(My background: non-professional home recording person, recording mostly myself and my kids. My recording time is leisure time, not working time, so I don't have deadlines, etc. I've been a musician for about 25 years, at varying levels of activity, but am fairly new to running the recording equipment myself. In the last couple of years, I've taken to voraciously reading books and websites on the topic, and am pretty satisfied with my current hardware setup, which I constantly mess with, both for learning and recording purposes. I have always had what I consider a good music "ear", but I quickly realized that it wasn't too transferable to recording ("engineering", if you'll allow me the use of that word, for illustration), but I'm developing that more quickly than I'd like now. I had never "modded" a microphone really until I got the group buy mics, and I don't have an electronics educational background or similar experience at all. The reason I'm saying all this is to provide a context for my comments below. We have all types on the board here, including many professionals.)
I got the ACM-2, ACM-3, ACM-4 (ribbons), and the ACM-310 and ACM-6802T (tube). Later, I picked up an ACM-1 (ribbon) on the aftermarket.
I've modified all the mics to a certain extent (and Marik is currently modifying the 6802T to a much larger extent). The ACM-2 and ACM-3 had ribbon tension problems, but other than that, they were all usable for me out of the box (the boxes are nice, too, btw). I very unscientifically retensioned those two - pulling the ribbon taught with a q-tip until it looked sort of level (not flat, since it's corrugated), and then reclamping them. I'm perfectly happy with the result.
I've replaced the transformers in the ribbons with Lundahls and Edcors. The stock transformers generally had higher output and less detail than their replacements. Build quality is good for the price - we've seen some awkward (but functional) electronic work in the tube mics -- indicates some hand wiring attention, in any event
ACM1: haven't really done much with it yet. Put Edcor in it.
ACM2: good for guitar amps - seems pretty flat response. Will use it in preference to a 57 or I5 for small amps - IMO it blows them away for slightly overdriven blues sounds. Haven't yet tried it on big amps. Edcor
ACM3: also good for amps, seems like it's a little mellower than the ACM-2. Lundahl
ACM4: also good for amps, seems good for vocals - Lundahl
ACM-310: I wish I had a stereo matched pair, but since I don't, this mic is my first choice for mono recording of nylon stringed instruments - uke mostly (preferred over SM81,MK-012,MXL990). It's good, if a little big, on steel string acoustic, too. I replaced the coupler cap with a polystyrene cap, and that lowered the output some, but didn't really improve the sound over what was there - I probably shouldn't have risked that mod.
ACM-6802T: I immediately swapped the stock tube for NOS GE 12AT7 - the mic sounded great to me at that point, and we did some vocal work with it. Marik is currently fitting it with a Peluso PK47 capsule, and soon a TAB-Funkenwerk BV314 transformer. We all have high hopes.
The 310 and 6802T came with nice flight cases, shock mounts, power supplies and cables. The ACM-4 came with a shock mount. The ACM-2,3,4 came with nice wooden boxes that I don't use, and the ACM-1 came with what seems like a thermos coozy and a cable.
overall GB#2 was the best deal on mics I've had (and I'm the guy who got the C414 for $100 last weekend). All of them seem to be noiseless to me, and sound very good. My intentions were to mod them from the start. But (after retensioning), if I had left them alone, I'd still be very happy and would be using them.
It was 6 months between the time I paid the initial invoice and the time I got the mics - this is longer than most participants, but everyone waited as they mics were built, shipped, etc. -- for me it was no big deal, since, as I noted, I have no deadlines. If you need mics like these for a project that's starting up in the near future, then you should keep this in mind. But if you're like me, or if you're commercial and simply want to get more mics in the locker on no particular schedule, then by all means, this is the way to go.
I have sound samples up in various posts in the microphone forum - if you search for threads started by me, you should find them all pretty easily.
(jeez - sorry for the heft - you asked for it

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