Mellotron/Chamberlin Patents

This is the first Chamberlin/Mellotron patent, and it somewhat resembles a Mellotron-like device.  There are tapes, heads, a long capstain, multiple tracks, multiple "stations" or sections on the tape, and a primitive mechanism to shuttle the tape between the stations.

Some things to note:

The capstain is in the front of the unit instead of the rear like production Mellotrons, and the tape runs toward the player instead of away.

There's a switch on each key to switch the tape head in and out of the circuit, presumably as an attempt at noise reduction.

During playback, after the tape goes by the tape head, the tape wraps around a wheel and tension on the tape is held by the wheel dropping down a slot.

There's a brake mechanism to insert drops into the playback sound.(!!!)

The motor drives the capstain with a friction roller drive; the motor shaft extends out with a roller on the end, the roller spins against the side of the flywheel, which is at the end of the capstain roller.

The rewind mechanism is a pulley mounted on a large C-shaped spring.

To shuttle the tape between stations you use this little lever.  Push the lever one way and the takeup drum spins, push the lever the other way and the supply drum spins.  There's a marker on the tape at the beginning of each new section and you have to work this lever back and forth until you're in position.

There's some insanity in this patent.  For one thing, it was filed 16 October 1953, but the patent wasn't issued until almost seven years later.  That's a long time.  So long that Harry Chamberlin's next patent, a set of improvements to this one, was issued before this one and so has an earlier patent number.(!!!)  So that's pretty confusing.

The drawings in the patent look absolutely nothing like a keyboard instrument.  Unless you're a major Mellotron fan, you'd probably mistake the drawings for a cotten gin or something.

The text in the patent itself is written... well... here's a sample:

As further shown in Fig. 2, each tape extends rightwardly from its idler 20, as indicated at 22 through a guide 23, across the upper surface of a driving roller 24 as shown at 25 over a guide bar 26 and then over a suppporting plate 27 which is curved around the upper righthand portion of the spool means 11, downwardly as indicated at 28 and under a small floating puller 29, as indicated at 30, to a channel 12 in the spool means 11, in which the rightward end of the tape is wound.

(Ah, where have the great writers gone?  Yeah, I'm reading through pages of this.)

This is the second Chamberlin/Mellotron patent, filed almost three years after the first one, but since the first patent took so long this was actually issued first.  It covers improvements to the implementation described in the first patent (although that's hard to tell from the title) and appears to be very close to the actual implemenation of the Chamberlin Model 200.

And the drawings still look nothing like a keyboard instrument.

Improvements include:

The tape playback reservoir box is introduced, replacing a wheel sliding in a vertical slot.  The rewind mechanism is now much faster because the return spring is no longer working against the weight of the wheel and you no longer have the inertia from the mass of the wheel.

There's an interlock to keep from playing the instrument and shuttling the tape at the same time and ripping the tape.

The shuttling mechanism seems to be improved, but the description is far too confusing to tell what's going on.

There's an indicator tape that slides through a slot in the front panel to help position the tape when changing stations.

For both of the drums, there's a screw adjustment for each note that humps up the circumference of the channel that the tape sits in a little bit to fine tune the station starting points for that note.

And the whole mechanism has been turned around, so the tape moves toward the rear of the unit during playback like production Mellotrons.  Ahhh.

The Chamberlin Model 200 ****

The third Chamberlin/Mellotron patent with more improvements.  The drawings are slightly looking like a keyboard instrument.

The split keyboard is introduced, "rhythm and harmony" on the left keyboard, "melody" on the right keyboard.  All three outputs are available separately for stereo mixes.

One of the rhythm keys can be operated with a foot pedal, to free the left hand for the harmony work.

Details about the construction that give you an understanding of how the machine is used are finally revealed: the keyboard is 35 notes, G to F, the tape speed is 7 1/2 ips, the tapes are 8 seconds long, there are 3 tracks on the tape, there are 6 stations along the tape.  The two keyboards can set their stations independently.  The rhythm, harmony and melody sections can set their tracks independently.   Examples of the musical content of the tape are given.

