What is the Kicker F.I.T. input circuit and why is it better?

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1 What is the Kicker F.I.T. input circuit and why is it better? F.I.T. input: Kicker uses a special circuit for the audio input to our amplifiers called Failsafe Integration Technology or (F.I.T.) for short. This highly specialized input circuitry is designed to make the installation of Kicker amplifiers very simple and noise free. It is optimized to work with any source of music signal. This music signal can come from an aftermarket head unit, factory head unit, factory amplifier, or even just a headphone output jack from a portable device. Line output converters: Line output converters or (LOCs) as they are often called, were designed for a several reasons. The first reason is isolation. Most amplifiers have what is called a single ended input. This means that all the RCA shields are connected together and then are connected to the chassis ground of the amplifier. The amplifier s chassis is then grounded to the chassis of the vehicle. By doing this, you have now connected your audio signal to the chassis of the car and possible source of engine noise. This noise can be very difficult to find and eliminate. Head units and amplifiers have floating ground outputs on the speaker wires. This means that the speakers wires are not, and cannot be connected to chassis ground. If you try to connect a speaker output directly to the RCA input on a single ended input circuit, you will short the output of the head unit or amp to chassis ground. This can damage the head unit or amp. The LOC will offer isolation from ground to prevent this from happening. Another function of an LOC is to reduce the voltage of the signal so it does not exceed what the amplifier can accept to operate properly. The speaker level output is too high for many car audio amplifiers. The signal will need to be reduced to an acceptable level for the amplifiers input. A 25 watt output from a speaker level signal is approximately 10 volts. Many amplifiers cannot not accept a 10 volt signal. The average maximum is 2 to 4 volts. The LOC will reduce the 10 volt signal to between 1 and 2 volts on average depending on the design and manufacturer. The whole purpose of an amplifier in car audio is to increase the voltage to make speakers play louder. Using an LOC is a step backwards. A lower voltage input signal must be amplified more times than higher voltage signals. The more an amplifier has to amplify the signal, the more distortion and engine noise can be heard.

2 The last reason why LOCs are usually needed is to allow you to physically connect the factory audio system to the aftermarket amplifier. Factory audio systems only offer high power outputs that have no RCA connections. The LOC will allow you to connect the speaker wires from your source unit to the LOC and then use a RCA cable to connect to the input of your aftermarket car audio amplifier. F.I.T to the rescue! F.I.T. was developed for a couple of reasons. Line output converters (LOCs) are not the best choice for quality audio. They can degrade the signal quality and in some cases can cause damage to the vehicle itself. As you input more power into many of the LOCs on the market, they will begin to narrow the bandwidth of frequencies they pass. This means they no longer have the same output signal as the input signal. Also, some LOCs use resistors to dissipate the extra power that is not necessary and they can get hot. This is very bad and can lead to vehicle fires in extreme circumstances. Kickers F.I.T. input circuitry is designed to solve all of these problems. With Kicker s F.I.T. input circuitry, it is not necessary to add a LOC between the Kicker amplifier and the source unit. F.I.T. will accept a 25 watt or 10 volt signal without issues so you do not need to reduce the voltage coming in to the RCA inputs. With a higher voltage coming into the amplifier, you do not need to amplify the signal as many times. This will give you better overall sound quality. F.I.T. inputs are isolated from chassis ground so it is safe to run speaker level output up to 25 watts per channel from a source directly into the RCA input jacks. It will not damage the amplifier or source unit in any way. Aftermarket radios with RCA outputs: Most aftermarket head units have two different outputs. One is the speaker level output. Speaker level outputs are floating ground and about 10 volts or 25 watts. Floating ground means that there is no direct connection to chassis ground. The other output type are RCA outputs. RCA outputs are common ground and can lead to engine noise because they are connected to chassis ground. The average RCA voltage on most head units is about 1 4 volts. This means the amplifier has to amplify the lower voltage signal more as compared to a 10 volt signal and can lead to more distortion and louder engine noise. RCA outputs in the past were true preamp outputs. This means they had a separate circuit that would pass the signal to the RCA jacks before it was amplified by the head unit s internal amplifier. This was very clean sounding and worked well. Currently, almost all newer head units use some form of LOC internally to drop the voltage of the speaker outputs from the internal amplifier before it is passed through the RCA output. Most of these are done using a

