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Channel separation, noise suppression and signal path shortening rely not merely on clever layout, mechanical separation and shielding says Esoteric. There's also the elimination of a conventional stereo potentiometer. Instead each preamp board gets its own IC with integral resistor network to adjust amplification factor directly.
This eliminates HF distortion and a long cable detour from board to pot and back. The audio signal leaves the preamp boards only once – directly to the output stage.
Here an International Rectifier chip modulates the signal into a ca. 800kHz square wave whose variable-width on/off pulses trigger six Mosfets (three per push/pull phase) from the same supplier. Post low-pass filtering to eliminate the carrier frequency—which would otherwise have the machine broadcast—the now amplified music signal appears at the speaker terminals.
Back to power supply and weight, the question becomes why no SMPS? The Japanese clearly reverted to a conventional power transformer and not even a toroid but a less efficient EI core. The first reply was brevity itself. "Because we like it." Perfectly adequate!
The longer reply explained that experiments with various switch-mode power supplies resulted in noticeably higher output power but inferior sonics, hence the usual ‘analog’ power supply. Ditto for no toroid. Though somewhat ‘slower’ than equivalent donuts, the EI was smoother and more pleasantly three-dimensional which in conjunction with the class D signature sound created the most desirable balance of attributes.
Finally a four-cornered enclosure section gets more effectively occupied by a four-cornered than round transformer. More effective use of space equates to a larger more powerful core with obvious sonic benefits. The 10kg iron block here manages 940VA.
Though the minimalist fascia wouldn’t let on, the I-03 is massively functional. There’s nothing lacking. Just don’t misplace the remote or 90% of the functions will go bye-bye. There are 3 x RCA and 2 x XLR inputs. RCA 3 can be converted to MM or MC phono (47kΩ or 100Ω impedance).
RCA 2 can be converted to direct/thru whilst bypassing the preamp stage (particularly practical for AV system integration). The pre-amplified signal can be tapped via the single pair of pre-outs three different ways – ON1 retains the power stage for biamping for example; ON2 deactivates the power stage to convert the I-03 into a pure preamp; REC presents the unattenuated signal.
What else can the machine do? Inputs may be named and input sensitivities assigned to equalize source voltage differentials. There’s balance control without additional circuitry since volume control is dual mono. This works discretely for each input. A propos volume, there are five preset tapers to customize how fast or slow volume ramps up. Things can go louder slowly first, then faster – or vice versa. How did one ever live without this?
More important perhaps is the headphone socket and that the power switch lives on the front. No more crawling behind the rack to grope for the mains switch. What innovation! The only salty crocodile tear will be shed by biwiring freaks who only get one pair of speaker terminals per channel.