best for long runs: mic level or line level?

[larzman]

i know that balanced signals are better than unbalanced signals, especially for long runs.
 
what about the level? if i need to do a long run, should i choose mic level (lo-z) or line level (hi-z)?
 
thanks!

 

[InnerSpace]

If you're talking about a small signal, e.g. a CD player or a DAC to an amp, then the connection needs to be at line level.  Balanced connection at line level offers twice the voltage swing and rejection of noise induced in the line along the way, but might be overkill in a domestic situation.  Runs shorter than 20 or 30 feet should be OK either way.
 
"z" means impedance, and the cable should be as low in impedance as possible. i.e. thick strands, and shielding is good too.  "Hi-z" has come to mean an input with a much higher than normal input impedance, designed to maintain output/input impedance matching ratios for devices with natively high output impedances like guitars.  I don't know of any hi-z inputs on domestic audio gear.

 

[larzman]

Thanks! That's helpful.
 
I have a Squeezebox Classic (SB3) which outputs unbalanced -10dBV. I have two KRK RP5G2 monitors, which accept balanced +4dBu.
 
Here are my two options:
 
A) Use short RCA interconnects from the SB3 to a direct box (DI) to get a mic-level balanced signal. Run 25 feet of XLR cable for each channel. Level match each channel from mic-level to +4dBu line-level. Use a short interconnect to the monitor.
 
B) Use short RCA interconnects from the SB3 to a direct box (DI) that outputs a +4dBu line-level balanced signal. Run 25 feet of XLR cable for each channel. Connect to the monitor.
 
Ceteris paribus, Which is better? A or B? It sounds like you think (B) is better.
 
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For (A), I'd use the Whirlwind pcDI and a transformer (like this).
 
For (B), I'd just use the Whirlwind LM2B. Simple!
 
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I'm leaning towards (B) with the LM2B. Do you think that's the better option?

 

[InnerSpace]

Don't the KRKs have unbalanced RCA inputs?  If so, try 25-foot RCA to RCA cables straight from the SB to the speakers.
 
If not, I think B is actually your only option.  A involves the pcDI, which is a passive device, unsuitable for driving long cables.
 
But try the RCA to RCA first.  Theoretically not ideal, because I'm sure the SB doesn't have the strongest output stage in the world, but interpolating the LM2B isn't ideal either, in that it adds another amp stage, with potential for noise and ground loops.
 
In this case, Radio Shack is your friend.  Try a cheap 25-ft RCA cable and see how it goes.

 

[larzman]

Thanks for the information.
 
I've already tried a pair of Hosa RCA cables. I'll try out the LM2B and see if sound quality improves at all.

 

[larzman]

So I compared these two cabling options:
 

1. 10-foot Hosa RCA cables
2. Whirlwind LM2B and Whirlwind 25-foot XLR cables

 
The former (the RCA cables) exhibited a fair amount of both high-frequency and low-frequency noise. The latter (the balanced solution) exhibited about the same amount of high-frequency noise, but it exhibited much less low-frequency noise.
 
As a result, the balanced solution is an improvement over the unbalanced solution at cable lengths of as little as ten feet. I expect that if I required fifty feet of cabling, the improvement would be dramatic.

 

[infinitesymphony]

Balanced signals are designed with certain impedances in mind. That's what the "Z" in hi-z and lo-z stands for. For proper balanced transmission, you want low impedance.