VAC Model 22.1 - Manual (Page 3)

SPECIAL INSTRUCTIONS FOR AT&T GLASS OPTIC USERS
For proper function with AT&T systems, the special attenuators provided must be used. These devices,
which resemble washers, are provided in five sizes. The thinnest provides the least attenuation, the thickest
provides the greatest attenuation. The correct size for your particular application must be found by trial,
much like fine tuning a turntable.
If your transport has a metal bezel on the ST jack, start with the middle thickness attenuator. This is to be
placed over the ferule (the thin shaft that sticks out of the connector) of the ST connector at the transport
end of the AT&T cable before the cable is attached to the transport. If your transport has a plastic bezel on
the ST jack, start with the yellow and red attenuators at the transport end and the green attenuator at the
DAC end.
The correct attenuator provides clear, detailed sound with no ticks or noise spikes. With incorrect values
you will hear less detail and, in extreme cases, digital no-sync noise.
These specials steps are required with the VAC DAC because of the special quality high resolution wide
bandwidth optical receiver employed.