While that argument is aesthetically pleasing it doesn't have much to do with the actual benefits of a monoblock amplifier.
The circuitry in a power amplifier, and particularly in the driver and output stages, uses a lot of power, and especially a lot of current.
For one thing this means that, especially when you're playing loud music, there is a lot of current flowing around inside the amp.
And, unless that amplifier has a fully regulated power supply, when one channel is playing loudly, it will be affecting the voltage of the power supply.
No matter how well filtered a non-regulated power supply is, as you draw more current from it, the voltage drops, and the noise on the power rails increases at least slightly.
And, depending on the actual design, the voltage on the power supply may actually vary in time to the music.
You can minimize these effects but you cannot entirely eliminate them - unless you regulate the power supply.
Both of these factors can lead to the performance of one channel affecting the other.
Those effects can involve the signal from one channel actually leaking into the other...
They can also involve the performance of each channel being affected in other ways by the effect the other channel has on the power supply.
(When the left channel plays very loudly, it causes the power supply voltage and noise level to change, and this change affects the other channel that shares that power supply.)
This was a major issue in the days of tube amplifiers, and of many early solid state amps...
because their audio circuitry was heavily influenced by the voltage and noise level in the power supply.
The ability of an amplifier circuit to AVOID being affected by these things is a significant design consideration in a good modern amplifier design.
(This is why single-ended tube amplifier designs require such overdesigned and expensive power supplies - because they have very POOR immunity to these effects.)
To be quite honest most modern amplifier designs are relatively INSENSITIVE to minor changes in power supply voltage and noise level.
However, at least in principle, you can make sure these effects don't happen at all by using entirely separate power supplies.
In modern designs that have a fully regulated power supply, like our new XPA and XPA-DR amps, this effect is virtually nonexistent.
The only reason NOT to use a regulated power supply in a power amp is that, until recently, big regulated power supplies were always big, heavy, and expensive.
However, in reality, these simply are not considerations in a preamp.
A preamp uses very little power, and the signals themselves are very small, so there is less chance of the signals affecting the power supply.
And, because the signals themselves are smaller, there is less likelihood that they will leak between circuitry that is simply located close together.
And, because the power used in a preamp is so small, most good quality preamps DO use a fully regulated power supply, which is totally unaffected by the power used by the signal.
(In most modern preamps, if any leakage occurs between channels, it occurs because both channels run through the same IC chip, or because wires arerun very close together.)
It's also worth remembering that, at the level of the incoming signal, it is really impossible to "keep the two channels separate" anyway.
Both channels of the stereo signal stored on a vinyl album are stored in the same track.
They are picked up by the same stylus, travel down the same cantilever, and are detected by a single magnet or motor structure.
This is why even the best phono cartridges have very poor channel separation compared to most electronic circuitry.
These tiny signals then travel down a pair of tiny wires, which run directly next to each other, down a single tonearm.
The result of this proximity and interaction is that the signals DO "run together" to a degree - which is why vinyl has such a limited channel separation.
The audio signals for both channels on a CD are actually part of the same data stream, traveling in a single wire, until they reach the DAC.
It is the DAC that produces two analog output channels from that signal.... yet digital circuitry still manages to deliver MUCH higher separation.
If you've ever actually used them, you'll find that using two separate Volume controls is very difficult, because you can never get them to match as well as you'd like.
In the days of do-it-yourself audio gear, preamps with separate Volume controls for each channel were common, and you may still find them in some kits today...
The reason is that high quality dual-channel potentiometers, especially ones with two channels that track together well, cost a LOT more than good quality single-channel controls...
(But they are really unpleasant to use to adjust the level of stereo music....)
The other reason people sometimes prefer monoblocks is that, with monoblocks, you can place each amplifier near the speaker that it powers.
This allows you to use really short speaker cables... which does have some benefits... although, these days, those too are more theoretical than practical.
But NOBODY would even consider putting a separate preamp next to each of those amps... and walking back and forth every time they want to adjust the Volume.
There is one final reason why someone might consider using two separate monaural preamps.
That would be if you have a matched pair of really old vintage preamps, made back before stereo preamps even existed, and you just want to use them.
For the sake of this discussion, let's assume two mono amps are better than one stereo amp. Full disclosure, I'm a monoblock fan.
If monoblock amps are so good, why not monoblock preamps?
If we take the left and right outputs from a turntable and keep them separated for the rest of the chain, wouldn't this provide a better listening experience? So we'd have dual phono stages, dual line stages, and dual amps.
Yes, there would be two volume controls, but you could wrap a rubber band around both so one would turn the other. The oxygen free rubber has the best sonics.
Seriously, other than two volume controls, wouldn't dual everything be simply the best signal path? The closest thing to crosstalk would be the close proximity of the wires within the turntable.
I've also heard some very nice systems and never thought to myself it was leaps and bounds above mine or if at all.
