For a wire run as short as that between the phono pickup and the preamp the benefits of balanced lines would not be significant.
Microphones have low level output, like phono pickups, but are often used with very long cables, and I bet that some mic preamps accept balanced line input. A mic preamp that I have has only single ended inputs, but it has a switch to cut in RIAA equalization so that it can also be used with a phono pickup. Your job is to find a mic preamp that has both these features. Start with the Shure catalog.
I like the questions you are asking. I have a balanced tonearm cable (hovland din to xlr) into a BAT vkp10SE with fully balanced inputs. It helps. More queit background, bigger stage. It wasn't huge, but did help. Also, I have a friend with a Io, that recently swithed to balanced off the cartridge. Simlilar experiences.
I wish I could answer your questions, but my personal experience leads me to believe you are making good assumptions.
i know an individual who runs 2 krell kpa's, balanced, one per channel. the connection is as you are wondering balanced from cartridge to phono stage to pre to amp...this is what i would call a true balanced system.
the kpa is otherwise a stereo unit
one of the better questions out there and one that requires a manufacturer to question why they go to single ended operation when the balanced is naturally available.
Great question. But phono signals are not balanced. They are floating. A balanced connection requires three signals, positive phase, negative phase, and reference (commonly ground). Cartridge coils have only two wires per channel. For balanced, the coil would have to be center-tapped.
That's the main reason it isn't done. However, one trick will do the job; you can receive with a center-tapped transformer. Tie the center tap to ground and the cart now has a solid low impedance common mode connection and you get positive and negative relative signals.
Many phono stages that have XLR inputs don't run true balanced or differential mode. They just tie one of the phases to ground.
My Trumpet Phono is fully balanced throughout, front to back. I suppose the BAT is too. Not sure anyone else is doing it.
Audio Research's PH2 was balanced ins and outs only. It is a fine sounding unit.
Mr. Hagerman exposes my lack of understanding of some of the finer points. I've read statements to the effect that "all phono cart's are inherently balanced devices" in audio magazines on a few different occasions, though I'm sorry I can't make specific citations. It's self-evident that a cart would generate a +/- voltage swing instead of +/0; that a cart should 'float' does also seem obvious, but the distinction regarding this vs. a 'balanced' condition is apparently where I (and some audio writers) went astray. (Though why the one will give you common-mode noise rejection and the other not is another can of worms I think I'd best leave unopened for the present...)
Having said that, JH's introduction of the topic of transformers seems tantilizing, since of course step-up trannies are commonly employed to add voltage gain for low-output MC's. Since I've always stuck to medium-output models going straight in, I lack the experience with step-ups, but is it common practice for these to be center-tapped and offer true balanced output? Again, sounds like a no-brainer if you're already using the tranny anyway.
P.S. - We could add Boulder to the list of true balanced phono pre's (but we couldn't afford one ;^)
Is there a problem with single-ended phono pickup connection? Not that I know of. Why solve a problem that doesn't exist? (Well I guess it's just for fun).
The floating vs balanced thing did occur to me, but if you tie together two of the four pickup terminls it looks like a center tap of the two-winding pickup.
Eldartford: My own experience with balanced connection in general is much like that of Jfrech and Sayas. I'm speaking specifically here of running a balanced source (in my case, a DAC) into a balanced preamplifier and doing instantaneous, level-matched A-B comparisions between balanced and single-ended connection. My assumption is that if there can be a worthwhile improvement with such a robust source (in the sense of output level and resultant S/N ratio) and short, well-shielded interconnnects, it stands to reason that a potential improvement at least as great, if not greater, could be had for a phono connection. And with the preamplification of the phono signal, again, the high gain factor required would lead me to believe that if balanced amplification is beneficial anywhere for its noise- and distortion-cancelling properties, it could be even more so here.
When it comes to sources other than phono, much gear does not offer a true balanced output, and to do so would necessarily be more costly, all other things remaining equal. So my holding the impression, reinforced by some audio writers, that all phono cart's, as a catagory of source, were naturally balanced devices as-is, to me obviously begged the question. To say there's not a 'problem' with single-ended connection and therefore we needn't worry is to miss my point - improvement is improvement, especially when it's conceivably available without having to start over with a new source (cart) purchase. Phono is noisy. I'm just trying to see if this is a way of making it less so.
I gotta agree that balanced connections are the way to go. Heck, that's why my top phono stage is done that way. It's beneficial in both interconnects and amplification. So many inherent benefits. The problem is that it costs so much, twice as many tubes!
Still, (to be a pain in the axx), you can't make a balanced signal generator with just two wires. +/- is the same as +/0 and 0/-. They are all identical.
Hagtech...A balanced line can be implemented with a two terminal source by leaving both the source wires ungrounded and providing a ground reference through a pair of resistors at the destination input. This configuration was used for powering AC tube filaments before we had good low voltage/high current diodes to provide DC. The resistors were usually implemented by a rheostat, ground on the slider, which was adjusted for minimum hum.
Zaikesman, I think Hagtech's suggestion is not difficult to implement if you use step-up transformers for MC cartridges. Just order step-up transformers with center-tapped at the secondary windings. In addition, as the signal from the catridge is noise canceled at the first winding, you get the advantage of balanced design at the input of step-up transformer. You have balanced all the way.
Yeah, you can receive the cart balanced using the tranny trick. As Eldartford mentions, you can also do it using a difference amp and matched resistors to a common mode voltage (such as ground). This, however results in a high common mode noise source of 47k ohms not shunted by the cart. So really, the source is more of a "floating" signal instead of balanced.
It's all relative.