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socket is used and how the switch is set.
In one position the two sockets are for either 4Ω or 16Ω, as indicated on the unit,
whereas with the switch in the other position either socket can be used to drive an
8Ω cab or both sockets can be used to drive two 16Ω cabs (in parallel), also indi-
cated on the unit.
When using more than one speaker cabinet the overall affective impedance should
be correctly worked out and the appropriate socket used.
For two cabinets in parallel this can be done as follows :-
Z
(total impedance) = Z
T
Therefore, as an example, if two 8Ω cabinets are used,
8 x 8 = 64 = 4 so the 4Ω socket should be used.
8 + 8 16
OUTPUT DAMPING
The OUTPUT DAMPING control determines how much effect the speaker cab has
on the output stage.
High damping, with control fully anticlockwise, provides a lot of negative feedback
which basically attempts to correct any distortions that are occurring in the output
stage and speakers, this produces a tighter, cleaner sound with flatter response.
Low damping, with control fully clockwise, restricts negative feedback and therefore
allows the speakers to be more loosely coupled to the amplifier. The speaker cabi-
nets own impedance/frequency curve is then superimposed on to the overall sound.
The effect will depend on what kind of speakers and cabinet are used but generally
this produces a looser, more harmonically rich sound with lots of bottom end.
When Channel 1 is selected, which is predominantly for clean sounds, more damp-
ing will automatically be applied to keep the sound clean and tight. The user does
have some control but it is over a smaller range than on Channels 2 and 3.
As stated before the further clockwise this control is set the less effect the PRES-
ENCE control will have, this is basically because less signal is being sent back from
the output transformer to the phase splitter for the PRESENCE control to work with.
PENTODE/TRIODE SWITCH
The power stage can be set to either PENTODE or TRIODE operation.
PENTODE position is the full power mode and has generally a more powerful
sound.
TRIODE mode produces around half as much power and therefore has less head-
room, this produces power amp distortion earlier.
x Z
1
2
Z
+ Z
1
2
21
22
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