Service manual
10
Switch LED Powering [All diagrams].
The status LEDs are powered by three constant current sources based round Q3, Q4 and Q5
[Diagram XL301_1.DGM]. The order for the first chain starting from Q3 is: PHANTOM,
INSERT, EQ, FILTER, mix 1 thro 6 ON. The order for the second chain starting from Q4 is:
mix 7 thro 16 ON. The order for the third chain starting from Q5 is: AUTOMUTE 1 thro 4,
SOLO, AUTOMUTE 5 thro8, MASTERS ON. All three chains finish at the negative rail (-V).
INPUT MODULE OPTIONS.
Direct output buffer.
When fitted,this buffer can be assigned pre or post fade by inserting the appropriate link in ST6.
It is built around IC20 as a unity-gain, phase-contrasting amplifier whose common mode rejection
ratio is set by VR5 [typically 85dB at 100Hz]. Diodes D53, D54, D55 and D56 are provided to
protect the direct output circuitry from damage by excess voltage. The output is routed via
connector A17 to the channel direct out socket on the mixer rear panel.
Dual inputs.
If the dual (A and B) input option is fitted, relay RL1 is used to select the currently active
input. This selection can be made by either the Earth lift switch or the mic/line switch depending
upon the settings of option links SL1, SL2 and SL3. Refer to drawing no. XL301_LK.DGM for
details.
A dual concentric gain control option is also available when dual inputs are used. When fitted,
a relay RL2 is used to select the section of the gain control active on the alternate inputs. On
standard single input versions this relay is replaced by a link R25 and the gain control is wired
as RV1b only.