This is the new Melloman,
years after its predecessor.
It was commissioned by Justin Vernon (Bon
Choir), and took me a little over a
year to complete.
Like the original Melloman, this is
my DIY design
of the classic Mellotron.
There are 14 Walkmans
inside the Melloman, running tapes of continuous notes. Each
tape has two octaves of a looping sound, and those
sounds are routed to the output when a key is pressed on the keyboard.
The new Melloman is a complete redesign of the original Melloman I
built in 2005.
The original Melloman
used only transistors to pass the sounds from each cassette to the
When I built that one, I experimented with photo resistive
opto-couplers, but had problems with the signals continuing to bleed
through after the note was off. I thought of a solution a few years
later, and implemented that in this new design.
The new Melloman now uses opto-couplers to gate the notes. In order to
remove the transient bleeding after the note is let go, a parallel
opto-coupler grounds the note. So each channel uses two opto-couplers,
and three transistors to switch them. When the note is pressed, one of
opto-couplers is energized, passing the signal to the output mix. When
the note is let go, that opto-coupler turns off, and the other
opto-coupler is energized. This sends the signal to ground to mute the
Using opto-couplers, the gating sounds smooth. Just using transistors
on the original Melloman, the gating was a bit clicky.
Here's the schematic for gating notes. It's simple:
On the new Melloman, each tape player can be tuned individually on the
control panel (by the
way, this new version uses Memorex portable tape players instead of
Sony Walkmans. But I still refer to the tape players as Walkmans). Each
player has a voltage divider trim pot inside
to govern the tape speed. On the panel, there are 13 pots wired in
parallel to each trim pot. But I added the 3v rail to each, so they can
be tuned up as well as down. Also, these tape players have
Auto-Reverse, so you don't have to rewind when the tape is over. I've
never actually used looping tapes. I tried using 3 minute looping tapes
years ago on the original Melloman, but there was too much bleeding
The tape set I included with the new Melloman is called "Poly-Ruth".
The first octave is my wife Ruth singing each note layered three times, the
second octave is from my Polymoog
doing the famous Vox Humana preset.
Like the original Melloman, each tape uses the Left and Right tracks to
provide two octaves. The left and right aren't actually routed as
stereo, they are mixed together with all of the other tape tracks to
produce a mono signal. When tuning on the control panel, each pot will
tune both octaves. But the Hi-C note has its own tuning pot.
There is a little red light under the Melloman logo that will flash
when the tapes are about to flip sides. Here's why: The Hi-C tape has
an open track. The left channel of the tape contains the highest note
on the keyboard, but the right channel is empty. In theory, all of the
tapes are rewound to the same point, and started around the same time.
The right channel of the Hi C tape contains some audio at the end of
each side that isn't routed to the output. Instead, the audio is routed
to the "Program Alert!" LED, causing a little light show. This lets you
know the tapes are about to flip sides, so be cool.
There is a drum track on the 14th Walkman, like on the original
Melloman. I provided two drum tapes for Justin. One was the disco
preset on the Wilgamat,
the other was a simple beat I programmed on the Trommemaskine.
When the drum tape is rolling, and the drum switch is in the On
position, drum beats are routed to the output. I added a groovy little
LED to flash in time with the drums. When the blue and red arcade
button is pressed, the beat momentarily switches to fill. This is also
optically like the notes, but instead of grounding the signal, the two
opto-couplers A/B the left and right tracks. Left channel is the main
drum beat, the right channel is the drum fill synched up with the main
beat (like the notes, these signals aren't stereo, they're mixed to
mono). What's cool is that the photo-resistors retain some energy, so
you hear trails of the fill in after you let go of the button. That's
what I was avoiding on the note tapes, but I used it as a feature on
the drum tape.
Tempo is controllable via a speed potentiometer on the panel. It's
wired the same way as the tuning pots, but has a wider range.
Other panel controls include main volume, tone control, and drum
volume. There's a switch that changes the output from internal speakers
to main 1/4", with a separate volume control for internal speakers.
To make room for all the tape players, and to get rid
of redundant features like AM/FM radio and alarm clock, I had
to remove the doors that keep the tapes in position. I also did that on
the original Melloman, but I was able to use rubber bands. Rubber bands
don't look so nice, and that solution didn't really work on this
machine, so I had to do something different. The solution was to use
Yamaha key-springs (thanks for the idea and the key-springs, Russ). I
cut the springs in
half, carefully bent them by hand, covered them in heat shrink tubing,
then glued a rubber thread cap to the tops. The solution works, but it
is kind of a pain to remove the tapes.
The keyboard that's used to play notes (aka gate the tape tracks) is
from a junked Casiotone. In order to make this work, I had to cut down
the keybed from 49 or so keys to 25, C to C. The original key contact
circuit board was used, but it also had to be cut. Next, the key
routing needed to be "re-matrixed". For the keying to work, each note
needs to switch to a common rail of 9v. This voltage is then routed to
the opto-coupler circuit board to gate the notes. To rematrix, you just
need an ohm meter, and you have to selectively short traces so that
ultimately, one side of each switch goes to a common point. Then you
solder the leads to the diodes. For this, the current doesn't really
need to go through the diode since all the keys are now discrete
switches. Though the voltage drop through the diodes would be small
enough to still turn on the transistors on the keying circuit.
On the new Melloman, each keyed track is sent to an active mixing
circuit. I used a TL072 opamp, and the final output is line
level mono. Switching on the Speaker Switch routes the output
through another amplifier stage to drive the two 4 ohm speakers wired
in series (8 ohm amp).
A small panel on the back of the instrument contains a grounded IEC
power socket, and 1/4" output jack.
The power comes from a switching supply that provides +/-12V and +5V
from 120VAC. Those voltages are sent to regulators to provide +/-9V and
+3v rails for the instrument.
Now please enjoy some pictures. There is a video clip at the bottom of
the page, and a link with pictures I took building the New Melloman
locked into place
Mellomen - The new
Melloman, the Drumssette, and the original Melloman