Balanced vs Unbalanced

Doug Jones · From: Oregon & Florida

Would you tekkies please enlighten us: It seems all modern day processors and power amps have balanced jacks for line level connections. What are the advantages of gear with Balanced (TRS) ins and outs over unbalanced. Also, is it ok to use TRS cords or just plain old line cords between units with or without Balanced jacks. Thanks in advance, -DJ-

David L. Donald · From: Koh Samui Island, Thailand

Main issue is hum and interferance rejection,
especially for low level signals,
like mics before preamps, over longer runs..

Also typically it is a higher level signal for line levels...
+4 dbm pro. vs -10 dbm consumer, in most cases.
There are other more esoteric benifits.

[This message was edited by David L. Donald on 07 March 2006 at 04:11 AM.]

Ray Minich · From: Bradford, Pa. Frozen Tundra

For a good time look up "common mode rejection" and "normal mode rejection" in any instrumentation text. The balanced circuit provides improvements in both. To the amp circuits and the ears it means a reduction in noise, hum, interference, etc.
Too bad solid state op-amps didn't come out until the '60's (Philbrick). Had they been invented about the time of the guitar pickup, maybe the input to the amp would be to the inverting and non-inverting inputs of an instrumentation amp(balanced), and not straight to the grid of a 12AX7 (unbalanced).

Michael Garnett · From: Seattle, WA

A balanced signal MUST be carried through a three-conductor cable, with either an XLR or 1/4" tip-ring-sleeve connector, with pin 1 or sleeve to shield, pin 2 or tip to hot, pin 3 or ring to negative as the industry standard. An unbalanced signal is carried through a 2 conductor cable and uses regular tip-sleeve 1/4" jacks. Your guitar's signal is a good example of an unbalanced signal.

The reason this is beneficial, a balanced signal carries one audio signal down one conductor, and that includes any noise induced in the wire from outside interference. The second wire carries the same signal, but 180 degrees out of phase (or just reverse polarity, whichever way you wanna look at it), but the outside interference is still in-phase with itself in the other wire.

What happens when the signal gets to the input of the poweramp, there is a "differential amplifier" which measures the difference in voltages between pin 2 and 3, or the tip and ring. Since you've got maximum waveform difference (one's way up, one's way down) you actually end up getting a +6dB increase in signal level at the input, and since the waveforms for the interference are identical (read no difference in voltage), they are completely cancelled.

So, the advantages are, better voltage gain for the input sensitivity of your power amp, less RF interference (theoretically, none), and more useless trivia stuck up in your noggin.

I've got a test on this in 30 minutes, glad you asked.

-MG

Larry Hamilton · From: Amarillo,Tx

Michael, hope you passed your test. Man this stuff is way over my head. The important thing for me to know is when to use an unbalanced or balanced jacks when they are available on an amp. I of course don't want any more noise that necessary.
Kinda glad this topic was posted. Always learn something new on this great forum.

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Keep pickin', Larry

Jack Stoner · From: Kansas City, MO

I most cases for short runs (20 ft or less), balanced/unbalanced doesn't really make a difference. Obviously it does if only one type of interface is available.

e.g. short runs(patch cables) between equipment in a rack wouldn't really make a difference.

Long cable runs are where the 600 ohm balanced (e.g. XLR connector cables) make a difference. There is little or no loss on the longer cable runs and with good grade cable there is very little outside interference that's picked up.

Dave Grafe · From: Hudson River Valley NY

Now that Michael G. has provided an excellent explanation of the circuit, here's the short answer to what's OK to do:

You can plug an unbalanced line into a balanced INPUT and it will not only work just fine but will give you 6db of gain over using an unbalanced input. Technically, that's better than fine.

If you plug an unbalanced 1/4" connector into a balanced 1/4" OUTPUT jack it will work but it will short out one side of the output circuit. This may or may not be a problem, depending on the design of the circuit, the owner's manual will tell you if this is OK or not. When in doubt, don't.

Ray Minich · From: Bradford, Pa. Frozen Tundra

Oops, as Rosanne Rosannadanna would say... "Nevermind".

