Quote:
Originally Posted by timoteus
This is from Mick Maloney of Supratek, a highly respected amp builder. What I take from it is you only need balanced output, which saves you money, and that it is best to stay single ended, which I already knew.
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I think the issues we're talking about are really quite separate from his gripe with balanced audio equipment. He's a single ended tube amp maker, and for him there really is no need for the signal path from the source to the amp to have any balanced componants because he only needs a single ended for that type of amp. And I agree with him. But he also seems to be somewhat confusing why high end makes use balanced signals and why professional audio gear has balanced connections.
In the pro audio world where you need to hook up all sorts of gear all sorts of ways in sometimes wickedly dense mires of cable and electrical equipment. In this type of equipment it is common (or I probably should say was common as most things are digital these days) to take an internal single ended signal and run it through a 600ohm audio transformer to make it balanced signal (a normal signal, a miror image inverted signal, and a shield). On the recieving end there would also be one of these 600 ohm transformers recieving the balanced signal and convert it into a single ended signal by grounding one side of the secondary of the recieving transformer and picking the single ended signal of the other side of the tranformer secondary winding. The advantage of this type of signal transmittion is that any time the cable would pick up a stray inducted signal it would be that same on both sides of the balanced drive. But this common mode (same on both wires) signal can't flow through the recieving transformer primary winding it gets rejected and won't interfere with the balanced mode signal making through the wire and into the next box. THis is called "common mode rejection" and is very important in tranmission lines. There are other ways to get high common mode rejection , with differential input amps amps for example.
NOw in high-end, single-ended stereo systems there isn't nearly the problems with needing to send signal long distances past lots of stuss spewing our stray and noise electromagnic fields, so there isn't much need for balanced transmission line techniques for common mode rejection of noise. BUT! When it comes to gripping a speaker (or headphone driver) by the cahones and forcing it to do what you want using a balanced drive is just the ticket.
Usually a speaker has a hot lead and a ground lead. On a headphone you have a hot lead to each driver and a common return wire that is shared by the ground return currents of both drivers. With a balanced drive, both leads are "hot" with audio signal; one is the normal signal and one is an upsidedown mirror image of the normal signal. When one is going up the other is going down and vice versa. This means that the speaker coild is being driven from both it's leads in a push-pull fasion. (Push-pull is really a term usually resrved for a certain type of amplifier output technology, but it presents an apropriate picture here.) It's like driving one speaker with two amps: each amp sees half the load; because as one goes up the other goes down you get twice the slew rate; and your driving the speaker with twice the power. It's a good thing.
Back to the signal being turned unbalanced to balance in the gear. In audiophile gear this rearly happens. In a truly balanced audiophile system the signal is NEVER in an unbalanced mode. For example, in a balanced phono stage the two wires coming off one one channel of the cartrage coil are each sent through separate but identical sets of electronics stages. In other words any high end balanced piece of gear is basically a four channel audio device: left+; left-; right+; and right-. In high end digital to analog converters there are FOUR d-to-a converters, one each for the above channels. [not promotional] For example in our Home and Max Balanced amps our DAC option has four d-to-a chips so that it is truely a balanced amp.
So what about if you want to go from something that is single ended (has RCA connectors) tosomething that is balanced (XLR connectors which hav two signal wires and a ground. The cheap way is to put the signal through a tranformer and use the secondary leads as the +/- signals. Sure you can use some very expensive and exquisite transformers, but there are phase splitting circuits that don't make you have to deal with the messy inductive/capacitive problems of driving a transformer with extreme precision. But hear to, in the end you almost allways end up with a slightly less than perfect mirror image copy of the origional single ended signal. That's the real cost of a balanced headphone system: you not only have to cough up the bucks for double the headphone amp and custom cabled headphones, you also need to buy a truley balanced front end to make it worth while. Systems like this easily run into 5 figure price tags.
On a personal note: I swear if I keep writing posts like these I'm never going to hit supremous status. There should be a catagory high word count per post ratio and I swear I'd qualify for that one.
