I'm confused - balanced and unbalanced lines

Bob-Dubery

I played at the open mic session at TJs on Thursday.

What I noticed is that they have a box on the stage that feeds a snake. This box has only 3 pin (Cannon?) connectors on it. These are the connectors I usually associate with balanced lines. OK... so the mikes get plugged straight into this box. This I understand.

But the guitars... They have leads with a jack plug at one end and the 3-pin plug at the other. Jack plugs say "unbalanced" to me. So now they seem to have a cable that is unbalanced at one end and balanced at the other. Which of course is not actually so.

They also provide little Behringer pre-amp stomp boxes for people who turn up with guitars with pickups that have a low output signal. These sit between the guitar and the box that is the stage end of the snake. I don't use their pre-amp, but this also suggests to me that they're not running balanced lines into that on-stage box.

What is going on here? I asked their sound guy and he said that it's all balanced.

AlanRatcliffe

Bob Dubery wrote: This box has only 3 pin (Cannon?) connectors on it.

Cannon or more commonly called XLR.

But the guitars... They have leads with a jack plug at one end and the 3-pin plug at the other. Jack plugs say "unbalanced" to me. So now they seem to have a cable that is unbalanced at one end and balanced at the other. Which of course is not actually so.

TS (Tip-Sleeve/mono) jacks are unbalanced, but you can also have a TRS (Tip-Ring-Sleeve/stereo) jack which is balanced - a lot of compact gear with balanced outputs uses TRS jacks (90% of my studio is TRS).

You can also get TS to XLR cables that have passive transformers built in to the XLR or a cable wart to convert from both HiZ and unbalanced to LoZ balanced.

They also provide little Behringer pre-amp stomp boxes for people who turn up with guitars with pickups that have a low output signal. These sit between the guitar and the box that is the stage end of the snake. I don't use their pre-amp, but this also suggests to me that they're not running balanced lines into that on-stage box.

Those boxes might be D.I. boxes, which will convert to LoZ and balanced for the snake. Otherwise, it is possible to run unbalanced through a balanced line, especially if it is already LoZ and/or the snake isn't a long one.

Bob-Dubery

Alan Ratcliffe wrote:
Bob Dubery wrote: They also provide little Behringer pre-amp stomp boxes for people who turn up with guitars with pickups that have a low output signal. These sit between the guitar and the box that is the stage end of the snake. I don't use their pre-amp, but this also suggests to me that they're not running balanced lines into that on-stage box.
Those boxes might be D.I. boxes, which will convert to LoZ and balanced for the snake.

Negative. They have a jack for input and for output. No 3 pin connection at all.

It's one of these.... http://www.muz.co.za/index.php?main_page=product_info&products_id=1559

Keira-WitherKay

hey Bob ... looks like they just boosted the signal, not converted it to a balanced line.... i assume they did not have DI box's available cos a DI also can boost a low signal.... and would make the use of that booster pedal unneccessary ....... everyone does things in their own way...and many venues don't have the budget to set up the correct gear, and anyway for a small venue an unbalanced line into the desk is ok...you losing some signal but not enough to notice unless you A/B it to a signal from a DI box...... just on big stages and in studio's it would be unwise...

peace and light
keira

AlanRatcliffe

Keira WitherKay wrote: looks like they just boosted the signal, not converted it to a balanced line....

I concur... ?

Bob-Dubery

Alan Ratcliffe wrote:
TS (Tip-Sleeve/mono) jacks are unbalanced, but you can also have a TRS (Tip-Ring-Sleeve/stereo) jack which is balanced - a lot of compact gear with balanced outputs uses TRS jacks (90% of my studio is TRS).

You can also get TS to XLR cables that have passive transformers built in to the XLR or a cable wart to convert from both HiZ and unbalanced to LoZ balanced.

OK... but if they're running the stereo jacks there's a good chance they won't get anything on the ring. Do they then just short the ring and tip together?

Thanks Alan and Keira for taking the time to answer these questions.

AlanRatcliffe

Bob Dubery wrote: OK... but if they're running the stereo jacks there's a good chance they won't get anything on the ring. Do they then just short the ring and tip together?

No need. Balanced inputs accept unbalanced signals with no problems.

Shorting tip and ring on the output would actually cancel the signal on the input. This is as the two signals are supposed to be mirror images of one another, with one flipped 180 degrees out of phase with the other (which is done at the balanced output of the source). In normal operation, the one is inverted again at the balanced input so that they are in phase again and the two are summed together. If the two are in phase to begin with, they will cancel each other when one is inverted and they are summed. Hope that's clear - It's early.

TomCat

Hi Bob

Were you playing acoustic or electric?

Any passive PUP guitar connected directly to Mic Preamps of a mixer is a major tone sucker as the high impedance of the guitar is swamped by the much lower terminating impedance of the mic preamp (unless the guitar has a built in Balanced output on XLR). A long mike snake cable will only make things worse as the line impedance falls even further.

If acoustic, A good DI is the only way to go. DOD make a very good passive one called the 260.

Others are Radian, BSS (very expensive but GOOD!!!) etc. it might be worth while getting your own and keep it as part of your Kit.

Of source for the electric route the only way to go is to Mic your amp.

Cheers

Bob-Dubery

TomCat wrote: Hi Bob

Were you playing acoustic or electric?

This is at an open mic session, so in defense of the sound guy he has no idea who is going to walk through that door and what gear they will have.

I was playing acoustic. My guitar has a Baggs pickup under the saddle and that has a little pre-amp built into the end-pin. I was also running a Baggs Gigpro pre-amp to clean up the sound. So the output of the guitar went into the pre-amp. The output from the pre-amp went into my chorus pedal. The output from the pedal went via one of these leads I am describing into the snake.

My sound was fine. I had no problems there. I was just puzzled by the leads having XLR at one end and jack at the other. They have long been like this at this club, I just never noticed it before (my hanging out on GFSA is making me more aware of such issues).

They do have people walking in with stick-on-the-soundboard type passive pickups. Hence the Behringer pre-amps.

They could mic the guitars, but these are not pro players and they will move around a lot and thus micing may not work well. Also it would take time to set up the mics, and to persuade the performer that he should use a mic rather than the pickup s/he bought.

Before anybody asks... yes thanks, my chorus pedal worked just fine ?

TomCat

Thanks for the clarity.

One risk for the sound guy and the rig is that if the cable between the guitar and the snake is a stereo jack to XLR then he runs the risk of frying his loudspeakers.

What happens is that if the ring of the jack is not shorted to ground by the jack socked, the unterminated ring line to the mixer acts as a high impedance antenna, the cable to the mixer acts as a tuned circuit and the input of the mixer could turn into a signal generator as the mic gain is turned up.

The resulting oscillation can be at a very high frequency, way above audio, causing the PA amplifiers to clip and thereby frying the loudspeakers. I have seen loudspeakers actually catch fire under these conditions (very exciting but somewhat terminal to the loudspeakers)

Neps

There is another way they could have connected that setup.. They could have just used an Unbalanced TS jack to XLR, and then only have connected the Hot and Cold, which I've seen numerous times, then at the other end the XLR head is taken off, and an TS jack is connected to it, and they plug that into the 'line in' on the mixer.. Also not good practice, but it does work. If they however still used the XLR end of the snake and went straight into the pre amps.. oeps.. they are quite lucky for not losing any channels yet if they do it that way.