Mellotronists

And now a report from our embedded reporter in Gene's garage:

The pictures in Frank's Mellotron book, Mark Vail's "Vintage Synthesizers",
and www.mellotron.com pretty much cover what it looks like. (Same pictures
at those three places, by the way.) In addition there is a good
under-the-lid shot at the web site. The M1 I got does not have the remote
unit and therefore does not have that extra add-on control box or external
wiring harnesses.

The cabinet is inexplicably short. I'm not sure what the intention was, to
put it on a low table or maybe on top of the road case that it comes in, or
what. Perhaps it was done that way to avoid blatantly copying the M400?

Much in the way that the Mellotron M400 is really one assembly that drops
into the wooden cabinet, inside of the M1 there is an assembly which is
pretty much the entire machine. It exists in the center of the unit with
airspace on all four sides. One major difference from the M400 is that the
two motors are not part of this assembly but rather are mounted separately
and independently. Yes I said two motors - one is a fixed speed AC motor
(looking much like a reel motor from an old reel-to-reel). This has a pulley
with a belt over it, to the big flywheel on the capstan (consult the picture
at Mellotron.com), and a spring-loaded idler pulley near the motor. The
other motor is on the right side of the machine (as you look at the
keyboard) and has four skinny rubber belts running up to a fairly small
(compared to the other one) pulley on a shaft that runs along the length of
the keyboard under the keys themselves. This shaft holds the reels where the
tapes are stored. The shaft spins in the direction that rewinds the tapes
after a key is let up (opposite of capstan rotation), and there is one reel
per tape (total of 35). The reels slip on the spinning shaft, with enough
friction to be moved by the shaft if the tape is not taut. There's a
setscrew in each reel to set this friction point but the tape has to be off
of it (i.e. in the take-up bin) to get to it. So this is how the M1 returns
the tapes, rather than using springs. Very compact, but it seems that this
method takes longer to rewind the entire tape than the M400 method. This is
a fixed-speed return, whereas the M400 snaps the tapes back however fast
they will travel under spring tension.

All over inside of this thing are paper labels created on a typewriter,
taped on to various surfaces, containing all kinds of useful information
about motor oiling, tape threading, take-up reel friction adjustment, pinch
roller and felt pad adjustment, and so on. There is a tape-threading tool
which consists of a long skinny brass "tape" about 6" long. There is an
allen wrench behind a little clip which is used to adjust the take-up reel
friction setscrews. There is also an extra motor pulley.

On top of the main assembly sits the keyboard, which is mounted on a square
aluminium frame. This is a wooden 35-note keyboard, much like the Mellotron,
except that the low "G" is a real low "G" in that it has the cutout in it
for the F-sharp rather than being like a "C" in shape. The cheekblock next
to the low "G" has the corresponding shape to match. Interestingly, the high
"F" has a straight side where the F-sharp would be, so all I can say is go
figure. Again the pictures on the Mellotron.com site show this clearly.

The keyboard can be removed by unscrewing four sheet metal screws which
mount it to the main assembly. No knurled knobs, get your screwdriver buddy.
The track selector at the right end needs to come out at this time as well,
since it covers the fourth screw. As soon as you unscrew the keyboard, it
pops up from spring pressure below. When you lift it off, you will see that
there are no pinch rollers or felt pads on the keys, just the front and back
adjustment screw shafts poking downwards. The pinch rollers and felt pads
are attached to spring-metal "fingers" that are mounted to a bar that runs
across the front of the chassis. Removing this bar exposes the tapes. At
1/2" each, the tapes are almost touching each other with AGO key spacing.
There are comb teeth separating and aligning the tapes, but they are very
skinny.

The tapes appear to be riveted to both the take-up reel and the anchor bar
at the rear of the chassis. I have not yet examined these rivets to see if
they are perhaps simple press-fit things that can be removed (hopefully), or
if they are the kind you need to drill out so don't even go there and ship
the whole thing back to Upland. Like that's gonna happen....

The heads in the headblock are 2-track heads. For any given head each gap
goes to a separate output, so there are 2 outputs. The track selector has
six positions:

1 and 3
2 and 4
3 and 5
4 and 6
5 and 7
6 and 8

Output electronics is under the left-hand cheekblock. Four pots, tone and
volume for both outputs. On/off switches for each output also. Under the
cheekblock is a linebox, inside of which is the circuit board with some
passives and a single chip (haven't ID'd it yet). The circuit board is made
out of vectorboard. Definitely not a mass-production effort here. On the
right-hand cheekblock is the track selector lever (once again seen at the
Mellotron.com picture), power switch, and pitch control. Hey wait didn't I
say that the capstan was driven by an AC motor? Yes indeed, behind the pitch
pot there is another piece of vectorboard with some electronics on it
(including a 3-terminal SCR-type thingey) so there is definitely some AC
waveform monkey business going on here. The pitch pot behavior seems to be
stable pitch for some of the pot's rotation, then a slight drop off, then
the motor drops to half-speed or so and then stalls. So I suppose that the
motor is intended to be slightly sharp and the pot set somewhere in the
"slight drop off" portion. This theory is reinforced by the existence of the
spare motor pulley with a note next to it that says "use this pulley for
A-440". So, tuning is set by pulley size, eh?

I've not yet been able to get a good listen to the sounds yet. The sounds on
this tape set is an assortment of strings, horns, flute, and vibes. Standard
set? Don't know. When I started to work on this machine there were two main
problems - first, all the keys were out of adjustment so I could not get a
well-played note anywhere. Second, the electronics seems to be gummed up or
otherwise dirty so there is a high-pitched squeal if the volume is turned up
at all. Long road ahead... I'll try to take pictures along the way.

Best Regards,

- Gene