The short answer is: very little.
The CLP-911 was essentially the Japanese domestic-market version of the CLP-811. Yamaha sold the same platform under different model numbers in Japan and export markets. The most comprehensive comparison table available explicitly states that the CLP-711 / CLP-911 are Japanese versions of the CLP-611 / CLP-811.
CLP-811 vs. CLP-911
Feature CLP-811 CLP-911
Release year 1996 1996
Keyboard 88 keys 88 keys
Polyphony 64 notes 64 notes
Recording 2-track 2-track
Split mode Yes Yes
Microphone input Yes Yes
Floppy drive Yes Yes
Amplification 120 W 120 W
Speaker system 6 speakers 6 speakers
Weight 61 kg 67 kg
Market Export Japan
The published specifications are essentially identical regarding sound generation, polyphony, speaker system, amplifier >power, recorder, and connectivity.
What differs?
The differences appear to be:
1. Market
CLP-811: Europe, North America, and other export markets.
CLP-911: Japan only.
2. Cabinet design
The CLP-911 has a slightly larger cabinet and weighs about 6 kg more.
Dimensions differ slightly, suggesting a different furniture design rather than different electronics.
3. Preset songs
The Japanese model contains a different built-in song library tailored to the Japanese market.
4. Documentation and labeling
The CLP-911 owner's manual was Japanese-only.
Panel labeling and bundled software/media were adapted for Japan.
Sound and action
As far as available documentation indicates:
- same keyboard action
- same AWM sound engine
- same 64-note polyphony
- same speaker configuration
- same amplifier power
Therefore, a blind listening test between a properly functioning CLP-811 and CLP-911 would be expected to yield virtually identical results.
If you're looking at a used instrument today
A CLP-911 is best thought of as:
| "A CLP-811 in a slightly different cabinet for the Japanese market."
If you find both in similar condition, the choice should be based on:
- physical condition,
- key wear,
- speaker condition,
- whether the floppy drive still works,
- and price,
rather than on any expectation of a sound-quality advantage. The electronics appear to be effectively the same.
One interesting detail: in this generation Yamaha's real jump in capability was CLP-611 → CLP-811/911. The move from 32-note to 64-note polyphony and the much larger speaker/amplifier system was substantial. The difference between 811 and 911, by contrast, was mostly regional branding and cabinetry.
