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Old 20-06-2005   #1
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Amps – The difference between all.

Amps are all the same I hear you say. Whats all the choice for, they all do the same thing pretty much. Well i hope this sheds some light on the matter, as theres more to them than originally meets the eye. I warn you this is a long one, but IMO its well worth reading!

Firstly, What actually is an amp?
An amp is commonly a standalone piece of equipment, which given power and a signal, will produce a powerful speaker output that drives your desired speakers. You will also find an amp in your headunit, albeit a less powerful one.

What can an amp actually do for me then?
Quite simple really, it can produce a much clearer louder signal to drive your speakers. Amps provide a much higher clarity and depth of music over the average headunit. Some speaker types (subwoofers inparticular) rely solely on a standalone amp to run as they require a lot more power than the amp in the headunit can provide.

Ok so I want a standalone amp. What am I looking for?
Firstly decide what you want to run off your amp. Be it a subwoofer, components or coaxials, all can be run off a standalone amp. With the right amp, you can run all of them off the same amp!

• So the first thing to look for is the amount of channels. The amount of channels is usually in pairs – so if you have a 6 channel amp, you can run 3 pairs of speakers. However, some amps are “bridgeable” which means you can turn 2 channels into 1 to make twice the power for a single speaker. For example, I have a 4 channel amp that’s got 300w per channel. If I was to run 2 subwoofers off this amp, I could turn the 4 channel amp into a 2 channel amp by bridging 2 of the channels. This would then give me 2 channels of 600w – which would adequately power most subwoofers.

• Ok so I mentioned power. This is the next big thing to look at. If you buy one that’s too powerful for your speakers, they will blow. Get one that’s too low for it, you will again have problems with clipping (where the noise distorts) at high volumes. The easiest way to find out what power is needed is to look at your speakers power rating. Ideally you want to match your speakers RMS rating with the amps RMS rating, or have the amp a little more powerful than the speaker to combat the chance of clipping at high volume. For example, I have a 600w RMS subwoofer. I would be best looking at a 600 to 700w RMS amp.

So what’s the difference between RMS and the more common MAX or PMPO power rating?
When shopping for an amp, you only want to look at the RMS rating – this is the continuous power rating that the amp can provide. With MAX or PMPO, this is what the amp can do at full tilt for no more than a few seconds before it goes pop. The RMS is always a lot smaller than the MAX rating, commonly about half if the amps efficiency is about 50%.

Ok now you mention efficiency. What’s that all about?
There are many different amp classes with different power ratings. Putting it basically, the different classes define how each amp is efficient with the given power. On a standard amp with 50% efficiency, to produce 500w RMS of power, it also wastes another 500w to heat. A more efficient amp will provide more power and less heat.

The classes and what they mean:
• Class A – Desirable for their high quality of sound repercussion, but runs very hot, therefore not very efficient on power.
• Class AB – This is the most common amp class. A class AB amplifier runs cooler, and therefore, more efficiently than a class A, with lower distortion and higher reliability.
• Class D - Class D amps boast higher efficiency, produce less heat, and draw less current than Class AB amps. However, they do produce higher distortion than a class AB amp, but this distortion occurs at high frequencies that are easily removed by a low-pass filter.
• Class T – These provide the same sort of audio quality as a class AB amp, but have the power efficiency of a class D amp. Class T amps are able to generate 2 to 4 times more power than a similar sized class AB amp.

I’ve heard about MOFSET on amps. What’s that all about?
A MOFSET (Metal Oxide Semiconductor Field Effect Transistor) based amp uses different configuration than normal conventional bipolar transistors. They are much more stable and efficient than the normal transistors used.

Ok you’re loosing me now. What’s a transistor?
Right, without going too much into the electronics behind everything, an amplifier uses an electronic component called a transistor. These turn a small power signal into a larger power signal. They have different configurations and power ratings. The more efficient amps use a better setup and more power conservative transistors (such as MOFSET), which also switch off when unused. This isn’t the case in a class A and class AB amp, which is why they are less power efficient.

Ive also heard about OHM’s and Impedance. What’s that about?
Amps and speakers require a matched resistance. This is measured in ohms, and often referred to as the amps impedance. The most common impedance is 4 ohms. Dropping the resistance can put up the power a lot, providing both your amp and speaker can support the lower resistance. Also, you can connect up the speakers in parallel or series on the same channel to manipulate the channels impedance. Wiring speakers in parallel halves the impedance. So you can wire two 4 ohm speakers in parallel on a single 2 ohm channel and have them powered ok. But this is much more complex than it sounds and not recommended unless the amp’s manual and the speakers says it’s safe.

Ok I hope you’re still awake and with me. There’s only a little more to go now you’ll be glad to hear.

So what else is there to consider when looking for an amp?
• Signal to Noise Ratio (SNR) – This is the measurement of noise in the amp compared to the level of the input signal. The higher the percentage, the greater the difference - which is better.

Ok, now last but not least, I will just run through some of the other features of an amp which can be extremely helpful to have.

1. Built in crossovers
A crossover can consist of both a high-pass and low-pass filter. What they do is filter out frequencies that aren’t within their set range. These can usually be controlled by a dial on the amp.
A LPF (low pass filter) will only let frequencies past that are lower than the set frequency.
A HPF (high pass filter) will only let frequencies past that are higher than the set frequency.

Using the crossovers allows you to set the amp to deal with a specific frequency range, which is highly important when phasing through your car audio system. This allows you to filter out all the high frequencies going to a subwoofer for example, or filter out the bass for the high range components, or both the bass and treble for mid range drivers!

2. Bass Boost
Some amps (usually mono bass amps) have a bass boost button or dial. This simply boosts the input signal between the 40 to 90Hz range to give more emphasis on the bass.

3. Speaker Level and RCA inputs
Some amps also have speaker level inputs as well as RCA inputs. Speaker level inputs allow you to connect a normal speaker wires to the amp and make benefit of using a standalone amplifier. This is good for those that don’t have a headunit with RCA outputs. RCA inputs are already levelled, and are much more common. These are better quality too compared to speaker level inputs – but if you haven’t got RCA ports, you cant complain!

4. Gain
The gain controls the sensitivity of the input signal of the amp. If you have it at full whack, you will have a much louder output, but also will distort much earlier when the volume is steadily increased. The common consensus is to keep the gain around half way

5. Remote input
This isn’t for a remote control, although some do have remotes that can be connected. In this instance it refers to a wire fed into the amp which switches on the amp when the headunit is switched on. This is a means of ensuring your amps aren’t switched on wasting power when they’re not needed.

Other parts of the amp should be the speaker output terminals and the power input terminals, but these are self explanatory I hope.


OK thats it! i hope thats cleared some things up, and now you can really get the most from your amp!
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Old 20-06-2005   #2
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Re: Amps – The difference between all.

Let me guess, you have a day off?
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Old 20-06-2005   #3
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Re: Amps – The difference between all.

Quote Originally Posted by darkcircuitUK
Let me guess, you have a day off?


I'll do the how to install a headunit one when my new one eventually arrives
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Old 20-06-2005   #4
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Re: Amps – The difference between all.

I think the how-to-install headunit one is pretty straight forward, but can differ for each car, for example the Punto has a code plug. You going to do one for each Fiat avaliable? If you are then I can provide you with one for the Mk2 Punto
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Old 20-06-2005   #5
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Re: Amps – The difference between all.

it wont be model specific. But will be from how to hard wire it in (no plugs like mine) and from a plug. No its not hard, but usefull all the same
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