Dual Differential / Balanced?

Nyhifihead
from what I’ve read it only matters if both the preamp and power amp are both truly balanced

That is a belief that is shared by many audiophiles, but it is a misconception IMO. A **well designed** balanced interface may be advantageous regardless of whether or not the internal signal paths of the connected components are balanced or not. And a **well designed** balanced internal signal path within a component may be advantageous regardless of whether or not the internal signal paths of other components in the chain are balanced.

The potential advantages of a well designed balanced interface include reduced sensitivity to cable differences, reduced likelihood of ground loop issues, as well as reduced susceptibility to noise pickup. Of course, as Kijanki mentioned it is not uncommon (especially in modestly priced equipment) for balanced interfaces to perform worse rather than better than single-ended interfaces that may be provided on the same components.

Cleeds
I’m pretty sure that the Integra Research RDC 7.1 is not "fully balanced."

+1. I say that in part because searching the 156 page manual for the terms "differential" and "fully balanced" yields no hits.

Nyhifihead
I was under the impression keeping the signal balanced all the way through with true dual differential output/inputs on the pre and power amp would be the best course of action?

As is usually the case in audio, how good the results are depends less on the design approach that is chosen, and more on how well the chosen approach is implemented. As a general rule of thumb I would expect that monoblock amps, dual mono amps, and fully balanced amps (which mean different things, as Cleeds indicated) would tend to have the greatest likelihood of being preferable choices at price points that are significantly higher than the price range you referred to. Especially given that you need fairly large amounts of power.

Kijanki
...connection with XLR cables is not always the best. Experience of many people on this forum was that RCA connection sounded better than XLR. I’m sure that Al (our technical guru) would agree with me - that balanced output, because of additional circuitry might not always be the best.

Thanks, Kijanki. Per my first paragraph above, yes, I of course agree. It depends on the specific implementation. I’m pretty sure Ralph (Atmasphere) would agree as well. As he said at the end of his most recent post above:

...the McCormick and Pass amplifiers are quite good and accept a balanced input correctly (many high end audio amps do not, likely because the designers don’t know that there is a standard for balanced line operation, defined by AES file 48).

Regarding balanced outputs having twice the impedance of unbalanced outputs, in the majority of cases components providing both balanced and unbalanced outputs utilize similar output circuits for each of the three signals that are involved (two balanced, one unbalanced), and in fact may often drive the single-ended output with one of the two signals in the balanced signal pair. The usual convention is that the balanced output impedance is defined based on the sum of the output impedances of the two signals in the balanced signal pair, so the output impedance number for the balanced output is often twice the output impedance number for the unbalanced output simply by virtue of that fact. Therefore, each of the two signals in the balanced signal pair will often have the same output impedance as the unbalanced output signal that may be provided by the same component, and the statements about output impedance by Ralph and Kijanki are in a sense both right.

My bottom line suggestion to the OP: Don’t choose based on topology. Although I’ll also say that in your stated price range, and especially given your power requirement, my expectation would be that more often than not you would end up with best results choosing a stereo amp (on a single chassis) that has an unbalanced internal signal path. And if it provides both unbalanced and balanced inputs, try both.

Also, for the OP’s info, the advantages and disadvantages of balanced differential design (that being one form of balanced design) are nicely explained in this paper at Ralph’s site.

Best regards,
-- Al

Al, I was looking at overall output impedance that speaker generated EMF sees, and that would be double.

Thanks, Kijanki. When I commented about the doubled output impedance question I had lost track of the fact that you were addressing power amplifier outputs. Yes, **everything else being equal** the load applied by an amp to back EMF from a speaker will be numerically doubled (corresponding to half the damping factor) if the outputs are balanced compared to if they are single-ended. Although in the case of most solid state amps, at least, that is unlikely to matter since their damping factors will be sufficiently high for most speakers anyway. Notwithstanding the belief among many audiophiles that, for example, a damping factor of say 500 may result in better bass control than a damping factor of say 50, everything else being equal. I know from many of your past comments about damping factor that you would agree with my disagreement with that popular (mis)conception.

Regarding your last comment, I believe you are envisioning a balanced amp configuration that is used in some designs in which each of the two input signals in the balanced input pair is processed through its own signal path throughout the amp, that is independent of the signal path through which the other input signal is processed. While I believe Ralph is addressing the configuration used in his (and other) designs in which each stage of the amp, including the input stage, is a differential amplifier that responds to the difference between the pair of signals its inputs are provided with. And I believe that your comments and his are each essentially correct in the context of the kinds of designs each of you is envisioning.

Best regards,
-- Al

Charles & Kijanki, see Ralph’s first post dated 3-22-2013 in this thread for a summary of what is necessary to make a balanced line-level interface insensitive to cable differences. And also for what I consider to be a compelling proof Ralph offers for his contention.

But also note a question I posed a few posts later in that thread, and the answer Ralph provided:

Almarg 3-27-2013
... to eliminate interconnect cable differences is it necessary that the component output actually BE driving a low load impedance (2000 ohms or less, to use your figure), or is it just necessary that it be CAPABLE of doing that?

Atmasphere 3-27-2013
You touched on an interesting point about the load vs the capability to drive that load. I have found that the capacity to drive the load plays a huge role, about 80% but for that last bit of cable artifact to go away the load must be there as well. Flipping the coin over- if the capacity to drive the load is absent, then its moot and there will be cable colorations.

I see that the MA-1 amplifier which Charles mentioned has a specified balanced input impedance of 200K. I’d imagine that one reason Ralph would have chosen to not provide a very low input impedance, such as the 600 ohm standard he refers to, is that most preamps made by other manufacturers would not be able to drive such a load with good results.

Best regards,
-- Al

My thanks to you also, Kirk.  Always great to see you posting here, and for us to have the benefit of your invariably brilliant insights.

Speaking of Bill Whitlock, since the interface-related noise that is being discussed may in many cases be caused or contributed to by ground loop effects, you'll probably find pages 31 through 35 of this paper to be of interest.  To whet your interest, its introduction states that "this finally explains what drives 99% of all ground loops!"

This was called to our attention a while back, btw, by member Jea48 (Jim), who as you may be aware is our resident genius when it comes to electrician-type matters.  I'd welcome any comments you may have on what Mr. Whitlock has to say on those pages.

Best regards,
-- Al
  

Meerzistar 4-25-2016
Who makes these terms up either its a "dual mono" or it is not? I form that in a question because I’m not entirely sure what the rules are or if I’m missing some. I know of some 2 channel power amplifiers that are labelled as being dual mono by the manufacturer yet they have but one power transformer.

As far as I am aware there are no formal rules, and my impression is that different manufacturers use these (and many other) terms with varying degrees of looseness. My single-chassis VAC Renaissance 70/70 amplifier is dual mono even to the extent of having two power cords, as well as completely independent power supplies and multiple power transformers for each channel, while I’m not surprised to see your statement indicating that a so-called "dual mono" amp from some other manufacturer has a single power transformer serving both channels. And certainly there are "dual mono" amps from other manufacturers that fall in between those extremes.

Regards,
-- Al