Manley SHRIMP - Manual (Page 8)

8
2. VOLUME AND BALANCE ATTENUATORS
The SHRIMP’s volume attenuator features two conventional logarithmic-taper resistance tracks,
with the notable exception that the matching of these two tracks is especially good over the
rotational range of the control. Invariably a headache with cheap dual potentiometers, this
enticing attribute of the NOBLE attenuator set translates into very good level balance between
channels as the control is adjusted.
As an added measure of level matching insurance, the gain profile of the SHRIMP’s gain blocks
have been purposely arranged so that setting the volume attenuator at the “12 o’clock” position
will result in unity voltage gain through the preamp. A hairy judgement about the overall relative
level of any given source, as compared to its neighbors, may then be drawn from the volume
control’s position.
The balance attenuator features a special track whose resistance is zero either side of center when
the attenuator set at the center-detent position. This helps ease the voltage amplification burden of
the first gain stage, as there is no parasitic balance-control resistance to overcome when driving
the attenuator network.
Use of these controls is self-explanatory, but caution is advised if it is found that extreme control
settings are necessary when operating the SHRIMP with associated signal sources and power
amplifiers. Under normal conditions the balance control should be very close or in the center-
detent position. Balance control settings below “10 o’clock” or above “2 o’clock” are indicative
of trouble elsewhere in the system that should be investigated. The volume control can then be
put to conventional use, to throttle back louder sources, such as a CD player, or boost quieter
ones, such as older tube tuners or tape decks.
Both the volume and balance attenuator output signals are buffered by the White-follower output
amplifier stage before being routed to the output jacks. This prevents the output loads from
interacting unpredictably with the attenuators, and lowers the preamp’s output impedance.
3. PUSH-BUTTON MUTE SWITCH AND MUTE INDICATOR
A specially illuminated push-button feature switch has been provided to permit invocation of the
ever-handy output MUTE function. The switch’s built-in lamp shows the status of the mute
circuit during warm-up cycles and normal operation and as we all know, BLUE LED's make gear
sound better. The mute circuit controls the mute relay whose contacts are arranged to quench
signals present at the output of the preamp.
A flashing lamp at power up indicates the beginning of a 30-second warm-up delay, during which
time the mute relay is closed; no sound will be heard from the preamp. A steady lamp indication
means that the manual mute circuit is engaged, cutting signals from the outputs (shorting them to
ground, to be more precise). To unmute the preamp, press the MUTE button. The mute relay will
relax, the mute lamp will darken and signals will be restored to the output. The MUTE button
features an alternating toggle action, or “press-on, press-off” type of behavior.
Note that the entire 30-second warm-up cycle will not fully recycle unless the preamp has been
deprived of mains power for more than a few seconds.