tape heads and 35 tape loops,
along with all of the capstans, pinch
wheels, springs, and rollers
necessary to make things work.
Again, according to Wikipedia (with
numbers corresponding to the parts
in Figure 3):
“Pressing a key (1) causes two
screws ( 2) to connect a pressure pad
( 3) with the tape head ( 5), and the
pinch wheel ( 4) with the
continuously rotating capstan ( 6).
Tape is pulled at a gradual speed,
counterbalanced by a tension spring
( 8-10), and stored temporarily in a
storage bin ( 7) until the key is
When the key is released, the
tape is quickly retracted in
preparation for another key press.
The eight second length of the
tape loops made playing the
instrument problematic. If you
pressed and held a key for more
than eight seconds, the sound
would end as the tape would run
out. If you wanted to hold a chord for longer than eight
seconds you would have to continuously move your hands
to play different chord inversions so that notes would still
sound. This technique of playing the mellotron became
known as the “crawling spider” because of the continuous
movement of hands on the keyboard.
With some versions of the
mellotron, the tape loops had
multiple tracks recorded onto them
and a switch on the keyboard
allowed selection of which tape
loop track(s) to play. The individual
tracks generally contained
recordings of different instruments;
so by switching the tracks, different
instrument sounds could be
Playing a piece on a mellotron
never sounded exactly the same
twice because of wow and flutter
(small changes in playback
amplitude and pitch) as a result of
the mechanics of the system.
Sometimes during extended play
periods, a mellotron would quit
playing altogether. I remember
reading somewhere that when a
musician wanted to bring a
mellotron along on tour they had to
bring a mellotron expert along with
them as the instrument was always
in need of tweaking.
The mechanical marvel that is a
mellotron can be seen in Figure 4.
Imagine the difficulty in trying to synchronize 35 different
tape decks at the same time in a machine that was meant
to be portable.
The mellotron project described in this article:
• Runs on a Raspberry Pi 3 model B, sporting a quad-core
64-bit ARM processor running at 1.2 GHz with 1 GB of
SDRAM, and built-in Wi-Fi and micro SD card interfaces.
• Uses a modified version of the Raspbian Jessie Lite
Linux operating system.
• Runs a customized version of SamplerBox software.
SamplerBox has a growing user community (see
Resources) that continuously enhances its capabilities in
an open source manner.
• Supports an unlimited number of sample sets up to 1
GB each in size.
• Uses an inexpensive USB digital-to-analog converter
(DAC) for quality sound reproduction.
• Is capable of 120 note polyphony, although that has
been dialed back to 10 note polyphony to reduce
latency in the version I supply with this article.
• Stores sample sets on an inexpensive USB Flash drive.
• Has a 20-character by four-line LCD display.
• Supports a traditional MIDI interface and the new USB
28 September 2017
■ FIGURE 3. The
(Fred the Oysteri. The source code
of this SVG is valid. This vector
graphics image was created with
Adobe Illustrator, GFDL,
■ FIGURE 2. A mellotron being played.
(Buzz Andersen from San Francisco, CA —
Mellotron | NAMM 2007, CC BY-SA 2.0,