VAC CPA1 User Manual
Page 2
power amplifiers.
Since the Passive-Buffered mode has zero gain, you may need to turn the volume controls well
clockwise...the exact position depends on the output level from your source, and the sensitivity of
your power amplifiers and loudspeakers. Many audiophiles have the belief that it is never good to
run volume controls wide open. With a circuit of this type, however, it is actually preferable to do
so. Don't worry about where the control is set, just be concerned with how it sounds. The Passive-
Buffered mode does not invert absolute phase with respect to the line inputs.
The
Active modes add a Class A amplifying triode tube to each channel, and causes the main
outputs to have inverted absolute polarity with respect to the line inputs. To correct for this you may
invert the polarity between your power amplifier and loudspeakers. In most systems, the Active
mode retrieves more ambient and reverb information.
Operation - Phono Stage
Begin by selecting the appropriate phono stage gain using the control on the top of the chassis at
the right rear. The high gain position is appropriate for most moving coil cartridges. The medium
gain mode is appropriate for some high output moving coils and moderate output moving magnets.
The low gain position is for use with very high output cartridges. If in doubt, feel free to experiment
and use the settings that sound best.
Mute the preamp before switching gain.
The phono stage delivers an inverted signal with respect to line inputs. Therefore you may wish to
invert the connections at your phono cartridge if its design permits.
Cartridge load impedance and capacitance are adjusted by two rotary switches on the back of the
unit. Start at 47k ohms and 150 pf. Listen for a bit, and then reduce the impedance to 22k.
Continue until you find the best impedance setting. Next, try raising and lowering the capacitance.
When you have found the best capacitance setting, listen to a few other impedance settings to
verify your earlier choice.
In general, higher capacitances smooth high frequency resonances. Lower impedances have a
similar effect, and can also improve subjective detail.
Often the load parameters you choose will differ from those recommended by the cartridge
manufacturer. This may happen because of dynamic load characteristics, which are typically better
behaved with vacuum tube circuits. Use the settings that sound best.
The available load parameters are approximately:
Impedance
Capacitance
47,000 ohms
0 picofarads
22,000
100
10,000
120
1,000
150
100
180
220