Yamaha v1.01 User Manual download pdf (Page 17)

AMPLIFIER SELECTION FOR USE WITH RS15 Page 17/58

• In cases where you don't know the gain of your amplifier (or want to check it) please follow this

procedure:

1) Unplug any loudspeakers from the amplifier outputs

2) With a signal generator, feed a sine wave at 1000Hz at a known voltage (say 0.5V) to

the input of the amplifier under test

3) Measure the voltage at the output of the amplifier

4) Calculate the gain using the formula Gain = 20 * LOG

(Vout/Vin).

Some examples:

Vin / Gain 20dB 26dB 32dB 37dB (1.4V sensitivity / 1350Wrms)

0.1 V 1 V 2 V 4 V 7.1 V

0.5 V 5 V 10 V 20 V 35.4 V

1 V 10 V 20 V 40 V 70.8 V

Remember that constant sensitivity settings will give a different gain value when the amplifier power is

different.

NEXO recommends low gain amplifiers: +26dB is recommended, as it is at the same time adequately

low and quite common amongst amplifier manufacturers. This gain setting improves signal to noise ratio

and allows all preceding electronic equipment, including the NX242 TDcontroller or GEO S12

TDController, to operate at optimum level. Remember that using a high gain amplifier will raise the

noise floor proportionally.

Operating Mode

Most two channel amplifiers available on the pro-audio market have the following operating modes:

• Stereo:

two fully independent channels deliver identical power into identical loads

• NEXO recommends Stereo Mode for all amplifier channels feeding RS15’s.

• Bridge-Mono:

the second signal channel processes the same input as the first channel, but with

reversed phase. The (single) load is connected between the two positive channel outputs using a

suitable connection. While the total output of the amplifier remains the same, the available output

voltage, the minimum impedance that can be connected and the voltage gain are doubled as

compared with stereo operation. Typically, only channel 1 input is active. Positive and negative

output connections vary depending on amplifier manufacturers.

• NEXO does not recommend Bridge Mono Mode unless amplifier power is clearly not sufficient.

IMPORTANT

When in Bridge-Mono mode, check your amplifier user manual for proper connection of

outputs 1(+) and (2+) in relation to input phase.

• Parallel-mono: the output terminals of the two channels are configured in parallel using an

internal relay. The (single) load is connected either to the output of channel 1 or to that of channel

2 (as if in stereo). While the total output of the amplifier remains the same the output voltage level

is also the same as in stereo mode. The minimum impedance that can be connected is reduced

by half due to the fact that current capability is doubled. Typically, only channel 1 input is active.

• NEXO does not recommend Parallel-Mono Mode for RS15 amplification.

Warning on amplifiers signal processing features

Some high-end amplifiers may include signal processing functions similar to those found in the NX242

TDcontroller or in GEO S12 TDController ("loudspeaker offset integration", "limiter", "compressor," etc.).

Moreover, when this processing is digital, computation latency time can introduce a few milliseconds

delay from input to output. These functions are not adapted to specific system requirements and may

interfere with the complex protection algorithms used in the NX242.

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Yamaha v1.01 User Manual Page 17

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