Arrakis Systems X-mixer-14-22 Operations Instructions download pdf (Page 42)

3-16d) OVERALL RECALIBRATION PROCEDURE

IMPORTANT

- Overall recalibration is only necessary under unusual circumstances. Recalibrate if all

trimpots are moved drastically away

from factory settings or when left and right trims are in substantially

different positions. This procedure takes some time and concentration.

INTERNAL BUS LEVEL

- The key to calibration of the 1200 Series console is to set the internal summing

bus audio level to -2dBu

(.615 VRMS, 1.7V peak to peak). This maximizes headroom and signal to noise

ratio (SNR) while it minimizes distortion (THD). After the bus

levels are correctly set the output levels can be

calibrated then the input levels.

To recalibrate the entire console, follow this procedure:

STEP 1

- RECALIBRATE VU METERS

To set the console‘s VU meters you must choose a nominal

audio operating level for all the equipment in your facility. This “0VU” reference audio

level is often “+4".

Other common station levels are “0" or “+8". +4dBu nominal station operating level (+4dBu = 0VU) is

assumed for this discussion.

0dBu = .775VRMS = 2.2V peak to peak

+4dBu = 1.23VRMS = 3.5Vpp

+8dBu = 1.95VRMS = 5.5Vpp

a) With an audio frequency tone generator, feed a midband (~1kHz) tone into any line level input

module. The level of this tone is not important at this time,

nor is the fader setting on the particular input

module, however the tone should be around +4. Feed the signal into both left and right inputs.

b) Connect a voltmeter, dB meter or oscilloscope to the PROGRAM LEFT output of the console.

Measure between PROGRAM OUT LEFT

(+)

and PROGRAM OUT LEFT

(-)

. This is a BALANCED

measurement (do NOT measure between PGM L and GROUND. That

would be an unbalanced

measurement). There should be no other load on the output. Do not put a 600½ load on theoutput

unless the output of

the console is to be wired to a 600½ transformer balanced device. Be aware that

some voltmeters are not accurate at midband audio frequencies since

they may be optimized for 60 cycles.

c) Adjust the level of the tone until the voltmeter, dB meter or scope indicates +4dB. This can be

accomplished by either adjusting the input module‘s slide fader

or by adjusting the tone generator’s

output. Do not be concerned with the console‘s fader and trim pot setting at this time as we are now only

setting the VU

meters.

d) Adjust the PGM L VU METER DRIVER trim pot until the PGM L meter reads “0VU”. The VU METER

DRIVER trim pots are located on the

Output Board. See following pages for trimpot locations.

e) Repeat steps b), c) and d) for the PGM R meter

f) After confirming that the MONITOR SELECT switch is selected to PGM, repeat steps b), c) and d) for

AUX L and AUX R VU meters.

STEP 2

- SET INTERNAL BUS LEVEL

The Internal Bus Level is identical to the levels found at the input

channel‘s IC4 OP AMP. The optimum bus level is -2dBu.

a) Connect your voltmeter, dB meter or scope between an input channel‘s IC4 PIN 1 and AUDIO

GROUND. This is an GROUND. This is an

unbalanced measurement of the LEFT bus level.

b) Adjust the input channel‘s slide fader until the voltmeter, dB meter or scope indicates -2dBu

(-2dBu = .615VRMS = 1.7Vpp). It is recommended to tape

the slide fader in place to retain its setting.

c) Move the voltmeter, dB meter or scope to the input channel‘s IC4 PIN 7. Adjust the RIGHT input trim

pot until the signal reads -2dBu. Now both left

and right audio buses are set for -2.

d) DO NOT MOVE THE SLIDE FADER OR TRIM POTS on the input module. Both left and right bus

levels must be held at -2dBu

throughout the next step, Output Board calibration.

Arrakis Systems, inc. --- 6604 Powell st., Loveland, CO 80538 --- 970-461-0730 --- www.arrakis-systems.com

INSTALLATION PROCEDURES

CALIBRATION (continued)

3-16)

3.26

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Arrakis Systems X-mixer-14-22 Operations Instructions Page 42

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