Manley Labs 16 X 2 Tube Mixer owner manual MIX Gains, VU Meters, General Test

ADJUSTMENTS

MIX GAINS:

There is a single trimmer on each tube board to set the summing amp gain. It adjusts the amount of negative feedback from a special tertiary winding on the output transformer back to the first tube stage cathodes. These trims are located near the top of each tube board, between the tubes. Adjustment can be done just by sliding back the top perforated cover once the two 4-40 screws that hold the cover are removed (from the back panel).

1)Using the EXT inputs, feed a +4 dBv (1.228 volt RMS) 1kHz sine wave into the mixer. Turn the MIX level to fully clockwise. Set the Monitor switch to MIX.

2)Using a known accurate VU meter, dBm meter, or multimeter set to AC volts, adjust the trimmers for an output of, 0 VU or +4 dBm or 1.228 (1.23) volts between the tip and ring of the Unbalanced MIX OUTPUTs (or XLR Pin 2 and Pin 3).

3)Alternatively, use the mixer's VU meters but this may not guarantee absolute accuracy because they also have trims that may be slightly out of calibration. Using a known reference, like a good multimeter, will show you if the VU meters also need trimming. Generally, the tube stage is expected to drift slightly especially if tubes are replaced but the VU meters should stay much more stable over time.

4)Switch channels and check and/or trim the other side too.

VU METERS:

There are 2 trimmers on the VU meter board to set the summing amp gain. It allows a few dB of trim range for calibration purposes. Adjustment can be done just by sliding back the top perforated cover once the two 4-40 screws that hold the cover are removed (from the back panel).

1)If you have performed the above MIX GAIN calibration and the VU meters are not at zero, adjust each of the VU trims (one for left, one for right).

General Test:

1)If this is a MIC VERSION, set all channels to "0" gain on the rotary switches. Otherwise, set the Mix Gain pot to fully clockwise and the Pan to Left. Feed a +4 dbm 1K tone into any channel and the left VU meter will pin hard & Mix Output should show a level of +14 dBm or 12.28 volts RMS.

2)Reduce the master MIX GAIN pot until the VU meter is at "0" which should be around 2:00.

3)Pan Right and the right VU should show near "0" VU. Don't panic if it is a bit out, there is usually a bit of variation in pots.

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