Re: What makes an overdrive "amp-like"?
Your original OD and Distortion pedals were essentially a stripped down gain stage with a rudimentary tone control sometimes. One or two small devices to make low voltage high, and some sort of diode to clip the signal's edges off. As pedals gained popularity (lol gain), people started adding multiple gain stages into a single pedal, started using more sophisticated clipping methods and designs, and started adding robust tone controls that started mimicking the amps they were in front of.
Those multiple gain stages in, say, a chip, allowed for the stages to push a little gentler and make for a more satisfyingly clear tone, instead of a one-and-done tone shred. Soon pedal guys developed the means to take transistors and chips (essentially a bunch of transistors in a tiny size, stuck in a single chip) and imitate a pseudo-tube/valve reaction with very gentle clipping.
After a tube-like rich distortion was able to be achieved, people started adding the tonestacks of major amp makers to the gain stages and essentially made amp-in-a-box pedals. The tonestack of an amp is largely how one amp sounds different than another.
Speaker output can pretty much be derived as an EQ section, and a fixed EQ can be pretty easy to make. Add an EQ tuned to, say, the same EQ checkmarks as a Celestion V30, and you have yourself a distortion pedal that largely reacts the same as the amp it's based on. Depending on who you ask.
But I think the basic answer to "amp-like" stompbox quality is the ability of the pedal to do multiple gentle gain stages and a gentler asymmetrical clipping.
ah, suggestions?
well, the Zendrive, Timmy, OCD, Xotic Effects boosters, and the old Klon are all very "amplike" without being too much like an amp in a box. Some of the best amp in a boxes come out of Catalinbread IMO, like the Dirty Little Secret and Formula 5f6. They've even got the RAH (Jimmy Page's rig at the Royal ALbert Hall show), Galileo (a combo of Queenesque pedals for Brian May's Day at the Races sound), and they even incorporated a tubey goodness in their Echorec and Belle Epoch delay pedals.
Wampler makes some excellent high-gain amp in a box, as does Lovepedal. JHS also does, but I have personal problems with them. They've swiped several pedal designs and sold them as personally developed.
Well...they all have really. If it isn't a tube screamer, it's a knock-off.
