3
Setup:
It is always recommended to remove all tubes before shipping the unit. Be sure that the
LS 300 is NOT connected to AC power and that power plug is disconnected from the
external supply and wall outlet. Install (2) 6922 signal tubes in 9-pin ceramic sockets and
(2) rectifier tube in ceramic octal sockets in preamp prior to use. All tubes may only be
inserted one way.
After tubes are installed, connect both Left (L) and Right (R) umbilicals to the ‘male’ 8-
pin barrel sockets on the back of the preamp, labeled PWR(L) and PWR(R). The
umbilicals must be lined up with pins and then outer barrel securely tightened until
connection is secure. Connect the other end of the two umbilicals to the two ’female’ 8-
pin barrel sockets on the external power supply labeled (L) and (R) and secure in the
same manner. Both umbilicals are identical, but they must be connected to the
corresponding (L) or (R) connector at both power supply and preamp end. If they are
not connected properly, the unit will not operate as intended. They will only fit one
way, via ‘male’ and ‘female’ pin connections at umbilical and chassis/jack connectors.
Only after this, should the power cord be connected to the external power supply.
The LS 300 has two sets of fully balanced inputs, located on the back of the unit, labeled
‘BAL IN 1’and ‘BAL IN 2’. The next two inputs are single ended RCA connections,
labeled ‘III’ and ‘IV’. The fifth set of RCA inputs is the Home Theater Bypass inputs,
labelled ‘HTBP’. Inputs are manually selected only, via the left hand rotary selector
switch. There are five positions, starting with BAL IN 1, BAL IN 2, III, IV and HTBP.
HTBP (Home Theater Bypass operation may be selected at any time by depressing the
HTBP button. All source inputs are received the same by the unit, except for HT/BP
input. HT/BP input should ONLY be used as input from a Home Theater
Preamp/Processor or other source with built-in volume control. This input only, may be
configured to bypass all gain and volume control stages, directly feeding RCA Main
outputs. When HT/BP button is depressed and LED illuminated, any input connected to
HT/BP RCA jacks will be routed straight to RCA main outs only, bypassing all gain
stages and volume control. CAUTION: WHEN LS 300 IS POWERED DOWN,
HT/BP INPUT AUTOMATICALLY DEFAULTS TO HOME THEATER BYPASS
MODE.
The LS 300 has two sets of fully balanced main outputs, labelled ‘BAL OUT 1’ and
‘BAL OUT 2’. There are also two single ended RCA main outs, labeled ‘MAIN 1’ and
‘MAIN 2’.
NOTE: There is a ground toggle switch on the rear of the unit labeled ‘GND(1)’ and
‘GND(0)’. When this toggle is in the GND(0) position, then RCA and XLR outs may be
used at the same time, with XLR outs acting as SE outputs, by grounding pin 3 of the
XLR jacks. When operating in fully balanced XLR output mode, you must flip the toggle
to the GND(1) position. This then allows fully balanced output operation ONLY. Use of
RCA outs with ground switch in GND(1) position will cause a system hum.
