X-Rack VHD Input Module Owner's Manual - Solid State Logic

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X-Rack Owner’s ManualH.4 Calibration InformationThe X-Rack VHD Mic Amp module is factory calibrated and should only need calibration if apotentiometer or other component has been replaced or if it is suspected that there is a problem withcalibration.In each of the following instructions it is assumed that the lid of the X-Rack has been removed and thatpower has been applied. It is also assumed that unless otherwise specified, all switches are released andall front panel potentiometers are at unity or minimum position as appropriate. The required accuracy foreach adjustment will be specified along with the target value. All level and distortion measurementsshould be made with audio-band 20Hz to 20kHz filters unless otherwise specified.All presets are accessible from the top of the unit.H.4.1 Microphone InputEquipment Required:Test Signal:Input and Output:Unit Setup:CMRR TrimAdjustment:Calibrated audio oscillator and audio level meter50Hz sinewave @ –12dBu, common modeOscillator to Mic Input and Output to the audio level meterSet the Mic Gain to mid-position, Trim to indent (0dB)Adjust VR9 for minimum level (normally < –40dBu)H.4.2 VHD Level/Distortion MatchingEquipment Required: Calibrated audio oscillator and audio level meterTest Signal:1kHz sinewave @ –20dBuInput and Output:Oscillator to Mic Input and Output to the audio level meterUnit Setup:Set the Mic Gain to mid-position, ‘VHD IN’ selected and ‘DRIVE’ atminimum. Trim to indent (0dB)Distortion TrimAdjustment:1. Note the output level.2. De-select ‘VHD IN’.3. Adjust VR8 until the output level matches the level measured in step 1.above. This will match both level and minimum distortion between thetwo modes.H.4.3 Line InputEquipment Required:Test Signal:Input and Output:Unit Setup:Level TrimAdjustment:Calibrated audio oscillator and audio level meter1kHz sinewave @ 0dBuOscillator to Line Input and Output to the audio level meterSet Trim to indent (0dB) and select ‘LINE’1. Adjust VR7 for 0dBu ±0.05dB.Page H-4
X-Rack VHD Mic Amp ModuleH.4.4 Output BalanceEquipment Required:Test Signal:Input and Output:Unit Setup:Adjustment:Calibrated audio oscillator, audio level meter and a ‘balance’ adaptor (seebelow)1kHz sine wave at +24dBuOscillator to Line Input and Output to the audio level meter via the‘balance’ adaptorSet the Line Trim to indent (0dB) and select ‘LINE’Adjust VR10 for minimum level (< 55dBr)H.4.5 ‘Balance’ AdaptorFor the output balance adjustment, a ‘balance’adaptor such as that illustrated here will berequired. This adaptor consists of a pair of closetolerance resistors in an in-line cable and isused to sum together a balanced output inorder to correctly adjust the level balance of themeasured output; perfect balance should resultin complete signal cancellation.From unitunder testNote0V+–12315K01**15K01**321–+0VTo measuringequipment1. Resistor tolerance should ideally be 0.01%2. Absolute level measured will depend upon the inputimpedence of the measuring equipment.2Page H-5
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X-Rack VHD Input Module Owner's Manual - Solid State Logic

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