Just one note of caution. XLR cables made all the difference for CMNR in connecting my Allegri Reference to my Wavelet. Should they? Maybe not. But there’s no mistaking the difference. Precisely because it shouldn’t have mattered, and many Iconoclast users report preferring the RCA to the XLR—albeit slightly—I tried the RCA. They went back via return mail the next day, not because of SW but because of noise.
No, I am not sure. It is getting confusing, with 2 different power amps that I am not familiar with. And using a XLR cable out from a single ended Allegri does not make it more clear.
I will have to study, and see how the XLR out of the single ended Allegri is working, and how these XLR cables are made (pin and shield architecture).
I’ll get back here when I understand.
There are a number of issues to settle when comparing XLR to RCA cables even in a single ended setting. Firstly are you comparing like with like ?
The cable itself RCA v. XLR of the same brand and line may be of different constructions or may be the same cable internally just connected differently. In the latter instance the impedance is likely to be nominally incorrect for one or the other (assuming e.g. if following AES standards) . The connector hardware can also make an audible difference. Neither RCA or XLR can properly maintain the correct 75 or 110 ohm standard due to their design but some more recent RCA designs ( e.g. WBT second generation) are better than their predecessors . Further by use of plastics where metal would have previously been used they are less prone to parasitic eddy currents ( e.g. WBT and Eichmann). The only XLR connector that I am aware of that follows this path is the Vampire Wire one.
Of course any comparison is also open to subjective preference anyway.
Finally there is a question of how well the equipment manufacturer has implemented each type of input. An equivalent competence for both should not be assumed 
Given these variables I guess that the final choice needs to be made on a suck it and see basis, balanced or single ended even if theory says that a properly balanced cable with balanced transmitting/receiving circuit should always reject more noise than a single ended one.
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Agreed. Sometimes there is no other way. If trying a new cable, make sure you can return it.
Agreed here as well, though as Iconoclast explains, they have gone to substantial lengths to make sure their respective RCA and XLR cables are as identical and AES compliant as possible.
Please read the article at the following link, to firstly understand in detail what is single ended, balanced, psuedo balanced, floating balanced and hard balanced.
Understanding is needed to cope with these 6 cases:
- Connecting mains floating unbalanced outputs to mains grounded balanced inputs.
- Connecting mains grounded unbalanced outputs to mains grounded balanced inputs.
- Connecting floating balanced outputs to floating unbalanced inputs.
- Connecting hard balanced outputs to floating unbalanced inputs.
- Connecting floating balanced outputs to mains grounded unbalanced inputs.
- Connecting hard balanced outputs to mains grounded unbalanced inputs.
If there is still no blood running out of your ears 
then we can go to look into what exact kind of outputs and inputs we are talking about here, and what cabling should be used, with what kind of internal architecture.
We need to determine the entire chain, from source, through preamp, into power amp. So we need to determine the blanks below:
1. Source:
dCS DAC: Analogue Outputs:
Output levels: 0.2, 0.6, 2 or 6V rms for full-scale preamp or power amp input, set in the menu.
a. Balanced outputs: 1 stereo pair on 2x 3-pin XLR male connectors. These outputs are electronically balanced and floating.
Output impedance is 3Ω, maximum load is 600Ω (10k-100kΩ is recommended).
b. Unbalanced outputs: 1 stereo pair on 2x RCA phono connectors.
Output impedance is 52Ω, maximum load is 600Ω (10k-100kΩ is recommended).
2. Preamp: Analogue Inputs:
a. Balanced:
b. Unbalanced:
3. Preamp: Analogue Outputs:
a. Balanced:
b. Unbalanced:
4. Power amp: Analogue Inputs:
a. Balanced:
b. Unbalanced:
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After some studying, this is what I found:
For the Allegri Reference passive, autotransformer volume control preamp:
Input: pseudo-balanced input, with on pin 2 of the XLR signal, and on pin 3 ground. [Pin 1 (ground) on the balanced XLR out from the dCS source is not connected, so ignored] Maximum signal level: 4V RMS 8Hz; 10V RMS 20Hz and up. At -10dB (normal listening) input impedance is 200kohm, for a power amplifier load with 20kohm input impedance.
Usual balanced pin assignment: Pin 1 ground - Pin 2 positive signal - Pin 3 negative signal, so the Allegri drains the negative signal from the dCS to ground. A simple method of driving a balanced line is to inject the signal into the “hot” wire through a known source impedance, and connect the “cold” wire to the signal’s local ground reference through an identical impedance. Due to common misconceptions about differential signalling, this is often referred to as a quasi-balanced, pseudo-balanced or impedance-balanced output, though it is, in fact, fully balanced and will reject common-mode interference. Internally, the Allegri’s design remains single-ended throughout, since there is no negative signal coming in, as opposed to a differential amplifier.
Output: transformer based floating balanced XLR pair, and unbalanced RCAs. This practice also assumes that the balanced input of a following power amplifier has proper differential summing.
