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Old 14th March 2007, 04:21 AM   #1
jarthel is offline jarthel  Australia
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Default twisted pair wiring on a tube amp

I'm not sure if this is okay but here goes:

I want to use twisted pair for the signal wires inside the chassis.

But only 1 side of the ground wire connected to ground. The other end is "hanging". Is this a good idea?

thank you.
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Old 14th March 2007, 04:41 AM   #2
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Default Re: twisted pair wiring on a tube amp

Quote:
Originally posted by jarthel

I want to use twisted pair for the signal wires inside the chassis.

But only 1 side of the ground wire connected to ground. The other end is "hanging". Is this a good idea?
When using twisted pairs, it's always a good idea to ground the shield at the high impedance end only. That way, it acts as a Faraday cage to shield against electrostatic interferance, but doesn't carry any return currents that can induce noise.
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Old 14th March 2007, 04:49 AM   #3
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Not sure about a twisted pair, but it's better than no shielding at all. And yes, one end, the sensitive end, should be grounded, not both, from what I have read.
Better though , to use shielded wire, like a guitar cable or even coax, to isolate it from interference. Some RCA cable hi-fi connectore wires are shielded too, if you find decent ones. My impression too, is that if you have a big enough chassis and there's nothing nearby within an inch or so (heater wires, etc.), that you don't even need any shielding.
Space is good, and also rotate your tube socket mounting so that the filament supply is away from the input. Shorter lengths are the best, as well, for the sensitive signal input.
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Old 14th March 2007, 05:38 AM   #4
jarthel is offline jarthel  Australia
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Default Re: Re: twisted pair wiring on a tube amp

Quote:
Originally posted by Miles Prower


at the high impedance end only

how does one determine which is the high impedance end?

I've seen schematics where ground is usually tap at the 1st cap. Is this a good choice?

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Old 14th March 2007, 05:50 AM   #5
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Default Re: twisted pair wiring on a tube amp

Quote:
Originally posted by jarthel
I'm not sure if this is okay but here goes:

I want to use twisted pair for the signal wires inside the chassis.

But only 1 side of the ground wire connected to ground. The other end is "hanging". Is this a good idea?

thank you.
You are indeed discussing a twisted pair with a shield around it, just to make sure, and are suggesting that only one end of the shield is grounded? Your responders assumed this, but I just wanted to make sure. As Miles & frank have suggested, yes this is good. If you really want to go all out, you can make that ground connection via a resistor, but this is usually overkill.
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Old 14th March 2007, 06:21 AM   #6
jarthel is offline jarthel  Australia
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maybe I wasn't very clear.
================

I have 2 pieces of wire (1 red and 1 black) that I have twisted together. The red wire is the signal wire. The black wire is connected to ground.

only 1 end of the black wire is connected to ground.

<b>There is no shield (like those found in coax) around the twisted wires.</b>
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Old 14th March 2007, 09:05 AM   #7
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Quote:
Originally posted by jarthel
maybe I wasn't very clear.
================

I have 2 pieces of wire (1 red and 1 black) that I have twisted together. The red wire is the signal wire. The black wire is connected to ground.

only 1 end of the black wire is connected to ground.

There is no shield (like those found in coax) around the twisted wires.
In that case, it would be better than nothing, but not so good as shielded audio cable or coax. For sensitive leads (such as connecting output to gNFB summing node) I prefer RF coax with the braid grounded at the high impedance end.
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Old 14th March 2007, 10:31 AM   #8
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On occassions it can be a good idea to "ground" the ungrounded end of the ground-wire using a small cap. Especiellay if there's a chance (risk) that HF-interference is picked up by the ground wire like an antenna, the cap shorts these HF-currents.
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Old 14th March 2007, 11:03 AM   #9
Salas is online now Salas  Greece
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Quote:
Originally posted by Miles Prower


In that case, it would be better than nothing, but not so good as shielded audio cable or coax. For sensitive leads (such as connecting output to gNFB summing node) I prefer RF coax with the braid grounded at the high impedance end.

When returning from the speaker connector + the feedback cable, if coax is used with shield connected to local earth node of first or split stage (where feedback is fed in a schematic anyway), there is also a - speaker connector point that needs to be ground referenced back there. Will it suffice to be a simple wire returning, twisted around the coax or it must be a second coax maybe twisted with main return coax, with both core & one way shield earthed in the small stage ground again?
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Old 14th March 2007, 12:02 PM   #10
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Be careful about the additional stray capacitances that this can cause. The cure may be worse than the disease.
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