There's already been some great info in this thread, but I'll kick in a few of my own thoughts as well, just to contribute.
The TLDR "I skipped the rest" answer:
My band is off for a couple weeks, and I didn't get a chance to wire the SGT into my board before the one this last weekend, so still need to try it out in a mix. But so far, I've really been digging the SGT from the start. It's obviously the Ampeg sound in a preamp/DI form. I think it'll shine in my band's IEM setup.
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It's pretty easy to dial up nice tones quickly if you're familiar with the Ampeg sound, but the SGT circuit lets you dig deeper to get a wider variety of both clean and grit-ty sounds. (sorry... couldn't resist.

) In particular so far,
really digging the combo of the SGT and my passive Fender P Bass V with dead roundwounds that don't quite reach the "warm thud" territory of flats, but they're not far from it. Love. And the Ultra Hi switch engaged seems to be the Goldilocks spot of adding just a little life and definition back without losing that "almost flats" thing going on.
The SCR-DI didn't appeal to me as I don't personally like the sound of the Scrambler circuit at all, so I admit I was skeptical about the SGT when it first hit. But after (re)watching a lot of (all?) the intro/review videos though, I ordered because it did seem like a different circuit even from Youtube demos... and I wasn't disappointed. It does seem like a different circuit, which Dom confirmed in that SVT Time podcast. Having both SGT voicings available adds some versatility to getting some great different sounds for different genres, and I like both circuits a lot. I also liked the "clean" boost setting
that Dom mentioned here. I kept the Grit level at unity instead of dimed and I wouldn't describe it as totally "clean," but I do agree with how he described it as more of a "feel" thing.
A feature of the SGT that's absolutely KEY, IMO:
FINALLY. A preamp with a drive circuit that has its own level control. With preamps like the Darkglass Ultras I've owned and or even my trusty Tone Hammer, settings can be quite different when you engage the drive circuit, requiring adjustments. As in, more of an on OR off thing. Having the Grit/Level control for the SGT circuit lets you keep unity volume either way.
The comp is a little more aggressive than I usually go for, but it's also not quite as overpowering as I was expecting. It can easily get to a point where it feels like it's squishing too much, but a little bit works nicely. I dialed it up until the yellow light
just started to come on and then backed it off a bit. It won’t draw me away from the Empress when I have it on my pedalboard, but it's also not unpleasant and I can see dialing in a little of the Comp if/when I use this as a standalone pedal.
One thing I've learned with Ampeg gear is to not be afraid of turning the knobs, and that's the case here as well. I found myself finding some sweet sounds with the controls at higher/lower settings that I'd use on other preamps, which I think is mostly due to where Ampeg has set the EQ and cut/boost points. I've experienced the same on my PF500, and other Ampeg amps I've tried. The parametric mids is a nice feature here... I found my sweet spot with a slight cut at 500Hz to dial out a bit of low mid honk.
In contrast to how much I like everything else about the SGT, I had the same thoughts about the cab sims that
@JeezyMcNuggles mentioned in his video. They seem to take away from the sound more than they add for my personal taste, and I'd most likely leave the factory cab sims off. But I do need to explore this feature more... Among my collection of IRs, I happen to have impulse responses that match my actual amp rigs: a pair of Bergantino 1x12s (
the Bergantino/Celestion IR package) and my pair of Ampeg PF115HE 1x15s (
Dr. Bonkers APFlex 1x15 pack). I've generally not found cab sims to be something I use, but I'll still try and give it a fair shake here.
So far, liking the SGT-DI a lot. And most importantly, it looks cool. Because that's the REAL reason we buy pedals, right?

5sg.