ELECTRO-VOICE 7200 (01) PDF Document

To re-strap the primary of the power transformer on your ELECTRO-VOICE 7200 for 220/240 V ac applications, use the following procedures. The amplifier is provided from the factory strapped for 120 V ac operation.

WARNING: Verify that the power transformer’s primary circuit configuration is correct for the intended ac line voltage BEFORE applying power to the amplifier.

1. Make sure the amplifier is not connected to any power source.

2. Remove and save the seventeen screws securing the top cover.

3. Locate terminal block TB1 located behind the AC main power switch. Reconnect the leads for 240 V ac Primary Wiring as shown in diagrams for the ELECTRO-VOICE 7200.

4. Install the top cover with the seventeen screws previously removed.

5. Install the 2.5A fuse, T2.5A /250V slo-blo or equivalent.

6. Install the 230 Vac 50/-60Hz and the T2.5A/250V decals in the proper positions.

Rack Mounting

The ELECTRO-VOICE 7200 amplifier may be installed in a standard 19 inch equipment rack. It requires 3.5 inches of vertical rack space and secures to the rack cabinet with the four rack mount screws and cup washers provided in the hardware kit.

Ventilation

The amplifier must be adequately ventilated to avoid excessive temperature rise. It should not be used in areas where the ambient temperature exceeds 50°C (122°F). To determine the ambient air temperature, operate the system in the rack until the temperature stabilizes. Measure the ambient air with a bulb-type thermometer held at the bottom of the uppermost amplifier. Do not let the thermometer touch the metal chassis because the chassis will be hotter than the ambient air. If the air temperature exceeds 50°C (122°F), the equipment should be spaced at least 1.75 inches apart or a blower installed to provide sufficient air movement within the cabinet.

WARNING: Do not operate the ELECTRO-VOICE 7200 amplifier within a completely closed unventilated housing.

Input Connections

Balanced input connections may be made to either the 1/4″ phone (TRS) or the female XLR connectors. For single-ended inputs, strap the low (-) input to ground (pin 3 on XLR or Ring on 1/4″ phone). Otherwise, the electronically-balanced input stage will see 6 dB less input signal level than with a balanced input.

Line Output Connections

The XLR and 1/4″ phone connectors are wired in parallel. Pin 2 of the XLR is the Tip of the 1/4″ phone connector, and pin 3 is the Ring. Since the input impedance of the electronically-balanced input stage is high (15 kohms), there is minimal loading on the signal source. When the input connections are made to one connector, the other may be used as an auxiliary line output to feed other high input impedance equipment.

Speaker wire size plays an important part in quality sound systems. Small wire gauges can waste power and reduce the damping factor at the speaker terminals. This can add coloration and muddiness to the sound. To help offset this problem, Table I has been assembled to enable you to calculate the power losses in the speaker cable.

Calculating Power Losses with 8 ohm Loads

To calculate the total power loss in the speaker cable, multiply the power loss per foot (or meter) of the 2-wire cable selected from Table I by the length of the cable in feet (or meters). For example, if an installer uses 160 feet of 10 GA 2-wire cable with an 8 ohm speaker system, the total power loss is 5.0 watts (0.0318 watts/foot x 160 feet). The actual load impedance becomes 8 ohms plus the cable resistance, affecting the total power delivered.

Calculating Power Losses with 4 ohm Loads

To calculate the losses when using a 4 ohm speaker system, multiply the loss at 8 ohms by 3. In the above example, the 10 GA wire would consume 15.0 watts of power.

Table I: 7200 Power Losses in 2-wire Speaker Cable

The damping factor rating is typically never realized at the load because of the resistance of the cable. The damping factor at the load should be 30 for general paging systems and 50 for high fidelity music systems, but economics may dictate cutting these in half. Once a minimum damping factor is determined, the following equation can calculate the maximum length of 2-wire cable in feet:

Max. Length of 2-wire cable in feet = (ZL – Zo) / (DF * DCR/ft)

Where:

ZL is the load impedance to connect to the amplifier.

Zo is the amplifier’s output impedance (0.08 ohms for the 7200).

DF is the minimum permissible damping factor at the load.

DCR/ft is the DC resistance of the 2-wire cable per foot from Table I.

For example, if ZL = 8 ohms, Zo = 0.08 ohms, minimum DF = 25, and using 18 GA cable (DCR/ft = 0.01302 Ω/ft), the maximum length is 18.4 feet.

It may be desirable to use in-line fuses to protect loudspeaker systems. Use 32 volt fuses if possible, as they typically have the lowest internal resistance. The values in Table II should serve as a guide. To use, determine the power rating and load value, then select a standard fuse of the next smaller value to the one listed.

The values are for fast-blow fuses. Other fuse values can be calculated with the following equation:

Fuse value = (Pout x ZL)^0.5 / (ZL x 1.35) amps

Where:

Pout is the output power rating of the amplifier.

ZL is the load impedance.

Table II: Calculated Output Fuse Values

Compression drivers are more susceptible to damage from low frequencies than large cone loudspeakers. To prevent potential mishaps from low frequency signals or hum, it is recommended to use a capacitor between the ELECTRO-VOICE 7200 amplifier and the compression driver to suppress low frequencies and possible DC.

