Roland TR-505
circuit bending diary
(under construction...apparently forever)

Please visit the updated Roland TR-505 pages
at the new GumiElectronic website.


Birthday Spanking (8mb)

New track made with the TR-505 featuring the IC1 'sequencer glitch', pitch modulation, and IC11 synth bends. I've now added trigger mutes and outputs to the panel. Reverb was added to the synth track and the parts were edited in Live.

One (5.1mb)

Two (4.6mb)

Here are the first recordings of my modified TR-505. Each track used IC1, IC11, and R39 exclusively (the rest of the ICs/mods haven't been wired yet). The pitch modulation is handled by IC1, which drives an LED at different rates. The LED shines onto a CDS cell, which then changes the resistance at R39 as it flashes. The second track features the synth tones of IC11. No FX or overdubs here, just good ol' mono 505 beep and bang.

IC1 "sequencer glitch" bend

We benders owe much to squidfanny for having the nards to bend IC1 (which resulted in possibly the raddest bend on the TR-505 ever) and for sharing what he learned.

I hope to clear up any confusion over how to bend IC1 here. In my opinion, this is a "must bend" for anyone tinkering with a TR-505. The pictures below should be rather self-explanatory, but if you're having trouble, post your problem on the burnkit forum and I'll do my best to answer you there.

This is a safe, easy bend for anyone with a little bending experience. I’ve found that any combination of these pins can be connected without any system crashes or resets. The only problem I've encountered so far is that, with certain combinations of (multiple) connections, all of the drums can become muted (but they bounce right back into the mix when unswitched), so a bit more experimentation is needed to weed out the little bugs.

It might be worth mentioning that my 505 is running program v1.1 (SN 690700 and up). I'm not sure this has any effect on the results of this bend.

IC1 (RAM) pins 1-8, 19, 22, and 23 connect to IC3 (CPU) pins 43-50 and 56-58. According to the Port Assignment chart on page 11 of the service manual, these pins are designated as "output, address bus" on the CPU (whatever that means). When these pins are connected, the sequencer glitches in a variety of ways, such as swapping drums, muting drums, swapping patterns, and stuttering triplets or 32nd notes, to only name a few. Neat-o.

But there's more. Squidfanny found that this bend also effects the individual trigger outputs, and it might even be echoed through the MIDI output too (though I have not yet tested these two things).

I found that some pin connections seem to have no effect (such as 23/2, 23/7, and 23/8), while other connections appear to be redundant, so there's still some sorting out to do.

You might want to avoid pin 24 on IC1. This is a (Vcc) power pin. I haven't gotten near it.

As always, cross reference this information with the service manual and perform these bends at your own risk. You should assume that I've made some mistakes here...

'In progress' pictures

DB25 connectors (mostly) installed. I removed the TAPE and DP-2 jacks. The DP-2 PCB points had to be shorted (tip to sleeve I believe), otherwise the 505 would begin playing upon power-up. I'm hoping to retain the stand-alone integrity of the machine, hence all of the DB25 ports. I'll likely need to install one more port, which will provide a total of 125 I/O connections.

The bends so far:
R46 (switch for IC11 synth tones), IC11 (ROM), R39 (pitch up), and IC1 (RAM). That's already 41 I/O connections, but who's counting?

IC1 pin wiring from beneath the board.
Bottom left wire is pin 1. Bottom right wire is pin 23. The pins marked with red (3 upper left and 5 upper right) connect to IC3 and are designated as "input, data bus" on the Port Assignment chart. I messed around with these connections a bit and I think they can be arranged to mute individual drums, but I didn't sort it out because I had several system crashes and resets, so I desoldered the wires. I have a feeling these are the pins used by the folks on ebay advertising their MIDI mutable TR-505s as "not a circuit bending type of mod at all and performs highly musical."

IC11 pin wiring from beneath the board.
Bottom left wire is pin 1. Bottom right wire is pin 27.

IC14 'volume boost' bend

As noted on burnkit, the pins of IC14 can be connected to boost the level of each drum or drum group. This can be handy for the IC11 synth tones, which are rather quiet on my 505 depending on how it's patched (I'm not yet outputting the synth tones via audio jacks).

This bend has not been thoroughly tested, but I had no crashes when making the single-point (pin 16 to pin 'x') connections below.

Connecting pin 16 of IC14 to these pins will boost these drums in the mix:
1 - congas
2 - cowbells
3 - all drums
4 - clap/rim
5 - snare drum
12 - bass drum
13 - hi-hats
14 - cymbals
15 - toms/timbale

AutoBender v.1

I built a MIDI controlled switching patch bay to automate the bends on my Alesis HR-16 and (eventually) my Roland TR-505. It uses the MD24 kit from Highly Liquid, which provides 24 +5v logic outputs that can be turned on and off with MIDI. I added a Panasonic AQV210EH photo relay to each of the 24 logic outs and wired them to a banana plug patchbay with SPDT switches (Toshiba TLP222AF photo relays would also work if you can find them in stock). Everything is housed in Hammond case #598HSGYPBK, the largest ABS instrument case I've been able to find for a reasonable price. The AutoBender can also be used as a stand-alone patchbay/switch bank by toggling the DIP switches on the front panel.

Lots of drilling...

The photo relay PCB. Yup, should have etched instead. Still gotta learn how to do that...

Inside the completed AutoBender...

The front and rear panels. The DIP switches can be toggled ON for stand-alone (non-MIDI) operation, meaning that the SPDT switches will connect (up) or disconnect (down) the patch points. With the DIP switches OFF, the SPDT switches connect patch points to the relays (down) or to nothing (up), so the MIDI sequenced switching can be muted and unmuted in real time.

Automating the bends on my Alesis HR-16. The green jacks connect to the DB25 port (I haven't installed one on the HR-16 yet). The black jacks are switch points 1-12, and the gray jacks are switch points 13-24, each of which can be sequenced via MIDI.