Roland Rhythm 55 - TR-55 Drum machine

Roland's Transistor Rhythm 55 (TR 55) drum machine came out in 1972.
Internally & sonically, its very similar to the Acetone FR6.
Controls: volume, balance, tempo, up tempo, power on-off, touch start 
Dimension: 130 (H) x 380 (W) x 235 (D) mm (5.1" x 15.0" x 9.3")

In that year (1972), Roland also released the TR-33 & TR-77
She weighs about 4 kg  (8.8 pounds) & has 13 buttons & 4 knobs.

The Start-stop Electro-static touch sensitive switch is a great feature.
You will see these on the Roland TR-77 also.
The diode above the on/off switch flashes in time with the beat.

The Up-tempo button is a double-time switch

There are 10 voices (split into 6 channels) & 10 patterns: Bossa Nova, Samba, Mambo, Cha-Cha, Rhumba, Beguine, Rock N' Roll, Ballard, Slow Rock, Waltz.
The variation knob splits the rhythms into two parts.: 2 Beat & 4 beat
- 2 BEAT: bass drum, bass + snare, foxtrot1, swing1, march and parade
- 4 BEAT: bass drum, bass + snare, foxtrot2, swing2, swing3 and tango

The 10 voices are : bass drum, low conga, high conga, cowbell, rim-shot, claves, snare drum, high-hat, cymbal, maracas

Sadly, there is no real way to mix the voices, however, the BALANCE knob does alter the balance between  bass/snare & hi hats/maracas.It allows you to cancel the HH sounds on every pattern - or to mix them to the pattern as loud as you want.

This is the base of the TR-55. It's quite portable. and comes with a carry handle.

bass/snare and hahats/maracas

Sadly there is no way to sync the drum externally.

Back panel jacks: main out low & high, plus a start/stop pedal switch.
This is ripe for modding. It's all analog with tons of  trimpots begging to be tweaked

If you pull off the backplate and tweak the trimpots you can get  that 808 bass and it's decay can be set to last forever !!!!
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For more info on the history of Roland Drum Machines click here