As a general rule, select a capacitor whose break frequency, with respect to the load, is 3 dB down at approximately 1/2 of the high pass corner frequency. Mylar capacitors with at least a 100 volt ac rating are recommended. Table III shows recommended values for popular crossover frequencies.

Table III: Compression Driver Protection Capacitors

The two octal sockets on the ELECTRO-VOICE 7200 permit a variety of plug-in accessories to be used. Normally, one “U” jumper is inserted between octal socket pins 8 and 1, and another between pins 7 and 6. These jumpers must remain in place for the amplifier to operate when not using any accessory modules.

To use an accessory module, remove (and save) the jumpers and install the module, making sure the key on its center post aligns with the groove in the female socket. For operation, refer to the instructions provided with the module. Schematically, the module will be inserted between the input connector and the balanced input stage.

Electronic modules are powered from a bipolar 15 volt supply in the amplifier, which is capable of supplying up to 25 mA DC of current. Currents in excess of 25 mA DC may prevent the amplifier from disengaging from its built-in protection mechanisms.

In the dual mode of operation, the channels of the ELECTRO-VOICE 7200 may be operated independently.

1. After installation and hookup, verify that the mode switch, located on the rear panel, is in the “DUAL” position.

2. Rotate the level controls fully counterclockwise (full attenuation).

3. Input a 0 dBu (0.775 V rms) nominal signal level and apply power.

4. Slowly increase the level controls until the desired output power is obtained.

5. If either “CLIP” LED illuminates, reduce the output with the channel level control or reduce the input signal level at its source.

WARNING: Never attempt to connect the outputs of the two channels in parallel.

Follow these steps to operate your ELECTRO-VOICE 7200 in Bridge Mode:

1. After installation and hookup, verify that the mode switch, located on the rear panel, is in the “BRIDGE” position.

2. Rotate both level controls fully counterclockwise (full attenuation).

3. Input a 0 dBu (0.775 V rms) nominal signal level into channel 1 only and apply power.

4. Slowly increase the level control of channel 1 until the desired output power is obtained.

5. If either “CLIP” LED illuminates, reduce the output level with the level control or reduce the input signal level at its source.

CAUTION: Be sure that no input connections are made to channel 2 and that its level control is fully counterclockwise (OFF).

WARNING: The bridged output mode provides a true balanced-to-ground output. Do not use any test equipment to test or evaluate this amplifier which does not have floating grounds.

The “PROTECT” LED illuminates when the corresponding channel enters thermal protection. Should the heatsink temperature of a channel remain excessively high, the affected channel will shut down automatically. When the output devices cool to a safe operating temperature, the channel will automatically resume normal operation.

If the protection LED illuminates and there is no indication of excessive temperature, the corresponding channel is in an internal fault mode. If this occurs, refer to service instructions.

If you are experiencing problems with your ELECTRO-VOICE 7200, please check the following items:

1. Verify that the amplifier is properly connected to an ac power source and that the source is active.

2. Verify that the input connections are properly made.

3. Verify that the output connections are properly made.

4. Check the input and output cables for proper wiring and continuity.

5. Check the signal source and the load.

6. Ensure that the two jumpers for each octal socket are properly installed (if not using optional plug-in modules).

7. Ensure that any accessory modules installed do not draw more than 25 mA DC of current.

8. Check that the mode switch is in the desired position.

WARNING: No user serviceable parts inside. Extremely hazardous voltages and currents may be encountered within the chassis. The servicing information contained within this document is only for use by Electro-Voice authorized warranty repair stations and qualified service personnel. To avoid electric shock DO NOT perform any servicing other than that contained in the Operating Instructions unless you are qualified to do so. Otherwise, refer all servicing to qualified service personnel.

NOTICE: Modifications to Electro-Voice products are not recommended. Such modifications shall be at the sole expense of the person(s) or company responsible, and any damage resulting therefrom shall not be covered under warranty or otherwise.

Equipment Needed:

1 – Digital DC volt meter

2 – 4 Ω load rated at 200 watts

1 – Small non-conducting flat-blade screwdriver or set of plastic TV alignment tools

Miscellaneous handtools (to remove the top cover)

Procedure:

1. Turn power off and disconnect the unit from its power source. Make sure the unit is in the Dual mode with 4 Ω loads connected to each channel.

2. Remove the seventeen screws securing the top cover.

3. Channel 1: Locate D04 and D06. Connect the positive side of the digital DC volt meter to the anode of D04. Then connect the negative side of the digital DC volt meter to the cathode of D06. Connect the unit to its power source and turn the power on. Adjust SVR1 so that the digital DC volt meter reads 2 volts DC (± .1 Vdc). Turn power off and disconnect the unit from its power source.

4. Channel 2: Locate D104 and D106. Connect the positive side of the digital DC volt meter to the anode of D104. Then connect the negative side of the digital DC volt meter to the cathode of D106. Connect the unit to its power source and turn the power on. Adjust SVR2 so that the digital DC volt meter reads 2 volts DC (± .1 Vdc). Turn power off and disconnect the unit from its power source.

5. Re-install the top cover with the seventeen screws previously removed.