Author: Matthew Towns/trism.

Introduction:

I see a lot of people asking about amplifiers, and what does what, and why is a mono block better than bridged 4 channels and so on. I hope that in this tutorial I can resolve some issues regarding it. I will endeavor to explain how amplifiers work, what the terminals on them are, and other things such as speaker level input converters, and pass through RCA's as well as what all those little knobs and dials on the amps do.

Amp Basics:

3 main things that all amplifiers have are power, ground and remote trigger terminals.

Power: This is the wire coming straight from the battery positive terminal. It should be fused no more than 45cm from the battery. Although this is optional in SPL, as due to the high current draw, they could blow right in the middle of a burp. This wire should grow in size in proportion to the power your amp puts out.

Ground: This goes to the car body/chassis. The best ground will have all paint around the ground point sanded off, so there is only bare metal showing. The size of the ground cable should be at least the size of the power wire, if not bigger.

Remote Trigger Wire: This comes from the Head Unit. It basically tells the amp when to turn on and off. It's a 12volt, low current wire.

Amplifiers also have Gain Controls, and most of the time will have Crossover Frequency Dials. The gain control is not merely a volume control for the amp. See here about gain and crossover setting.

Bridging: This is where two channels of an amp are joined to create a high power output. For example, the negative terminal on channel 1, and the positive terminal on channel 2. These are often marked on the amplifier, and in the manual, as they are internally configured to produce the output for those channels. So:

2 Channel Amplifiers

Like the name says, these have 2 channels. So when you look at them, they have the power, ground and remote terminals, but 4 other ones as well. Two are for channel one and the other 2 are for channel two. These are normally used for front stage amplification. 2 channel amplifiers will have only two RCA input sockets, one for left, one for right. Therefore, channel 1 will be one side of the car, and channel 2 will be the other side. Since each channel will play different sounds, it is important to get it right, to obtain the desired "stereo" effect.

Most 2 channels amplifiers are designed to run only speakers. They can be bridged, but often only 4 ohm stable, and not providing a whole heap of power, as they aren't designed specifically to run subs. Take my old MTX RT202. At 2 ohms stereo it produced approximately 2x75wrms, but bridged it made 150wrms at 4 ohms, and was only stable to this. Not a heap. The Jaycar 2x150wrms on the other hand will bridge to 500wrms, although it is only stable when bridged to 4ohms. Some though, can be bridged for crazy high amounts of power down to 2 ohm without smoking.

4 Channel Amplifiers

4 channels will be like the 2 channels, but with an extra 2 pairs of speaker output terminals, an extra pair of RCA inputs, another freq crossover knob, and often another gain knob. These can be used for either front and rear stage (so channels 1 and2 for front, and 3 and 4 for rear) if you are running an active front setup (channel 1 and 2 for tweeters, 3 and 4 for woofers) or even a three way setup (channel 1 and 2 for front woofers and tweeters run passively, and 3 and 4 running midbass woofers).

They can also be used to run front stage and a subwoofer. A lot of the time, in a budget setup, this is the case. Therefore, some 4 channel amps will produce more power when channels 3 and 4 are bridged, than when channels 1 and 2 are bridged. Let's take the Alpine MRV-F545 for example. When the first two channels are bridged, it only makes 125wrms but when 3 and 4 are bridged it can make 500wrms at 4 ohms. Once again, most will only bridge down to 4 ohms, some will go to 2 ohms.

Monoblock Amplifiers

Only 1 channel. The only have one gain knob, one crossover knob, and one pair of RCA inputs, but can also feature loads of other ones, like phase control, subsonic filter, and others, which I will move onto in a minute. Monoblocks are designed for one thing, and one thing only, to push out subbass frequencies. They have beefy power supplies, often draw lots of current, and can be very very powerful. Monoblocks generally produce best power at 2 or 1 ohms. If your amp is stable to 1 ohm, then wire it down to it. If not, best to leave it at 2 ohms. Some amps though, can be wired down to as little as 0.5, or 0.25ohms! The SPL boys and girls do it quite a lot, even sometime when the amp is only rated to 1 ohm!

