Hmm... Thanks for the suggestion to seek Jan's advice, Stew, but I've honestly not felt any concern about returning the MG3 because I have from minute one assumed that at voltages higher than 15V, every MG3 out there would generate a detectable hiss with my Definitive Technology SM45 speakers. I get a similar hiss with these same speakers when using the Emotiva Mini-X a-100, but it's more faint than with the MG3 on 24V power - and I never found a way to dial out the hiss coming from the Emotiva Mini-X a-100.
I should emphasize that the hiss I hear from the MG3 into my speakers on 24V power is easily less than 10% as loud as the hiss I hear when using the MG3 with my LCD-2 in the absence of an impedance match. That much louder hiss heard with the LCD-2, even when playing music, indeed sounds like the cassette tape hiss you once described (or was it Gary?) The amount of hiss I can hear with my speakers from the MG3 on 24V isn't a problem when playing most tracks, as it can only be heard in those moments with some music where the absence of complete blackness is annoying because it can mask some of the very lowest level signals, stealing away the realism, but it's not constantly heard, as with the hiss I get using the LCD-2 without an impedance match.
I'm probably beating this to death in my struggle to quantify the SPL of the hiss heard at 24V with my 8-Ohm speakers, but trust me when I say, it's very faint. My home is completely silent as a rule, but when the air conditioning cycles on, just the sound of the air rushing through the overhead vent (which itself isn't whistling or in any way annoying normally) is nearly loud enough to drown out the hiss I hear is at its loudest with the 8-Ohm speakers - when the MG3 is on 24V power.
All that said, I'm completely content with the MG3. I really don't think it has a problem - especially given that I can extinguish that faint hiss completely by using 15V or less, and I rather like the sound I get at 15V.
On that point, every review I've ever read on the MG3 speaks of how different it sounds at 12V vs. 24V power. I have solidly concluded that this has nothing to do with using a battery supply (internal or external) vs. the switch-mode AC adapter that comes with the MG3. No. It has everything to do with the voltage. 12V and 24V are simply two points on a sound-tailoring curve that runs from about 9V to 30V. (9V is where a set of eight AA alkaline batteries would be fully discharged.) At this point in time, I'm going to refrain from attempting to describe the audible changes that occur, but it's not subtle to my ears, nor those of several reviewers, but these sound signature differences lie along a continuum - where we are free to choose precisely the sound we want, just by selecting a particular voltage among an infinite number of points along the 9V to 30V curve - not that anyone is likely to detect a difference between 15.0000V and 15.0001V (or even between 15V and 16V), but the choices are indeed infinite between the two extremes. I'm encouraging people to abandon comparisons of only 12V vs. 24V - there's some good stuff happening in between!
While I'm on this soap box about supply voltage vs. sound signature, I feel compelled to point out something that's not at all profound - that the voltage coming from any battery pack will constantly decay during use - which, for the voltage-aware MG3, means (more profoundly) that the sound signature will constantly drift toward those traits that reviewers associate with 12V power. No matter what voltage your battery pack starts at when fully charged, the sound signature will constantly drift during use - away from the sound signature associated with 30V power, toward that had at 9V. With the 16,8V four-cell LiPo packs I've decided to use with the MG3 into my Definitive Technology SM45s, I'll be starting at 16.8V, with the 3-volt per cell audible alarm going off as a pack reaches 12V, but I don't think I'll want to wait that long to replace one LiPo pack with another fully charged pack, because I don't like the sound signature I get with 12V as much as I like the MG3 at around 15V!
And thus... later today, I will be testing the MG3 with the five-cell Energizer XP8000 battery pack plus the XPAL Willy Cable WI15 - an inline voltage regulator that maintains a constant 15V output while the 21.0V XP8000 discharges internally from 21V down to 15V, at which point, the regulator shuts down. For the MG3, a constant voltage will translate to an unvarying sound signature. In my experience and that of at least a dozen other Meier Stepdance owners, the XPAL Willy Cable WI15 voltage regulator injects absolutely no noise into an amp. I've found that to be true with my DACmini CX and iBasso PB2 as well.
Edited by zilch0md - 8/24/13 at 11:54am