Roland TR-626 ROM Expansion


Back when I first did my expansion board for the Roland TR-505, I was regularly asked if it would work in that machine’s big brother, the TR-626. The two are very similar visually but are quite different electronically, so a new modification was in order. The TR-626 uses a 256kB ROM, twice the size of that in the TR-505, on account of it having many more sounds. The organisation is different also, but still draws on the same ideas of interleaved sounds as it’s based around the same custom chip which first appeared in the TR-707.

Sample encoding / address map

As with the TR-505 and TR-707, the sounds are encoded in ROM as 8-bit linear PCM at 25kHz sampling rate. Some are stored in sequential order, while others are interleaved in pairs. Cymbals are stored in 8K blocks, with a byte being read from each block in order. The TR-626 even uses a standard JEDEC-type ROM pinout for its sound ROM; unlike the TR-505, which had an awkward custom pinout. The only real catch with the TR-626 sound ROM is that address lines 6 & 8 are swapped. It’s easy enough to swap them back using an EPROM pin swapper utility though.

The sounds are arranged in ROM according to this table:

Sample at address Sample length Starting address
Open High Conga 8K $0000
Low Tom 1 8K $2000
High Tom 1 8K $4000
Mid Tom 1 8K $6000
Hand Claps 4K (even bytes) $8000
Cowbell 4K (odd bytes) $8001
Claves 4K (even bytes) $A000
Tambourine 4K (odd bytes) $A001
Rimshot 4K (even bytes) $C000
Bass Drum 1 4K (odd bytes) $C001
Open Hi-Hat 8K $E000
Crash Cymbal 32K (4x 8K blocks) $10000
Ride Cymbal 16K (2x 8K blocks) $18000
Snare Drum 1 8K $1C000
Snare Drum 2 8K $1E000
Low Conga 8K $20000
Low Tom 2 8K $22000
High Tom 2 8K $24000
Mid Tom 2 8K $26000
Mute High Conga 4K (even bytes) $28000
Low Agogo 4K (odd bytes) $28001
Shaker 4K (even bytes) $2A000
High Agogo 4K (odd bytes) $2A001
Snare Drum 3 4K (even bytes) $2C000
Bass Drum 2 4K (odd bytes) $2C001
Closed Hi-Hat 8K $2E000
China Cymbal 32K (4x 8K blocks) $30000
Cup 16K (2x 8K blocks) $38000
Low Timbale 8K $3C000
High Timbale 8K $3E000

The expansion board takes two ROMs. Initially one of these was for the original TR-626 sound ROM to install into, in order to retain the factory sounds, and the other took a 512kB flash ROM containing two new banks of sounds. Since April 2021, the kit is now supplied with a second flash ROM which contains a third bank of new sounds, as well as a copy of the factory sounds, so the original ROM is no longer required.

Expanded sounds

The expansion board's sounds are spread across four banks, selectable with two toggle switches. Bank 1 covers LinnDrum and LM-1 sounds, Bank 2 covers DMX and TR-707 sounds, Bank 3 covers TR-909 and TR-808 sounds, and Bank 4 is the original factory sounds.

I should mention that the way in which the 8 voices are allocated is kind of strange on the TR-626. Despite the fact that some sounds share the same key, they don’t necessarily share the same voice. For this reason, some of the key assignments for my new sounds may seem a bit odd, but the reasoning is so that you can play certain sounds together - i.e. the LM-1 hi-hats and bass drum. A full list of the sounds, and their mapping to the buttons, can be found in the manual (see below).

As the TR-626 lacks an individual output for claps, I duplicated these sounds into the china cymbal and cup memory locations for the Linn / LM-1 and DMX / TR-707 banks, so they can come out of the crash / ride cymbal outputs. These voices for some reason also have a much wider tuning range than the actual claps voice does.