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Request for help - tonearm cable puzzle

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Request for help - tonearm cable puzzle

Postby TheScorpionsTale » 03 Jul 2012 16:25

This is my very first turntable mod, and also my first post here. I'll be very grateful for assistance identifying the correct way to connect up a new arm cable.

I play both vinyl and 78s, and for this reason have a Rek-o-Kut CVS 14 on which the supplied cheapo arm has packed up (cueing no longer works). I've replaced it successfully with the Rek-o-Kut Transcribe 12-inch arm sold by Esoteric Sound, which seems to be an un-badged Jelco, not quite identical to the 750LB.

My query is where to connect the wires from the (separately bought) Jelco arm cable.

To explain: this turntable has a vertical/stereo switch to enable the playing of vertical cut discs. Hence, the arm cable does not go straight out to RCA plugs in the back of the pre-amp. I've had to remove the RCA plugs in order to solder the cable's internal wires to points on the turntable's circuit board. But the wires are not the expected colours, and they're doubled up.

Whereas the old arm had a thin black ground lead and a woven shield both soldered to one point of the turntable's circuit board, and the thin white/blue and green/red cables issuing from the arm soldered to other points, the new arm cable I have (which connects to the arm base with a 5-pin DIN plug), contains two blue and two white leads inside the left channel cable, and another two blue and two white leads (not red and green) inside the right channel cable. Both right and left sides also have a woven copper shield encasing the four wires. There is a separate, third, ground cable.

Presumably for left, I solder both blues and both whites to the points on the turntable's circuit board where there had been one of each colour before ? Should I do the same with the right, making the assumption that white is equivalent to red, and blue the equivalent to green ? And what about the copper shields - do they connect somewhere? :?

I have searched in an effort to find an explanation for the blue/white in both sides, but to no avail. Any pointers will be very gratefully received, and apologies if I'm being really dim and have entirely the wrong cable...! Thank you.

GRAHAM
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Re: Request for help - tonearm cable puzzle

Postby pogo » 04 Jul 2012 00:04

I presume it's too late to determine by examining the plugs you removed? It sounds like definitely strange construction for what you would expect to be a five wire cable. Is this a DIY cable? I'm curious, but not enough so to cut a plug of my jelco cable just to see what's inside. I wouldn't make any assumptions -- if you really want to know (which you do) you're going to have to buzz the thing out somehow to see how it's wired. Put a headshell on it and check where the headshell leads are connected to. I just opened a Sony tonearm that had apparently been rewired by someone (rather sloppily). Two black wires comprised the right channel and two red wires were the left channel. I don't know what's available to you, but you can probably find a VOM suitable for this purpose for little cash if you have anything like this in your area. You can also rig a low voltage lamp to a battery and a couple of wires just to verify continuity. Good luck, Graham, and welcome to the forum. Do post and let us know what you find out.
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Re: Request for help - tonearm cable puzzle

Postby TheScorpionsTale » 06 Jul 2012 09:36

Thanks for your reply Pogo, which has re-directed my thinking. Rather than just seeking an explanation, which although useful won't necessarily get me any further, I've made some tests as you suggest to find out what's going on. Having attached the cable to the arm base, and cartridge and headshell the other end, I've metered for resistance and find that in both left and right cables, the white leads represent the expected white or red cables, and blue represents the expected blue and green. I suspect the use of just white and blue may be to do with economy of manufacturing. I don't suppose Jelco expect people to start dismantling their leads!

In each case, both the leads of each pair run to the same pin of the DIN plug / cartridge. I hadn't thrown the plugs away, and dismantling them (why didn't I think of that?) find that the two whites are tinned together and connect to the centre pin of the RCA plug. The two blues make contact with the outer. The copper shielding is also connected to the outer of the RCA plug (wrapped with the blue-sheathed cable), but I can find no connection between the shield and the ground (or any other of the five pins) of the DIN plug.

I'll connect up to the switch and the PCB on this basis now, with fingers crossed in the hope that I have a working unit at the end !

Thanks again for your pointers !

GRAHAM
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Re: Request for help - tonearm cable puzzle

Postby TheScorpionsTale » 06 Jul 2012 18:30

We have sound ! :D

Thanks again.

GRAHAM
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Re: Request for help - tonearm cable puzzle

Postby pogo » 06 Jul 2012 22:25

TheScorpionsTale wrote:We have sound ! :D

Thanks again.

GRAHAM

Graham, outstanding! And thanks for letting us know what you found. WRT the shield termination. Connection to ground/signal return at one end only is normal. The purpose is to "shield" not to create a redundant ground path. (That's how ground loops are created -- one way anyhow).
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