Monday, 10 October 2011

KR-55 clock-in mod

The Korg KR-55 (or Rhythm 55) is a great sounding drum machine. Originally released in 1979, it followed on from the MiniPops series of preset rhythm machines and was in direct competition with Rolands CR range. While it is not programmable, it is pretty flexible with lots of variations and some excellent fill-ins. There are no individual outputs but at least it gives some control over the voices with seperate(ish) volume pots. You can hear the KR-55 on many late 70s, early 80s tracks - Mute Records guvnor Daniel Miller made great use of it's trigger output, driving his ARP sequencer and of course the excellent snare drum can be heard throughout Depeche Modes Speak & Spell album.
It's one major drawback is that it has no sync or clock input and this makes it a bugger to integrate into your set-up...
...here's a pair of KR-55s waiting for the external clock-in mod.
It's a fairly straightforward process, lifting one resistor and using a switched jack, but there's not a lot of room on the rear panel to mount the new jack socket...
care needs to be taken when fitting the jack socket so as not to foul the top pcb when the machine is re-assembled.
The KR-55 runs at 8ppqn so a clock divider is required if you want to sync it to midi or sync24. The clock output on the Kenton midi to cv converters is ideal for this (divide by 3).

Here is some further information on the Clock Input mod for those interested…
There are two large circuit boards inside the KR-55, the upper pcb is the voice board and the lower one is the logic board and this is where you need to work…
The upper voice board needs to be removed, there are five screws securing it, remove them and carefully lift the board over… You may also need to carefully unplug the connecting cables to give you more room. You can now unscrew the PCB pillars to remove the lower logic board...

Locate R48 on the logic board (it's just below IC3, see pic below)… this is where to access the internal clock. Lift (de-solder) the right-hand side of R48… connect a wire from the new mini jack "tip" to the lifted leg. Connect a wire from the mini jack "contact" to the pcb pad the leg was lifted from. Connect a wire from the mini jack "sleeve" to any 0v point (gnd).

Now, when a jack is inserted to the new socket, it disconnects the internal clock from R48 and inserts the external clock signal instead… Removing the jack restores the internal clock. You can, of course, use a separate switch to select between internal or external clock but I chose the switching mini jack as there really is very little space inside the rear panel.
The clock input should be 5v positive pulses. Do not use gate or trigger signals that are more than 5 volts without some form of attenuation.
When using an external clock you will need to press the Start button on the KR-55 before sending the clock signal - this puts it in "ready" mode.




Disclaimer: Only attempt this modification if you are confident to do so and understand what you are doing. I accept no responsibility if you damage your machine.


29 comments:

  1. Hi There,
    I am trying to add DIN sync to my Kr-55 but we are having trouble locating info online to complete it. Do you have any instructions for doing this? We have the schematics but they dont show where the clock is or where the tempo control pot is to trace back...
    Thanks in advance,
    slipmath@yahoo.com

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  2. Yes, I can give you some info on how to add the external clock input... I'll email you details.
    J

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    Replies
    1. ...and yet another one in Sweden :)

      tom at kmh-skolan dot se

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  3. hi, i need some info too for add external clock input and voices triggering.....
    please could you send me some info to
    aliensynthfriend@yahoo.es
    thanksssssssss
    ivan.

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  4. hi.. please send me info as well if you can -- don't have a machine or interface to do Trigger Ins yet, but slaving the KR-55 to another clock would be a nice start.

    Thanks!
    toddsines [AT] gmail [DOT] com

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  5. Hi, I'm looking for a schematic of this modification. I have a drawing for a much more complicated Sync24 modification, but I'd also really like to see this simple trigger input (and any other KR55 mods). If you happen to reading this, and you have some of this info, please email me: synthbay at gmail dot com.
    Thanks!!

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  6. Hey

    Im also interested in the simple clock input which resistor do I lift etc.. please mail me at grierjamie at hotmail dot com

    Good schematic for sync 24 here http://www.flickr.com/photos/31603983@N05/5118129592/sizes/o/in/photostream/

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  7. Hi. I too would dealy love to know how to do the clock-in mod (and individual outs, tuning and envelope mods etc. etc. but one thing at a time,eh?) if that's possible.
    Thanks.