Some monoblock amps will have 2 sets of terminals, with a label bridge across them. This is for ease of wiring. Take my Blaupunkt Velocity Burning Desire, at 4 ohms it makes 1x 1000wrms, at 2 ohms it makes 1x 1750wrms and at 1 ohm it makes 1x 2000wrms. I have Single Voice Coil 4 ohm subs. To make my life easier, I can simply wire each one to its own pair of terminals, creating a 2 ohm load, therefore the amp will produce 1x 1750wrms, and each sub will get half of this. If I had one of them, then I would bridge it, for a 4 ohm load, getting 1000wrms going to the sub. Also remember that the more you load an amp down, the more power you need to supply. A run of 4 gauge power wire may be suitable when an amp is only running 1 sub at 4 ohm for 500wrms, but if the same sub is loaded down to 0.5 ohm, and 4000wrms, then it will need a whole lot more power, so the wire will need to be upgraded to cope with the added current draw.

Other Components Of An Amplifier:

Speaker Level Input: You may have seen the David Navone LLC. Some amplifiers have these built in. They are often of inferior quality, and it is best to use an external one, such as the David Navone one, or another brand.

Pass Through RCA's: Basically this allows the use of two amplifiers without RCA splitters. So if I have two subs and two amps, then I can have one RCA cable from the Head Unit to the first amp RCA in, and then from that amp, from the marked RCA output into the second amps RCA input. Jaycar amplifiers have these, although many people have seen that the quality of them is not so good. Basically it just splits the RCA signal inside the amp. Doing this is also referred to as "daisy chaining". BE AWARE THAT THIS IS NOT THE SAME AS STRAPPING AMPS!

Strapping Amps: Strapping is basically joining two monoblock amps together to make one super big amp. Note that not all amplifiers can be strapped. Basically it is like bridging two amplifiers together, so taking the positive from one amp, and the negative from the other. There is a master and a slave amp, the master receives the RCA’s from the H/U and the slave receives from the master. There are switches on them to set what is master and what it slave. There are some amps that are not able to be strapped, but strapping modules can be bought, such as a Crossfire VR2000, but modules such as these can be very hard to come by. Also remember to continually check power going to amps, as strapping can draw a lot more current then you think.

Phase Control: Basically determines what phase your sub is in. If your sub sounds muddy or laggy from the front seat, maybe it is out of phase, so you can adjust it from 0 degrees through to 180 degress.

Subsonic Filter: When subs are in ported boxes, playing below the port frequency is very very bad. For example, if the box is tuned to 45Hz, and you play a 35Hz tone, the sub will bottom out, lose cone control, and get into all types of trouble. The subsonic filter allows you to block out any frequencies below the cut off point, similar to a high pass filter, but in complete reverse.

Bass Boost: This goes up from 0dB. Basically just increases the output level of bass from the amp.

Damping Factor: Damping factor is a value that tells you how well an amplifier controls a speaker system. The larger the number, the better it is. At 1000 or above, it's pretty darned good. Below 50 or so, it's pretty poor. When one amplifier's damping factor is higher than anothers, that tells you that the amplifier with the higher damping factor can better control the speaker systems, and all other things being equal (frequency response, phase shift, distortion, etc) that it is a better amplifier.

How an amplifier drives a speaker system is effected by the amplifier's output impedance. The lower it is, the more current is provided. The better an amplifier provides varying current without changing voltage, the more accurately the speaker can reproduce sound.

Why a speaker requires more/less current given a particular voltage is that the impedance of the speaker system changes depending on what direction the speaker drivers are moving when the voltage is applied, how fast they are moving that way, and where they actually are in the first place. In other words, because the speakers impedences changes as it moves.

Because the speaker impedance will vary due to movement when voltage is applied, the amount of current that the speaker needs will vary widely as well. The amplifier needs to present the applied voltage correctly no matter what the speaker impedance is. If it can do that, the speaker's cone movements will give the most accurate reproduction of the applied voltage. Hence the least distortion will occur because the speaker will move to the desired position with the least amount of error.

Since music is comprised of constantly voltages and the speaker is always moving in some complex pattern, the amount of current consumed by the speaker varies over a wide range. So the amplifier must supply current and not change the voltage for accurate reproduction.
If the voltage changes (not current), then speaker will not reach the intended excursion, and distortion is the result.

Damping factor is calculated by dividing the load impedance by the amplifier's output impedance. Hence Damping factor decreases with lower loads.