First Foray into XLR

I always did and still do, only to a point, believe that the main reason to choose XLRs over RCAs is to reduce noise, when long cable runs are necessary.
Recently, while doing some A/B comparisons, with a friend, between a PrimaLuna, Dialogue, Premium HP, tubed power amp and a VAC, Phi-200, tubed power amp, I had a mind changing experience. We intensely listened and compared both amps through a pr. of Wilson Audio, Sophia-II speakers. We listened to the PrimaLuna, using the EL-34 tubes and the KT-88 and KT120 tubes. While the EL-34s sounded smooth and warm, the PrimaLuma needed the KT-88s or KT120s to come close to the overall, dynamics, power and presentation of the VAC. While the PrimaLuna, sounded very nice, indeed, it was not quite on par, in terms of dynamics, detail and overall scope of the stage, with the much more expensive VAC. Then we decided to run the VAC through it’s XLR, balanced circuit. I thought nothing could be better than what we had already heard, but WOW! Switching the VAC to XLR was mind blowing. We switched back and forth several times, ea. time concurring what we heard.
As mentioned by others - running XLRs, if your amp’s XLR posts simply tie into the RCA circuit and the amp doesn’t have a dedicated, fully balanced circuit - will net no gain. I’m now convinced, however, that with a very good amp, having a true, fully balanced circuit - I would choose the XLRs...IMO...Jim

From my observations many people mistake the 6db boost you get from xlr to be "better sound".
I know I did to start with...lol.
You would need to level match the rca and xlr inputs ( if possible) to draw a more realistic comparison.

Switching the VAC to XLR was mind blowing. We switched back and forth...

Unless the output signal is verified within 0.1db across the whole spectrum, back and forth switching is rather pointless.

If the cables are not identical, then cable deltas could swamp the electronic.

Different connectors of the same type with identical cables can be audible.

Uncontrolled variables have been skewing results since time immemorial.

@ieales We did not simply do A/B switching (I am not a fan of simple A/B switching). We extensively listened to both amps and to the VAC in both RCA and XLR inputs, at various volumes, and assorted genres of music, experimenting with two different, quality RCA ICs - a .5m pair of CablePlex Silvers and a 1m set of low capt. high res 99.9% copper. The result (even when compensating for volume) was consistently, a wider, deeper stage, with more air around individual vocals and instruments, when the Vac was running through it’s balanced circuit.
With your logic, nothing is, or sounds, any different than anything else - it’s just a matter of volume.
Even when adjusting for volume, we did not expect to hear an improvement on the VAC’s already incredible performance, but we did...Jim

I don’t doubt differences were heard.

when compensating for volume

Since you adjusted volume, then you concur that matching volume has merit. Exactly how did you compensate?

With your logic, nothing is, or sounds, any different than anything else - it’s just a matter of volume

Not so. I did not say that. Never have, never will.

I’m not trying to be obtuse, but I’ve endured far too many "night and day" / "blows the doors off" claims only to find that levels were not matched and when they were, deltas diminished drastically.

No mention is made of the driving device.

The effects ascribed to the XLR input could be impedance mis-matching. The VAC Phi200 does not list bal/unbal impedances.

The Phi200 manual states there are switches for bal/unbal. What was the power setup and is there a possibility of a ground loop with the unbalanced that is mitigated in the balanced mode?

When properly implemented, there should be extremely little difference between balanced and unbalanced at home HiFi distances. I spent a couple of decades designing electronics [not power amps] and made sure there were none.