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zigzagflux 19th June 2007 01:48 PM

Shielded vs twisted pair in internal wiring
I was expecting to be successful searching on the subject, but found nothing here, AA, or Google. The only thread was short lived, and provided advice to use coax (which doesn't excite me).

So, what has experience shown us with input/output wiring to RCA's? Is twisted pair sufficient, or is shielded recommended? If we are able to neglect the effects of capacitance, it would seem to me shielded would be best.

On the one hand, a low impedance source should have no problem driving a little extra shielded wire; so we should be able to use shielded for output wiring. However, it can also be argued that a low impedance source is not susceptible to induced pickup, so twisted pair would be fine.

With inputs, I see a better case for shielded, as the nodes are typically of higher impedance, therefore more likely to pickup noise. As long as the additional capacitance won't adversely affect our FR, I would think shielded is the way to go.

I ask because of course I'm in the middle of a preamp, but also most of the pictures I have seen of DIY projects use twisted pair.

Gordy 19th June 2007 02:24 PM

If you use manual rotary controls move them to the rear of the enclosure to cut the cable wiring, and operate them with extension rods to the front panel. There is usually no good reason for mounting the input selector switch through the front panel. People do it like sheep follow each-other.

Switch both signal and signal return at your input. Ignore those who call signal return "ground".

Consider co-axial cable for your pre-amplifier internal wiring for inputs and outputs.

kevinkr 19th June 2007 04:15 PM

Twisted pairs work fine inside enclosures and may be somewhat more effective where magnetic fields are present as opposed to electro-static fields. Coax is more effective in the presence of electro-static fields where the primary coupling mechanism is capacitive.

I frequently use twisted, shielded pairs in noisy environments, best of both worlds.. ;)

Personally I like to avoid coax when possible due to the additional capacitance and the sometimes not so good d/a of cheap coax insulation. Not all of my sources (tube anyway) have very low output z.

The suggestion to move the source select switch close to the inputs is a very good one. I have had some difficulty in finding shaft extensions in the past to do this, and sometimes there is a lot of stuff in the way as well by the time I have figured out how to lay it all out. Of course an additional bracket must be fabricated for the switch as well. I don't switch grounds, and I don't have ground loop problems either - getting it that way though was not trivial. I just prefer as few unreliable contacts in the signal path as possible.

jduffy 19th June 2007 10:48 PM

What you wind up doing is trying shielded or twisted in different applications. Then swap 'em around to see or rather hear the difference. Trial and error is kind of fun actually. Great way to learn.

BTW I've never used shaft extensions. Never a problem for me, and I come up with my own layouts. I'm not following what other people do. A good layout is organic in nature. If you've got something wrong, you'll probably hear it and figure out a solution. That or just keep listening to the mess you've created and live with it. Not me though. Problem solving is fun!

Listening to Zappa right now playing Black Napkins. Zappa on vinyl, does it get any better? :cannotbe:

nhuwar 19th June 2007 10:59 PM

Hey I have a good idea twinax cable is twisted on the inside and has 2 sheilding braids if I remimber right.


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