Oberheim OB-Xa

The Oberheim OB-Xa was a synthesizer created by the Oberheim company as an overhaul of their first compact synthesizer, the OB-X.[1][2]

OB-Xa
ManufacturerOberheim
Dates1980 - 1982
PriceUS$4595 - US$5595
Technical specifications
Polyphony4, 6 or 8 voices
TimbralityBitimbral
Oscillator2 VCOs per voice
LFO2
Synthesis typeAnalog Subtractive
FilterSwitchable 12dB/oct and 24dB/oct resonant low-pass
Attenuator2 x ADSR; one for VCF, one for VCA
Aftertouch expressionNo
Velocity expressionNo
Storage memory32 - 120 patches
EffectsNone
Input/output
Keyboard61-key
Left-hand controlPitch
Modulation
External controlOberheim system

History

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, facilitating troubleshooting, 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 in June 2016,[3] Coolaudio[4][5] and Alfa[6] all started re-manufacturing some of these chips 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 which is considerably more flexible and dynamic than the basic implementation offered in the OBX. In place of this feature on the OB-Xa front panel is Filter Envelope modulation for oscillator 2, which allows the pitch to be modulated by the envelope. Another new feature to the OB-Xa is a second filter mode labeled "4 Pole".

Behringer clone

In 2017, Behringer announced it would replicate the CEM3340 VCO chips used in the OB-Xa synthesizer.[7] The widow of chip creator Doug Curtis released a statement clarifying that the replica was made without permission and that Curtis "would be deeply saddened by the attempt of others to trade on his name and to make unsubstantiated claims of equivalency to his original inventions".[8]

References
  1. "Blast from the past: Oberheim OB-Xa - MusicRadar". Musicradar.com.
  2. "Obxd: free VST plugin synth inspired by Oberheim OB-X - MusicRadar". Musicradar.com.
  3. "Home". Curtis Electromusic Specialties. Retrieved 5 July 2018.
  4. "V3340D Voltage Controlled Oscillator". Retrieved 27 April 2020.
  5. "V3320 Voltage Controlled Filter". Retrieved 27 April 2020.
  6. "Semiconductor production". Retrieved 27 April 2020.
  7. Crute, Adam (2019-07-01). "Learning the basics of FM synthesis and how it works". MusicTech. Retrieved 2019-11-06.
  8. "Curtis chip company speaks out against vintage synth cloning". FACT Magazine. 2017-03-22. Retrieved 2020-05-21.

Further reading
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