VAC DAC Mk II - Manual (Page 5)

The analogue output stage is all triode tube, pure Class A, zero global feedback, point-to-point wired
by hand, with both balanced and standard outputs. All components are selected based on careful
listening tests.
Front panel indication of sync and de-emphasis is made via an electron ray tube, the glowing green
'eye' familiar to collectors of antique radios. Visually stunning, this indicator is superior to both
LEDs and matrixed numeric displays because it does not generate and radiate noise.
SPECIAL INSTRUCTIONS FOR AT&T GLASS OPTIC USERS
For proper function with AT&T systems, special “air gap attenuators” must be used. These devices,
which resemble colored washers, are provided in various 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 a 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 yellow and red attenuators at the transport end and a green
attenuator at the DAC end.
Alternatively, you may employ a very long optical cable. Many users prefer this.
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.