Confused about cables and diffs. between Hi Z/Lo Z

Posted: Sun Feb 04, 2007 9:43 am

I've just begun to record outside of the virtual realm and now that I've started to work with outboard gear such as pre's, mics and guitars I'm unsure of which cables to use for which applications. Please, indulge me:

-Are all TRS 1/4 cables suitable for balanced inputs/outputs? What are the differences between balanced & unbalanced?

-What type of cable should be used in a situation where a DI, for example, has a Hi Z 1/4 input? TRS or tip-ring? Which for Lo Z?

-Do the differences between Hi an Lo Z refer to impedence?

-Is it better to use matching cable types on your I/O? For example, XLR on the input but 1/4 on the output. Beneficial to have XLR on the output as well?

It's these rudimentary chips of knowledge that are hopefully gonna save me time and money. Hope those questions made a little sense.

Posted: Sun Feb 04, 2007 1:34 pm

Balanced cables have two conductors running inside a screen. They can be terminated in 3-pin XLRs or 1/4 inch TRS jacks. Unbalanced cables have only one conductor running inside the screen. They almost always terminate in 1/4 inch TS jacks, but sometimes in XLRs using only 2 of the 3 pins.

So if you are running balanced output to balanced input (mic to pre-amp for example), use balanced XLR-XLR cables.

A DI box takes the unbalanced high-impedance output from a guitar pickup and converts it to a low impedance balanced signal for sending to a microphone input of a mixer. Hi-Z and Lo-Z mean "high impedance" and "low impedance".

Which type of cables and connectors you use on the inputs and outputs of equipment depends on the equipment. There is no concept of "matching" connector types for in and out.

Don't confuse types of cable with the types of connectors. For example, a TRS jack can have two unbalanced cables connected to it. "Insert leads" are of this type, where the jack carries the output and the input to/from the inserted equipment, both unbalanced.

A couple of practical points. A jack plug (TS or TRS) can momentarily short out its signals to ground as it is being plugged or unplugged. For this reason, it is inadvisable to use jacks on microphone circuits where phantom power is being supplied from the preamp to the microphone. A TS jack can often be plugged into a socket expecting TRS jacks, in which case the ring connection will be grounded.

Beware that some power amplifiers have 3-pin XLR connectors for their outputs. The mating XLR plugs for these should be the high-current type (not microphone type), and should be wired with speaker cable, not screened cable.

Posted: Sun Feb 04, 2007 1:38 pm

Thanks very much Boswell. That's what I needed to know.

Posted: Mon Feb 05, 2007 4:43 pm

great info... he's got ya started real well... as an aside if your contemplating making your own cables... the 2 most important criteria are that it be low capacitence (can relate to frq response) and the % of shield coverage (rejection of RF interference)

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