Roland announced the CR-68 and CR-78 together on 1 August 1978. The October Japanese catalogue priced the CR-68 at ¥62,000 and the CR-78 at ¥105,000. In Roland’s January 1979 US list the same separation was $495 against $795. The preset model was therefore roughly two-fifths cheaper without being presented as a toy or a different class of sound source.

Both machines offered 34 factory rhythms, A/B choices, fills, rolling variations, break, accent and trigger output. Both used microcomputer control and analogue percussion. The CR-68 was the smaller machine—260 × 275 × 180 mm and 4.5 kg in its service notes—while the CR-78 was wider, heavier and carried the denser programmer panel.

The decisive difference was writable memory. The CR-78 could store four original rhythms entered with its WS-1 write switch and retain them through a rechargeable backup system. It also added fade controls and extra instrument functions. The CR-68 removed that whole programming and retention layer while preserving the immediate rhythm-arranger controls.

Roland’s catalogues place the two machines side by side in the same CompuRhythm range; they do not label the CR-68 as a home model and the CR-78 as a professional one. The visible distinction is simpler: the CR-68 cost less and omitted the CR-78’s write-and-retain system. It offered the same new family of analogue sounds and performance variations to players who did not need user memory.

That choice also reduced practical complexity. There was no write procedure to remember, no user pattern to protect and no backup battery whose failure could erase work or leak onto the board. Selecting a rhythm and pressing START produced the intended result immediately.

The cheaper sibling was therefore not simply an incomplete CR-78. It was Roland’s second answer to the same 1978 question: should a rhythm machine begin with a blank pattern, or should it begin with a useful arrangement that the player can redirect in real time?

Roland’s 1981 catalogue makes the lineage unusually visible by placing the CR-68 directly beside the older TR-66. The TR-66 is described as a compact rhythm maker; the CR-68 is offered as the more fully equipped performance machine. Roland was still selling both approaches together, but the newer model added a computer-managed phrase vocabulary rather than merely shrinking or replacing the preset box.

Each coloured rhythm button addresses two factory patterns, selected by the A/B switch. Press two buttons together and the processor combines two patterns. If three are held, the manual’s priority order decides which two survive, so combination is structured rather than an unlimited pile-up.

Begin with one rhythm and listen to its density before adding anything. The BALANCE control does not crossfade between complete patterns; it changes the emphasis between lower percussion and brighter cymbal/hi-hat material. ACCENT changes the force of programmed accented events. Those two controls can make the same ROM pattern sit very differently beneath another instrument.

Automatic variation is counted in measures. The MEASURE selector can call a variation every 2, 4, 8, 12 or 16 bars, allowing the CR-68 to articulate a phrase without user memory. In MANUAL mode, the front-panel button or footswitch requests the variation; an internal latch holds that request until the processor reaches the correct measure boundary.

FILL IN offers seven stored alternatives. ROLLING adds repeated high-bongo or snare events, while BREAK substitutes a measure of interruption. The A/B variation position can also be reversed for the variation measure, so change can come from density, repeated percussion, silence or an alternate factory pattern.

FILL IN 1–7 should be auditioned against the selected base rhythm rather than treated as a ranked list. A fill that sounds crowded over Disco may provide exactly the right syncopation over a sparse ballad; another may preserve the bass-drum footing while changing only the upper percussion. The relationship is the feature.

ROLLING HB and ROLLING SD impose two very different kinds of energy. High bongo occupies the upper-middle register and can lead into a section without imitating a conventional rock fill. Snare roll is more declarative and can dominate the mono output, so its usefulness depends strongly on ACCENT and BALANCE.

BREAK is arrangement by subtraction. Because the CR-68 normally supplies an unbroken grid, withdrawing that grid for a measure can produce more drama than adding further percussion. A band can sustain through the gap, stop with the machine or use the empty bar to expose a pickup into the next section.

RHYTHM A/B makes the variation measure borrow the partner pattern behind the same front-panel selection. This keeps the genre family stable while changing its internal event map. It is often the least conspicuous option and therefore one of the most useful for long performances.

The 12-measure interval is especially revealing. It is not a conventional power-of-two phrase length, and it lets the arranger support blues-derived or asymmetrical forms without a player manually calling every turn. The 16-measure position suits longer pop sections; 2 and 4 measures make the machine noticeably busier.

The processor reads control settings at the measure boundary after START. This is why a well-timed request feels orderly rather than chopping the current bar in half: the player asks for a change and the control logic places it into the next valid musical position.

TRIGGER OUT carries a +15 V pulse derived from the combined bass-drum, snare-drum and high-bongo timing. It can coordinate a compatible sequencer or synthesizer, but it is not MIDI and it is not a neutral metronome output. The receiving device must tolerate the voltage and will follow the rhythmic pulse selected by the machine.

A practical arrangement might begin with a sparse A pattern, introduce a second button for the chorus, use an eight-measure fill cycle, call BREAK by foot for the bridge and rebalance toward high percussion for the final section. None of those decisions is stored, which makes the performance itself the missing memory layer.

That is the user-facing lineage from TR-66 to CR-68: the first machine lets a player choose and combine the groove; the second can also negotiate musical form. It does not yet remember a new beat like the CR-78, but it can behave differently at the boundary between one phrase and the next.

The service documentation divides the CR-68 into three physical domains. GL-10 contains the µPD8048 computer and its scanning, decoding and variation logic. VG-12 contains the analogue percussion generators. RS-16A carries power-supply and output functions. Following those board boundaries prevents a control fault from being mistaken for a sound fault.

