Solid State Logic 82S6XR0A0B A.4 Calibration Information, A.4.1 Microphone Input, CMRR Trim

X-Rack Mic Amp Module

A.4 Calibration Information

The X-Rack Mic Amp module is factory calibrated and should only need calibration if a potentiometer or other component has been replaced or if it is suspected that there is a problem with calibration.

In each of the following instructions it is assumed that the lid of the X-Rack has been removed and that power has been applied. It is also assumed that unless otherwise specified, all switches are released and all front panel potentiometers are at unity or minimum position as appropriate. The required accuracy for each adjustment will be specified along with the target value. All level and distortion measurements should be made with audio-band 20Hz to 20kHz filters unless otherwise specified.

All presets are accessible from the top of the unit.

A.4.1 Microphone Input
Equipment Required:	Calibrated audio oscillator and audio level meter
Test Signal:	50Hz sinewave @ –12dBu, common mode
Input and Output:	Oscillator to Mic Input and Output to the audio level meter
Unit Setup:	Set the Mic Gain to ‘36dB’ (mid-position)
CMRR Trim
Adjustment:	Adjust VR7 (CMRR) for minimum level (normally < –40dBu)
A.4.2 Line Input
Equipment Required:	Calibrated audio oscillator and audio level meter
Test Signal:	1kHz sinewave @ 0dBu
Input and Output:	Oscillator to Line Input and Output to the audio level meter
Unit Setup:	Set the Line Gain to indent (0dB) and select ‘LINE’
Level Trim
Adjustment:	1. Adjust VR6 (0dB) for 0dBu ±0.05dB.
A.4.3 Output Balance
Equipment Required:	Calibrated audio oscillator, audio level meter and a ‘balance’ adaptor (see
	below)
Test Signal:	1kHz sine wave at +24dBu
Input and Output:	Oscillator to Line Input and Output to the audio level meter via the
	‘balance’ adaptor
Unit Setup:	Set the Line Gain to indent (0dB) and select ‘LINE’
Adjustment:	Adjust VR8 (BAL) for minimum level (< 55dBr)

A.4.4 ‘Balance’ Adaptor

For the output balance adjustment, a ‘balance’ adaptor such as that illustrated here will be required. This adaptor consists of a pair of close tolerance resistors in an in-line cable and is used to sum together a balanced output in order to correctly adjust the level balance of the measured output; perfect balance should result in complete signal cancellation.

	1		3	–
	0V
		1
From unit	2	5K01**
	+				To measuring 2
under test		1	2	+
	3	5K01**			equipment

–

1 0V

Note 1. Resistor tolerance should ideally be 0.01%

2.Absolute level measured will depend upon the input impedence of the measuring equipment.

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