Post Number: 22
|Posted on Monday, December 05, 2005 - 12:08 am: |
A friend and I were discussing sound reinforcement and were wondering why no one (with few exceptions), including high end mfgs., use balanced cable and jacks for guitars, basses, or amps. Is there a good reason for this or is there no benefit to using them? Just curious.
Post Number: 2153
|Posted on Monday, December 05, 2005 - 12:20 am: |
I AM a technical moron!
Wat is a "balanced" cable???
Used by thight-rope walkers???
Post Number: 23
|Posted on Monday, December 05, 2005 - 12:32 am: |
Hi, As I understand it, a balanced cable uses a tip-ring-sleeve (TRS) plug as opposed to a tip-sleeve plug. This means that there are 2 conductors plus shielding (like an XLR) as opposed to 1 plus the ground. As I understand it this eliminates noise by cancelling it out. I have a very basic knowledge of this myself and was wondering if anyone could help me out? And yes, I suppose incredibly stupid and/or brave circus performers could use it for tightrope walking.
Post Number: 3
|Posted on Monday, December 05, 2005 - 8:00 am: |
A balanced cable cancels out the hum and noise picked up by the cable, more critical the longer the cble length. It is more crtitical with Microphones, as low power signals are more prone to noise than at line level. A balanced cable will work, however, I wish the FX-1 had Transformer Balanced TRS connections, as the Cannon style probably will not fit. I always wondered if that could be added...
Post Number: 24
|Posted on Monday, December 05, 2005 - 8:56 am: |
I've used the XLR jack as an output to the amplifier (set in "post" mode) and it works well. Please read the following response sent to me by Rick Turner. There seems to be some value in it, but no one does it on a regular basis. Maybe someone at Alembic will respond with their take on this subject.
From Rick Turner:
No, it would not necessarily be true if the noise were generated in the instrument itself.
I have done balanced pickups and onboard wiring with low impedance passive pickups, then going to a studio mic preamp. This was with close to 600 Ohm Litz wire wound pickups. It worked fine, probably better than fine; it sounded great in fact. The only problem is that it is so non-standard that there's little commercial reality to it.
One of the guys who used to work at Bass Player had a set of J-bass pickups I did this way, and he said the only thing bad about them was that he could hear how bad the strings were on his bass. The clarity is amazing.
Rick Turner, Luthier
Renaissance Guitars and Basses
Post Number: 121
|Posted on Monday, December 05, 2005 - 5:04 pm: |
The balanced line is preferred for long cable runs with low level signals because it allows for better shielding and much better resistance to picking up emitted electrical interference.
In a regular, unbalanced guitar cable the signal is carried on a center conductor of your cable. Every circuit needs a return path, and in a regular cable this is the woven or foil shield which surrounds that center conductor. Because the signal level is low there needs to be a shield that will try to carry electrical noise off to ground, and in this case, that shield = ground = part of the signal path. The conductivity of the center conductor and the shield aren't matched so that may affect signal quality (this is part of why long guitar cables lose treble).
In a balanced cable, there's a separate matched pair of wires for signal + and - and they're insulated and twisted together their entire length. There's a shield around that that's completely electrically isolated from the signal carrying pair. So the shield can now intercept electrical noise and shunt it off to a ground which is completely independent of the signal. The signal wires are a perfectly matched pair so the electrical characteristics are more ideal.
The core difference between balanced and unbalanced is something really clever. In an unbalanced system, the center conductor is carrying the signal which is relative to ground. The amp takes that signal and amplifies that, but because any noise that the shield intercepted is being dumped into the ground too the amp will amplify that too.
In a balanced system, the signal comes from the microphone or pickup and goes into one side of a matching transformer. The other side is connected to the signal lines in the balanced cable. Because of the way that transformers work, what comes down the cable is "differential"; the difference between the + and - wires is equivalent to the original signal and can be recovered by using a matched transformer on the other end. There's a bunch of interesting things about differential signals, but one neat thing is that the transformers can passively change the voltage so it's a higher level signal passing down the wires (which is more immune to noise pickup). Another neat thing is that any electrical interference that's picked up along the way is induces the same absolute signal in both sides of the signal pair but since they're "subtracted" from each other at the receiving end, that induced noise will be cancelled out (and the shield is more effective now anyway). That's why the signal pair is twisted - even though the two signal conductors aren't physically in the same space, when it's averaged out over a twisted pair, they are effectively equal. It's way cool.
The bad part about balanced connections are that they are a lot more expensive - it will take twice as many conductors in the cable, and you'll need transformers on both ends. For electric guitars, they just didn't start out that way, and haven't really changed since.
