Oberheim OB-Xa
| OB-Xa | |
|---|---|
| Manufacturer | Oberheim |
| Dates | 1980 - 1982 |
| Price | US$4595 - US$5595 |
| Technical specifications | |
| Polyphony | 4, 6 or 8 voices |
| Timbrality | Bitimbral |
| Oscillator | 2 VCOs per voice |
| LFO | 2 |
| Synthesis type | Analog Subtractive |
| Filter | Switchable 12dB/oct and 24dB/oct resonant low-pass |
| Attenuator | 2 x ADSR; one for VCF, one for VCA |
| Aftertouch expression | No |
| Velocity expression | No |
| Storage memory | 32 - 120 patches |
| Effects | None |
| Input/output | |
| Keyboard | 61-key |
| Left-hand control | Pitch Modulation |
| External control | Oberheim system |
The Oberheim OB-Xa was Oberheim's overhaul of their first compact synthesizer, the OB-X.
The OB-Xa was released in December 1980, a year after the OB-X was released. Instead of discrete circuits for oscillators and filters, the OB-Xa (and the Oberheim synths to follow) switched to Curtis integrated circuits. This made the inside of the synth less cluttered, reducing the labor required to replace bad parts, and reducing the cost of manufacture. It was getting more difficult to service the OB-Xa due to the scarcity of Curtis chips; however, Curtis started re-manufacturing these chips in June 2016 (http://www.curtiselectromusic.com/) which has breathed new life into the longevity of the OB-Xa and many other synthesizers that use these chips.
Aside from hardware changes, the OB-Xa had better interface features than the OB-X. These included being able to split the keyboard into two halves with different voices and the ability to layer voices to create thicker sound (essentially making two notes sound for every key pressed). Polyphony stayed the same - again 4, 6 and 8-voice models were offered.
One function that did disappear from the OB-X voice architecture was cross modulation, or frequency modulation of the first VCO with the second VCO. When done with analogue circuits, it's a unique sound made famous by the Sequential Circuits Prophet 5 and its poly-mod section. The lack of this feature somewhat reduced the range of sounds possible on the OB-Xa.
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