The bass drum is a triggered, damped oscillator adjusted by VR7 for a 62.5 Hz centre frequency and VR8 for a 100 ms decay. Its factory amplitude is checked separately. A trigger initiates the event; positive feedback sustains a short low-frequency ring; losses in the network make that ring collapse. Pitch, duration and level can therefore drift independently.

Low conga, low bongo and high bongo repeat the resonant principle at progressively higher frequencies. Roland specifies 208 Hz / 100 ms, 400 Hz / 40 ms and 600 Hz / 40 ms. The long, lower conga carries body; the two short bongos supply quicker punctuation. VR5/VR6, VR3/VR4 and VR1/VR2 separate frequency from decay for each voice.

Cowbell builds an intentionally non-acoustic metallic interval from two components around 800 and 555 Hz, adjusted independently at VR9 and VR10. Because the frequencies are not treated as a conventional musical chord and the envelope is short, the ear groups them as a struck object. A fault in either branch leaves a thinner, more obviously pitched remainder.

Rim shot and claves occupy the high resonant end of the board at approximately 1.48 and 2.63 kHz. Their very short events provide edges rather than bodies. The front-panel selection and shared trigger routing must be separated from the generators themselves during diagnosis: a missing label does not automatically mean its oscillator has failed.

A selected 2SC828 transistor operates as the noise source for maracas, hi-hat, cymbal and snare. Noise is a continuously irregular voltage containing a broad range of frequencies. Each voice filters and gates a different portion of it, which is far more economical than building four unrelated random sources.

Maracas uses the briefest noisy envelope, about 18 ms, so it reads as a dry grain. Hi-hat extends to roughly 50 ms. Cymbal lasts around 250 ms and exposes more of the metallic/noise spectrum. Snare occupies about 60 ms and shapes its noise to leave a stronger central attack rather than a wash.

VR11 and VR12 participate in shared amplitude setting across voice groups. This is why Roland’s check order matters: moving a common level control while examining one voice can change several voices that were already correct. Factory amplitude is a relationship across the mono mix, not eleven independent fader settings.

Accent changes the level of events designated by the pattern data. The balance network then weights low and high percussion before the main VOLUME control and the 220 kΩ high-impedance / 10 kΩ low-impedance outputs. A dull machine may therefore have healthy generators but a fault or loading problem later in the shared mix path.

For diagnosis, trace one event completely: confirm the processor issues its trigger, observe the pulse at the VG-12 input, inspect oscillation or noise after the generator, follow the envelope, then check the shared level and output stages. Only then compare its frequency, decay and amplitude with Roland’s table.

Use the correct service notes for the serial revision and observe mains-isolation precautions. Record every trimmer’s existing position before adjustment. Roland’s test arrangement uses an external negative-going pulse to trigger voices individually because the computer does not make each internal pulse conveniently available at the bench.

Confirm the supply rails and the tempo generator first. Next check that the processor scans controls, advances through a measure and issues valid triggers. Only then move to VG-12: measure each voice at the specified point with a high-impedance oscilloscope, separating frequency, decay and peak-to-peak amplitude.

The adjustable resonant targets are 62.5 Hz / 100 ms for bass drum, 208 Hz / 100 ms for low conga, 400 Hz / 40 ms for low bongo and 600 Hz / 40 ms for high bongo. Cowbell’s two components are checked around 800 and 555 Hz. Do not use an amplitude adjustment to disguise a wrong decay or tune a healthy circuit merely to match another aged machine.

For the noise family, confirm the noise source before chasing four apparent failures independently. Roland specifies approximately 18 ms for maracas, 50 ms for hi-hat, 250 ms for cymbal and 60 ms for snare. Shared level circuitry means one adjustment can affect several voices, so repeat the group in order after any change.

Finish musically as well as electrically. A scope can confirm a waveform but not a dirty selector, intermittent jack, noisy balance pot or variation switch that fails only in performance. Re-run the complete front-panel test at slow, medium and fast tempos and preserve the before-and-after measurements with the machine’s service record.

The two audio sockets on the rear panel are parallel connection choices for the complete percussion mix: a 220 kΩ high-impedance output and a 10 kΩ low-impedance output. Selecting the low-impedance socket does not reveal a second voice. Bass drum, snare, bongos, cymbal and the rest have already met in the machine’s balance and output stages.

The adjacent TRIGGER OUT is different again. Roland describes it as a nominal +15 V timing pulse derived from the combined bass-drum, snare-drum and high-bongo events. It carries rhythmic events rather than recorded percussion, and its combined pulse does not behave like isolated kick and snare audio.

Sakuma’s recollection is therefore a practical response to a real interface limit. To record the two drums separately, the studio needed more than a cable from the CR-68’s rear panel. His custom sync box let the rhythm system participate in a recording method the stock machine did not expose on its own.

Separate recording tracks change what can happen after the performance. Kick and snare can be balanced, equalised, compressed, muted or sent to effects independently instead of being committed to the CR-68’s internal mono relationship. The rhythm remains machine-timed, but the record no longer has to preserve the factory mix.

This is the bridge between a self-contained rhythm box and the networked studio instruments that followed. Roland’s later TR-808 supplied individual audio outputs directly; Sakuma’s CR-68 practice shows why a musician would want them before the feature arrived on the product itself.