ARP Omni2 -1977    Weight= 43Lbs. Number mfg.= ? MRP=$2450


User Manual:Koltsov
Reset Proceedures: N/A
Operating System code: N/A
MIDI or other control protocol:N/A
Software related Links:N/A
Patches or knob settings:
Circuit Overview:
Scematics/Service Manual: fdiskc archive or Lo-Res
Common Service Issues/Tips:
Parts Sources: Keys knobs semiconductors misc
Uncommon chips/modules used:MK50240 TOS, TDA0470(0) Trans. arrays, MN3002 BBD, CA3086 trans. array.
Modifications: gearhack page incl. Tim Smith's filter mod. (Tim was a friend of mine who died a few years back.)
General Info Links: Vintage Synth Explorer
ALSO check out The Synthesizer Playground's Promotional recording!





















Circuit Overview:
     TOS chip creates HF square waves of octave and they are divided down and filtered on 'upper' and 'lower' voice boards to create waveforms for synth, Bass and string timbres. BBD's are used to create the phaser effect. There is a 'single trigger' switch which causes the envelope for BOTH the synth and bass section not to retrigger until all keys are lifted at once. However this does not affect the 4 string presets whose Attack envelope is triggered by the first key struck and remains at sustain preset level as long as any particular key is held. When any key is released they enjoy their independent release envelope. However the attack is always "Single trigger" on the string section.

















Service Tips:
     Lots of Tanatalum caps that tend to go south on these. I just replace them all. Both the 22uF ones that are abundant on voice boards (envelopes) and power supply ones fail often which includes those used to locally filter voltages on other boards. While expensive tantalums may last longer (though..these didn't...Tellason tells me because on certain settings voltage may exceed 25V slightly.) I use cheap 22uF 35V electrolytic caps and they work just great for the envelopes...as though that's any surprise. Roy Tellason informs me they used Tantalum caps because the tolerences were tighter at the time. These days I don't see a lot of variation in a typical lot of electrolytics.
      The last Omni one I worked on had three failed sections in 4069 inverter chips, a broken lead on a capacitor killing the string signal coming back from the phaser board.
     Also I've seen the op amp fail that mixes signals in front of the left rear plug and a few other miscellaneous components on these. Unfortunately the schemos aren't great. Someday..hopefully a better copy will appear.


















Parts:
Lots of discrete parts in these. I have a scrap Omni Mk 1 unit with no upper board. Always feel free to ask or check my Parts
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