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 10

mF to 33mF capacitor in

the specified pc board location (polarity does not matter). Refer to

the following table:

Channel

Remove Resistor

from:

Place 10

mF 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