2
WARNING!
PLEASE READ THE FOLLOWING LIST CAREFULLY
A. ALWAYS fit a good quality mains plug conforming to the latest B.S.I.
standards (UK only).
B. ALWAYS wire the plug in accordance with the colour code attached to
the mains lead (UK only).
C. DO NOT attempt to remove the amplifier chassis. There are no user
serviceable parts inside.
D. ALWAYS have this equipment serviced or repaired by competent,
qualified personnel.
E. NEVER under any circumstances, operate the amplifier without an earth.
F. NEVER use any amplifier in damp or wet conditions.
G. ALWAYS ensure that the impedance of the amplifiers speaker or
speakers connected does not fall below the minimum impedance rating.
I. PLEASE READ this instruction manual carefully before switching on.
INTRODUCTION
Marshall have specialised in the production of valve amplification
since 1962.
The unique tone and playing response of the valve has formed the
cornerstone of the Marshall “Sound of Rock”, which we have modified over
the years to cope with the changing demands of the evolving guitar player.
The JCM 900 models split into two distinct product ranges, the Master
Volume SL-X and the Dual Reverb. Though they share common ancestry
and have similar rear panel functions their applications are quite different.
REAR PANEL FUNCTIONS
The Hi Gain Master Volume SL-X and Dual
Reverb models feature comprehensive connection
and control facilities on the rear panel which are
common to both ranges.
50 Watt Models 2500, 4500,
4501 & 4502
1. Effects Loop Level Control
Adjusts the level of the effects loop from -10dBV
to + 4dBm. Higher settings match modern effects
processors and lower settings match floor pedals.
NOTE:
Some effects such as distortion and compression
are best suited to connection via the front panel
input as opposed to the loop.
2. Effects Send Socket
Jack socket for connection to the input of external
effects processor.
3. Effects Return Socket
Jack socket for the connection from the output of
external effects processor.
4. Recording Compensated Line-Out
Socket
Jack socket for direct connection to recording
equipment or PA system. The signal is specially
filtered for optimum recording performance.
5. Direct Line-Out Socket
Unfiltered pre-amp signal for connection to
external power amplifiers.
6. Impedance Selector Switch
Two-way switch for matching the amplifier to
speaker impedance. Amp heads feature 8 or 16
Ohm operation. Combo versions feature 4 or 8
Ohm options.
7. Loudspeaker Output Jack Sockets
Parallel wired jacks for linking speaker cabinets.
Ensure that the speaker system is easily capable of
handling the full amplifier power and that the
impedance (item 6) is correctly selected. If in doubt
consult your dealer.
8. Output Mode Switch
Switches the amplifier from high to low power
output. The “low” setting configures the output
stage to “triode” operation, which gives half the
rated output (i.e. 25 Watts on 50 Watts models - or
50 Watts on 100 Watt models). The “high” power
position gives “pentode” operation for the full
rated output.
9. Valve Failure L.E.D.
Indicates red when output valve fails and causes
valve fuse (item 10) to operate.
10. Valve Failure Fuse
Operates in the event of an output valve failure and
prevents any internal damage to the amplifier.
NOTE:
On 50 Watt models items 11 & 12
DO NOT
appear.
13. Mains Power Input
Connects the amplifier to the mains power supply.
NOTE:
Always ensure that the incoming mains voltage
matches that of the amplifier. If in doubt consult
your Marshall dealer.
14. Mains Power Fuse
Protects the amplifier and mains supply in the
event of a fault.
NOTE:
Always ensure that the fuse value matches the
labelling on the amplifier rear panel. If in doubt
consult your dealer.
REAR PANEL FUNCTIONS
100 Watt models 2100, 4100,
4101 & 4102
Items 1 to 8 follow the same format as the 50 Watt
models.
9 & 10. Valve Failure LED (OPV1-OPV4)
Valve Fuse (OPV1-OPV4)
In the case of output valve failure (OPV1-OPV4),
the fuse (item 10) will operate and illuminate LED
(item 9). The amplifier will continue to function on
reduced power (Using OPV2-OPV3 Only). Service
should be obtained as soon as possible to prevent
the premature ageing of (OPV2-OPV3).
11 & 12. Valve Failure LED (OPV2-OPV3)
Valve Fuse (OPV2-OPV3)
Similar functions to items (10) and (11) but
operating on OPV2 and OPV3.
13. Mains Power Input
Connects the amplifier to the mains power supply.
NOTE:
Always ensure that the incoming mains voltage
matches that of the amplifier. If in doubt consult
your Marshall dealer.
14. Mains Power Fuse
Protects the amplifier and mains supply in the
event of a fault.
NOTE:
Always ensure that the fuse value matches the
labelling on the amplifier rear panel. If in doubt
consult your dealer.
5
SL-X hbk 4/3/05 12:22 pm Page 6
