OK another newbee question RE balanced/unbalanced

[Mbira]

I'm sure this has been covered but a search didn't pull up what I was looking for. Maybe this can go to the newbe meta?

I understand a balanced signal is essentially two unbalanced signals in opposite phase to cancel out noise, etc.

So in a microphone input, where there already is a balanced input, does that mean that a balanced preamp will essentially be two preamps-one for each half of the signal?

An unbalanced signal going into a preamp-the signal will need to be split and the phase reversed on one of the splits and then output balanced? Is that split usually done at the begining of the circuit to keep noise of the circuit from being introduced?

What is "electronically" balanced?

In transformer balanced, is that the point of a 1:1 input transformer? Are there like two secondaries that spit out the signal balanced?

Am I just way the hell off track here?!?

I am a newbee. Thanks very much!!

Joel :guinness:

 

[BuzAllen]

Try these, they might answer some of your questions.

http://www.jensen-transformers.com/an/an003.pdf

http://www.jensen-transformers.com/an/an002.pdf

http://www.jensen-transformers.com/an/ingenaes.pdf

http://www.dself.dsl.pipex.com/ampins/balanced/balanced.htm


Brian

 

[Svart]

simply yes, the two signals are identical, one is just 180deg off. the preamp takes those two and flips one signal 180deg again. now both signals are identical, but any noise coupled onto the two signal cables is now 180deg opposite. it combines these signals and cancels the noise. now the preamp might be balanced output too..


balanced output is the reverse, a single signal is split and one is phase reversed.

the mic input is really two inputs at first but combine a little later in the circuit. this can differ from design to design.

electronically balanced is doing this with ICs or discrete semiconductors. pretty much anything that needs power to do this.

the other choice is of course transformers.

transformer ratios are nothing but number of turns on the primary vs. turns on the secondary. this really doesn't have much to do with balancing(the way you hook it up is what matters for balancing), just changes in current/voltage. a trafo can also be single output if you ground one side of it and use the other for the signal output, or of course balanced if you use both of the leads for signals.

most circuits are unbalanced due to costs and complexity(double everything, make sure it STAYS in time with the other signal, etc). you can certainly balance all the way through something but most of the time good grounding, shielding and design will keep the noise so low that you will not need to be balanced all the way through.


just a quick and dirty explaination. if you need more clarification you are in the right place!

:guinness:

 

[Mbira]

Thanks guys!.
So I can see the G9 is changing the signal to unbalanced at the input transformer.

Without the input transformer in the G9, how does the circuit remain "electrically balanced"?

Is it correct that the Green Pre is remaining balanced thruout the whole circuit?
Here's the green schematic:
http://recording.org/users/kev/Mozart_2.pdf

Thanks.
Joel

 

[Kev]

[quote author="Mbira"]... Is it correct that the Green Pre is remaining balanced thruout the whole circuit?[/quote]

no
:roll:

differential floating input

That says a lot more than just 3 words. Difficult to explain in depth without many, many words. The above explainations and PDf files are all good so study them and don't be in a hurry to understand to all as soon as you have finished reading.

I understand a balanced signal is essentially two unbalanced signals in opposite phase to cancel out noise, etc.

although that is OK
it does explain it all and shows some mis-understanding.
I don't want to offend here but it could be an example of a little knowledge is dangerous.

I suggestion might be to back all the way up to twisted pair cable and why it is cool.
Then work you way to balanced sends and recieves. This might be able to answer the question,

What is "electronically" balanced?

A few of the favourite DIY projects here are perfect examples of the various input and output construction styles. The GSSL shows a electronic I/O and Project 2 and the JLMx project shows a few examples of output methods.

Back to the twisted pair.
The two wires provide a send and return path for our audio signal. The fact that there are twsisted evenly together means they are similar in length and are subject to same outside influences.
This is the magic bit.
The same outside influences ... noise. This we might call common.

A differential input might cancel what is common to both lines leaving what is different in both lines .... send and return.
That's the stuff we want.

any of this make sense ?
some of the experienced guys might not like my lose explaination of this stuff.

I'll let you think about that for a while.

 

[alk509]

Just a small thing: I see some talk about phase and signals being 180 degrees off... Well, that's not exactly right. It's the polarity of the signal that is inverted in a balanced system, not its phase.

Peace,
Al.

