Do I need sheilding for my twisted pairs wires for internal connections? I will run balanced signal inputs from two 25 pole d-sub connectors on the back panel to mute-switches on the front panel of the summing unit/bus comp I'm building. Unsure if the shielding is needed for this...?
From watching various build pics it seems it's not commonly used.
And also: I understand awg24 wire is recommended for internal connections, but is there any downside in using awg20? I've got loads of awg20...
Thanks for reading!
/T.
From watching various build pics it seems it's not commonly used.
And also: I understand awg24 wire is recommended for internal connections, but is there any downside in using awg20? I've got loads of awg20...
Thanks for reading!
/T.
Twisted pair wiring needs no shield if used as designed with a balanced signal.
As the noise on each part of the balances twisted pair is in phase, the balanced amplifier/receiver ignores the noise and does not reproduce it.
The use of thick cable has no advantage as practically no appreciable current is flowing making it unnecessary.
If not used for heater wiring or balanced line, it is not suitable.
As the noise on each part of the balances twisted pair is in phase, the balanced amplifier/receiver ignores the noise and does not reproduce it.
The use of thick cable has no advantage as practically no appreciable current is flowing making it unnecessary.
If not used for heater wiring or balanced line, it is not suitable.
A quote from this Grounding and Shielding Audio Devices
"For optimum balanced performance connect the shield to chassis ground at the point of entry. This means that the shield conductor, to avoid spraying any induced RF energy into the box, never passes the chassis' outer plane"
"For optimum balanced performance connect the shield to chassis ground at the point of entry. This means that the shield conductor, to avoid spraying any induced RF energy into the box, never passes the chassis' outer plane"
"Twisted pair wiring needs no shield if used as designed with a balanced signal."
- That's what I thought but I wasn't sure.
@ scottjoplin: So I should only wire hot and cold from the DB25 inputs to my mute switches? I did a mute switch in the past for unbalanced signal and had the switch short "signal" to gnd for muting, how is this done with balanced signal?
Gee, I didn't think this would be so hard to figure out but I find these things very confusing...
Thanks for the input everyone!
/T.
- That's what I thought but I wasn't sure.
@ scottjoplin: So I should only wire hot and cold from the DB25 inputs to my mute switches? I did a mute switch in the past for unbalanced signal and had the switch short "signal" to gnd for muting, how is this done with balanced signal?
Gee, I didn't think this would be so hard to figure out but I find these things very confusing...
Thanks for the input everyone!
/T.
Ahh, you wrote MIKE signal, I kind of missed that! So since my signals are balanced lines from inputs to switches and back to the summing PCB, I can do without shielding up to this point, but after the passive summing the signal is turned into balanced MIKE signal and from here to the preamps for makeup gain I should use shielded twisted pairs. Right?
This is only true at the frequencies that the circuit remains balanced. The higher the interference frequency the less likely the circuit is still balanced. Then at even higher frequencies the input semi-conductors act as RF detectors rather than amplifiers.
"...at the frequencies that the circuit remains balanced..."
-What? Is a balanced line signal only balanced at certain frequencies? Also, I thought that power supply hum would be the biggest problem.
RFI, are we talking about getting radio broadcasts on my recordings...?
My signal at mic level will only travel a few inches and will be shielded twisted pair, it's the balanced line-level signal that I plan to wire without shiedling, but I'm still unsure about many things it seems.
-What? Is a balanced line signal only balanced at certain frequencies? Also, I thought that power supply hum would be the biggest problem.
RFI, are we talking about getting radio broadcasts on my recordings...?
My signal at mic level will only travel a few inches and will be shielded twisted pair, it's the balanced line-level signal that I plan to wire without shiedling, but I'm still unsure about many things it seems.
Yep, the higher the frequency the less likely the circuit will remain balanced. Bill Whitlock often writes about this problem.
In the modern world any new product that uses electricity has the potential to generate interference.
If the Neil Muncy (RIP) shielding rules are followed (and with low-pass filtered inputs), then it's less likely that interference will get into a metal chassis.
THAT Corp has a lot of info on the subject.
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