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Which shielded cable for internal amp wiring?
Which shielded cable for internal amp wiring?
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Old 28th August 2019, 10:01 AM   #11
scottjoplin is offline scottjoplin  Wales
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Is the chassis metal and is signal ground connected to it?
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Old 28th August 2019, 10:43 AM   #12
tcpip is offline tcpip  India
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Yes it'll be a steel-and-aluminium chassis and the signal ground will probably need to be connected to it at some point. This last bit is a question I'm not sure about, and it involves me diving into the can of worms called grounding.

When I think of an audio circuit conceptually, I find that the entire circuit is finally tethered to the transformer secondaries, and there is no need for any current flow between the circuit and mains or chassis earth, therefore there is no need to connect any part of the audio signal related circuit to chassis earth. Shields of XLR connectors may be connected to chassis earth, but that's only because XLR has separate conductors for shield and signal ground. Otherwise, probably there's no need to connect signal ground to chassis earth.

What do you advise?
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Old 28th August 2019, 10:57 AM   #13
scottjoplin is offline scottjoplin  Wales
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Quote:
Originally Posted by tcpip View Post
When I think of an audio circuit conceptually, I find that the entire circuit is finally tethered to the transformer secondaries, and there is no need for any current flow between the circuit and mains or chassis earth, therefore there is no need to connect any part of the audio signal related circuit to chassis earth.
You would think so, have a look at this thread and see what you think was happening problem with earth gnd Bonsai is the author of the presentation on grounding I linked to
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Old 28th August 2019, 11:13 AM   #14
tcpip is offline tcpip  India
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I don't know what was happening in the OP's initial case. Left to myself, I'd do exactly what you've asked him to do: connect audio ground to the point between the two filter cap banks of the PSU. And I'd connect the earth pin of my IEC power socket to the chassis. Whether I'd then connect this midpoint of my capacitor bank to the chassis earth, I don't know. I'll look for advice.
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Old 28th August 2019, 11:29 AM   #15
scottjoplin is offline scottjoplin  Wales
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If I'm understanding the OP correctly, the hum only disappeared when he connected the audio ground to the chassis. It is usually suggested this is only done for safety reasons.
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Old 28th August 2019, 12:11 PM   #16
lcsaszar is offline lcsaszar  Hungary
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Shielded cable is not needed for amplifier internal wiring.
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Old 28th August 2019, 12:11 PM   #17
tcpip is offline tcpip  India
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Quote:
Originally Posted by scottjoplin View Post
If I'm understanding the OP correctly, the hum only disappeared when he connected the audio ground to the chassis. It is usually suggested this is only done for safety reasons.
Yes, that's what it appeared to me, and I am surprised that this was what was observed. It does not match my (mostly theoretical) knowledge.

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Originally Posted by lcsaszar View Post
Shielded cable is not needed for amplifier internal wiring.
This is the first time I'm hearing this.
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Old 28th August 2019, 12:30 PM   #18
scottjoplin is offline scottjoplin  Wales
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Quote:
Originally Posted by tcpip View Post
Yes, that's what it appeared to me, and I am surprised that this was what was observed. It does not match my (mostly theoretical) knowledge.
I have had the same experience, hum disappearing when signal ground connected to chassis. Screened cable inside a chassis isn't necessary unless there is RF ingress or generation internally.
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Old 28th August 2019, 08:48 PM   #19
Speedskater is offline Speedskater  United States
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Quote:
Originally Posted by lcsaszar View Post
Shielded cable is not needed for amplifier internal wiring.
Well that depends on a lot of things.

For a Shielded Twisted Pair inside a chassis, I use Belden 8450 solid conductor.
Belden 8451 & 9451 stranded conductor would also be OK.
Only connect the shield to the chassis at one end.
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Old 28th August 2019, 10:45 PM   #20
drpro is offline drpro  United States
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Which shielded cable for internal amp wiring?
TCPIP, Mogami or Canare both make cables like you are interested in. Additionally they are not very expensive.
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