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.
...here's a pair of KR-55s waiting for the external clock-in mod.
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).
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.
Yes, I can give you some info on how to add the external clock input... I'll email you details.
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.
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.
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.
Yes me too, it's very tempting, I'd love to know the specifics of the mod.
Can you please send me the details on how to sync this wonderful machine?
another one here who would love to try this. is there a trig mod (convert S to V) for this, too, you have?
and yet another one please if you would be so wonderful!
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 !
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 ?
This is one of my best rythmbox, really good sounds !
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!
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!
...I might do a Youtube vid for the mod if there's enough interest... although it would make it too easy!
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!
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?
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.
Thanks for your work Alienated Synthesist -- I just picked up a 55b and am curious about the din sync 24 modification as well.
Could you send me some information -- drawings, schematics, for the mod.
I totally understand your concerns -- I am actually interested in doing both trig in/clock in and also the din sync mod to be able to have the flexibility of both trig/clocking methods for my old korg/roland machines.
I'm an amateur circuit bender and am not trying to put any old timers out of business, however I am also interested in increasing the functionality of my gear and am on a budget. When I find a piece of hardware and a MODs group that can really do some great mods to that machine that I could only dream of doing, then I'd gladly send it their way! This is more for personal practice, since this is just a single mod and one that is relatively ubiquitous.
If you feel like having a correspondence, then please do drop me a line in my email!
Hi a little tip and a little problem. First, thanks for posting this ,the KR55 has really beefed up my tracks! Now the tip, the korg SQ1 will spit out 16x1 sync which the modded KR55 seemed to work well with. The little problem is that the KR55 freaks out a little before settling in. Any help with an immediate sync would be appreciated!
Hello Alienated Synthesist and thank you for this page and all the things you've shared.
Does the "Trig selector" of the KR 55 have any utility or reaction with a Trig in signal?
Thank you. Best wishes for 2018.
Hey I followed your directions on the mod, but when I trigger it externally using my roland 707 RIM OUT it clocks it really slow, sounds almost like it's half speed? Any suggestions?
Hello Mak, It needs a clock signal of 8ppq (pulses per quarter note) - a trigger out from a 707 or similar is not a clock signal... you can obviously only have a maximum of 16 triggers per bar. You need a clock divider, either derived from midi clock or dinsync... both midi clock & dinsync run at 24ppq so you need to divide by 3 to get the 8ppq that the KR-55 expects. The Kenton midi to cv converters all have a dedicated clock output that can be divided to anything you like, probably loads of other similar devices too. Don’t feed it trigger signals more than 5v or you’ll likely damage it... the 707 trigger is certainly way too hot without some kind of attenuation!
Just to get back to this -- Correct me if I am wrong, but I believe KORG runs at their standard 48PPQ and not 8 PPQ as you suggested. I believe this to make sense since I had to double the scale on the 707 as a work around to get the necessary PPQ that the KORG runs at to keep it in time with my 707(Roland runs at 24ppq).
Actually, with more research I am getting conflicting information regarding what the KORG 55's clock runs at -- 8ppq or 48ppw, not sure what is accurate.
8ppqn if you want to sync to midi or Roland Dinsync - both send 24ppqn hence the divide by 3 setting required if you’re using a clock divider. If you’re triggering it with 16ths, ie from a trigger output or rimshot etc then it will run at half speed - hence using 32nd scale from something like the 707. Later Korg drum machines used Dinsync at 48ppqn - KPR-77 and the DDM digital machines. The KR-55 was not designed with an external clock or trigger input... it’s up to us to work out a way to achieve it to suit our own requirements!
8PPQN is correct -- I have a MIDI to CV converter that I built and programmed to run DINMIDI to CV clocking functions; it works, I have to divide by 3!
Great, happy to hear everything is working.
hey-- I got it to work by sending the kr-55 a bar of 16 rim trigs and using 2:1 scale. The 707 was synced to a CR-8000 and both the CR-8000 and the KR-55 were in sync! Though now I understand what you are saying about getting the KR-55 8ppq, it is just a temporary work around until I get a MIDI to CV converter. I also referenced a second blog that describes an attenuation mod, so it should be fine! Thanks again.
Great, glad to hear you attenuated the trigger pulse & got it working... I actually love all the little workarounds needed to get all the old gear talking to each other!
Thwnk you for sharing this tutorial. I just wonder of it really is important to lift (de-solder) the right hand side of R48. I came across another tutorial (Cavisynth website) where its shown how to make a protected mod for KR55 - a very similar procedure, but without de-soldering the R48 - only soldering the tip of the jack to left side of the R48 without interrupting the circuit.
Hello TZL, it’s possible of course to do the modification in different ways... either a trigger input or clock input. Diode protection is a good idea if you’re going to be using pulses of more than 5v or if you’re not sure of trigger levels. I prefer to interrupt the internal clock if using external pulses, hence lifting R48... just personal preference.
I did it without lifting the resistor, added the protection circuit with diodes and my KR-55B is is finally modded and can sync to other gear as well as act as a master clock if the jack is unplugged from the trigger output. Wonderful. Thanks again for sharing this!!!
I’ve modded two KR55s with the clock in. The first one works great but the second one is have some clock issues when the clock in is not being used. Could you recommend anything to look for when dealing with drifty clock?
Thanks, one more question. The tempo speeds on both my kr-55 vary greatly. One when the tempo knob is half way is at a reasonable bpm i think around 115 bpm. The other is at like 155bpm. A little bongled. any ideas?
I am a *complete* novice at electronic music. I've been playing with synths for a few years, making cool sounds, but I'm primarily a guitarist (and you probably know how dull we can be ;) ). Anyway, I have a KR-55 as I wanted something I could play along with that's controllable with a foot pedal. Now I'd like to start filling out the sound with some small (like Volca sized) synths that I can sync together or drive from a common step sequencer - and I think you see where I'm going here - what do I need out of that sequencer? Is one "trigger in" as good as another? (see, I really am a novice) Since I need the rhythm to be foot-controlled, I want the KR-55 to be the master - but I could play a sequence on another drum machine and mute the 55 if I wanted.
But yeah, that's it. And sorry for the dumb question, but most synth forums assume such basic knowledge. I found your blog because I'm a tinkerer, build my own pedals, not afraid of soldering - but I just don't know how to drive a sequencer with the trigger out from the 55; and what specifications I'd need in a sequencer.
Sorry for the rambling, and thanks.
For instance, would this work?
"start the SQ1 while holding start/stop. Set the knob to CV duty, so active step and step jump are on. Power the unit off and on.
This will make it start on the first trigger and not wait for the next to calculate a clock."
SQ-1 isn't the most powerful sequencer, but it's a) $100, and b) works on Hz/V, and I've got an MS-20 Mini. I'd prefer a few smaller units to play out; but have some patches I really love at home and can always multitrack.