ELECTRO-VOICE MA-1212 (01) PDF Document

The ELECTRO-VOICE MA-1212 Professional Mixer/Amplifier includes the following features:

• Level controls for each input and a master volume control.

• Individual bass and treble tone controls.

• Automatic muting circuit with threshold adjustment.

• 600 ohm transformer-isolated line input for paging, with automatic muting of all other inputs.

• Low distortion.

• Output protection circuit.

• Auxiliary line level inputs with internal mixing for stereo source.

• Balanced line level output.

• Insertion point between preamp and amplifier.

• Phantom power on all microphone inputs enables microphones to be used without separate power supplies.

For proper installation of your ELECTRO-VOICE MA-1212, please follow these guidelines:

Cabling: To avoid hum in the output, ensure that all input cables are physically separated from power wiring and transformers. Speaker cables should also be kept away from input cables and power cables.

Grounding: Ground the chassis of the unit using the ground terminal on the back panel. For the best grounding, connect the amplifier to an earth ground such as a cold water pipe or ground rod. If other equipment is installed with the amplifier, ensure their chassis are connected together to reduce noise and hum.

Ventilation: To dissipate heat generated by the power amplifier, provide ample ventilation around the unit. Do not block or impede the vent slots in the cabinet. Locate the unit in a place free from direct sunlight, humidity, dust, and vibration.

The Mic inputs on the ELECTRO-VOICE MA-1212 can be accessed by either XLR or 1/4″ phone plug connectors. These inputs are designed for use with balanced Low Impedance (approx. 200 ohms) or unbalanced high impedance (approx. 20k ohms) microphones.

For high impedance microphones, it is recommended to keep cables as short as possible (under 30 feet) to avoid loss of High Frequency response.

Wiring for Balanced Microphones:

• For a 3-pin XLR plug, wire the signal cables to pins 2 and 3, and the shield to pin 1.

• For a stereo 1/4″ jack, wire the signal cables to the tip and ring, and the shield to the sleeve.

Wiring for Unbalanced Microphones:

• For a 3-pin XLR plug, wire the signal cable to pin 2, bridge pins 1 and 3 together, and connect the shield to this bridge.

• For a mono 1/4″ jack, wire the signal cable to the tip and the shield to the sleeve.

Phantom power on the ELECTRO-VOICE MA-1212 allows you to use condenser microphones that require external power without needing separate power supplies. When enabled, 24V DC is supplied to pins 2 and 3 of the Mic input’s XLR connector.

To enable phantom power for a specific input, locate the sensitivity switch for that input on the rear panel and move it to the “24V” position. It is recommended to only operate this switch when the master volume is set to minimum.

Important Safety Note: Connecting unbalanced microphones when phantom power is switched on could cause severe damage to the microphone. It is mandatory to only plug or unplug a microphone cable when phantom power is turned off. Ensure phantom power is also turned off when using microphones that do not require it.

The ELECTRO-VOICE MA-1212 features a “Voice Priority” function that allows audio from Input 1 to automatically mute (or “duck”) all other Mic and AUX inputs. To set this up:

1. Connect your primary microphone or paging source to Input 1.

2. Set the “Mute” function switch on the front panel to the “on” position.

3. On the rear panel, adjust the threshold control so that a typical voice level (and not background noise) activates the mute circuit.

When configured, any announcement made through Input 1 will automatically lower the volume of all other audio sources. To defeat this function, simply move the front panel “Mute” switch to the off position.

High-level unbalanced sources such as CD players, AM/FM tuners, or tape players can be connected to the Aux 1 and Aux 2 RCA jacks on the back panel of the ELECTRO-VOICE MA-1212.

These inputs are designed to accept a stereo source. The left and right RCA jacks for each AUX input are internally mixed through series resistors, so you can connect a stereo source and get a mono sum. If you have a monaural source, you can plug it into either the R or L jack.

For turntables, they must be equipped with a ceramic or crystal cartridge. Turntables often have a separate ground wire; connect this wire to the ground terminal on the back panel to minimize hum.

When connecting speakers to your ELECTRO-VOICE MA-1212, there are several important considerations:

1. Matching Speaker Impedance: The amplifier delivers its rated power into a rated load impedance. Connecting speakers with a significantly lower impedance can cause the amplifier’s protection fuses to open, especially at high volume. Avoid using speaker loads with impedance below the amplifier’s rated value.

2. Power Loss in Speaker Wire: The impedance of speaker wire can cause power loss, especially over long runs with small gauge wire. This reduces the power delivered to the speaker. To minimize this loss, use the shortest possible wire runs and the largest practical wire gauge. High load impedances allow for the use of longer, smaller gauge wiring with less power loss.

3. Balancing Speaker Levels: For installations with multiple speakers, using a high-impedance constant-voltage system is the easiest way to balance sound levels. These systems use speakers with transformers that have multiple power taps (in watts), allowing for easy adjustment of individual speaker levels.

The ELECTRO-VOICE MA-1212 supports constant-voltage speaker systems (25V, 70.7V, and 100V), which are ideal for installations with long wire runs or multiple speakers.

To set up a constant-voltage system:

1. Ensure all speakers in the system have transformers with the same voltage rating (e.g., all 70.7V).

2. Connect the speaker transformer primaries in parallel to the appropriate constant-voltage output terminals on the amplifier (e.g., COM and 70.7V).

