VAC Vintage Preamplifier - Manual (Page 3)

mechanical or acoustic stimulation encountered when the unit is properly installed and
playing music. Replace the offending tube if excessive mechanical sensitivity or ringing
occurs.
It is best not to subject the tubes to tapping or the chassis to repeated mechanical jars, as this
may damage the precision of the tubes and cause them to become more microphonic.
About Noise
Every amplifying device produces some amount of noise. In fact, even a resistor produces
noise in the presence of current flow. Acceptability is not a question of whether this
characteristic is present but rather the degree to which it is present.
The most likely source of phono stage noise are tubes V1 & V2. The audibility of noise
produced in the phono stage is influenced by the output level of your phono cartridge.
Pickups with output levels lower than approximately .4 mV may be problematic. With a
pickup rated at .4 mV output and low noise 12AX7s (V1, V2), the subjective level of
electronic noise will be approximately 1/3 of the groove noise on a good direct to disc
recording.
The most likely source of line stage noise is V6. The audibility of noise produced in the line
stage is not affected by the volume control setting, and is determined by the sensitivity of the
power amplifier and the efficiency of the speakers. With a speaker of extremely high
efficiency (for example, a Klipschorn) the preamplifier itself may be modified by VAC for
more appropriate noise and output levels. Noise should be insignificant with speakers in the
typical efficiency range.
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