[This message was edited by Ray Minich on 07 March 2006 at 10:48 AM.]

Michael Brebes · From: Northridge CA

In response to Dave's remark about +6dB gain on a balanced input, that is only if it is a certain type of electronically balanced input. Transformer balanced will not change the gain.

Bill Terry · From: Bastrop, TX

Eric West · From: Portland, Oregon, USA, R.I.P.

YEs Dave, it is as you said, dependent on design.

I wasn't aware that the Podxt had TRS output jacks until reading extensively on their Internet Board. I wondered why you could feel an extra "bump" when plugging them in. They are meant to be plugged in commonly as unbalanced lines. IN fact few people even know they are TRS outputs.

I was told that it was for using XLR/TRS adapters for plugging into boards, or I guess into TRS equipped amps with balanced TRS chords. There aren't an overabundance of the latter, I understand.

Something nice to know I guess if plugging direct into a PA or recording in Mono with a balanced signal and wanting an unbalanced line to an amp for a monitor or stage amp. Haven't tried it that way though.

I'm told that unbalanced signals aren't much different at 10 feet or less. I certainly can't tell.

EJL

[This message was edited by Eric West on 07 March 2006 at 08:05 PM.]

Dave Mudgett · From: Central Pennsylvania and Gallatin, Tennessee

It's all been pretty well covered. I think of balanced lines operating much in the same way as a humbucking pickup or transformer, although the physics are not necessarily the same. As Ray suggests, the issue is common mode rejection, which means that a noise signal common to both "hot" leads is largely canceled because one is added to the other after being inverted. This raises the signal-to-noise ratio. Another benefit, as mentioned, is that a balanced output is generally driven by a low-impedance source, and a balanced XLR connector can be used to drive long lines. As also mentioned, if an active circuit "adds" the two hot signals, it also increases the signal level.

From a practical point of view, most guitar amps don't have balanced (either TRS or XLR) connectors, so there's no point in going balanced into such a guitar amp. But I use a TRS-to-XLR adapter to take the output of my Pod or other device to go into any PA with XLR inputs. My personal experience is that this makes the front-of-house signal much less noisy.

As Ray mentioned, the history of amplification is one of the big reasons for unbalanced connections and high impedance pickups. If solid-state op-amps had been in general use at the beginning of instrument amplification, it would have made a lot of sense to make low-impedance pickups to drive a balanced output. In fact, there is a guitar that does this - the Les Paul Personal and Recording guitars. These have low-impedance humbucking pickups transformer-coupled to a balanced output. I believe Les specifically specified this on his personal instruments to get a clean, clear sound with low noise, able to drive long lines. I'm sure Bill Lawrence would have a lot to say about this also. Rockers shun these low-impedance models, but I think they sound great for jazz, country, and other styles which prefer a clean, clear sound.

Michael Garnett · From: Seattle, WA

Well, Dave, I know very little about guitar amps and even less about pickups. But I'd guess that most guitar amps don't have balanced plugs because most guitars don't have balanced plugs. And I dunno about the history reason, I'd put money on the "it's cheaper to send an unbalanced signal" method of guitar and cable manufacturing. Plus, pickup impedances have a huge impact on guitar tone.

An instrument cable doesn't need to be much longer than 20 feet, and at that, length is a non-factor. I just really can't think of a studio or live-sound reason why anyone would want to be that far from their amplifier or a DI box. And you'd never want to plug a high-impedance unbalanced signal into the snake, so once again, the long lines is a non-factor.

I wonder what that TRS-XLR converter you're using is doing; is it just a plug, or is it an impedance transformer as well? Also, does your Pod have a balanced output, or is it simply stereo?

-MG

Michael Garnett · From: Seattle, WA

http://mywebpages.comcast.net/riceaudio/html/Wired.html

There's a good page for the geek-friendly.

-MG

Jay Ganz · From: Out Behind The Barn

I've been running my PODxt using the balanced
output for months now (into the balanced input
on my power amp). All I know is, it made a
heckuva difference! In addition to the
volume boost, the overall fidelity improved too.

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