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Copyright Kevin Lightner,
used with permission. |
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 Manuals
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 * Audity Brochure 1980
188 KB
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 * Audity Voice
Architecture 1.2 MB
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Audity Zero Project - VCO's
Audity Voice Card The Audity is designed with a single voice on one large PCB. The voice card is less complex than I had feared, as the trimmers are manual and not under computer control. There are
calibration patches, but manual trimmers make for an easier implementation.
Circuit Description The two VCO's are based around LF353 Op
Amps, and they are a unique design never seen before or since at E-mu Systems. The parts are easy to find, so these VCO designs can be easily cloned.
The early Prophet 5 synthesizers that used SSM2030 chips were prone to pitch and
temperature instability so Dave Rossum was keen to design a much better VCO built with descrete components. He also added a very stable power supply and used a stable reference
voltage in the VCO core. This Audity VCO is similar to modern 21st century analog designs, such as the Oakley Sound Systems VCO. Dave used a LM394 transistor pair for the exponential converter.
The auto-tune VCO circuit is software based and quite sophisticated with both frequency and
track controls. In a mono synth auto-tune is less of an issue, so I will probably ommit this complexity. There is also a very stable set of reference power rails for the VCO cores, to ensure pitch stability. I will be replicating these.
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