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  8. Yes me too, it's very tempting, I'd love to know the specifics of the mod.
    It's a wonderful machine.
    lucamanga at tiscali dot it
    Thanks.

    ReplyDelete
  9. Hi,
    I can imagine you are getting tired of the same requests:)
    Can you please send me the details on how to sync this wonderful machine?
    Would be a great help!
    margueritarecordings at gmail dot com
    Thank you.

    ReplyDelete
  10. hello
    another one here who would love to try this. is there a trig mod (convert S to V) for this, too, you have?
    brotmanandshort at gmail dot com
    thanks!
    j

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  11. and yet another one please if you would be so wonderful!

    n at thenormanconquest dot net

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  12. Hello to all who have asked about the KR-55 clock input mod... I will post details here soon including schematics...
    A.S

    ReplyDelete
  13. Hi, another KR-55 owner here... I'd really love to try this too! :-)

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  14. I too would like info... skunk3 (at) gmail (dot) com

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  15. Hi, I'd also love to have the information about the KR 55 mods ... I think this could radically change my use of this BAR. Thanks in advance !
    my mail : romain (dot) mascagni (at) gmail (dot) com

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  16. hi there. yet another chasing details of this mod. woz_r (at) hotmail (dot) com. greatly appreciated

    ReplyDelete
  17. OK, I've added some info on the Clock Input mod for anyone that's interested…

    ReplyDelete
  18. I modified my KR55 a lot and I made a clock with midi trigger but I have some step errors ... Can you give me infos about your clock input ?
    My email is playboysbend - at - gmail.com

    This is one of my best rythmbox, really good sounds !

    Thanks a lot
    best

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  19. Hi everyone! Thanks for sharing this experience. I am indeed interrested into doing this mod, I think information here should be enough to complete it for my tech. There is one more mod I would really like to perform, I know some people have done it but can't find any other infos. What I want is to add some insert points right after the individual volume knobs, so that you get multi output, but only when you actually insert a cable on individual tracks, unless it stays grouped to master. This way you can take 1 or 2 instruments off the mix to make separate treatment, especially for BD and snare. Anyone tried this at home and want to share experience? Thanks!

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  20. Hello, I have a KR MINI (KORG), do you have any idea how can I add an external clock?? Another idea I have is to add a MIDI input to control the device externally, do you think this os possible?? Thanks!

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  21. Thanks for sharing this...will try my best to do accomplish this mod. The info already postee seem to be enough. Man....if you could do a youtube video of this...

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    Replies
    1. ...I might do a Youtube vid for the mod if there's enough interest... although it would make it too easy!

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  22. for those asking about individual outputs for the KR-55... it's pretty simple to tap an output from the instrument volume knobs. Obviously you'll get some grouped sounds but you'll have individual outputs for the key ones. It's a more complex task if you want the sounds cancelled from the main mixed output though. Personally I've not added individual outs as I prefer not to modify vintage machines too much...

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  23. Hey there, Love you blog posts about the Kr55 mods. Can you help with a suggestion? I am looking for a device to send tempo info to a modded Kr55 as well as a microkorg so I can get the arpeggiator on the microkorg to work in time with the Kr55. I am new to the field of electronic music (I am a singer/songwriter) So I feel pretty naive!

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    Replies
    1. Dave, with the Microkorg you're going to need to involve MIDI. Unfortunately there's no simple way of syncing the two on their own... you need something with a master clock (DAW, midi sequencer etc) and a midi to sync clock converter for the KR-55. The Kenton midi to CV converters will do the job. I'm sure there are other devices also that will achieve the same thing. The Microkorg arpeggiator can be awkward to sync even with modern gear let alone pre-midi machines like the KR-55...

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    2. Thanks for the reply! Great to have a little help on this. Looking at their site, Kenton makes a lot of products any in particular that work best?

      As a follow up, would it be easier to use the trigger out from the KR 55 to trigger a midi device like the Microkorg? If so, is there a converter needed?

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    3. converting analogue triggers to midi clock is not straightforward unfortunately... there is information out there on the subject and there are guys that specialise in midi sync systems - have a look at the Innerclock website, some great stuff there.
      Easiest way to integrate the KR-55 into midi set-ups is via something like the Kenton Pro Solo - clock out into the modded KR-55 clock input...

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