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Kawai R-100 U24 Voice ROM Bends

Kawai R-100 U24 Voice ROM Bends

June 9th, 2010  |  Published in Kawai R-100  |  8 Comments

The main R-100 modifications are centered on U24*, which is the voice ROM IC. All you need to do is connect various pins on U24 to get a variety of nasty sounds, everything from rippling ring modulation to crunchy distortion to stuttering delay-like effects. The trick is figuring out which pins can be connected without frying the machine. This tutorial shows you how to do the mods safely, though keep in mind you’re taking this on at your own risk.

*There appears to be a discrepency between the component numbers shown in the service manual and those actually marked on the PCB. I’m using the PCB numbers here.

Shown above is U24, the voice ROM IC. All of the pins numbered in orange can be connected. I've left the other pins out because they're connected to ground or +5V. This leaves us with 25 usable pins--perfect for a DB25 port.

Here is U24 as seen from beneath the PCB. I prefer to solder the wires here because I think it provides a more reliable connection. Plus you can drop in a ROM switcher without having to rewire anything. But you can just solder the wires directly to U24's pins on the component side of the PCB if you never plan on swapping the voice chip.

Here is U24 with the wires soldered to the pins. The wires run to a DB25 port.

This is the inside of the case with the wires running from U24 to the DB25 port I installed on the rear of the R-100.

Here is the DB25 port installed on the rear of the case. You can connect a DB25 cable (aka SCSI) to a breakout box for patching.

Responses

  1. aphxero says:

    March 29th, 2011at 6:44 am(#)

    This is a great mod! With the u40 mod it’s super nasty!

  2. Vitja says:

    February 24th, 2012at 11:26 am(#)

    Hi.

    1 question.

    Is it safe to connect the pins of ROM and DAC.

    I’m planning to do all this mods and would like to know this.
    I want to have all usable connections in one box.

    Thanx allot!

  3. gumi says:

    February 24th, 2012at 11:48 am(#)

    Hi Vitja. In my experience it’s safe to make connections between the ROM and the DAC. Just be sure to use only the “safe” pins on each chip as I’ve documented on this site. I’ve been patching the ROM and DAC together regularly for a couple of years now without any issue. That said, do it at your own risk.

    I hope you’ll post a link documenting your R-100 when it’s finished!

  4. Vitja says:

    February 27th, 2012at 6:33 am(#)

    Great!
    I just don’t know how to run all the wires to breakout box.
    The DB25 can carry only the ROM pins.
    Is there a bigger DB for all the pins that I can use?
    I’m just about to go to local electronic shop to buy some material :)
    Happy circuit bending monday!

    and thanx for info!

    All best,

    Vitja

  5. gumi says:

    February 27th, 2012at 8:51 am(#)

    There is a 36 pin port you could use. Or you could install a 25 pin and a 9 pin, which are easier to deal with in terms of finding cables in my experience. But there’s also plenty of room on the upper right panel (near the power switch) to install DAC switches or banana jacks for patching if you prefer to keep the cabling to a minimum. Actually, there’s a ton of space for installing switches/jacks along the top panel but it requires complete disassembly of the R-100 to drill the holes. Have fun!

  6. Vitja says:

    March 13th, 2012at 2:00 pm(#)

    Hi, it’s me again!

    Two weeks ago I finished ROM bends. I followed your instruction and it works great!
    I bended just ROM chip. There was no cable that can handle more than 25 pins to breakout box. So I made my box with 25 outs which 5 of them have a switch to turn them on and one switch that you can insert between two outs so you have remote for that. There is a simple 3 channel mixer to combine 3 outs. That’s it for now.
    I will post some pics and sound samples in near future.

    I’m planning to do DAC bends also, but first I have to experiment with it, just to see how it sounds.

    Thanx for support and inspiration!

    Vitja

  7. Vitja says:

    June 19th, 2012at 11:36 am(#)

    Me again :)
    So far so good. No problems at all, I also made a controller in Abletone Live for R-100.
    I would love to make a pitch mod. How can I do this.
    Any help would be very appreciated!
    I had no time-money for DAC bends, but I had lot of fun with it.
    I love the trigger out. I can use it with my moogerfoogers and slim phatty.

  8. gumi says:

    September 23rd, 2012at 3:59 pm(#)

    Apologies for the late reply Vitja, this comment slipped by me.

    I haven’t had the time to document the pitch mod yet. But it’s the standard method of injecting an external oscillator into the R-100′s oscillator (X1 I think? Not sure, check the service manual). I use the LT1799 precision oscillator. You can buy kits from getlofi.com.

    I will document all of these updated R-100 mods eventually…

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