Well, I've now spent a week with my newly adopted 1970 M-85 bass and I've gotta say, I am so happy to have it in the stable!
The neck carve and feel is almost identical to my 1970 Starfire, which is excellent! As comfy as they get (at least to my hands). Compared to 60's Starfires I've owned and played, these 1970 necks feel just a smidge chunkier. Maybe the shape of the carve changed a bit or maybe it's due to the poly finish they started in this year, even though it's not a heavy finish by any means. There is also no volute on these 1970 basses, but I have no preference in that regard one way or another.
As mentioned in a previous post, I had thought these early M85 basses were hollow-bodies with the addition of a block just underneath the bridge, so I was surprised to find that this one is actually proper semi-hollow, with a solid 3-piece maple block running down the center. Since it's a deep body, the center block is pretty massive, and correspondingly the bass is a bit heavier than the Starfire, though still under 9 lbs. Balances nicely on a strap with no discernible neck-dive.
Comparing the M85 to the Starfire unplugged the difference is pretty impressive! In this context, the Starfire is notably louder and has a much more mid-forward timbre. Notes resonate differently in different areas of the neck, with varying sustain, which is something I've experienced with most of my basses and have learned to use that variation strategically for different tone effects depending on the song. The M85 is acoustically pretty quiet, with a much thinner/brighter timbre, but notes resonate remarkably consistent across all areas of the fretboard and the sustain is exceptional. So in that regard, these two basses have wonderfully different qualities that can come in handy in different musical contexts. Both basses are overall very resonant and, kind of like a big lovey-dovey purring lap-cat, their necks and bodies vibrate like crazy when notes are ringing out.
Some may wonder why even analyze the unplugged timbre of an electric instrument, but keep in mind, all the sound of the electric signal starts with the vibrating string, so I think these acoustic qualities are important to note, especially with broad-frequency response pickups like the Hagstrom Bisonic. The whole allure of these pickups is that they faithfully capture all of the nuances of the vibrating string (or at least as much as a passive pickup can). In my experience, the nature of string vibration directly corresponds with the resonant character of the wood of the instrument -- which can be good or bad, depending on a player's taste/preferences! I recall one Fender Precision bass that I didn't keep for very long because it had the most honky overpowering middy sound, that you could clearly hear unplugged too and which didn't go away even with a completely different set of strings. Similarly, I briefly had a Jack Casady Signature Epiphone bass that had super boomy notes in some areas of the neck and completely dead notes in others.
Anyway, plugged in, both basses offer huge, rich tones, that are clearly related, but easily distinguishable from each other -- granted the Starfire has an active resonant-filter preamp and the M85 has standard passive electronics, plus their pickups are oriented in opposite directions and the M85's pickups are slightly farther apart. That said, the barky mid-forwardness of the Starfire still comes through in comparison to the M85, which has a little more of a "scooped-mids" flavor. Both still have that lovely familiar Bisonic pickup clarity. I might add a spacer to each of the M85's pickups, just to bring them up a little closer to the strings. There are stock risers in place, but they might be a little low for my preference.
Another interesting thing to note about this bass is the impressive stiffness of the neck. A lot of times, after 53 years of string tension, you run into the need to heat-press or reset the neck. Absolutely not the case here, in fact the truss rod is practically pristine and it's actually difficult to get a "normal" amount of relief! Considering my tendency to "dig in" when a jam really gets cookin, any kind of low tension string won't really work for me on this bass, which unfortunately includes my beloved NOS Maxima flatwounds. I put on a set of Maximas but their relatively low tension barely creates any bow in the neck. Even with the truss nut completely loosened, the neck was pretty much flat. Really not a big issue though, as I always keep various extra string sets on hand. I found a nice heavy, worn-in set of D'Addario Chromes that sound excellent on this bass and the extra tension gets the perfect amount of relief. On a related note, the impressive stiffness of the neck may well result in some of that very unusual evenness of resonance and sustain across the fretboard, that I would normally only expect from some kind of carbon-fiber or aluminum neck.
Off-hand, that's all I can think of to report at the moment. Will keep adding thoughts and observations (and eventually recordings) to this thread as they come along.
Thanks again, Happy!