Gain Structure - Lab.gruppen PLM Series Operation Manual

12 APPLICATION GUIDE
of 30 A; therefore, more care must be taken to
ensure that no breaker blows if different loads
are used.
All of the examples given will work, although the
first examples for both 230 V and 115 V operation
have a slight advantage due to their "power sharing"
ability.
As the PLM is equipped with PAL, the power supply
will limit its mains current draw (both momentary
current draw and current draw over time) to be less
than 28 A for the 230 V version and less than 53 A
for the 115 V version over time.
The 230 V version of the PLM is equipped with a
slow blow 30 A ceramic fuse.
The 115 V version is equipped with a metal cylinder
instead of a fuse due to suitable fuses at the required
current rating being unavailable.
Safety approved equipment is not required to have
a fuse, as long as this does not pose any fire hazard
under fault conditions, as is the case with the
PLM.

12.3 Gain structure

The architecture of the PLM Series provides gain
adjustments at a number of points in the signal flow
path. Thus, there are many places in which one can
adjust the levels in the PLM. Each point serves a
different purpose. The following can be used as
guidelines for adjustment of the gain settings, from
input to output. The block signal flow diagram (figure
8.1 on page 22-23) is useful as a reference to help
in understanding the signal path through the PLM's
architecture.
Locations for setting gain in the following
paragraphs refer to the Dolby Lake Controller
PLM Edition software.
Input headroom (Analog Inputs). As a rule, this
should be set to 12 dBu if the source is (or can be)
limited to 12 dBu; otherwise it should be at 26 dBu.
This setting has no direct influence on the rest of
the gain stages in the PLM, or on the overall noise
floor. The PLM's variable input gain is strictly meant
60 PLM Series Operation Manual
to provide the appropriate headroom at the input
stage. (Adjustments made in I/O Config window,
Input Configuration, left side.)
Input mixer. This setting should be left at "0" or
most setups. If only one input channel is used, the
other can be set to "- inf". (Adjustments made in I/O
Config, module pane.)
Input gain. This is used to adjust the level between
different cabinets in the system. It should be left
at 0 dB unless you want to lower the level for the
cabinet(s) driven by this module (Adjustments made
in I/O Config, module pane).
Module output gain (Levels). Two points of gain
level adjustments are provided per Module output.
They are used to balance the mutual gain between
frequency bands in a multi-way set up, and can be
described as follows:
- Manufacturer gain: This is "hidden" within the
module file and is set by the creator of the file. As
such, it is not user editable.
- Gain: This is editable by a user. The module file (part
of the fingerprint) contains a default value for this as
well as the manufacturer gain. If the manufacturer
gain is set to a non-zero value, then the default gain is
zero dB so that the user can easily see any changes
that have been made to this setting. Normally it
should not need to be adjusted by the user.
Output gain (Levels). One adjustment is provided
per output channel in the module to balance the
mutual gain between frequency bands in a multi-way
set up. Generally, this setting is derived from the
LoadLibrary "fingerprint" data within the PLM preset.
As such, it should not need to be adjusted further.
(Adjustments made in I/O Config, module pane.)
Attenuator. One adjustment is provided per output
channel in the PLM. This control replaces the traditional
knob found on conventional amplifiers. It should
typically be left at 0 dB during use. (Adjustments
made in Lab.gruppen Info, Status tab).
Amp Gain. Corresponds to the gain adjustment in
a conventional system if the amplifier was outside
the PLM. It should retain the same settings as in
the module file that is loaded: The limiter and output
gain settings in the output stage of the module were