 

[tmbg]

good point! Something that's 180degrees out of phase would be leading or lagging, rather than just vertically flipped. Makes no difference for a continuous sine wave, but makes a big difference for anything real

 

[Mbira]

A differential input might cancel what is common to both lines leaving what is different in both lines .... send and return.
That's the stuff we want.

I get that. That is the CMRR. This is what Svart was explaining when he said:

the two signals are identical, one is just 180deg off. the preamp takes those two and flips one signal 180deg again. now both signals are identical, but any noise coupled onto the two signal cables is now 180deg opposite. it combines these signals and cancels the noise.

Hence the importance of equal interference in both signals-right?

differential floating input

So are the + and - seperating themselves from the ground reference-hence floating?

You're right, I don't get it yet. I'll certainly keep reading and asking questions. :? Why is it even the things you think will be simple are hard :?
Joel :guinness:

 

[Kev]

[quote author="Mbira"]Why is it even the things you think will be simple are hard [/quote]
cool
that's something probably worth remembering.
There are more than a few simple things that do get complex if you dig a little deeper.
These things are often repeated in digital and just go to show that digital can't solve everything as some seem to believe.
We do say phase when we often mean polarity and there is a phase shift in EQ's even if they are digital.

Knowing the simple things well can help you cut through much of the BS in publicity blurbs.

Back to the balanced thing.
You will find that the differential input brings much of the benefit. An unbalance low imp output into the above can work a treat.
Going all unbalanced can require good grounding techniques. Mastering houses do sometimes set themselve up this way.

The way gear interfaces with each other is half the battle in setting up you control room /studio.

 

[Svart]

yes, I assumed that timing was the same between both signal wires regardless of phase. properly designed devices and wiring should already have taken into account timing issues, if they haven't then the design is not complete in my eyes! we could allow for a small amount of lead/lag but the amount should be minimal if all things are considered beforehand.

grounding is another animal entirely even though it reaches into the balancing area. the signals are referenced to ground to keep strange things from happening like building unlike potentials and current flow between devices, but in a properly set up system the ground(shield) in a balanced cable doesn't do much more than attempt to drain off interference that it intercepts before that interference can reach the signal wire. everything should have already been grounded properly or you will get ground loops and the like.

in short:

a third ground wire is not *necessary* in balanced systems as long as you can guarantee that all the devices are sitting at the same ground potential, but with so many designs and so much difference between manufacturing practices it's become almost an expected necessity.


phase may probably be the most correct term for the 180deg reversed signal because it refers to the time constraints in a cycle, and by definition, phase is "The fraction of a complete cycle elapsed as measured from a specified reference point". assuming that the device(s) are built properly and are sending/receiving the signals at the same time, then phase does apply because the angles of the signals at a given moment should be exactly 180deg from each other. this timing is the phase part of it. In measurement they may not be *exactly* timed alike, but for all practical purposes should be alike enough to not generate problems. again this goes back to proper design.

but aside from that its the term that most people understand when talking about balancing, especially when reading media hype, regardless of the true definition. should we fault them or the people who write buzzwords on a magazine page to sell more product, regardless of the correctness?

sorry to hijack the thread, we'll get back to the learning now.. :green:
:guinness:

 

[Mbira]

So what is the difference between saying this has a "differential floating input" and saying this is balanced thruout the whole signal path? Is there a different ground reference going on?

Sorry-I'm just trying to go one question at a time...(Oh, I mean two questions :roll: )

Joel

 

[alk509]

[quote author="Svart"]yes, I assumed that timing was the same between both signal wires regardless of phase.[/quote]

No, if there's a difference in timing, there's a difference in phase and viceversa. In a way, timing = phase. And most importantly, phase does not equal polarity.

[quote author="Svart"]phase may probably be the most correct term for the 180deg reversed signal because it refers to the time constraints in a cycle, and by definition, phase is "The fraction of a complete cycle elapsed as measured from a specified reference point".[/quote]

Again, if there are "180deg reversed signals" in a balanced system, the system won't work. What's needed are two polarity-reversed signals. PHASE DOES NOT EQUAL POLARITY.

As stated in your definition of phase, a difference in phase implies that the signal has moved in time, which you don't want. You want to flip a signal "in place", i.e., you want to reverse its polarity. Furthermore, when talking about a compound signal like audio, phase becomes useless, since a 180deg phase change at one frequency implies a different amount of shift at other frequencies.

