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A quick, simple question about balanced and unbalanced I/O


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Hey all,

 

I was talking to a retailer today, and if I understood him correctly, he said that any instance of an unbalanced connection automatically makes the whole signal chain unbalanced. Is this true with mixing consoles as well? If I have unbalanced outs coming from my keyboard to a Mackie 1402 mixer, are the outputs of the Mackie (despite being XLR) now effectively unbalanced? I would think (and have always thought) that the Mackie would convert all signals to balanced line level at the output.

 

Any clarification is appreciated -- thanks again.

 

Clancey

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The circuitry inside a mixer is unbalanced after it goes into the inputs. You could easily have a scenario where a long mic cable is run balanced (to avoid picking up noise) and terminated in a transformer, which converts it to unbalanced for feeding into a mixer that lacks balanced I/O. In this case, you've still achieved most of the benefits of a balanced system, because the biggest possible problem is the mic cable noise pickup, and the balanced line minimizes that.
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Craig, maybe you can speak to this.

 

The mnfrs. rep for Ebtech described how several outputs (certainly the aux's) on Mackie's VLZ PRO, CFX, etc. mixers are not differentially balanced, and therefore provided no common mode rejection, hence no protection from RF induced into cables. Is this true, to your knowledge?

 

The Ebtech rep said this is their prime marketing point for their Hum Eliminators. Everyone who owns a Mackie should have several channels of Hum Eliminator to differentially balance the aux outputs, and possibly others. I don't remember if he mentioned the 1/4" main outs (Not even sure about the XLR's) as differential or not.

 

Neil

It's easiest to find me on Facebook. Neil Bergman

 

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I reckon the Ebtechs are just trannies. A good trannie does cost a lot.. Six of those should cost the same as a Mackie 1402. I'd rather go unbalanced out of the Mackie that sticking some cheap iron in between.

 

Plus, the CMRR is seldom needed in a home studio enviroment. Actually, it's better that it's unbalanced (shorter signal path).

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when i first started recording at home (after much work in commercial facilities) i was obsessed with "balanced" connections... paranoid that one unbalanced line somewhere would prevent me from getting a professional sound...

i got over it~

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oops pressed "return" by accident.

uh, in any case, i agree with hiraga that unbalanced lines work fine in a home studio environment (at least with my synth setups).

just use high quality cables if and when you can.

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I'm not sure what is meant by "differentially balanced," but the common mode rejection occurs at a balanced input, not at the output. As long as the output generates signals that are exactly equal in amplitude and out of phase, they've satisfied the requirement to be balanced. At that point, it's up to the input stage to provide the common mode rejection needed to reject the common noise.

 

BTW a balanced input is called a "differential input" in electronic engineer-speak because it amplifies the difference between two signals.

 

Hope this helps...

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Originally posted by Anderton:

I'm not sure what is meant by "differentially balanced," but the common mode rejection occurs at a balanced input, not at the output. As long as the output generates signals that are exactly equal in amplitude and out of phase, they've satisfied the requirement to be balanced. At that point, it's up to the input stage to provide the common mode rejection needed to reject the common noise.

 

BTW a balanced input is called a "differential input" in electronic engineer-speak because it amplifies the difference between two signals.

 

Hope this helps...

 

As a tech guru, would you do the honors of contacting Ebtech for a clarification. The basic jist of their comment is that Mackie mixers do not take advantage of Common Mode Rejection at the Aux's. Maybe they mean the aux returns.

 

Could you.. Would you...

 

 

 

------------------

Neil

 

Reality: A few moments of lucidity surrounded by insanity.

It's easiest to find me on Facebook. Neil Bergman

 

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And while your at it Craig, drop Whackie an email and ask 'em 'bout where I can get those *world class preamps for 900US$*?? I've tried all their products on mackie.com, but they all sucked.

 

They must be hiding that gem pretty good...

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LatinMusic & Wiggum, Balanced and unbalanced I/O is a reference to using 2-wire and 3-wire cabling. Here is a basic comparison...

 

When referencing "unbalanced" 2-wire schemes, the general inference is that you are referring to signals in consumer equipment. You will see things like "-10dBu", and typically will be connecting with RCA and 1/4 inch cables. At 0dBu, you will be putting out 0.316 volts.

