Roland CR-8000 Mod

This drum machine from 1981 is a close relative of Roland CR-78 and TR-808. It has a couple shortcomings, such as no user editable sounds, a Snare Drum with a lot of tone (what is called “Snappy” on 808) but a lack of noise / high frequency content. It sounds like a tom. Also the Hand Clap is low volume, at least on this specimen.

This CR-8000 was modified for individual audio outputs for each instrument group, a louder Hand Clap, as well as couple of potentiometers for Bass Drum and Snare Drum tuning. The BD now has two controls: Pitch and Decay, the SD has two controls: Pitch of the “snappy” portion, and Noise level.



The BD and Clap modifications are taken directly from gumielectronic. The exact changes with component values are listed further down in this article.

When servicing or modifing synths I try to conform to the part of Hippocrates’ oath that states “First, do no harm”. Therefore I made a break-out box, instead of drilling holes in the CR-8000 exterior. Also I left the original parts in place where possible, should someone want to reverse this mod in the future.

The break-out box sticks to the metal back plate of  the CR-8000 with neodyne magnets. The wires are directed through existing vent holes in the back.

The following list is an excerpt from gumielectronics’ extensive CR-8000 modifications. The red markings are the ones I chose to use (since there was a limited space on the break-out box) along with my component selections. The Snare Drum are my own changes, as some of the suggested changes didn’t make that much diggerence. C47 is Snappy Pitch, the changes after Q7 is the SD Noise portion boost.

Snare Drum specifics. The original SD sound isn’t available as it is now, it has a bit more noise content.

Here are a couple of images of the PCB and break-out box internals:

Bass Drum (green wire and some resistors) and Snare Drum Snappy (yellow wire bridging R34):

Snare Drum Noise Boost (red wires) and Snappy pitch (blue wires):

Individual outputs:

Tidying up a bit:


Caveats

Individual Outputs: The CR-8000 was not designed to have separate outs to begin with. Some things are not ideal because of this. The Clap for example, is a lot lower at the individual output than it is in the main mix. Also the accent effects are not applied to the individual outs, so in some cases the Main out instruments will sound beefier than the indy versions.

BD Decay: The Bass Drum will not have the oomph of the TR-808, maybe because of a shorter trig pulse, or some other envelope characteristic that is different.

SD Decay: Decay of the Snare Drum is hard to modify, unlike the Bass Drum. The mod point called “decay” in gumi’s description doesn’t change the overall decay of the instrument, only the length of the Snappy portion within the (very short) total length of the Snare Drum, and this change is hard to hear to be honest. I think it would take a longer trig pulse to make the Snare longer, but I haven’t tested this idea.

Conclusion

Nevertheless, I believe the changes described here are a significant improvement to the CR-8000.