors for + amd - of the other.   The Turret board has 5 solder turrets for the 4 arm wires plus arm ground.  I soldered the arm tube ground to the turret next to the screw where the grounds are connected in the arm base.  I exposed the braided shield of the Canare inside the arm base and solder a ring terminal onto it.  That attaches along with the existing ring terminal that holds that ground from the slider mount.  That braid is also routed next to the inside of the turret that I soldered the arm tube ground to and I add some solder there.  So the original grounding scheme is retained plus the Canare shield. I used a smalled tie strap to secure the cable to the turret board.  The other 4 wires from the arm soldered to the 4 remaining turrets along with the 4 Canare conductors.   At the RCA end I break open about 6 - 8 inches of the Canare , comb out the braid (PITA) and leave about 3/4" neatened up and folded back over the Canare jacket. I seperate the whites and blues into pairs and keep them twisted and wrap each pair with some teflon tape.  Then I steal enough of the braided shield from a length of the same cable and slide a length over each wire pair.  I fold the main braid back up over the two braids and solder the main braid to the two braids over the pairs.  I Clean up any sharp solder edges with a small file.  Slip a length of heat shrink over each, now shielded pair.  And 2 or 3 pieces in layers over the break out.  At the plug ends, I trim the braid back, leaving enough wire to solder into the RCA plugs.  I build up the RCA plug end of the pairs with 3 or 4 more short sections of heat shrink (covering the braided shield)  in layers so there is enough diameter for whatever plug I use to clamp snugly (usually the Switchcraft RCA plugs).  Then I just use my meter to make sure I have the right wires ... one condutor to the RCA pin the other to the plugs shield for each pair.  The braid isnt connected at the plug end.   It's easy but it takes a little time.  BTW, I use the small/mini version of the Canare quad (L-4E5C).  I didnt want to alter the cable clamp for the arm base plate and didnt want to shove the cable in there.  Right now I just have the cable secured at the plate with a couple tie straps to one of the screws.  I'll probably make something, or buy a clamp for round cable (Mcmaster) to more permanently secure it.  Those split clamps must be ok to use, but I really hate the way they crush and bend the cable and cant bring myself to use them.  Im sure it's fine, just one of my many peeves.

 

[sl-15]

okay now i understand your configuration. you went through a lot more work for the shield than i did. i like the idea of using the thinner version of the canare, i was using the thicker one because i had that lying around. on my other technics 1200 i used a twisted wire cable from mogami #2552. it is not a star quad but has one pair of twisted conductors inside instead of four. it was much easier to work with. to my ears i could not hear a different between the mogami and the canare but i also never tried too hard. i get tired of doing AB comparisons and never found the time so far to compare the two. i always wanted to send one of the technics to KAB to get the arm rewired, thats why I never got the turret board. altering the clamp is pretty easy. i just took off material with a sharp knife. i cut away material of the lower part of the clamp that presses on the cable and rounded the corners of the groove so that there are no sharp edges left. then i widened the opening of the upper part. it still clamps the cable but it does not press into it as deep. your configuration inspires me to connect the braided shield separately to ground instead of connecting it to the negative of each channel like i did. thanks for that.

 

[Laudanum]

Yeah, if I used two cables, I would probably just use twisted pair instead of quad.  But some prefer using the quad with two conductors for + and two for - like you've wired yours.  I've tried it that way for interconnects and couldnt hear a difference between it and the Canare twisted pair.  The main reason why I dont use two twisted pair cables for turntables is because I dont like to deal with the two seperate braided shields inside the arm base.  It's more work on the RCA end with the way I do the Quad but neater and easier inside the arm base.  But then again, the arm base for the 1200 is huge.  For the rega and project arms, and many others, there isnt much room in there.  Same reason why I use the mini version.  And I basically use it just like I would if it were for a regular interconnect in respect to the shield ... just grounding it at the source (turntable base) end.  As long as it's quiet, it's good ... as long as you like the cable, sonically.  I like the Canare fine and it's cheap.  Aside from experiementing, I only use the quad for turntables or when I make an adapter, like mini stereo plug to RCA.  Just easier using two twisted pairs (or a single run of quad for each channel if you like that better).

 

[VoltSecond]

http://search.digikey.com/us/en/products/LFB360230-300/240-2287-ND/703473

At the phono-amp inputs, I've placed both left and right RCAs through the center hold of a part similar to this one. The ground wired DOES NOT go through the part.  I found my part at an electronics junk yard. This part at Digikey looks pretty close to what I used.  I could only fit one on my cable. Two would be even better.

This will encourage high frequency shield noise currents to go down the drain wire instead of the signal wire. The part does not affect the signal currents (differential) that we want to keep.  Adding the part was a small, but noticeable improvement. 

 

[Doc B]

Very interesting...thanks Paul!

 

[Grainger49]

V-S,

I discovered these in 1984 attached to the first generation GE Digital DC drives at the tach input.  There is a wide range of permissivity permeability in these.  I tried some from scrapped GE drives around my audio cables and it squelched the high frequencies.  I should have put them around only the audio conductor.  Instead I found they worked well around power cords.

I now have them on the hot leg only of my Paramours' incoming power.  There are about 25 wraps through 3 toroids.  But now with a regenerator it is a moot point.  The regenerator is analog.

 

[VoltSecond]

These toroids (High Permeability Ferrites) are best as common mode chokes. Common mode means signal high and signal low are wrapped through the middle at the same time.  The same goes for Power high and power low being wrapped through the middle at the same time.

Even with a regenerator, they may offer some help. At $6 a pop, they