[quote author="Svart"]assuming that the device(s) are built properly and are sending/receiving the signals at the same time, then phase does apply because the angles of the signals at a given moment should be exactly 180deg from each other.[/quote]

If the devices are sending/receiving the signals at the same time, the phase difference between them is exactly 0 degrees, which is what makes a balanced system work! PHASE DOES NOT EQUAL POLARITY

Hey, let's graph this real quick. Two signals get added, first time 180deg off, second time polarity-flipped:

[quote author="Svart"]but aside from that its the term that most people understand when talking about balancing, especially when reading media hype, regardless of the true definition. should we fault them or the people who write buzzwords on a magazine page to sell more product, regardless of the correctness?[/quote]

This is exactly why I brought this up, because lately I've been noticing more and more people misusing the term "phase". It may not matter in most recording situations, but it sure makes a hell of a lot of difference to a designer, DSP programmer, EE, etc. It's like using the words "lungs" and "heart" interchangeably just because they're both squishy and live inside the chest! :wink:

Peace,
Al.

 

[BuzAllen]

There is kind of a funny train analogy on this topic at the bottom of this pdf.

http://www.prosoundweb.com/studyhall/studyjump.php?pdf=polarity_and_phase

Brian

 

[Svart]

I think I must have written what I was trying to say in a way that doesn't translate well because much of what you just wrote is just retelling what i said in a different way.

al wrote: Again, if there are "180deg reversed signals" in a balanced system, the system won't work. What's needed are two polarity-reversed signals. PHASE DOES NOT EQUAL POLARITY.

yes, 180 degree off signals do cancel... IF THEY ARE TIMED IDENTICALLY, but you forget that the differential receiver flips that 180 degree off signal back to alignment with the normal signal then combines the two. and no phase does not equal polarity, where did i say that? phase is defined in this instance by measuring the potential of the signal at a specific time. so we are considering TIME AND POLARITY TOGETHER.


i said this : "yes, I assumed that timing was the same between both signal wires regardless of phase."

---- sorry, I meant to say "regardless of angle" but i was trying to write quickly and didn't proof read myself. my bad.


al said: If the devices are sending/receiving the signals at the same time, the phase difference between them is exactly 0 degrees, which is what makes a balanced system work! PHASE DOES NOT EQUAL POLARITY

again no one said that polarity equals phase. phase is only partly time based, the other half of it, the cycle based portion, is the polarity. they go hand in hand. I was trying to show this but again i think i just confused readers instead.

polarity at a given point in time constrains only one signal, the other signal will have it's own polarity at a given time. we are meerly comparing the two to each other. thus when we discuss phase, we assume that they are timed identically, we also assume that either signal will be flipped and they will be combined.

again i have to stress that timing is not phase alone as you insinuate, they go hand in hand.

but i digress since i don't have time to continue this right now.

peace!!!!!

:guinness:

 

[alk509]

Rather than me trying to explain this whole thing again, can somebody maybe explain it in different terms? I got some DSP books that make this whole subject clear as day, but that may be overkill...

Not to pick on you, Svart, or sound like a *******, but you really are getting this wrong and I honestly can't explain it any better :grin: :guinness:

Peace,
Al.

 

[Mbira]

So what is the difference between saying this has a "differential floating input" and saying this is balanced thruout the whole signal path? Is there a different ground reference going on?

 

[Kev]

[quote author="Mbira"]So what is the difference between saying this has a "differential floating input" and saying this is balanced thruout the whole signal path? Is there a different ground reference going on?[/quote]

A circuit that is balanced thruout is possible although unusual and yes it might have a DFI (diff float input)
These two do not have to be inclusive or mutually exclusive.
A circuit that is balanced thruout does not have to be interested in looking for a differential.
:roll:

can we leave the balanced all the way circuits for the time being as I think it will just confuse.

In it's lowest form just think of the twisted pair and a trafo at each end. Don't even think of the ground yet.

 

[PRR]

> what is the difference between saying this has a "differential floating input" and saying this is balanced thruout the whole signal path? Is there a different ground reference going on?

Go back to basics. WAY back. Once upon a time the only audio device was a microphone. A diaphragm, a magnet, and a coil of wire with two ends. And sitting on a wooden bench.

What is the output? The difference of voltage between the two ends.

Is it balanced? Unbalanced? The question has no meaning. (un)balanced compared to WHAT?

Say you live in outer space, and you "hang" a painting. Is it "level"? Level compared to what?

So the first mike is neither balanced nor unbalanced.

Same for the first speaker, which in fact is just a mike used the other way round. Even today, most speakers have no ground reference.

