Nexo PS Série Manuel D'utilisation page 27

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professional applications, is easily detected when the manufacturer specifies the same input sensitivity
for all its range (like 775mV/0dBm or 1.55V/+6dBm). This translates into very high gain values on higher
power models.
Other brands do offer constant gain, but often only within a given product range (like higher gain on all
semi-professional amps).
Even if a manufacturer is aware of this problem and applies the constant gain rule to all its models, the
value chosen is not necessarily the same as other manufacturers.
Some manufacturers deliver products where manufacturing tolerance on the same model is ±1dB or
more. Worse, the manufacturer might agree to modify this gain at the customer's request without clear
and visible identification on the device. Other amps feature internal gain switches that make it difficult to
know the amp gain without measuring or opening it.
In cases where you don't know the gain of your amplifier (or want to check it) please read the following
instructions.
1/ Unplug any cabinet from the amp
2/ With a signal generator feed a sine wave (freq. within the audio range, 1000Hz for example) Amplitude
Vin is not important (1V is rather convenient),
amp input!
3/ Measure the Amplitude Volt at the output of the amp. Gain = 20 * LOG10(Vout/Vin)
Some examples:
Gain
Vin
0.1V
0.5V
1V
Remember that constant sensitivity settings will give you different gain values when the amp Power is
different.
Gain value
NEXO recommends low gain amplifiers: +26dB is recommended, as it is both adequately low and quite
common. This gain level considerably improves signal to noise ratio and allows all preceding electronic
gear, including the TDcontroller, to operate at an optimum level. Remember that using a higher gain
amplifier will proportionally raise the noise floor level by the same amount.
Advanced protections
Some high-end amplifiers may have some advanced functions similar to those found in the NEXO
TDcontrollers ("loudspeaker offset integration", "limiter", "compressor"...). These functions are not well
adapted to NEXO system requirements and may interfere with existing protection within the TDcontroller.
NEXO recommends disabling these functions.
PS SERIES MANUAL REV3 10/10/05
AMPLIFIERS
20dB
1V 2V
5V 10V
10V 20V
u taking care not to choose a value that will overdrive the
26dB 32dB
4V
20V
40V
P.27
37dB (1.4V
sensitivity /
1350Wrms)
7.1V
35.4V
70.8V