Martin Audio MA1.3s 5.1.1Gain, Sensitivity, 5.1.3Options, Stereo mode, English, Contents, Print

CONTENTS

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		GUIDES

The DIP-switch

Different gains and function can be selected for channel A and B, by appropriate setting of the DIP switch. Selecting the maximum gain of the amplifier is always a trade off between noise and headroom. A low gain amplifier amplifies less of the noise of the preceding equipment (mixer, crossover, equalizer etc.). A higher input level is then required to attain full power output, so the headroom will be decreased on mixer or crossover outputs. In an actively driven system there is usually a dedicated loudspeaker processor or controller, for the loudspeaker system. Most loudspeaker manufacturers recommend a specific gain for the amplifiers for use with their controllers.

5.1.1Gain

There are eight positions of gain selectable, from 20dB to 41dB in 3dB steps. The different settings for the DIP- switches are listed in the table below. The three switches to the very left are for channel B, and the three to the very right are for channel A. The two switches in the middle select the operating mode of the amplifier, Stereo or Link /Bridge A+B.

5.1.2 Sensitivity

Sensitivity is the level in volts (rms) or dBu (referred to 0.775Vrms) that is required to obtain full output power. As the output power varies with the load impedance, usually 4 ohms is usually taken as the reference.

We recommend calculating the sensitivity if this is necessary.

As a guide the table below gives the input level in volts rms, and dBu, versus gain, for full power output @1% thd 1KHz sine wave.

Gain dB	20	23	26	29	32	35	38	41
Input dBu	+16.7	+13.7	+10.7	+7.7	+ 4.7	+1.7	- 1.3	- 4.3
Input V rms	5.30	3.75	2.65	1.88	1.33	0.94	0.67	0.47

5.1.3Options

As the DIP-switch is recessed, a sticker can be placed across the cut out to prevent unauthorized tampering. Another option is to remove the DIP-switch. This should only be done by authorized service personnel. This corresponds to all switches set to “OFF ”, i.e. 32dB gain and stereo mode.

5.2Link switch

The Link switch located on the rear panel (the central DIP-switch) is for changing the operating mode of the amplifier (see below, section 5.3).

5.3Operating modes

5.3.1 Stereo mode

In this configuration, both channels operate independently of each other. This is used for all 2-channel operations, e.g. bi-amp and stereo. Stereo mode is selected by placing the two central switches in the ”OFF”position (Down). The attenuators on the front panel control the respective channels levels.

Never connect either output terminal to ground or in parallel. The recommended minimum nominal impedance, for stereo or tandem operation, is 2 ohms per channel.

5.3.2Notes for amplifier testing

NOTE: Channel B is always polarity reversed on the input, and polarity reversed back on the output. On channel B the positive output voltage with respect to 0V appears on pin -2 of the Speakon connector. Channel A is connected with normal polarity. By having channel A and B operating in opposite polarity, the energy storage in the power supply is more efficient. This is significant for signals below 100 Hz (sub bass etc.) and improves the power

ENGLISH

All material © 2007. Martin Audio Ltd. Subject to change without notice.

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Martin Audio – MA1.3s Amplifier