Monday, 9 February 2015

Roland CR-8000 CompuRhythm - mods

The Roland CompuRhythm CR-8000 came out in 1981 & is without a doubt one of  Roland's finest drum machines. Often referred to as the "poor man's 808" I think it has its own unique character that is neither TR-808 nor CR-78.... but something in between. It's high hats are legendary and that bass drum certainly has a kick to it, but it has a few flaws. A lack of individual outs, and its very basic programmability are some of the limitations.

Moddifying the drum will help this instrument reach its true potential.
My friend Paul A (aka: Cobramatic), has given me permission to document some of his mods.

Paul used a combination of mods from Josh Gumi's excellent site GumiElectronic and some
Analogue Solutions mods but he also came up with a couple of mods to the mods on his own.
Most of the mods involve replacing fixed resistors with pots. The mod for the bass decay is awesome and uses just a cap and a few more resistors.

Gumi's site describes dozens of mods but Paul wanted to keep everything within the original case. So due to the lack of room a choice had to be made re the ones that appealed the most.

With this many mods there is just enough room to get 24 mini pots and switches in the top cover
(maybe a few more if you are brave) but closing all up afterwards is a real challenge with all those wires.

Obviously a breakout box is another way to go for those with the skill and patience to use ribbon cables and connectors. Plus you could also add switches to everything & even some "tone pre-sets" using fixed resistors if you are really game.

Paul did the 6 main individual outs - a must-do in his opinion. It's also theoretically possible to take out all 13 drums but this involves much more wiring. And beware, that steel plate on the back is 2mm thick and needs some careful and rigorous drilling to get through.

Paul doesn't like the suggestion of utilising the existing footswitch and sync jacks
because then you loose that valuable functionality. (especially the sync pulse outs). They are invaluable with CV/gate synths and modular's. He also uses it to sync up his modded Bentley Rhythm Ace for even more analog goodness.

 Josh's suggested voice swap to get the Tom's on a different output is a very good idea which will possibly be a future mod. For now Paul has left it out ... you know, you can't do everything.

"The sound bending is way way greater than a normal machine of course - going from crazy tuning to booming decays (open up decay all the way) and overdriven sounds". Paul now has tuneable bass drums, hats, cowbells, toms, snares and to top it off, "the worlds snappiest clap".

At the last minute he added the snare boost circuit and mounted that next to the on off switch
(so he didn't have to open her up again!).

Final thoughts
"There are an amazing set of tones now available. the Bass Drum (make sure you also do the separate decay mod circuit), Snare, Clap and Tom's are really worth doing. Hats are great too - I did my own hats mod to switch between  808 style and noise/sizzle maracas sounds which also gives the ride cymbal a fantastic harder metallic strike. The cowbell is cool if you love it but I notice it did  introduce a slight noise hum into the snare channel - no idea why, but it is not critical  and can be turned down when not using the Cow Bell"..

"Be very careful when you open her up - there is a high voltage power section that you must be very careful with while testing the mods". Paul taped plastic over this section so he wouldn't accidently touch it.
It's good to play safe. Electricity can KILL YOU

"I (Paul) also blew the fuses because I accidently let the voices board slip onto the programming board while powered up - ooopps, this could have blown the whole project and I did it twice!!! Be a lot more careful than I was and don't even try it if you cant identify the High Voltage power zone from the rest. You have been warned!"

(Sorry that the pic is upside down)

Some people say that the CR8000 is a poor mans 808 - but with these mods Paul say's he will take it any day of the week  Plus at way way way less than an 808 price even if you add $100 of pots, components, knobs and wires, you can get for yourself a highly customisable & awesome sounding analog drum machine with dinsync in and out (get a dinsync / midi swing convertor and you are set).
This coupled with the amazing "Register and Arranger" section which are not available on any other machine.
make this one brilliant piece of kit.

It's great for jamming. Plus you get to have 8 programmable 2 bar presets and 4 programmable fills which you can mix with the other presets at will. Programming it is easy once you get the hang of it (but yeah, obviously not as good as on a 808 style machine).

"This baby is definitely my favourite drum machine now - hands down.(thanks again to Josh Gumiela for the well documented mods and info on his site)".

Many thanks to Paul for his efforts. May it encourage others to get out their soldering irons and have a go.

More Links:
1. CR-8000 description & features.
2. Roland CR-8000 :: GumiElectronic
3. Roland CR 8000 with mods mov - YouTube
4. Roland cr 8000 analogue solutions tonal mod video

For more info on the history of Roland Drum Machines click here


  1. Hi,
    where did you get those variable resistor pots? I am looking all over for small footprint pots, but the smallest I've found are from a manufacture/distributor in Australia that ships only domestic; they are ~9mm wide.
    What are the specs on yours?

    all the best,

    1. Jarcar in Australia sells these. If you live overseas try Tadya or Mouser. Hope this helps. Jono

  2. This comment has been removed by the author.

    1. tRY Tayda

      or Modular addict

      They are not exactly the same but also have a small footprint. Hope this helps. J