All three test discs were distributed to Optigan® service technicians. This makes them among the most rare of Optigan® discs.
T123 Test Disc
This test disc features a sine wave tone on all 57 channels. It’s mostly useful for diagnosing volume discrepancies.
- Known Revisions: —
- Rarity: ER
T125 Test Disc
This test disc features a sine wave on all even numbered channels. It’s mostly useful for diagnosing crosstalk problems, because when you open a channel that’s supposed to be silent, you can hear exactly how much signal is bleeding through from the adjacent channels.
- Known Revisions: We’re not sure if this counts, but some copies of the T125 disc are marked with a hand-scrawled “X1” just after the typeset “T125.” There is no noticeable difference in the sound of the disc, so it’s not clear what the “X1” indicates.
- Rarity: ER
T110 Test Disc
This test disc (Brian Kehew’s personal favorite of ALL the Optigan® discs!) actually features NO signal at all on any channels. It is used for diagnosing key-popping-type sounds, though we don’t see any reason why you can’t diagnose this problem by simply leaving the disc drive empty!
- Known Revisions: —
- Rarity: IR