The Mellotron’s basic system is the same on all models.
The model M400 is the one which will described in this page. Because of its simplified mechanism, the M400 should help you to understand more easily the way the instrument works.
The system is basically the same as a tape recorder.
Each key on the keyboard reads a magnetic tape.
The keyboard has 35 keys, so there are 35 tapes and 35 magnetic heads.
Each tape has 3 tracks, named A, B and C.
A selector switch places the heads on the desired track (A, B, C).
An intermediate position allows you to place the heads between 2 tracks, allowing the mixing of 2 sounds: A + B or B + C.
Each recording lasts for 8 seconds. Once the tape has been played in its entirety, you have to release the key to be able to play the tape once more.
The motor drives the capstan (1) by means of a belt.
When you press a key (2), the tape (3) comes in contact with the replay head, thanks to a felt pressure pad (4), and with the capstan, thanks to a pinch roller (5); thus, the tape can play.
As long as the key is pressed, the tape plays and then folds up in a wooden compartment (6).
When the key is released, the tape returns to its initial position, thanks to a spring (7).
Basic maintenance
Contrary to popular belief, the Mellotron is a reliable instrument that requires little maintenance.
As with a tape recorder, it is necessary to regularly clean the capstan and the tape heads. After several hours of operation, it may also be necessary to demagnetize the heads.
Adjustment of the keyboard
With changes in temperature and humidity, the keyboard must be adjusted in order to maintain optimum reading of the tapes.
Warning: use only demagnetized tools to avoid any risk of erasing the tapes.
Each key has two screws, aimed at adjusting the height of the Pinch Roller and the Pressure Pad, in relation to the tape.
This is the only method, used by Streetly Electronics, to adjust your keyboard properly:
Pressure Pad
While pressing the key, turn the screw anti-clockwise until there is no sound anymore.
Then, release the key, to allow the tape to come back to its initial position.
Press the key again, and turn the screw clockwise until sound is just heard.
Then, give ONE full turn of the screw.
Pinch Roller
While pressing the key, turn the screw anti-clockwise until the tape slows down and stops.
Then, release the key, to allow the tape to come back to its initial position.
Press the key again and turn the screw clockwise until a correct driving speed is obtained.
Then, give TWO full turns of the screw.