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DACS TEST LAB - Audio test box

Designed for engineers to provide swift but rigorous fault investigation, either on site or in the workshop, the Test Lab was conceived in the field by DACS installation engineers and developed by the company's design team to address the tests they needed to solve technical issues which arose during installation and live sound projects. Further optimised after input from audio professionals, the result is a portable test unit operated by battery or AC power where available.

Tests include cable and signal path integrity of both remote and local signals using an LED bargraph and loudspeaker; correct wiring of cable connectors by cycling through pins to reveal open, shorted or reversed connections. The inbuilt signal generator can send low distortion tone at three frequencies or pink noise to external units. The power inlet provides an indication of the presence and voltage of the AC supply; illumination is provided for soldering or checking connectors.

The Test Lab is constructed in a rugged steel case with a non-slip base, 168 x 130 x 58 (l x w x h)mm. The majority of controls and connectors are on the upper surface. The centre of this surface is dominated with two columns of LEDs which show audio output and input levels on the two banks of connectors which flank the LEDs. Above the columns, a row of three LEDs show if the unit is running off the internal battery, 110V AC or 240V AC. At the lower end of the columns a rotary control adjusts the output level from the signal generator, and below that are two columns of three LEDs which are used for the cable testing mode . Below these is the rotary 'Mode' switch.

On the left, the first output connector choices are a pair of terminals with sockets for 4mm plugs and a Neutrik NL4MD Speakon connection. Both these are fed by a power amplifier capable of driving four ohm loudspeakers. Further output connectors are an isolated RCA (phono) socket, a three-pin, male XLR and a 3-pole, 6.35mm jack socket. Input choices on the right are Speakon, isolated RCA (phono) socket, and a three-pin, female XLR combined with a 3-pole, 6.35mm jack socket.

Signal path testing

To check the level and content of an incoming signal, the unit is switched on and the cable is connected to one of the 'Audio In' sockets. The incoming signal level is indicated by the right hand LED bargraph meter, from -19dBU to +8dBu in 3dB steps. The signal content can be auditioned for anomalies on the built-in loudspeaker, it's volume can be adjusted using the rotary control on the top surface. Note:The output is on Speakon circuits 1+/1- and 2+/2-; the padded (26dB) Speakon input also reads circuits 1+/1 and 2+/2-.

Cable testing

To test cable connections, the mode switch is set to 'Cab test' and the test circuitry sends a test voltage from each of the connector pins in turn. The two ends of the cable are connected to the appropriate 'Audio in' and 'Audio out' connectors. The 'Audio Out' side of the three LEDs shows which wire and pin is under test and the 'Audio In' side shows which wires and pins to which it us connected, or if it is not connected to any. A special facility for testing Speakon connections helps to identify connection on a 4-wire connector by reducing the illumination level for circuit 1+/1- to 2+/2- and 2+/2- to 2+/2- tests.

Remote testing

The remote female XLR socket provided with the Test Lab mirrors the 'Audio Out' LED column on the main unit . Hence, for example, by plugging the female connector of each cable into the Test Lab itself, and the male end into the remote socket, two people, each at either end of the cables, can test the continuity and connectivity of multiple cables very rapidly. For remote testing to work, however, at least two conductors must be connected.

Test tones - Mode switch

The switch offers the following choices: 70Hz, 1kHz, 4.5kHz test tones; frequency cycle (the three frequencies in order, repeated continuously); pink noise. The level of the oscillator output is shown on the 'Audio Out' LED column and may be adjusted using the control provided. The Speakon and parallel-connected terminal outputs are fed by a internal power amplifier which is capable of driving speakers directly down to impedances of 4 ohms at a maximum level of +8dB (assuming AC operations or sufficient battery power).

Power and lights

The sides of the Test Lab extend above the upper surface to provide protection and to provide a mounting place for illumination LEDs - which light up the connectors while they are soldered or inspected - and an LED torch on the side for inspecting equipment. The illumination LEDs can be either white or red, the latter to help retain night vision. A rotary 'Power & Light' switch has six positions, 'On' referring to 'power on': Off, On, On with red illumination LEDs, On with white illumination LEDs, On with front torch, On with front torch and white illumination LEDs.

Power - Battery

The Test Lab is normally powered by a pair of 9V, PP3 batteries housed in a dual compartment. One battery powers the test circuitry, the other powers the illumination LEDs and the front torch. A battery power LED is lit during battery powered operation. To conserve battery life, only the top LEDs of the bar-graph meters are fully illuminated during battery-powered operation. The remaining LEDs are illuminated at a slightly lower level. The Test Lab will automatically switch to 'Sleep' mode after approximately 10 minutes if the mode switch has not been changed. To exit Sleep, the switch must be turned to a different setting or the unit turned off and on again. Sleep mode does not operate when the unit is powered by the AC. When the battery power falls below 7.6V, the battery power LED will start to flash off and on. The length of the LED off-time is proportional to the extent of the voltage drop below 7.6V - the longer the off-time, the lower the voltage. As a further indication of low battery power, the bar-graph display will also alternate between full and reduced illumination levels. Should the battery powering the test circuitry run out, it is easy to swap with the illumination battery, which is likely to be less depleted.

Power - AC

Battery power is automatically turned off, and the red 'Battery' LED is extinguished when a live AC connection is plugged into the IEC socket at the rear of the unit. Depending on the voltage of the AC input either of the two other LEDs will light up; the yellow showing that 110V AC power is being supplied to the input, or the green, showing that a 240V AC supply is being provided; a useful test for mains cables, giving immediate information as to whether an IEC cable is live or not.

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