3 resistive network. They bleed most of the power off as heat and dissipate it through the heat sink on the back of the head unit. When using the RCA output of a newer aftermarket head unit, you are still using the internal amplifier in the head unit. The internal amplifier is still operating with the channels loaded down even if only the RCA output is used. The RCA shield on the head unit is also connected to chassis ground and may cause engine noise. Even if an aftermarket head unit has a discrete preamp circuit, the signal is still unbalanced because the RCA shield is connected to chassis ground. When you use the speaker level output of the head unit to send signal to the F.I.T. input, you will not be putting a lot of demand on the head unit s internal amplifier. The F.I.T. input is about 2500 times less load on the internal amplifier than conventional speakers present to it. This means F.I.T. will have even better frequency response, less distortion, better signal to noise, and better dynamic range when using the speaker level for input signal. So basically, we are stating that it is almost always better to use the speaker level signal to feed signal into Kicker amplifiers. Even if the head unit has RCA outputs, it is better to use the speaker output wires to send signal to the amplifier. It will be much easier, sound better, and will be noise free. And there is more! Another aspect of the Kicker F.I.T. input is how the amplifier gets signal to turn on. As we all know, the most popular way to trigger an amplifier to turn on is with a switched 12 volt signal. This is great if you are connecting an amplifier to an aftermarket head unit that has a dedicated switched 12 volt output specifically to turn an amplifier on. But what if you are connecting an amplifier to a factory head unit where most of the electronics are on the CAN bus circuits and you do not have a switched 12 volt circuit? This is very common on many newer cars. F.I.T. offers a fantastic and easy solution. All Kicker amplifiers with F.I.T. inputs have a circuit that will sense the DC voltage that is present on the speaker outputs of almost all aftermarket and factory audio systems. This is called DC offset. It is a constant DC voltage that is not affected by the volume control on the head unit. It is present the entire time the head unit is switched on. By connecting the speaker outputs directly to the RCA inputs, with F.I.T. you generally do not have to run a separate wire to tell the amp to turn on with the head unit. This will save the installer time and will not require him to locate and cut into another switched 12 volt circuit or install a switched 12 volt CAN bus adaptor. The third and final way to get your amplifier to turn on is by sensing AC voltage on the RCA input. This requires a specific level of AC voltage on the input of the amplifier to turn on. This can be somewhat problematic if not set up correctly but will work as a last option to turn on an amplifier. This option is available on several of the Kicker amplifier models. When using the DC offset or signal sense methods, the remote input terminal of the amplifier that normally would receive a 12 volt signal to turn the amp on, now sends a switched

4 12 volt signal out to turn on other electronics that do not have DC offset sensing. This can be very handy if you have other audio gear that does not have DC offset sensing. Some Kicker amplifiers allow you to select what type of trigger they need to turn on. There is a switch on either the front or back of the amplifier that will allow you to choose which you want to use. If there is no switch, the amplifier will automatically try to use DC offset first. If it does not find DC voltage on the input, it will require a separate switched 12 volt source to trigger the amp into turning on. F.I.T.2 The F.I.T. input was a revolution for input circuitry but it became clear the factory head units were changing the game again. Some of the factory audio systems no longer have ½ of the battery voltage (5-7 volts) on the speaker outputs of DC offset. Some cases, this voltage is lower. The F.I.T.2 input lowers the DC offset threshold from 4.5 volts to 2.5 volts. This will ensure that the DC offset voltage is sufficient to trigger the amplifier to turn on. Some of the new smart radios are now incorporating protection circuitry that will either throw a fault code to the vehicle s onboard computer or may even shut off output from one or more channels. They need some form of load or speaker on the outputs to work properly. The F.I.T.2 inputs have a radio detect switch that will present the factory, smart head units a 65 Ω load to simulate a load or speaker being connected. This is enough to fool the head unit into operating as if it has a speaker connected but not enough to load down the outputs of the head unit. This switch should only be used on factory head units if no output is heard from the amplifier or if the amplifier seems to cut out at moderate or high volumes. The last issue that F.I.T.2 addresses has to do with factory head units that have changed the way they send output to the factory speakers. Until very recently, all powered outputs were driven off of either the positive speaker lead or both the positive and negative leads. Some of the newer smart OEM radios now only drive the speaker from the negative speaker lead. Leaving the positive lead to only complete the circuit and carry DC offset voltage. F.I.T.2 now incorporates a half wave rectifier to compensate for this new type of output. It will maintain an acceptable level of DC offset to keep the amplifier turned on. F.I.T. vs. Differential inputs: Some car audio amps have a differential inputs as opposed to a single ended input. This means that there is a buffer on the shield of the RCA inputs to isolate it from chassis ground. This is a better input than single ended but it is still not the best. F.I.T. and F.I.T.2 both have an extra isolation circuit on the positive connection or the center pin of the RCA input. This is like a differential input with twice the isolation from noise! It is by far the best for noise suppression and currently the most noise free input to an amplifier you can get. Adapting speaker leads to RCA connections:

5 It can be a challenge to connect RCA cables to the speaker output of your head unit because most RCA cables use extremely small wire. Some of the better RCA cables use a twisted pair design that does make it easier because the wires are easily stripped and are easy to identify. Kicker blue RCA cables are twisted pair and will work if you cut the RCA connectors off. The other option is the Kicker KISL. This is a simple RCA to speaker wire adaptor that uses 16 gauge speaker wire that will easily connect to the speaker output wires of your head unit or factory amplifier. It has no electronics that will affect the signal quality. It is just a simple way to connect speaker wires to the RCA input. The KISL can connect it directly to the amplifier after you run speaker wires from your source to it. Another option is to use a standard RCA cable for an extension to reach the amp if it is connected behind the audio source.