 

"Balanced" circuitry adds an extra wire. Using a "differential" amplifier the "minus" signal isn't really grounded. It acts kind of like an out of phase version of the positive signal. This allows for higher voltages to be generated. It is referenced more as "+4dBV", and typically uses XLR and 1/4 inch "stereo" connectors ( labeled as 'tip/+', 'ring/-' and 'sleeve/gnd' ). At 0dbV, you will be putting out 0.775 volts.

 

When you connect an unbalanced signal output to a device expecting a balanced signal, the meter will appear to be down about 11.8dB. This is where concern usually comes in. Some mixers will switch to match the "least common denominator" So, if you plug in an unbalanced connection and all of the inputs switch down, too, then your other signals will run about 11.8dB hot. This may cause saturation and distortion.

 

Way back when, it was expensive to make audio gear that consumers could afford. Although there were other variations in use in the "early days", the "+4dBV" was the de facto standard. But, to get audio electronics to the consumer, the "-10dBu" standard was born. Although there were noticeable differences in the quality of audio between these two standards back then, today, are not not nearly as far apart from each other in quality... for the most part.

 

Hope this small novel helps!

 

"It's all about the... um-m-m, uh-h-h..."

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Wiggum,

 

> If I have unbalanced outs coming from my keyboard to a Mackie 1402 mixer, are the outputs of the Mackie (despite being XLR) now effectively unbalanced? <

 

You got a lot of replies, but I don't think anyone answered your question directly. http://www.musicplayer.com/ubb/smile.gif

 

If you run the line out from your synth to a line in on the Mackie, then only that cable is unbalanced. The Mackie's main out - which goes to your power amp or whatever - remains balanced. However, this may introduce a ground loop between the synth and Mackie, which could in turn result in hum at the output of the Mackie. If you don't hear hum or buzz you're probably okay.

 

--Ethan

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I missed that part, in my update. It really depends on the mixer.

 

I looked at a Behringer Eurorack schematic. The way *they* set up the input op/amp, putting in a 2-wire (unbalanced signal) will tied the "minus" input to ground. The result will be a reduced gainon that input. If all the other channels are "balanced", then you will either have to lower them or raise the gain of the "unbalanced signal to match. Also, on this particular mixer, outputs have seperate op/amps driving the outputs -- the (+) and (-) lines. To short the (-) to ground would again reduce the signal. After checking this out, I noticed the output meters follow the "+4dBV" and "-10dBu" levels. Since these mixers seem to be copies of Mackies, I'd venture to guess they would work similarly.

 

Anyone else find similar results?

 

"It's all about the... um-m-m, uh-h-h..."

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Originally posted by AudioMaverick:

LatinMusic & Wiggum, Balanced and unbalanced I/O is a reference to using 2-wire and 3-wire cabling. Here is a basic comparison...

 

When referencing "unbalanced" 2-wire schemes, the general inference is that you are referring to signals in consumer equipment. You will see things like "-10dBu", and typically will be connecting with RCA and 1/4 inch cables. At 0dBu, you will be putting out 0.316 volts.

 

"Balanced" circuitry adds an extra wire. Using a "differential" amplifier the "minus" signal isn't really grounded. It acts kind of like an out of phase version of the positive signal. This allows for higher voltages to be generated. It is referenced more as "+4dBV", and typically uses XLR and 1/4 inch "stereo" connectors ( labeled as 'tip/+', 'ring/-' and 'sleeve/gnd' ). At 0dbV, you will be putting out 0.775 volts.

 

The standard nominal levels are -10dBV (un-balanced consumer gear) and +4dBu (balanced). 0dBV is by definition 1.000 Vrms. 0dBu is 0.775 Vrms (this is derived from the old dBm standard, which was the voltage required to drive a 600 ohm load with 1.0 mW of power). It is also important to note that the +4dBu/-10dBV standards are nominal levels - actual signals can exceed these levels by typically 15 to 25 dB (headroom, which varies depending on the equipment).

 

When you connect an unbalanced signal output to a device expecting a balanced signal, the meter will appear to be down about 11.8dB.

 

Simply connecting an unbalanced signal into a balanced input should not result in any change in the level. You are just putting all of the signal on one leg of the differential input. Going the other way, you could see a 6dB drop (depending on the equipment: some balanced output circuits will detect one of its outputs being shorted and apply all of the signal to the other, resulting in no drop in signal level).

 

Also, if you are converting between dBu and dBV, there is a factor of 2.21dB (0dBV = 2.21dBu).

 

Al Pickard

Digital Audio Labs, Inc.

Al Pickard

Digital Audio Labs, Inc.

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