The way I understand it, in most devices except phone cartridge output, the signal is in a combined state (unseparated) and to get it to balanced, it has to go through another set of circuitry to separate the signals into balanced componenets for the XLR output. Whereas the RCA output does not go through the additional circuitry. And at the other end (e.g., my Krell) it has to go through the reverse process to recombine the signal.
In other words keeping the signal on the unblanced RCA path results in a circuit path with fewer components. Thoughts?
If you have a differential input with any kind of decent Common Mode Rejection Ratio, the input transformer is really just a formality, serving nicely to limit RF input, which can wreck havoc on class D systems.
In most solid state and vacuum-tube balanced differential setups, as much care should be taken as possible to limit RF out-of-band intrusion as possible (of course, this is true of single ended circuits as well- RF isn't good for **anybody**).
What happens is out-of-band for balanced also means that it may not be balanced anymore either. Rectified RF can thus be amplified, just like in SE circuits. This is avoided by chassis work that shields RF (aluminum rather than steel), proper grid/base/gate stop resistors, proper grounding and proper B+/Vcc/Vdd bypass, just like in SE.
RF frequencies within-band will be rejected, just like high frequency AF noises (like from a power line or motor).
There are fully-differential true balanced line high end audio products. Since 1985 all Atma-Sphere products have been fully-differential and balanced in every aspect from input to output. Our MP-1 was introduced in 1989 and appears to be the first balanced line preamp made for home audio use.
One more thing - Input does not have to be directly an OP-Amp. It could be, and often is, coupling transformer. Transformer is a very effective method of removing common mode, breaking ground loops, blocking DC and limting rf (filter).
Transformers add a little THD at the lower frequencies. Rowland is using very good Lundahl input transformer in their new Icepower based amps.
Bob - you asked "For example, if an op amp has a bandwidth of 10 MHz, what happens when its fed a 100 MHz signal?"
Most likely RF rectification - conversion to DC or low frequency noise if 100MHz (or higher frequency) is modulated. It is caused by different response for positive and negative slope and is present in practically all OP-Amps or Instrumentation Amps.
OP-amp should always have RC filter if front of it to prevent it. Common mode rejection of differential (balanced) connection works at lower frequency range while normal mode rejection (filter) prevents RF rectification.
I prefer to stay with the design of the system. If the components are not truly balanced to begin with then I try to stick with RCA connectors.
I go with the alternative balanced connections when I am running the signal to a secondary listening area as this is the only alternative since my pre has only one set of RCA and another set of outputs that is balanced.
In reality there are very few sets of components that are truly balanced to begin with.
Eldartford is right on the money. There is so much confusion about this I used to actually print and hand this pamphlet out to seasoned pros who were still debating the pin 2 pin 3 hot issues. Handy for the DIY types or for general snake oil detection.
It's my understanding that while fundamental RF is not much of an issue because it is too high in frequency, spurious lower harmonics can be picked up down to the lower limit of RF of around 3K.
With balanced systems and cables you also eliminate ground as a signal reference which can pick up and carry noise and RF.
The more important point I was trying to make is that balanced systems eliminate lots of noise that is more subtle than just the gross 60hz hum or loud obvious hiss heard through the speakers. In unbalanced systems, noise is intertwined with the music in subtle but profound ways that are not noticed until you hear that noise removed by a balanced system.
Bob...RF signals will not get through either the (+) or the (-) input of a balanced interface, so talk about how such signals are cenceled is meaningless.
Bob...Exactly my point. Although some op amps may be usable at RF frequency, the ones used for audio applications, especially when wired up in an audio circuit probably max out at 250 KHz or so.
Balanced interfaces do a great job on 60 and 120 Hz hum.
Davemitchell...Please explain how a differential amp input stage having frequency response appropriate for audio signals can reject signals at RF frequency.
The false notion that balanced operation is really only beneficial in studios and for very long cable runs, pops up every time a balanced vs. single ended discussion occurs.
Balanced is beneficial no matter how short your cable runs are. The common mode rejection in a truly balanced differential system will eliminate RF picked up by circuit traces as well as cables, both of which act as antennae. The noise reduction benefits go far beyond the gross example of hearing noise when putting your ear near the speaker.
Noise in audio gets woven into the fabric of the music and reduces our ability to hear subtle details. A properly executed balanced system will remove layers of noise that you didn't know were present. Music emerges from a quieter and "blacker" background with better clarity and resolution as a result.
Are there great sounding single ended systems? Absolutely. Is balanced necessary to achieve superbly musical results? No. But when executed properly, balanced is better. The only catch is that the system will become more revealing or less forgiving, so if there are tendencies in the system toward brightness, sterile sound, or anything else you don't like subjectively, you may hear more of it when running balanced.
On an electrical circuit way of thinking balanced always seemed "BETTER" to me...Now to the world of sonics brought to you by your instruments--your ears!! I have been through the balanced/ unbalanced system changes and comparison for 10 years now and must state in all cases I have found single ended rca to be sonically superior for home critical listening.......Thats my take... Ended up with a Quad amp and preamp and can say without a doubt the quads run with the balanced Quad Links are flat sounding...lacking definition,drive and richness in tone. Add Cardas golden and neutral reference into the game and " yes, that sounds great"... Now, comments such as, the cardas are better cables and that if the Quad Links were of superior construction balanced would again reign king. Can't buy that because have had similiar results with Krell, BV audio, Cary and Anthem to name a few. Possibly on stage with long runs in the concert hall or at the McMansion with a 200 ft. run from Audio Room to the Library it is better. OR--possibly I like the distortion and "noise " inherent in single ended set ups-- I don't know and I guess no longer care..... Good Luck spending that Buck--as they say in Gitsonia- "let your ears do the choosing"
By the way, the noise immunity of balanced lines can be achieved using active circuitry only in the receiving end of the connection. The HI wire of the balanced connection carries the single-ended signal. The LO wire is simply connected to the single-ended return (usually ground) through a resistor of value equal to the output impedance of the active signal. The LO wire picks up the same noise as the signal wire, and the noise is cancelled by the differential input circuit of the receiver. Clever.
Yes that is true but the logic that says "simplification" or "purity" improves sound quality is actually a bit of a misnomer. Understandably, it appeals to our logic. To show that this is an audio "myth" - simply think of an old Edison cylinder or Victrola with not one electron between the needle and the resonating diaphragm....the "purist" mentality is actually pretty wooly but it makes great marketing brochures!
The additional circuitry is a unity gain stage, which inverts the signal. Unity gain stages are easy to design and build with virtually no distortion or noise, so I wouldn't worry about that. The balanced interface is much more immune to noise pickup, and almost unaffected by wire characteristics (which make some single-ended interconnects so expensive).
On the other hand, especially for short runs, single-ended interconnects are fine. Only replace them if you experience a problem, or if the equipment you bought, for other reasons, happens to have balanced interfaces. (Or if you need status points among your audiophile friends).
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