The Roland Rhythm Plus PB-300 was manufactured around 1983, and was designed as a complete accompaniment device, similar to the ones found on home organs from the same era. A keyboard can be connected via midi and trigger bass lines, arpeggios or chords along with the preset rhythm selected. The Owner’s manual specifically mentions the HP-300/400 Keyboard and PR-800 Roland devices to go along with this unit. As I’m only using the unit for its preset rhythms, I’ve never hooked it up via midi to trigger the accompaniement, so I can’t comment on the arpeggio/chord/bass sounds. Maybe I’ll try it someday, but I’m not expecting much…
The PB-300 has 16 preset rhythms, plus a “fill-in measure” knob that can insert a break every 2,3,8,12 or 16 bars. You can also trigger the break manually with a button on the front panel, or with a foot switch. On the back of the unit there’s an accent knob, that allows some amount of volume variation within the rhythms.
I like the sound of this unit, which is a mix of CR and TR-era Roland drum machines. The bass drum is nice and crisp, it sits very easily in any mix; as for the snare, it’s a bit too soft for my taste; the cymbals and hi-hat are unlike any of my other drum machines — very soft and ringing, and don’t sound like a noise burst. It’s not too hard to find samples of the sounds on the web if you look around a little (see links at the bottom of this page).
The 8 sounds are: bass drum, snare drum, low tom, high tom, cymbal, open hi-hat, closed hi-hat and clave.
Below are some instructions on how to modify the unit for separate outs, and a copy of the owner’s manual.
Technical Info / Service Notes
Roland PB- 300 Separate outputs modification
One of the main problems with this drum machine, like many others from that era, is that all the sounds are bundled into one mono output. Furthermore, this machine doesn’t have any mixing capabilities, so you’re stuck with the factory set mix. Fortunately, it’s not too hard to modify the unit in a completely reversible way, with minimal work and only two solder points.
Most vintage drum machines have three jacks at the back: two outputs (same signal, high and low impedance) and a jack for the start/stop footswtich, so the quick and easy way to add more outputs is to use these jacks. I have no use personally for a footswitch-controlled start/stop, so I really don’t mind losing that feature.
In the case of the PB-300, we are fortunate enough to have FOUR jacks at the back, thanks to a totally useless “mix-in” jack allowing a signal to be routed through the drum machine and back out with the main signal. Why anyone would feel sorry losing this “feature” is beyond me!
Of course, four jacks means we won’t be able to separate all eight sounds available. For that we’d need to add more jacks, which is a more extensive and time-consuming modification than I’m willing to undertake at this moment.
My priority is always to isolate the bass drum. If I can manage that, I find the usefulness of the drum machine to increase dramatically. Here’s the output configuration I chose for this mod:
Output 1: Bass drum
Output 2: Snare
Output 3: Low and High Toms, clave
Output 4: Cymbal, Hi-Hats
I poked around the unit to find the individual sounds, and found most of them located along this big 12-pin cable, which I’ll label “connector A”:
Here’s the pinout (pin 1 is the white cable on the left):
- ??? (supply voltage maybe)
- Low tom
- High tom
- Bass drum
- Full mix
- Full mix (low volume)
- BD trigger in
- Snare trigger in
Unplugging this cable completely is not an option, because the BD and SN will disappear, so I had to find a way to pull out the sounds I wanted in a non-destructive way. Fortunately, I realized that the individual cables can be pulled out of the connector fairly easily. On the side of the connector (not the one that actually plugs in), you’ll notice a row of small holes, one for each cable. By using a tiny screwdriver, you can push in the tiny metal strip that’s keeping the cable in place, and can then pull it out easily. As it turns out, each of those cables is actually a little connector in itself, that can be then be inserted somewhere else very easily. So all I needed to do was figure out where to plug which cable, and reroute the signal as I pleased.
Next step was to free up the three jacks: mix in, fill in, start/stop. I quickly found the wire related to each of these (connectors C and D below), but simply unplugging them didn’t work; some extra rerouting would be needed in order to keep the front panel “start/stop” and “fill-in” working (connector B below).
Here’s the complete procedure for rerouting the sounds to the four back panel jacks:
- Pull out connector C, and remove the three wires going to it
Remove the middle wire from connector B, and insert the middle wire you just pulled out of connector C in its place. Solder the two remaining wires from connector C together. This will allow the start-stop button on the front panel to continue working.
- From connector A, take out pins 2,3,4,6 and 7.
- Plug the pin 6 wire into connector C, pin 1
- Plug the pin 7 wire into connector C, pin 3
- Plug connector C back in place. Now the BD and SN are routed to the play/stop and fill-in jacks.
- Remove pin 5 (the white wire) from connector D. This is the “Mix in” input wire. Solder this wire to wires 2,3 and 4 you removed from connector A. Now the toms and clave are routed to the “mix in” jack.
- Finally, wrap exposed wires with electrical tape to avoid short circuits.
After this mod, the original output jack only has the cymbals and hi-hat left, because all the other sounds have been pulled out and rerouted. With four outputs instead of one, this machine suddenly becomes much more versatile. I wouldn’t mind a few more presets, though!
|Sounds||8 (bass drum, snare drum, low tom, high tom, cymbal, open hi-hat, closed hi-hat, clave)|