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The first thing one should ask any muscle amplifier is, what kind of low-level resolution does it maintain at whisper levels. The power and glory stuff is expected. But how often do you really listen like that? Far more relevant is whether the paralleling -- and hence, matching -- of output devices needed to generate high power remains tight down into the more subliminal levels of perception. If the micro realm is handled well and the power supply up to snuff, the macro range of such amps ought to follow suit for the occasional rock-out session.

Already conceptually, the KWA-150's single gain stage and capacitor-less signal path are very promising. Despite its significant size and weight -- and the innards clearly aren't empty -- stout power is generated as simply as possible to avoid complexity from staggered gain stages. To test my question, I reached for the 97dB/12Ω-ish Zu Essence where a little input voltage gets converted efficiently into relatively high sound pressure. Choking the volume to midnight levels at the speakers reduces what comes knocking at the amplifier inputs down to mini voltages. What would the ModWright do with those?

Even on music you don't know -- so expectations can't fill in the gaps -- very low bass activities are plain; like watching someone's heart beat in the little hollow beneath the
throat. You don't hear or feel that heartbeat. You see it. Very faintly. And that's enough. Ditto for the ModWright. Raising the volume for later confirmation, the heart beat plainly peels out like putting ear to chest. But you already sensed the beat when it was still mostly subliminal - exactly like that nearly imperceptible expansion and contraction of an artery beneath the skin. That is phenomenal. It also proved beyond the ken of even a superior valve amp like KR Audio's VA350i aka 'Baby Kronzilla' which was in for review during the same period.

At such whisper levels, attention has to peak. We must penetrate the aural twilight. So we become far more participatory than at high volumes. Then the hardware lays it all out, half our senses could shut down and we'd still get the picture. Way down in output though, cloudiness sets in. Yet the ModWright still has emphatic transients stick cleanly out from the surrounding thicket. A bass whack, cymbal accent, foot stomp or key clack still jumps with a goodly semblance of that startle factor we know from normal levels but habitually forego way down low in volume and frequency. Boring is what most call such levels in fact. Not so with the ModWright. Its dynamic range continues to operate where other amps give up to cleanly separate and delineate. The KWA-150 illuminates and makes things more legible at very low volumes.

Let's briefly compare the music signal to a cut lawn. A transient four times louder than the median would be four times as tall. If whisper levels mow the lawn back to 1 millimeter, our transient is cut back equivalently to just 4mm. Naturally, a 30cm difference at medium levels is far more obvious than a 3mm difference at barely there. But it's precisely those tiny signal fluctuations called microdynamics that are all which stand between us and boredom when circumstances require super polite SPLs. What use is a bruiser amp whose wake up call comes far later? Big, expensive and boring is the answer. But the ModWright is different. It's definitely not a delayed reactor but an amp whose quality begins well within that first watt. [
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Back to big bad bruisers and bass. Premium bass is expected. Yet what's that sound like? More intelligent. It shows how specific sounds were made. Any of my SETs, over the right speakers, will portray the 'what' -- a double bass, a big drum, a synthesizer -- reasonably well. In that respect, very little goes missing actually. It's in the 'how' where the distinction lives and w
here single-ended valve amps of even sterling pedigree drop out of the race sooner. It's in cleanly separating, down to the bone as it were, the nearly coincident attack of mallet or fingers on a drum skin from the subsequent air compression; that from the excitation of the resonant cavity; and that from the final release of secondary energy with its various harmonics dying off in stages.

A sophisticated muscle amp like the ModWright shows how that bass note instant is really a process layered over time. It's not a singular blot. And this amp unravels that. It's no longer just about sounds. It's about actions where a finger on a string connects it to a hollow but floor-spiked body via a bridge; where a fuzzy mallet connects with a skin that's tautly stretched over a frame. Let's recall that the twelve semi tones of the bottom octave are crammed into -- and thus defined by -- a mere 20 cycles per second. That's not even a 2-Hertz difference per note. The same octave in the presence region spans 1000 cycles. That's why humans lack differentiating power down low. When you next pass a musical instrument store, venture inside. Finger a piano's 3 left-most keys. Besides being moistly resonant and rumbly, how clearly can you actually call out their pitch? Can you distinguish the A flat from the A sharp and the B?

The low-power FirstWatt F4 and F5 transistor amps too illuminate those areas better than SETs. What the KWA-150 adds is mass. That one still expects from powerful amps. But then it does that very same thing -- though certainly scaled back in magnitude -- at very low volumes. As gain increases, it tracks the differences between median and empathic transient bass pulses quite beyond where my lower-power amps begin to compress. That's a form of distortion not readily audible like clipping or a rubbing voice coil. It's distortion by omission. A massed crescendo for instance will get disproportionately louder in the mids and highs than the lows. Unless you hear it differently to understand compression by contrast, you won't ever know. That's because clipping or voice-coil dirt create obvious distortions. They add something so obviously wrong that you know it shouldn't be there. Dynamic compression however subtracts. That's much harder to spot. You can't miss what you never had. On that topic, the KWA-150 seems rather more non-subtractive than most.

Its bass also isn't of the overdamped dry fart or jack-hammer-on-concrete sort. It's not transient obsessed to the detriment of bloom and decay. Process and action aren't foreshortened. Unless generated by a drum machine to be deliberately unnatural and stark, bass is properly plump and rings out naturally. So behaviorally, the ModWright mimics a fast, wide bandwidth low-distortion amplifier of lower (non-complex) power. Where it differs is in ultimate LF impact and macrodynamic linearity. More relevant 95% of the time, it is microdynamically astute and, probably due to lower noise floor, superior to the kind of simple single-ended triode circuits I'm familiar with when the volume is ultra subdued.