3. The sum of the power tap settings on all speakers (in watts) should be equal to or less than the amplifier’s rated output power. For example, for the 120-watt MA-1212, the sum of all speaker taps should not exceed 120 watts.

Avoid connecting a total power load that is greater than the amplifier’s rated power, as this will drop the total load impedance below the amplifier’s rated load.

The ELECTRO-VOICE MA-1212 provides an insertion point between its preamplifier and power amplifier stages using the “PRE OUT” and “MAIN IN” terminals on the rear panel. This allows you to connect an external signal processor.

1. Remove the bridging-strip that connects the “PRE OUT” and “MAIN IN” terminals.

2. Connect a cable from the “PRE OUT” terminal to the input of your external device (e.g., an equalizer).

3. Connect a cable from the output of your external device to the “MAIN IN” terminal.

This setup routes the mixed audio signal from the preamplifier through your external processor before it is sent to the internal power amplifier.

The front panel of the ELECTRO-VOICE MA-1212 features the following controls:

1. “Mute” function switch: Turns the “Voice Priority” or page “ducking” function for input 1 on or off.

2. Auxiliary 1 & 2 / Input 1-10 Level Controls: These knobs adjust the individual volume levels for the two stereo summing auxiliary inputs and the 10 multi-use inputs.

3. Music signal monitor output level control: A screwdriver adjustment that sets the volume for headphones connected to the “MONITOR OUTPUT” jack or a small speaker connected to the rear panel monitor terminals.

4. MONITOR OUTPUT: A 1/4″ jack for connecting headphones for monitoring.

5. Overload indicator light: Illuminates when the amplifier’s output is overloaded. The output signal is interrupted until the volume is lowered or the load issue is resolved.

6. Power Switch and Power Indicator: Supplies power to the unit. The indicator lights up when power is on.

7. Master: This control adjusts the overall volume level of the combined input signals sent to the power amplifier.

8. Treble: Adjusts the high-frequency response, providing up to 7 dB of boost or 12 dB of cut at 10 kHz.

9. Bass: Adjusts the low-frequency response, providing up to 7 dB of boost or 12 dB of cut at 100 Hz.

The rear panel of the ELECTRO-VOICE MA-1212 features the following controls and connections:

10. Main cord connector: For the supplied AC power cord.

11. AC fuse: Protects the unit from electrical faults. Service should be done by an authorized service center.

12. “GND” screw: For grounding the amplifier’s chassis if the main outlet does not provide a ground conductor.

13. Terminals for DC battery supply: Allows connection of an external 24V DC power source, such as a battery, for backup power.

14. Output terminals: Screw terminals for speaker connections, supporting 25V, 70V, 100V constant-voltage systems and low impedance loads.

15. “PRE OUT” terminal: Outputs the mixed audio signal from the pre-amplifier section.

16. “MAIN IN” terminal: Input directly to the power amplifier section. Used with PRE OUT for an effects loop.

17. “AUX 1” and “AUX 2” inputs: RCA connectors for high-level unbalanced sources like CD players or tuners.

18. INPUT 1-10 jacks: Combination XLR and 6.3mm (1/4″) jacks for connecting microphones or line-level sources.

19. INPUT 1-10 sensitivity switches: Selects between LINE, MIC, or 24V (phantom power) for each corresponding input.

20. AUX1-2 input sensitivity switch: A 4-position switch to match the input sensitivity for different sources like CD players, tuners, or cassette decks.

21. TEL. Paging input level control: Adjusts the volume of the telephone paging input.

22. LINE OUTPUT CONNECTOR: A balanced XLR output that provides a mix of all audio signals, which can be set to a fixed or variable level.

23. Input “TEL.Paging”: Terminals for connecting a 600-ohm auxiliary paging signal. This input has voice priority and overrides all other inputs.

24. “Priority” terminal: When these terminals are short-circuited (e.g., with a switch), the audio from AUX1, AUX2, CASSETTE, and TUNER are attenuated, while inputs 1-10 remain unchanged.

25. Output terminal for auxiliary loudspeaker: Provides a 1-watt, 8-ohm output for a small monitor speaker.

26. DC switch: Turns the DC battery supply on or off.

Please adhere to the following safety precautions when operating your ELECTRO-VOICE MA-1212:

1. The power supply voltage is high enough to risk electrical shock. Never install, connect, or disconnect the equipment while the power supply is switched on.

2. The metal parts of the equipment are earthed through the power cable. If your power socket does not have an earth connection, have a qualified electrician earth the equipment using the rear terminal.

3. Ensure the power supply cable cannot be trodden on or crushed by objects.

4. There are no user-serviceable parts inside. Do not attempt repairs not described in the manual.

5. Ensure that no objects or liquids can get into the amplifier, as this could cause a short circuit.

6. If the equipment is not used for a long period, switch it off and disconnect the power supply cable.

7. If the equipment emits a strange odor or smoke, switch it off immediately and disconnect the power from the supply cable.

8. Contact authorized service personnel if the equipment does not function normally, the power cable is damaged, objects or liquids have entered the unit, or it has been subject to heavy impact.