Please 'Boom' Responsibly As most of you have noticed, the noise ordinances have become much tougher lately. Most of this is due to idiots, yes IDIOTS, who drive through residential areas with their windows down while their system is playing at full power. To make things worse, the music they listen to has all sorts of foul language that's not suitable for small children, (who may be playing outside). There are even a few people, who are even beyond idiot status, that play their systems at full power through residential areas after 10:00 PM (when many people go to bed). I don't believe that this type of behavior is good for the industry. If the fines get too stiff, people will stop buying large systems. If this happens, more people will get out of car audio (who wants a mediocre system). People get interested in things because they're exciting. A deck and four 6.5" speakers are not going to interest many of the younger car audio enthusiasts. If car audio enthusiasts keep annoying more and more people, the fines will keep getting tougher. All of this will only reduce interest in the equipment that fuels the industry. If you want to listen to your system at full volume, get out on the highway where there's little chance of bothering anyone. When you get to a red light, turn it down. If the only thing attractive about you is your 'system', you have some work to do. Bottom line... Think about what you're doing. Think about other people. It's not the end of the world if you have to turn the volume down for a little while. |
Amplifiers: A power amplifier takes an input signal, usually a preamp level signal, which has both low current and low voltage characteristics, and produces an output which will have higher current and voltage levels. The power supply available to the audio output IC in a head unit is limited to the battery voltage of the vehicle. This means that the head unit can produce an audio signal with a limited (by the battery voltage) voltage swing, and therefore a limited power output to the speaker. Most amplifiers have a special circuit (switching power supply) to boost the available battery/charging system voltage to a higher voltage. The higher voltage developed in the amplifier's internal switching power supply will allow the audio output voltage swing to be greater. This allows the amplifier to produce more power into the speakers connected to the amplifier's output terminals. Gain Controls: Most amplifiers will have some sort of level or "gain" control. This control is used to match the output of the head unit to an amplifier. The maximum audio output voltage from different head units will vary. If there were no gain controls, some head units would not be able to drive the amplifier to its maximum power level. Other head units may drive the amplifier to full power at a fraction of its volume control's range. More gain info can be found on this page. Note (rant): There have been many people who have said that the gain controls were not volume controls and they are right, to a point. Some amplifiers' gain controls are used precisely like a volume control (one end of the potentiometer connected to ground, the other end connected to the pre-amp signal and the wiper connected to the amplifier's front end). This configuration will allow you to reduce the output to nothing at the minimum gain position. These are not very common but they HAVE been used on some amplifiers. I know because I took the cover off of a few amps to see why they had absolutely no output (Doh!). Others are connected similarly but there is a small amount of resistance between ground and the formerly grounded terminal of the potentiometer. This small resistance prevents the gain control from reducing the output to zero output. These are very common on amplifiers made in Korea and China. There are other amps that use the potentiometer to pull the signal toward ground. The pot is the lower half of a voltage divider and may use only 2 legs of the potentiometer. This type of gain control was used on at least one brand of Japanese manufactured amplifier. You can also put the potentiometer in the feedback loop to control the overall gain of the amplifier. The point to all of this is... There are many ways to use a potentiometer to control the output of the amplifier. Some are used precisely as volume controls and others are not. You can not make a blanket statement such as 'gain controls are not volume controls'. Battery, Ground and Remote Connections: Virtually all amplifiers have battery, ground and remote connections which must be connected for the amp to operate. The battery connection is the high current +B source that's connected to the battery via a properly fused wire. The size of the power wire is determined by the current the amplifier draws and the length of the wire (from the battery to the amplifier). The ground is another high current connection and is connected to the chassis (body/floor pan) of the vehicle. The ground wire is typically as large as the power wire. The remote connection is a low current control input that tells the power supply of the amplifier to power up. Remote Input Current: The remote input current for amplifiers varies with the amplifier and the model. Some draw minimal current. Others draw a little more. The upper limit of a properly functioning amplifier is approximately 50ma (0.05 amps). If you're using/controlling more than 2 amplifiers, it is (in my opinion) much better to use a relay to control the amplifiers. Actually I really prefer having a relay in the remote circuit (no matter how many amplifiers I'm using) because it protects the head unit's remote output circuit in case of a short circuit. The following chart shows the remote input current for various amplifiers I had laying around the shop. |
Manufacturer | Model | Current Draw (mA) |
MTX | 2300 | 14 |
Jensen | LXA300 | 43 |
Pioneer | GMX602 | 1.5 |
Autotek | 7150 | 16 |
Punch | 200x2 | 14-45 |
Autotek | 200x1 | 17 |
Coustic | Amp162µ | 22 |
Orion | 275SX | 28 |
Crossfire | CFA1000D | 5 |
Lanzar | Vibe 250 | 17 |
Test conditions: 14.3vdc; Fluke model 79 DMM; The meter was inserted in the remote supply line. |
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AMPLIFIER INSTALLATION NOTES:
When installing an amplifier:
Installing an
Amplifier
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You should remember:
1.A car audio amplifier takes a low voltage low current signal
and increases both the voltage and current drive abilities of the
signal.
If you find a problem
with this page or feel that some part of it needs
clarification, E-mail
me. This is a link to this site's home page. |
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