I think this actually goes all the way back to Alexander Graham Bell who was a very, clever guy.
Post Number: 515
|Posted on Saturday, December 10, 2005 - 9:14 am: |
I'll proudly lump myself in with Brother Paul as a technical moron.
As I understand it, this balanced/unbalanced business is separate from impedance. Les Paul always griped that guitars should have been low impedance for the obvious advantages of cable length, lower noise, less freq attenuation, etc.
And this all gets more confusing as I tend to think 'low impedance' always implies XLR connectors, which usually implies balanced connection, both of which ain't necessarily so.
Then we speak of 'low impedance pickups' and it just swirls in my head in a dizzying fashion.
I recently spoke to Butch Ammons at Bayou Cables who repeated something I've heard before: As regards some short patch cables (2') for an in/out, send/return loop between my amp and a G*Force processor, he advised that the balanced cables aren't needed for these short runs. I understand it, but yet 'by the book' it should be balanced. Even TC repeats this in the manual.
Can you suggest any good reads so I can begin to untangle this ball of snakes?
J o e y
Post Number: 2172
|Posted on Saturday, December 10, 2005 - 11:43 am: |
Let's make a deal!
As soon you understand it in your lingo you explain it in real moron-lingo to me ...like we did with set up Alembics ...hope I'll get there once understanding what I am playing thru
Post Number: 125
|Posted on Sunday, December 11, 2005 - 8:35 am: |
Your observation about cabling is correct - balanced/unbalanced is completely independent from impedance and also separate from the connector issue.
As I mentioned above, the distinction between balanced and unbalanced has to do with how the signal is being carried. If it is carried as an absolute waveform relative to ground, then it's unbalanced. If it is carried as the differential between two lines (and independent of ground) then it is balanced. Because of the requirement for two signal lines separate from ground, a balanced setup will always require more conductors in the cable. As you can guess, these are the three pins of a regular (microphone) XLR connector - the two signals and the ground pin which is connected to the shell and to the shield of the cable. You can also build a balanced cable with a TRS "stereo" headphone jack, but this is not a normal configuration.
Impedance is somewhat complicated. It's sort of the alternating current (AC) analog of resistance in direct current (DC). Things like coils of wire (in your pickups or speakers) and magnets don't have complex effects on resistance because a DC signal doesn't create an electromagnetic field. AC signals do all that and the result is that the impedance is dependant on level and frequency. Mathematically describing things like impedance require the use of complex/imaginary numbers which is making this discussion worse rather than better!
You can sort of visualize impedance if you think about shaking a rope that's tied to the wall to make a wave pattern. If you made a new rope with a heavy piece of rope tied to a light one and shake it you can see that the wave that arrives at the wall will look different than what you sent (probably bigger). If you were shaking the light end the resulting wave at the heavy end would be smaller and, if you shake hard enough, you'll see some of the signal reflecting back into the light section at the junction with the heavy. This doesn't really model what's happening with impedance, but you can get a sense of what mismatched impedance (the different thicknesses of rope) might have.
Just to make things a little more confusing, it turns out that the optimal setup for audio isn't matched impedance. You actually want the output impedance to be significantly lower than the input impedance of the amp for the best fidelity.
The traditions of high-Z and low-Z levels go back to the early days of electric instruments. If you wind more wire on the pickups, you get more signal out which means you have a better chance of getting the signal to the amp without too much noise. That's the way the original pickups and amps for instruments were made and it remains that way to this day. You can make a low-impedance pickup by winding less wire on the coil (which improves high-frequency response as well) but the natural output level of the signal is too low to go very far. The way that was solved for microphones was that they include an amplifier at the microphone to boost the signal which could then be passed over a low-impedance (and usually balanced) connection.
Alembic was the first manufacturer to really push onboard active electronics back in the 1970s. By adding onboard preamps with low-impedance output, they eliminated cable losses, etc. Just as balanced and lo-z are not strictly related, having active electronics is also independent but often all three are bundled together.
For short cables (I would think that 10') should still be OK, there's nothing wrong with regular old unbalanced cables. When you get to 25' with passive pickups you definitely will be having an audible effect. If your effects have unbalanced inputs and outputs then you'll require matching transformers to have balanced cable runs, so it's definitely not worth it. If you have effects with balanced ins and outs, you'll get better sound if you use them and the rest of your system can too.
I wish that I knew of good reading material on this, but I don't off the top of my head (it was pounded in there many years ago in college). But I'll keep an eye out.
Post Number: 518
|Posted on Sunday, December 11, 2005 - 8:46 am: |
J o e y