OK I spent all day playing with this. I did swap the stock tube for a vintage GE I had. This is my cleanest tube from my stock; I have tubes I've selected for more pleasing harmonic distortion, but this is a nice clean one.
First reaction: the gain staging is complicated. The manual spells out some things I wouldn't have known before, but are probably unchanged from other MP versions. The input gain control is for the first opamp stage, and the +20dB switch increases tube gain. There are separate output gain controls for analog and digital output. I'm guessing this is the second opamp stage, maybe it's fixed gain at +10 and the controls independently attenuate that level
The metering is cool. There is a dedicated LED strip for the digital outs, with peak hold. The VU meter is switchable between output and "tube", which shows you how hard the tube is being drive.
Armed with this knowledge, with the plate voltage set on high, I cranked the input gain to +20dB and engaged the +20dB switch, for max possible tube drive. Those settings would be suicidal on the MP, but generally they worked fine here. Checking the difference in tone between the two voltage settings, I don't hear a reason to ever use the low voltage setting. It distorts earlier and more nastily.
I tried it with acoustic guitar, electric, and bass DI, and it was great for all three. Also did a vocal with no complaints.
In summary, I think ART has gone from making a good DI box to a great DI unit. I wish I had a decent vocalist to try it with mics
but with all the gain options and the impedance control, it seems you could dial in about anything.
Edit: On the basis on the "Ramones Rumble" track being too prejudicial to the poor MPA, here's a few bars of "Every Breath You Take", NO SINGING!:
Full Voltage Police
At the end there is an arpeggio at the 13th fret, once with max tube gain, once with min tube gain, you can hear the range there pretty well. Note that this is
a Gibson The Paul (thinbody Les Paul), so it's a pretty mellow instrument to start with. I like mellow
This is with both pickups on, and full volume/tone on both, DI, no effects, dynamics, or EQ whatsoever!
Here's the Ramones Rumble thread for those looking to hear something funny:
http://www.homerecording.com/bbs/showpost.php?p=1736455