Nexo PS8 User Manual

Also see for PS10: User manual User manual Quick start guide

Contents

Nexo PS8 User Manual Manual pdf 28 page image

AMPLIFIERS___________________________________________________________________________________________________P.28Fuses and MainsMains Voltage selection, safety fuses and Earth-Lift configuration are located under the safety cover onthe front panel.The mains power cable can be located on the front or on the back of the PS10Amp. No other control orconnection exists on the back of the amplifier. At installation nothing else is required than sufficient air flowpath on the back of the PS10Amp.Stand alone AmplifiersRecommended PowerNEXO recommends high power amplifiers in all cases, budget constraints being the only reason to selectlower power amplifiers. If a problem occurs on an installation without protection, the use of a lower poweramplifier generating half their rated output power (-3dB) will not prevent possible damage. This is due tothe fact that the RMS power handling of the weakest component in the system is always 6 to 10 dB lowerthan the amps' ratingCurrent RatingIt is very important that the selected amplifier behaves correctly under low load conditions. A speakersystem is reactive by nature, on transient signals like music it will require much higher instantaneouscurrent than its nominal impedance would indicate (four to ten times more). Amplifiers are usuallyspecified by their continuous RMS power into resistive loads (which is irrelevant); the only usefulinformation in that regard is the specification into a 2 ohms load. It is possible to make an amplifierlistening test by loading the amplifier with twice the number of cabinets considered for the application (2speakers per channel instead of one, 4 instead of 2…) and modulating at high level (onset of clipping). Ifthe signal does not noticeably deteriorate the amplifier is well adapted (overheating after approximately tenminutes is normal but thermal protection must not operate too quickly after starting this test).GainIt is very important to know the voltage gain of all amplifiers present in your set-up. This will ensure thecorrect alignment of your system and may be obligatory (for reliability) in cases where only oneTDcontroller drives several amps. The tolerance should be about ±0,5 dB. In practice this can be difficultto achieve:• Some amplifier brands have an identical input sensitivity for models of different power ratings (this meansDIFFERENT VOLTAGE GAIN for each model). This problematic practice, inherited from non-professionalapplications, 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 allsemi-professional amps).• Even if a manufacturer is aware of this problem and applies the constant gain rule to all its models, thevalue chosen is not necessarily the same as other manufacturers.• Some manufacturers deliver products where manufacturing tolerance on the same model is ±1dB ormore. Worse, the manufacturer might agree to modify this gain at the customer’s request without clear