Buzz Audio ma-2.2stereo microphone preamp - Manual (Page 10)

9
Internal Adjustments
continued
• Initial Setup.
See the previous page for the location of the trimmer pots. Set all
front panel switches (except for the PWR obviously) to the UP
position. Set the GAIN knob fully anticlockwise. The MA 2.2 should
be powered up for 1 hour before making adjustments. All
measurements are referenced to 0dBu = 0.775V RMS, (sometimes
called 0dBm).
• Maximum Gain Adjustment.
Connect an audio voltmeter to the channel output to be adjusted.
Apply a –50dBu 1kHz balanced sine wave signal to the channel input.
Turn the GAIN knob fully clockwise and adjust the MAXIMUM GAIN
trimmer to obtain +15dBu at the output. This sets the maximum
gain of the MA 2.2 to 65dB.
• PK LED Threshold Adjustment.
Connect an audio voltmeter to the channel output to be adjusted.
Apply a –20dBu 1kHz balanced sine wave signal to the channel input.
Adjust the GAIN knob to obtain +18dBu (or your desired threshold
level) on the audio voltmeter. Adjust the PK LED trimmer so that the
front panel PK LED just lights.
• Low Frequency and High Frequency CMNR.
CMNR is the Common Mode Noise Rejection, the ability of the
amplifier to reject noise common to both “legs” of the balanced
input.
Connect an audio voltmeter to the channel output to be adjusted.
Apply a +10dBu approx 1kHz square wave signal to both PIN 2 and
PIN 3 of the channel input connector. Set the GAIN knob to the
51dB marked position. Adjust the LOW FREQ CMNR trimmer for a
minimum reading (dip) on the audio voltmeter.
Change the input frequency to 10kHz adjust the HIGH FREQ CMNR
trimmer for minimum reading on the voltmeter. Return to the 1kHz
input frequency and check the LOW FREQ adjustment, re adjust as
necessary. Finally, check the HIGH FREQ adjustment null whilst still
applying a 1kHz square wave input.
•
Problems ?
Contact your dealer or Buzz Audio.
MA 2.2 USERS MANUAL VERSION-1 PAGE 9