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Which shielded cable for internal amp wiring?
Which shielded cable for internal amp wiring?
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Old 29th August 2019, 12:23 AM   #21
tcpip is offline tcpip  India
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Quote:
Originally Posted by Speedskater View Post
For a Shielded Twisted Pair inside a chassis, I use Belden 8450 solid conductor.

Belden 8451 & 9451 stranded conductor would also be OK.
The 8450 looks really attractive. Easier to work with solid core if I need to put the cable ends into PCB holes. Will see if someone will sell me a reasonable length at a reasonable price. Thanks.

Quote:
Only connect the shield to the chassis at one end.
One end: yes. Should I connect to the chassis or to the PSU ground point between the capacitor banks?

Last edited by tcpip; 29th August 2019 at 12:26 AM.
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Old 29th August 2019, 10:19 AM   #22
DF96 is offline DF96  England
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The shield should be connected to your signal reference point. This should not be the chassis and probably should not be the PSU capacitor junction.
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Old 29th August 2019, 04:06 PM   #23
tcpip is offline tcpip  India
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In the context of this shield grounding discussion, here's one interesting page I found:

Cable Shield Grounded At One End Only - EMC Standards
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Old 29th August 2019, 04:52 PM   #24
scottjoplin is offline scottjoplin  Wales
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Since you are interested in Shielded Twisted Pair....... Cable shield as a Faraday cage
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Old 29th August 2019, 07:58 PM   #25
Mark Tillotson is offline Mark Tillotson
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If the signals are at low impedance you won't need any shielding at audio frequencies unless you are obsessive (or running very long cables around, or have very high bandwidth amps) - though it definitely looks more professional to use shielded cables, the electrons may not care!

If at high impedance you will need to take tha shielded cable's capacitance into account in case its affecting the frequency response (usually not an issue with solid state, the impedances are too low)

If you want pluggable connections I'd suggest using RF patch leads with SMA connectors, they are reliable (gold plated) and easily sourced.

If soldering very stiff coax (such as teflon/silver), you will need strain-relief as the stuffness of the sheath is enough to break the centre conductor if it can move around.
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Old 6th September 2019, 03:54 PM   #26
wiseoldtech is offline wiseoldtech  United States
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And remember....
If using those infamous Directional Audio Cables, if you hook them up incorrectly, the music will play backwards.
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Old 6th September 2019, 04:02 PM   #27
tcpip is offline tcpip  India
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You know what? I never subscribed to those audiophile beliefs, but coming from where I am coming from, even I thought of one scenario where a cable might, just might, deliver slightly different "sound" when flipped on its end, all else being equal.

This applies to my basic belief that one will get much better noise shielding even with unbalanced connections if one uses a 2-core+shield cable. If one constructs such cable, one will connect the shield to the signal-ground conductor of only one RCA plug, i.e. only at one end. Otherwise one will get a ground loop.

So, you now actually get an asymmetric cable; a cable where the earthing of the noise depends on which end's RCA plug is connected to the appliance which has better earthing. So, in theory, I think it's possible that such a cable may give you (some) audible difference in the sound when flipped on its end, when connecting a specific pair of appliances. The difference will be in the difference in the quality of noise earthing.
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Old 6th September 2019, 04:51 PM   #28
wiseoldtech is offline wiseoldtech  United States
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Indeed you're talking about grounding issues, and that's important. But remember, electrons in a wire do not know which way they are going, nor do they care. Only fussy audiophiles care about such things.
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Old 6th September 2019, 05:32 PM   #29
Mark Johnson is offline Mark Johnson  United States
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Which shielded cable for internal amp wiring?
I use Mogami W2697 and/or W2901 microphone cable. It's very very small diameter ("lavalier") microphone cable, not the big fat rope that vocalists nervously fiddle with while they sing. I bought both types of Mogami from a US website called "Redco Audio".

Both of them have two signal conductors plus a ground shield, see attached diagram.

I use one signal conductor for "signal hot", connected at both ends. I use the stranded copper shield for "signal cold" a/k/a "ground", connected at both ends. I also connect the other (the second) signal conductor to ground, at the source end but not at the destination end. What I mean by source and destination is:

RCA input jacks ---> amplifier PCB: Source = RCA jack, Destination = PCB

PCB --> volume control potentiometer: Source = PCB, Desgination = Pot

I prefer to use the copper shield for "ground" at both ends, because it is bigger and heftier (more massive) than the second signal conductor. So it provides better mechanical support at each end of the cable, thus the weight of the cable is not pulling on a tiny and fragile stranded wire signal conductor. That's what I tell myself anyway.

_
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Old 6th September 2019, 05:39 PM   #30
tcpip is offline tcpip  India
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I'll check these cables out, but why use the shield for signal ground and the inner second conductor for a one-end connection?
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