To maintain the integrity of the Fractal™ wired transformers, Townshend strongly advises to use their Fractal™ Interconnects for both the input and output cabling. The balanced version of Fractal-Wire™ incorporates two strands of the ultra-fine enamelled copper conductor spiralled together with a parallel drain wire but no shielding, it is terminated with Neutrik XLR plugs. In the unbalanced version, the signal travels through a very thin polyester coated enamelled copper wire, which is spiralled around a much thicker bare copper ground. But technically, all standard XLR cables (balanced pin assignment: Pin 1 ground - Pin 2 positive signal - Pin 3 negative signal) will work.
The Allegri has no active or amplifying audio electronics in the signal path. However, the sources used must have sufficient output to drive the following power amplifier via the controller to the required maximum output power, with some headroom for those quieter recordings.
So, if I understand correctly, setting up the Allegri between a dCS source and a power amp, you will get best SQ when using XLR cables for both its balanced input and output. 6V out from the dCS source will work best. Depending on the balanced input sensitivity of your power amp, you can set the Allegri’s minimum attenuation according to the table posted above, using the formula also posted above to determine its line out voltage.
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Excellent research there Erno 
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Thanks Erno. That helps explain why I have less noise in my system with Iconoclast XLR cables. FWIW, I like the Townshend Fractal cables a lot, and they are much easier to route than Iconoclast, but I prefer to have the same cables throughout, and my brain has convinced my ears they sound slightly better.
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Erno thank you so much for all the research and the patient explanations for people like me. I’m happy to say that your advised configuration is working out as well for me as it has for Greg.
I’m sure it’s hard to grapple with some of the different scenarios, particularly when some of them are hypotheticals for now.
I don’t (yet) have any of the T+A gear, but know that they’re going to feature in an upcoming audition. The things I’ve learnt on this forum (and tried at home) have meant that I now approach possible purchases with a bit more thought than I used to. Seems some time spent matching equipment pays off! Hence me trying to work out whether I should consider T+A’s PA3100HV integrated or the A3000HV power amp with the Allegri Reference that I love so much. Your posts are helping enormously.
Speaking of which…and bringing this post a bit more on topic…I spent a very, very enjoyable weekend working out whether it would be the Pass XP-30 or the Allegri Reference sticking around for the New Year.
The answer for me was the Townshend. It wasn’t my preferred choice for everything, but had choosing favourites been easy it wouldn’t have taken all weekend! More often than not, the Allegri had my grin wider and my feet tapping harder, and that’s why I spend the time and the cashish.
The XP-30 is an incredible preamp, and it wasn’t at all difficult to find it a new home. Highly recommended. It has has left a rather large hole in my rack — I especially miss its look. Going from an industrial full-width, three-boxer to the diminutive half-width Allegri is taking some getting used to.
For my simple needs (one input and a way to bleed away some of the 6V from the DAC) though, the Allegri Reference has worked out brilliantly. Bring on the tunes!
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Ben, I have started looking at my savings, in case I could not resist, after a home demo of the Allegri Reference. I found a dealer nearby… First resolution for 2021 
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Ha — I’ll end up trying the Benchmark as you try the Allegri Ref 
A fair exchange 
Congrats Ben! Took me a while to get accustomed to the deep but narrow appearance of the Allegri Ref, but I no longer give it a second thought. And the sound is just superb.
Hi.
Is it possible that my Bartok sounds much more better with 6v rather then 2v?
I mean more vivid and brilliant?
Or is just suggestion and it just a volume matter?
I have made a lot of tests and seem to be that 6v is really better.
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Owning a Bartok for almost two years now, I definitely prefer the 6v output setting. So much more dynamic. I have an Audio Research Ref 6 preamp and that can take 15v on the XLR inputs before overloading.
I guess you might hope dynamics would improve with 6v. But what for me was unexpected, is the ambient space or atmosphere of a (good) recording is more palpably present. Difficult to put into words, hope it makes sense.
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Thanks!
Exactly my opinion.
I have and Audio Research too (An integrated Dsi200).
I was afraid it was suggestion.
But I am experiencing a real difference.
ambient space or atmosphere are the right words
Naim 500 series user here. I prefer the 6V setting on my Rossini.
Dunc also runs a Naim 500 set and uses 6V as well.
Best
Gregg
I prefer the 2V over the 6V setting on my Vivaldi into my Momentum HD pre-amp. I have a bit more flexibility with the volume control and “if” there is a SQ differences between the two voltages it isn’t worth considering in my set-up.
Yes, the choice of voltage setting is very much related to the individual circumstances of the user. That is why dCS have made it a choice, there is no universally applicable " best".
Like you 2V is the optimum line level voltage for me. 6V into my preamp would exceed the rated maximum output voltage of 5V so I see a potential problem there. Directly into my power amps ( sensitivity 0.5V) I would find myself with the volume control set between -30dBfs and -20dBfs. Too much resolution loss and kind of awkward as a user experience too.
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