Sure. But watch the voltage rating if this is a tube circuit. Most standard communication cable is rated for 300 volts max.
Now days you have to be even more careful I have seen some serial and USB cables that are rated at 32 volts!
Coaxial works when the core is truly axial to the screen/shield
The core must be in the middle of a circular screening layer to get best interference attenuation.
Inserting a twisted pair inside a screen can NEVER get the core in the middle of the screen.
An ovalised screen is not as good. An off centre core is not as good.
Twisted 4 core inside a circular screen can achieve the ideal if accurately manufactured.
It is more often used as micophone cable where the best interference attenuation is required for the very low signal and particularly the silence between the signals.
Whats wrong with a twisted triplet?
The core must be in the middle of a circular screening layer to get best interference attenuation.
Inserting a twisted pair inside a screen can NEVER get the core in the middle of the screen.
An ovalised screen is not as good. An off centre core is not as good.
Twisted 4 core inside a circular screen can achieve the ideal if accurately manufactured.
It is more often used as micophone cable where the best interference attenuation is required for the very low signal and particularly the silence between the signals.
Whats wrong with a twisted triplet?
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That is not what is required.
Whereas the twisted 4core does get the current centroid into the middle of the screen.
A dual polarity supply passing along a 3conductor cable carries some current along the +ve feed and returns some of that current along the zero volts feed. the rest of the current returns along the -ve feed.
If the +ve and -ve currents are identical then the zero volts feed carries zero current.
If the load is drawing alternate +ve and -ve currents along the two conductor while it is delivering an AC output then the two +ve and -ve currents can NEVER be equl. the zero volts carries the return currents during each alternate half wave.
Thus the cancelling currents are using the screen for the return.
It is only for the special case where the load is drawing a DC current that is identical on both the +ve and -ve conductor that the screen carries zero current and in this the twisted pair does achieve a net cancellation of the field at infinite distance. But this is DC and there is no AC interference effect. No need for the screen.
Whereas the twisted 4core does get the current centroid into the middle of the screen.
A dual polarity supply passing along a 3conductor cable carries some current along the +ve feed and returns some of that current along the zero volts feed. the rest of the current returns along the -ve feed.
If the +ve and -ve currents are identical then the zero volts feed carries zero current.
If the load is drawing alternate +ve and -ve currents along the two conductor while it is delivering an AC output then the two +ve and -ve currents can NEVER be equl. the zero volts carries the return currents during each alternate half wave.
Thus the cancelling currents are using the screen for the return.
It is only for the special case where the load is drawing a DC current that is identical on both the +ve and -ve conductor that the screen carries zero current and in this the twisted pair does achieve a net cancellation of the field at infinite distance. But this is DC and there is no AC interference effect. No need for the screen.
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Thanks. Nothing wrong with triplet other than untidy outside the equipment. Would it be better? My thinking is the twisted +/- ~15V and 0V on the screen would be (almost) as good. The regulation would be at the preamp end.
Yes. by 4 core, you mean star quad? I hadn't thought of that
Yes. by 4 core, you mean star quad? I hadn't thought of that
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As long as you decouple the rails within the supplied unit, as the supplies are balanced, anything will suffice and there will be no noticeable difference in performance. Make sure the screen is heavy enough to carry the sum of the current drawn.
Adhere to insulation and voltage/power ratings, that is all to worry about.
Adhere to insulation and voltage/power ratings, that is all to worry about.
I don't think this is a necessary condition.
The screen carries the alternate half wave currents from the +ve & -ve supplies. It does not carry the SUM of the currents.
A low resistance screen is necessary for a completely different reason: to minimise the difference in voltage between the two ends.
Thanks everyone. Star quad is better then, I tend to use that for balanced interconnects anyway but I hadn't considered that it was more centrally located than twisted pair.
The alternative would be a tightly twisted sheathed (for neatness!) triplet, can anyone point me towards something like that? Thanks, 1A would be plenty.
The alternative would be a tightly twisted sheathed (for neatness!) triplet, can anyone point me towards something like that? Thanks, 1A would be plenty.
This is being taken way out of context!
Right. But there is no absolutely harm in using the screen as a return either in this application. As long as it's the same gauge as the other wires.
The idea here is a nice looking cable that serves the intended purpose electrically. There is no need to kludge together exotic parts.
The OP simply wants to use shielded twisted pair for a +/- 15V preamp power supply harness.
Of course a 22awg STP cable will work just fine. It's carrying DC voltages that are most likely decoupled at the preamp. Why are we worrying about cable geometry in this ultra simple application?
STP audio cable, aka Belden 8451 and 9451 are the mainstay of the broadcast and AV industry. There must be trilllions of feet installed since the 1950s.
Just get a piece of surplus 22awg STP cable and be done with it.
Right. But there is no absolutely harm in using the screen as a return either in this application. As long as it's the same gauge as the other wires.
The idea here is a nice looking cable that serves the intended purpose electrically. There is no need to kludge together exotic parts.
The OP simply wants to use shielded twisted pair for a +/- 15V preamp power supply harness.
Of course a 22awg STP cable will work just fine. It's carrying DC voltages that are most likely decoupled at the preamp. Why are we worrying about cable geometry in this ultra simple application?
STP audio cable, aka Belden 8451 and 9451 are the mainstay of the broadcast and AV industry. There must be trilllions of feet installed since the 1950s.
Just get a piece of surplus 22awg STP cable and be done with it.
I twisted some speaker wires like that, used a drill, no heat shrink. Thankfully I'd watched a youtube video on how to do it (let it untwist a little whilst maintaining tension) else I'd have ended up with a coiled up mess on the floor
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