JBL GTQ240 Owner's Manual

Contents

JBL GTQ240 Owner's Manual Manual pdf 7 page image

7ro-romheadlifieri-r-cili-foreak-om-n onanyles.t-inerinplifi-typenic5.2 Crossover FrequencyAdjustmentsThe GTQ amplifiers include built-infrequency selectable crossovers. Onecrossover is connected in series with theamplifier circuitry and the other cross-over is connected to the preamp level out-put jacks. These crossovers can be set ineither the “F” (full bandwidth operation),“L” (subwoofer operation), or “H” (satel-lite operation).The crossover frequencies are set bychips inside the amplifier. These chips aresimply a set of resistors, connectedacross the pins and molded into a singlepackage. The crossover frequencies maybe changed to any value desired bychanging the resistor network. JBL haschips available in the popular values list-ed in the table which follows. If none ofthese suit your system, you may purchasecompatible resistor networks from a localelectronics store, or you may build yourown custom values from discrete resis-tors mounted on a 14-pin DIP Headerusing the instructions which follow.Frequency Resistor JBL PartValue Number50Hz 47k Ω 1-23-75080Hz 33k Ω 1-23-817120Hz 22k Ω 1-23-820200Hz 12k Ω 1-23-821250Hz 10k Ω 1-23-810375Hz 6.8k Ω 1-23-822500Hz 4.7k Ω 1-23-815650Hz 3.9k Ω 1-23-8232.5kHz 1k Ω 1-23-8245kHz 470 Ω 1-23-8165.3 Custom Chip ConstructionRegardless of whether you build or buy it,the necessary resistor network has thefollowing configuration:• Each resistor in the package has thesame value.• If you know the crossover frequency youwant, you can calculate the resistor valuenecessary by solving the following equa-tion:ResistorValue =in ohms• Use the following equation if you have aresistor pack of a known value, and wantto find its crossover frequency:Frequency=in Hz• To build chips from discrete resistors,solder the resistors to a standard 14-pin“DIP Header” according to the diagram. Ifa DIP Header is not available, you maybend the leads of 1⁄4-watt resistors 90degrees, trim them to 3mm-length, andinsert them directly into the chip sockets.2,500,000Frequency in Hz2,500,000Resistor Value in ohms