VAC CPA1 - Manual (Page 3)

Grounding
Noise and hum may often be eliminated by connecting a wire from the binding post on the power
supply to the ground post on the preamplifier. The other traditional methods of curing ground loops
may also be tried. Some forms of noise may be temporary and associated with warmup of the
preamplifier and/or power amplifier. Determine correct grounding after all components are fully
warmed up. Sound quality may also be affected by power cord polarity of your components.
Tubes Compliment
V1 6DJ8/6922/E88CC phono input - should be tested for low noise
V2 12AX7A/E83CC phono
V3 12AX7A/E83CC phono
V4 12AU7A/E82CC line amplifier (active modes) & tape buffer
V5 12AX7A/E83CC output impedance buffer
Phono noise is most likely caused by V1. Line stage noise (active mode) is most likely caused by
V4.
(Historical note: The earlier CPA1 and CPA1a used a 12AT7 in the V1 position. The CPA1 Mk II
and Mk III use a 6DJ8 as indicated above.)
The V4 position has no impact on the sound of the preamplifier in the Passive Buffered mode.
Please note that power cords will have a profound influence on the character of reproduced sound
inspite of the CPA1's extensive power supply filtering and regulation, as will floating the ground
conductor.