So when you have a mike and a speaker, both on the same wooden bench, how do you connect them? Two wires, from 2 mike terminals to two speaker terminals. Ground is still not in the picture.

Ah, but talking from one end of the bench to the other is pretty silly. Run a long wire to the next town. Actually 2 wires, of course. "Of course"? Wire is expensive, and lossy. When you have a few miles of it, you have hundreds of ohms of resistance. But if you drive a long metal rod into damp dirt at both ends, you only have 100 ohms of resistance. So you can do long lines cheaper and better if you run one copper wire to the next town, and drive a dirt-rod in each town. This actually started before telephones: many telegraphs used earth return. (And the problem of this scheme, great reception of lighting, appeared in telegraphy long before anybody heard storm-static in a telephone.)

Or.... the signal is weak so you invent an amplifier. All vacuum tube audio amplifier stages have one tube-pin (usually cathode) that is Common for both input and output. And usually common for all stages in a multi-stage amplifier.

With few exceptions, transducers are 2-terminal and naturally Floating.

With few exceptions, amplifiers are naturally 3-terminal for in and out, forcing a Common terminal between In and Out.

And when you have amplifiers, you amplify interference, and this problem is lessened if as much of the amp as possible is connected to a large conducting surface (typically the earth).

A plain naked mike or speaker is Floating. If you add a third terminal halfway along the winding and connect it to something you agree to call Ground, it becomes Balanced (each side same but opposite relative to the "Ground"). If you ground one terminal when you connect to a simple amplifier, it becomes UNbalanced.

A transformer winding is naturally floating, though in many cases we connect one end or a tap in the middle to a ground.

Note that context affects the answer. A dynamic mike with XLR plug is normally floating; but if I use a XLR-1/4" adaptor to plug into a guitar amp with grounded chassis, it is now unbalanced.

So the question reduces to: are the two signal terminals connected to ground....

1) not at all?

2) at one end?

3) smack in the middle?

 

[CJ]

Great answer, as usual.


I might add that in a single-ended line, the signal travels down one conductor and returns along a shield. This is the simplest form of audio transmission, since it is essentially the same AC circuit you learned in highschool physics. The problem here is that any noise or interferance that creeps into the line will simply get added to the signal and you will be stuck with it.
In a differential line, there are three conductors. A shield, a normal "hot" lead, and a third lead called the "cold" lead or "inverting" lead, which carries a 180 degree inverted copy of the hot lead. Any interferance that creeps into the cable thus affects both the hot and cold leads equally. We hope at least. At the recieving end, the hot and cold leads are summed using a differential amplifier, and any interferance that has entered the circuit (called "common mode information" since it is common to both the hot and the cold leads), gets canceled out. Differential lines are thus better suited for long runs, or for situations where noise or interferance may be a factor.
The single ended system is called unbalanced transmission and is very susceptible to hum pickup and cannot be used for low level signals, like audio, for more than a few feet. The differential system is called balanced transmission. A balanced input is sensitive only to voltaqe that appears between the two input terminals. Signals from one terminal to ground are canceled by the the circuit. The simplest way to connect between balanced and unbalanced equipment is with a transformer. The signals are magnetically coupled thru the core of the transformer and either side may be balanced or unbalanced. Good transformers are expensive however, and they are cheaper methods that can be used in some instances.
An unbalanced output can be connected to a balanced input. To connect the balanced output of something to an unbalanced input requires different techniques depending on whether the output is active balanced(each side has a signal with respect to ground) or floating balanced ( for instance the secondary of a transformer with no centertap connection). If it is an active balanced output, you can simply use half of it. Connect pin 2 to the unbalanced input, and pin 1 to ground, leaving pin 3 floating. If this dosen't work, (no or very weak signal) connect pin 3 of the output to pin 1 and ground and leave pin 2 connected to the unbalanced input center pin. Some active balanced outputs, particulary microphones, use the balanced circuit to cancel distortion, so this hookup may result in higher distortion than if a proper balanced to unbalanced converter such as a differential stage or a transformer were used.

cj

 

[Mbira]

Ouch-was that my head exploding? So to keep it way back at the microphone. I understand that the two wires coming off a mic are "floating" with no reference to ground, but then when you have that third wire connected to the body of the mic and going to the chassis of a preamp -the ground. Have those+ and - floating wires now bwcome referenced to that ground and now become "balanced"? Is that ground automatically "in the middle of the two polarities"?