Marshall Amplification 30th Anniversary 6912 Handbook page 6

43. Series/Parallel Selection Switch Selects series or parallel effects loop operation. Series
Operational Note F: Effects Loop
The main effects loop on this amplifier can be configured either as a series or a parallel loop by using the
series/parallel selection switch (item 43). The parallel loop (switch out) splits the pre-amp signal into two, retaining the
direct signal within the amplifier itself, whilst sending a parallel signal out to the effects processor. By turning the direct
signal within the processor to zero only an effects signal is returned to the amplifier where it will be mixed back in with
the direct signal. This leaves the original direct signal uncoloured by any circuitry within the processor. By using the
effects level control (item 28) your ideal mix of dry and effects signal can be easily set up.
The series loop (switch in) diverts the whole pre-amp signal through the effects loop and switches off the internal direct
signal. The effects level control (28) now acts as an overall master level control.
In terms of application, units that are time based (eg Chorus, Delay, Reverb etc) are best suited to the parallel loop.
Real time effects (eg. Graphic or Parametric EQ, Compressors etc.) suit series loop operation.
It is worth noting that the line in (40) and line out (38) circuit could be used as a series effects loop at 0 dBm, giving
you the ability to use both types of loop simultaneously.
44. Loop Level Selector Switch
45. Effects Send Jack
46. Effects Return Jack
47. Damping Select Switch
Operational Note G: Damping Control
This unique feature controls the power amp damping. Effectively this is the way that the amplifier drives the speaker.
High damping gives tight speaker movement and is ideal for clean sounds, where a precise and defined response gives
sweet clear picked notes and chords.
Low damping, with greater speaker movement, suits breathing heavy overdrive and full distortion. In the auto position
the amp automatically selects high damping for clean selections and low damping for crunch and lead. It is probably
best to leave the amplifier in auto mode for normal use.
48. Power Selection Switch
Operational Note H: Power selection
This useful feature gives excellent flexibility for all playing situations. When switched to half power, with only 2 valves
working, these two valves will be driven harder than normal and will therefore have a shorter working life. If a low
power selection is required for long periods then it would be better to use the pentode/triode switch (Item 52). 'Triode'
operation will give a slightly different tone to half power. 4 valves give 100 Watts in pentode - 50 Watts in triode. 2
valves give 50 Watts in pentode - 25 Watts in triode.
connection is most suitable for Graphic Equalizers,
compressor limiters etc. Parallel connection suits delay,
reverb and chorus effects. It is generally not advisable
to link distortion effects through the loop.
Selects the general level of the effects loop (-10 or
+4dB) to match processor linked to (45 & 46)
Output for connection to the input of an external
effects processor.
Input for connection from the output of external
processor.
Three position switch to select high, low or auto
damping positions. (See operational note G).
Two position switch to select high power (all 4 valves
working) or low power (2 valves working). The amplifier
must be switched to standby before selection.(See
operational note H).
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