The pulleys-and-long-springs rewind mechanism is introduced, replacing the large C-shaped spring.

The track selection mechansim is introduced.

Electric station selection is introduced.  An extra control tape has holes punched in it at specific locations, electrical contacts sense when the holes are in postion, some relay logic decides which direction to move and drives the motor off, forward or backward, and the motor drives a chain wrapped around the two drums.

The fourth Chamberlin/Mellotron patent, and it's very similar to the previous one in presentation and layout.  The drawings are very very close.

Here there is a discussion about recording the harmony tapes as root-fifth-root for 12 notes up the chromatic scale, and then three diminished chords for the next three keys.  Playing one of the third-less chords together with one of the three diminished chords provides a way to get many chords out of 15 keys.

The track selection circuit is different here.

This is a patent for the Chamberlin Rhythmate, the first drum machine (at least the first one that doesn't involve actual drums).

It's a tape-based drum machine.  The tapes are in 6 foot loops, nominally running at 7-1/2 inches per second.  Since tuning is less important for percussion sounds the tape speed can be adjusted over a wide range of tempos.  The tapes share a single Mellotron-style roller capstain.  A single tape head is mounted with a pressure pad on a carriage that is movable between the tapes; the user mechanically raises a lever and positions it into one of the slotted positions.

Each tape has three tracks with compatible drum parts, and the user can mechanically position the head to select individual tracks or mixes of adjacent tracks.

The later model Chamberlins improved on the Mellotron's pulleys-and-long-springs mechanism that rewinds the tape.

A motor drives a shaft perpendicular to the tapes, these wheels are mounted on the shaft, one for each strip of tape, and the back end of each tape is attached onto its wheel with a small fastener. The wheels mount on the shaft with a ring of felt, so they slip. There's a screwdriver adjustment on each wheel to set the amount of slippage. The shaft spins opposite the tape, and the wheels provide a roughly constant back force to rewind the tapes.

Advantages include a more constant rewind force than possible with the pulleys-and-long-springs mechanism.  Also since the tape isn't sliding through plasitc pulleys there's less static charge buildup.  The wheels also a lot less room.  A disadvantage of the system is that you can't use it on instruments with multiple stations.

It's the Birotron!  This is a Mellotron-like instrument that uses an array of commercial 8-track tape players to provide the sound source.  The keyboard is a simple organ keyboard, one or two poles per key, and each key switch connects its tape player output into the mix.

As a refresher, an 8-track tape cartridge holds 1/4-inch magnetic tape spliced into a continuous loop.  Inside the cartridge the tape is wrapped around a single reel, pulled off the inside at the hub, runs by the head, and is then wound back on the outside of the reel.  The playback head is stereo, and is mechanically moved through four different positions. The tape moves at 3-3/4 inches per second, there's about 10 minutes worth of tape in the cartridge, so four head positions will get you through an album.

In practice the Birotron might have 20 stereo 8-track tape players, each supplying two notes, for a total of 40 notes on the keyboard, and you can use the track selection mechanism to switch between four different sounds.

Compared to a real Mellotron, the Birotron has no touch sensitivity.  The keyboard is just switches, and varying the pressure applied to the keyboard does nothing.  Also, since the Birotron uses tape loops it's not possible to have sounds with attacks or transients.  On the other hand, it's possible to play faster on a Birotron, and there's no 8 second time limit.

Also included in the patent is a technique for recording the cartridges when the source material is a short tape loop.  The source loop is played on a machine with two playback heads and a fader pot that sweeps between them, and the operator gets to watch the splice and fade away from the head nearest the splice.

Rick Wakeman's Birotron patent is very similiar to David Biro's.  In fact, a number of paragraphs of the patent text are identical or near identical.

In this version, the commercial 8-track tape players are replaced with a single playback mechanism with a common roller for the capstain.  The tape heads are all mounted on a single bar, and that bar can be mechanically switched between the four track positions.  8-track tape cartridges plug into the rear of the unit, all in a row, with little clamps to hold them in place.