Why Single-Ended?

Thanks, Peter. Regarding the first point, yes, a provision that an RCA input is to be used in conjunction with a jumper inserted between pins 1 and 3 of an XLR input likely reflects a grounding approach in the design that is non-optimal at best.  Such as pin 1 being connected to signal ground, or signal ground and chassis ground being common.

Regarding the second point, my comment addressed the inputs of power amps, that do not provide a volume control.

Best regards,
-- Al

Lowrider, if you were to change from an amp having a single-ended internal signal path to a fully balanced amp I would expect that the differences in the intrinsic sonic characters of the two amps, and perhaps also differences in their interactions with the particular speakers, would most likely greatly overshadow whatever difference may result from providing that amp with an unbalanced vs. a balanced input. Also, my guess would be that finding a fully balanced preamp providing sonics that are as much to your liking as those of the UV-1, for a comparable price, would be a tall order if not impossible.

Regarding your mention of impedance differences, many amps providing unbalanced and balanced inputs connect the center pin of the RCA connector directly to one of the two signal pins on the XLR connector, usually the non-inverted input on XLR pin 2. When the RCA input is used in those cases the unused signal pin on the XLR connector is simply grounded, via either a jumper inserted into the XLR connector or via a switch on the rear panel. And in those cases the doubled impedance that is usually specified for the balanced input, compared to the unbalanced input, simply reflects that the balanced input spec is based on the sum of the input impedances of the two balanced signal lines. So in those cases connecting an unbalanced signal to the XLR input via an adapter, for example, would result in the same input impedance as connecting the unbalanced signal to the RCA input.

Best regards,
-- Al

Can somebody give definitions and explain differences between ....

First, keep in mind that these terms are often bandied about in a loose manner, and some are inherently ambiguous. So you may frequently see a given term used to mean different things. And there may be legitimate disagreement about some of the following definitions. But FWIW I’ll give it a shot.

Single-ended: Either not balanced or not push-pull, depending on context. I have interpreted the OP’s question as referring to "not balanced."

Balanced: If referring to a pair of signal lines, the two lines have equal impedances relative to the ground of a circuit, or the two lines are not referenced to a ground. If referring to a pair of signals, the signals have nominally equal amplitudes but opposite polarities. If referring to a circuit or component, the circuit or component processes signals having nominally equal amplitudes but opposite polarities in a symmetrical manner.

Truly balanced: Not a technical term, but sometimes used to distinguish between an XLR connector on which a balanced pair of signals is present, and an XLR connector on which just one signal is present. Also sometimes used to mean "fully balanced."

Fully balanced: The entire signal path of a component is balanced.

Differential: A circuit within a component, or the entire signal path of a component, responds to the difference between two input signals. May also refer to a form of balanced design in which the signal path of a component consists of a series of differential circuit stages.

Differential balanced: Usually used in a loose manner to mean "fully balanced."

Full differential: Usually used in a loose manner to mean "fully balanced."

Truly full balanced: Usually, a somewhat redundant way of saying "fully balanced."

Truly full differential balanced: Usually, a somewhat redundant and clumsy way of saying "fully balanced."

Regards,
-- Al

Good to see you back here, Herman.

Not sure that I agree with you, though, regarding:

BTW despite what Ralph contends phono cartridges are NOT balanced as there is no ground, no ground pin connection, only 2 lines out.

All sound sources are single ended, compressions and refractions.

When you get to the speaker they are all single ended, they move in and out, no balance.

It is true, of course, that when a cartridge is not connected to anything its output is "floating" with respect to whatever ground reference one may choose to define. However if the two output lines of the cartridge are connected to a properly balanced input of a phono stage, both the impedances and the signal amplitudes of its two lines will be balanced with respect to the ground of that phono stage. In other words, the nature of a cartridge is such that connection of its output lines to a balanced input causes its output to become balanced.

The same goes for a speaker, when connected to a power amp having balanced outputs.

Compressions and refractions (I think that should be "rarefactions") that occur in the air as acoustic waves propagate are a different and unrelated matter, as I see it.

Regards,
-- Al

DB, yes, it appears that the JC2 BP does not provide a tape loop or anything equivalent, so assuming you have more than one source I don’t see a way of connecting the KUBE into the system other than between the preamp and power amp.

Kijanki, thanks. It’s interesting, though, that the Pass amps which are fully balanced and therefore presumably have minimal even order distortion (for example, John Atkinson’s measurements of the XA30.5 state that its "THD is almost pure third harmonic") seem to generally be considered as having a sonic character that is a bit on the warm side. As always, there are countless factors that contribute to the sonic character of a design, in addition to its basic topology.  And therefore, as you said, "I would buy an amp if it sounds good and not because it is fully balanced."

Best regards,
-- Al

+1 Charles.

Regarding this comment in Kijanki’s post:

In order to provide good common mode rejection two halves of FULLY balanced amp cannot be independent. Negative cross-feedback has to be used to equalize gains of each half and that might be far from perfect.

With some fully balanced architectures the need for negative cross-feedback, or even any feedback, can be minimized or avoided. For example, Ralph’s designs employ an architecture based on differential stages, and are typically spec’d as using just 1 or 2 db of feedback. And in the solid state domain many fully balanced Ayre amps employ zero feedback, and I believe most or all fully balanced Pass amps use very minimal amounts of feedback.

Also, as stated in one of the papers at Ralph's site, "for a given number of stages of gain, differential amplifiers have about 50% more parts," rather than being closer to the equivalent of two single-ended amps that are otherwise comparable. Although with some other balanced architectures the parts count may indeed be close to double.

Best regards,
-- Al

DBPHD, for the benefit of others who may respond I’ll mention that the manual for the JC2 BP states that it "uses a fully differential balanced circuit and its balanced outputs do not require or use phase inverters." Also, while as far as I can tell from its literature the JC1 does not appear to be fully balanced, it is described as using a differential input stage. And the manuals for both components recommend balanced connections where possible.

So what you might consider doing, at a cost of a bit under $600 plus some additional cabling, would be inserting Jensen transformers between those components and the inputs and outputs of the KUBE. Or, at a cost of around $300 plus some additional cabling, only between the KUBE and the power amps.

Those would convert the unbalanced signals to or from a true balanced pair of signals. They would provide essentially the same noise reduction benefit and reduced susceptibility to ground loop effects that a well designed balanced interface between components would provide. In this particular case, however, I doubt that it’s possible to predict whether the net result would be an improvement, or little or no difference, or perhaps even a slight loss of transparency. Reports here by users of Jensen transformers have generally been very positive, although a few, including Ralph, have provided comments that are a bit mixed.

Suitable models would be the PI2-XR at the input side of the KUBE, and a pair of model PI-RX located near the inputs of each of the amps. Here is a good supplier, although they can also be ordered directly from Jensen, at a slightly higher price in some cases.

Regards,
-- Al

In addition to the good points that have already been made, I would cite the following highly technical and abstruse factor: Traditions die hard :-)

Related to that, I'd imagine that a factor in many cases is that designers tend to use approaches they are familiar with, and that build upon their previous work, unless there is a compelling reason to change. And the fact that any given design is likely to be used in many systems in conjunction with associated components that are single-ended would seem to make the case for change less compelling.

Finally, making a design fully balanced adds complexity, and with it presumably more opportunity to go wrong, and more opportunity for the design and development process to become more costly and lengthy than desired. Especially if the designer has not previously used fully balanced approaches.

Best regards,
-- Al