My TR-505 ROM Expansion has proven itself to be a popular kit, but I was regularly asked if it would work with the TR-505’s big brother, the Roland TR-626. The answer was no, as even though the two machines look and sound quite similar, the electronics inside are incompatible. Eventually, somebody very generously offered to send me a TR-626 to keep if I could produce an expansion kit for it. Naturally I accepted.
Sample ROM address map / encoding
The TR-626, although it has more sounds than the TR-505, fundamentally works in exactly the same way. Samples are played back at 25.0 kHz, and once again 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 cyclical order.
The TR-626 even uses a standard JEDEC-type ROM pinout for its sound ROM; unlike the 505’s which had a horrible custom pinout, requiring a complicated adapter board. The kit I designed for the TR-626 does still use a board, but this time it’s to allow for two ROM chips to be switched. The only real catch with the TR-626 sound ROM is that address lines 6 & 8 are swapped (in the data). It’s easy enough to swap them back using an EPROM pin swapper utility.
Once the address lines have been swapped and the ROM’s contents are unscrambled, the sounds are arranged 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|
|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 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|
|China Cymbal||32K (4x 8K blocks)||$30000|
|Cup||16K (2x 8K blocks)||$38000|
For the new sounds, I reused all of the classic sounds from my TR-505 version, although there’s also some TR-707 sounds in there as well, thanks to the TR-626’s larger ROM size. The new sounds are spread across two banks, with LM-1 and LinnDrum sounds in one, and DMX and TR-707 sounds in the other. There's also a socket to install the TR-626's original sound ROM, so you can keep using those sounds as well.
The TR-626 has several strange quirks. One is the way polyphony is assigned across the 8 drum voices. 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 snare drum. A full list of the sounds 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, so they can come out of the crash / ride cymbal outputs.
- Schematic diagram
- PCB artwork (EAGLE)
- ROM contents (29C040 or compatible)
- Installation instructions & sound chart
This project is available for purchase as a self-install kit. It includes the pre-assembled daughterboard, DIP socket and toggle switches.