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shield

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Electronman

New Member
Hello guys,

I ever use shield wires for sensitive mics (i.e electerets).
A question that arises is does those wires affect to the signal itself? Does they affect and weak or reduce the signal power of the input signal inside the shield wire too?

Another question is do I need to use those wires on sensitive parts of a device, I mean suppose a very sensitive op-amp and you need to connect a pot as the feedback resistor, do you use those wires if there is a 5 to 6cm or even more distance between the op-amp leads and the pot itself or just you use those wires for inputs?

Thanks

P.s. Is that important putting both ground wires across a shield wire to the ground or just one is enough?
 

unclejed613

Well-Known Member
Most Helpful Member
i'm not exactly sure what you're getting at but i think you are asking whether to use grounded shields on microphone cables and long wiring in high gain circuits. yes it's always a good idea. generally if you have long wires in the feedback loop of an op amp going to a pot on the front panel, it's always a good idea to have them shielded, but with the shields terminated only at the circuit board end. just be careful what kind of shielding you use, as with high gain circuits, the capacitance of shielded cable can have an effect on frequency response. with the mic cable, if the FET preamp is in the mic capsule, then the impedance is low enough to use standard microphone cable. if the FET preamp is not in the capsule, but on the board, use low capacitance cable. even small amounts of capacitance with high microphone impedances cause high frequency rolloff.
 

Electronman

New Member
Thanks,

What values or marks I should ask when I want to buy the shield wires?
Can somebody response the the P.s too?

What is rolloff?
 

unclejed613

Well-Known Member
Most Helpful Member
it's always good practice to ground the shield at one end. shields are usually grounded at both ends when going from one chassis to another.
 

Sceadwian

Banned
Grounding at both ends can create ground loops if done all the time though.
 
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