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Tonearm wiring

A

andres

New Member
Hello fellow 'karmers,

I bought a NOS Jelco SA-370D to mount on an also NOS Sony PS-2251 (:D, I'll post pics when it's done, promise). This arm has 2 ground wires
coming out the tube (4 colored wires + 2 black ones): is it ok to
solder these together to the shield on a Cardas 4x 33 awg wire? I was planning on leaving the shield unsoldered on the RCA end.
In case it helps, this arm is a copy of a Sumiko MMT (or reissue, since Jelco manufactured the original MMT).

Thanks!
Andres
 

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Since when do you put two channels in a single cable?

To my knowledge each channel should be in it's own cable with its own shield. The shield is connected to the signal ground of each channel--so the blue wire is soldered to the left channel shield and the green wire is soldered to the right channel shield.

The black wires are electrical grounds that should be soldered to the ground wire that exits the turntable and goes to the ground post on the amp.
 
I must have really misunderstood what I've read then.
How would I run this 4x33 tonearm cable straight from cartridge clips to RCA? I would have to split it into separate cables once it exits the tonearm?
Doesn't make much sense to me.. I must be missing something here.
It's my first time doing this, so there is a definite possibility I'm screwing things up.
Thanks for your help.
Andres
 
Well, I'll look up some links, but I guess my reasoning was that if this cable is recommended to rewire tonearms, using the same cable to continue the tonearm wires all the way to the phono pre would be appropriate.
 
In looking at this wire on the Cardas site it appears it was intended for headphones. I know that people have run the Cardas wire all the way to the RCA, but individual wires--not in a shield. And I don't know how they accomplish that as most turntables are extremely sensitive to EMI and need to be well shielded.

Yes, see if you can get me some links to what you were reading.
 
Howard is right Blue/White one channel, Red/Green the other. Some arms have a ground wire to the clamping collar. This ground is outside the signal grounds. It is to carry the ground to the headshell. The shell is sometimes wired with a 5th wire that goes from the pin spud to the clamping bolts for your cartridge to carry a complete ground to cartridge body. So 5 wires is the most I have ever run into and the black one is common electrical ground.
 
Andres, yes, according to the DIY thread, you would solder the black wires to both the shield and to your ground wire, and let the shield float on the other end. That doesn't sound like it should work, but supposedly these guys have done it successfully. I see Broc is in agreement with me regarding the conventional arrangement.

How soon are you planning this project? I have cable with 4 conductors and a shield that can simulate this setup and I can rig up a cable like that on an old turntable with two RCAs at the opposite end and test it. I am curious to see if it will work. I might not be able to get to it until the weekend, though.

If you want to start earlier, just go ahead and try it. The worst that can happen is that you'll get hum, and the remedy would be to cut the Cardas short and solder the four inner wires to either a pair of jacks or directly to coaxial interconnect cables (or via a terminal strip).
 
im wondering if youll hear radio mosco if your shield is not perfect

and it may be a little microphonic when you tap the cables

speaking as a manufacter...i only use the very thin cardas cable for inside the arm...as soon as it can be soldered onto proper and thicker shieilded cable in the arm base the better

any questions please just ask:D
j7
 
audioorigami said:
im wondering if youll hear radio mosco if your shield is not perfect

and it may be a little microphonic when you tap the cables

speaking as a manufacter...i only use the very thin cardas cable for inside the arm...as soon as it can be soldered onto proper and thicker shieilded cable in the arm base the better

any questions please just ask:D
j7
Click to expand...
Hey j7,

I'm glad you chimed in. I was thinking of asking you about this. I was always of the thinking that the signal grounds should be connected to the shields (each channel in it's own shield) and that for maximum effect they should be connected at both ends. And that coax is the most appropriate cable for unbalanced interconnects, which these are. What say you?
 
Well, this was quick. I soldered the Cardas wire to the existing tonearm wires and there is terrible hum. I followed what was on the DIY page and I soldered the two black wires from the tonearm to the shield on the Cardas, leaving the shield floating on the RCA's end.
I either screwed something up, or you were right on the money all along. I'm inclined to believe the latter is true.
So, what now? What cable should I use? Hopefully not something obscenely expensive since I'm already $50 and 7 days waiting into the Cardas. You mentioned coax, some particular type of coax?
Thanks for your help.
Andres

Edit: The hum gets a lot louder when I touch the arm, if this means anything to anyone.
 
Edit: The hum gets a lot louder when I touch the arm, if this means anything to anyone.
Click to expand...

Yes, it means the ground is faulty.

Andres, I thought you were rewiring the entire arm with this stuff, the idea being an uninterrupted circuit from cartridge to RCA. If you're leaving the existing arm wire intact (which is fine, as far as I'm concerned), there is no logical reason to use this Cardas cable. My suggestion is to hold onto it and if you ever decide to actually rewire an arm, just use it for that and connect it to RCA cables.

Now as to what to use? I assume you already have RCA connectors for this project, so all you need is cable. You can't do much better than this:

http://www.markertek.com/SearchProd...&sort=prod&skuonly=0&search=1505a&pagesize=20

This cable is double shielded (foil plus braided copper)--similar to the premade Petra cables I like, but more flexible. Nice, low capacitance (17pF/ft), which is important if you're using an MM cartridge. I have tried this and it works great for phono. 35 cents a foot, and just so you get an idea, 12 feet shipped to PA came to just under $15 total. Comes in different colors, too. :D
 
Yes, the idea was to rewire the whole thing, this was just a quick test.
Your link doesn't work for me. Seems to be for the Belden 1505A, correct? Looks good! and cheap!! :D
Is it possible to solder tonearm wires directly to coax, or will I need female RCAs too?
Thanks.
 
andres said:
Yes, the idea was to rewire the whole thing, this was just a quick test.
Your link doesn't work for me. Seems to be for the Belden 1505A, correct? Looks good! and cheap!! :D
Is it possible to solder tonearm wires directly to coax, or will I need female RCAs too?
Thanks.
Click to expand...
Yes, it's the Belden 1505A. You can solder tonearm wires direcly to coax. I'd either first brace the coax to the inside of the tt base or solder them to an anchored terminal strip to keep the coax from inadvertantly tugging at the delicate arm wires.

I have to tell you this, though. I have never rewired an arm using wires wrapped in a shield. Typically one just uses individual wires. So I don't know if it would behave differently inside the metal pipe. My inclination would be to keep the shield isolated.
 
I went to my local electronics store to get the Belden cable, but they only sold it by the roll.
Before I ordered it online, I thought I'd try one more thing. On post #18 on the diy page (by tubenut) he suggested making a "star earth", basically joining the black wires from the tonearm to the shield and also to a separate ground wire that is to go to the amp.
Works like a champ, no hum at all.
I still might try the cable you suggested to compare since it's so cheap, but this works perfectly.
Thanks,
Andres
 
andres said:
I went to my local electronics store to get the Belden cable, but they only sold it by the roll.
Before I ordered it online, I thought I'd try one more thing. On post #18 on the diy page (by tubenut) he suggested making a "star earth", basically joining the black wires from the tonearm to the shield and also to a separate ground wire that is to go to the amp.
Works like a champ, no hum at all.
I still might try the cable you suggested to compare since it's so cheap, but this works perfectly.
Thanks,
Andres
Click to expand...
Oh, okay I thought you did do the star earth. Great, so with the ground wire, it works. So really now it's just up to you do decide what you want to do.
 
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