Telex MCE325 manual True Sidetone Adjust

8Repeat for channels 2 through 4 by activating the TALK buttons, connecting to the test points and adjusting the potentiometers as indicated in Table 4.4.

True Sidetone Adjust

1Configure the DYN MIC HEADSET jack for stereo mode (See Section 3, “MONO”)

2Set all front panel buttons to off.

3Connect 51 ohm load resistors across the left headphone output (J2 pins 3 and 4) and right headphone output (J2 pins 3 and 5).

4Connect an AC voltmeter across the left headphone output.

5Remove the signal generator from the mic input, and connect it across intercom channel 1. Adjust the generator output to –1 dBu (0.69 VAC), 1 kHz.

6Activate the CH 1 TALK button, and adjust the CH 1-3 volume control (R1) until you measure 11.2 dBu (2.82 VAC) across the left headphone output.

7Disconnect the signal generator from intercom channel 1. Adjust the generator for minimum output, and reconnect it across the DYN MIC HEADSET jack mic input (J2 pins 1 & 2). Readjust the generator output level to –45 dBu, 1 kHz.

8Turn on the MIC ON button.

9Adjust R37 (sidetone) on the MCE325 main board to obtain 8.7 dBu (2.1 VAC) at the left headphone output.

Level and Frequency Response Check, Intercom Channel to Headphone

1Set all front panel buttons to off.

2Remove the signal generator from the mic input, and reconnect it across intercom channel 1.

3Adjust the signal generator output to –1 dBu, 1 kHz.

4Preset the CH 1-3 volume control to the 2 o’clock position.

5Activate the CH 1 TALK button. The left headphone output level should be 11.2 ±2 dBu (2.2 to 3.6 VAC).

6Adjust the CH 1-3 volume control to measure 11.2 dBu (2.8 VAC) at the left headphone output. Check for no distortion or clipping in the output.

7Adjust the signal generator output to –1 dBu, 100 Hz. The left headphone output should read

10.2dBu ±2 dBu (1.9 to 3.2 VAC)

8Adjust the signal generator output to –1 dBu, 10 kHz. The left headphone output should read

7.8dBu ±2 dBu (1.5 to 2.4 VAC).

9Repeat the test for channels 2 through 4. For channel 3, continue to use the CH 1-3 volume control and monitor the left headphone output. For channels 2 and 4, use the CH2-4 volume control and monitor the right headphone output.

Table 4.4 Channel 1-4 sidetone trimmer adjust.

TALK BUTTON	TEST POINT	POTENTIOMETER
CH 1	U5 pin 7	R57 (Sidetone 1)
CH 2	U5 pin 1	R73 (Sidetone 2)
CH 3	U7 pin 1	R88 (Sidetone 3)
CH 4	U7 pin 7	R104 (Sidetone 4)

4-6C S I - 2 0 0 U s e r I n s t r u c t i o n s