Specifications

5
English –
INTERNAL MODIFICATIONS
WARNING!
Voltages in this equipment are hazardous to life. No
user-serviceable parts inside. Refer all servicing to
qualified service personnel.
Disassembly
To access the printed circuit board (pc board) for internal
modifications, use the following steps:
1. Unplug the power cord.
2. Remove the knobs and retainer nuts from the front panel
(See Figure 2).
KNOB ASSEMBLY
Figure 2
3. Remove the four screws at each corner of the back panel.
4. Remove the two screws at each bottom corner of the front
panel
5. Slide the back panel and pc board out from the rear of the
chassis.
CAUTION: When reassembling the SCM268, DO NOT OVER-
TIGHTEN the knob retainer nuts. Use a minimal amount of force
to secure the nut (0.6–0.8 N⋅m (5–7 in⋅lb)). Damage to the internal
components will result if too much force is used.
Low-Cut Filter
To bypass the built-in low-cut filter for a given channel, re-
move the specified resistor and place a 10mF to 33mF capacitor in
the specified pc board location (polarity does not matter). Refer to
the following table:
Channel
Remove Resistor
from:
Place 10mF to 33mF
Capacitor in:
1 R18 X17
2 R28 X27
3 R38 X37
4 R48 X47
To select a particular corner frequency for the low cut filter,
remove the R18, R28, R38, or R48 resistor for a given channel as
specified above. Then, in the corresponding pc board location
(X17, X27, X37, or X47), place a capacitor of the specified value
(polarity does not matter). Refer to the following formula for se-
lecting the correct capacitor value for the desired corner frequen-
cy.
26.5
F
C =
where:
C = value of capacitor in mF
F = corner frequency (–3 bB) for low-cut filter in Hz
The following table lists the low-cut frequency corners for
some of the most common capacitor values:
Capacitor Value (mF)
Low-Cut Frequency Corner (Hz)
.033 803
.047 564
.068 390
.1 265
.22 120
.33 80
.47 56
.68 39
1.0 26.5
2.2 12
Phantom Power Disable
To disable phantom power for a given microphone input, re-
move the specified resistor as listed in the following table:
Channel Remove Resistor:
1 R15
2 R25
3 R35
4 R45
Line Pad
To insert a 50 dB line pad for a given microphone input, re-
move the specified resistor and short the solder points at the spe-
cified pc board locations. Refer to the following table:
Channel
Remove Resistors: Short Solder Points:
1 R12, R13 X11 and X14
2 R22, R23 X21 and X24
3 R32, R33 X31 and X34
4 R42, R43 X41 and X44