A, AB, D or All Three? Pick Your Amp!

Amplifiers, such a range but which is right for you? I’d like to discuss amplifier types and applications.

As a Four Master, Car and Home Stereo are recognised as one of the leading car audio installers in the country. Our knowledge and experience mean that we are ideally placed to choose the right equipment and install it to the highest standard.  We offer a no pressure approach and are happy to offer advice on choosing the right equipment; just recently I had a great conversation over Facebook with an enthusiast in Australia over the benefits of the magnificent Rainbow Profi speakers.

Commonly I am asked “how many Watts is it?” but there is so much more to an amplifier than that. In reality, the Watts figure is often not the most useful specification when choosing between amplifiers. True it gives a simple indication of power but all too often that figure is heavily massaged to look higher. I have tested some so-called 3000W amplifiers to discover that they only made 200W at the terminals into a speaker load. Still an impressive output but certainly not 3000W as claimed.

But I digress; we are looking today at amplifier types and their uses. There are three types of amplifiers in main use today they are classed as A, AB and D. Although they all have the same purpose there are some fundamental differences between them that make them suit different applications.

At the heart of an amplifier are the power transistors, these are responsible for taking a small signal and making it larger, the classification describes how the transistors are used. Of course, there is a massive range of qualities and performance variations related to each type but we will stick to classes.

Class A, a typical sound wave.

As we know, Sound is an oscillating wave. This wave has a positive and a negative component but is symmetrical about the ‘t’ axis. So all we need is one big transistor that can amplify the whole signal to whatever power we want right? Well yes and this is the ideal solution for sonic accuracy; the high output signal is an exact copy of the small input signal. The best amplifiers I have ever heard have all been A class with a sound that is open, transparent and simply a joy to listen to.

The magnificent Audison Thesis Venti

However, all this purity comes at a price; huge power consumption. Those massive transistors are switched on all the time regardless of whether there is a signal there or not or how loud it’s playing. This means heat and lots of it which has to be dissipated. So we need massive power supplies and large heatsinks which make the amplifier large and somewhat inefficient, typically around 20%. That’s why we need to use such large power cable!

So how do we get better efficiency? Class AB.

 

There are many considerations here but in very simplistic terms it is possible to use one transistor to amplify the top half of the wave and another matched transistor to amplify the bottom half. This means that smaller transistors can be used and they are only on for half the time leading to efficiencies of 50 to 70%. This means less heat and smaller power supplies which help to keep the cost down.

The JL Audio JX360, a mainstay of many audio systems

There are some drawbacks to class AB, principally of which is crossover distortion.

As a matched pair of transistors has to amplify the whole wave it is essential that they turn off and on at exactly the right moment (the class B part). Imagine two people writing the letter S where one person only writes one-half and the other person completes it, there is bound to be a little error. The same is true in the amplifier leading to a very slight distortion of the output wave but in truth, modern design can almost eliminate this meaning we can have a really great sounding amp that is pretty efficient. This has meant that AB design has dominated the market for decades.

The highest efficiency is class D.
Let’s get something straight, D does not stand for digital. Class D is just another design type, a really clever one. This design uses pulse width modulation to generate the amplified output which involves switching the output transistors on and off at a very high rate typically around 300 kHz. This High switching frequency means any noise is well above our audible range and the PWM leads to astonishing efficiencies of around 95% or higher. So, at last, we have a very high power, high quality and very efficient amplifier. It is fair to say that most mainstream car amplifiers today are D class as they are smaller, lighter and generate less heat than their A or AB counterparts.

The JL Audio XD400.4, small but powerful

As with almost everything, there has to be a downside and with D class their Achilles heel is radio interference. The switching frequency mentioned might not be audible but it can do a fine job of broadcasting in the FM radio range. This can lead to reduced radio reception at certain frequencies, of course, modern design does mitigate the problem but nevertheless, it can still be an issue.

So to sum up, Class A for the best possible sound (ideal for tweeters), Class AB for improved efficiency (ideal for midrange) and Class D for maximum power from the smallest chassis (ideal for subwoofers). Wouldn’t it be great if there was an amplifier with all three? Well, there is and it is called the 5.1K from Audison.

 

The superb and versatile Audison 5.1K

This is one of my all-time favourite amplifiers and it is the amp that powers my own personal system. The detail of the class A front stage is phenomenal while the AB class mid-stage offers an amazing amount of punch. The D class sub stage has enough power to rattle the windows but offers a fidelity that allows a seamless blend with the rest of the audio stage. This unit never fails to impress and is not too big to make it impossible to fit. It does get hot if driven hard but does not require special cooling if mounted sensibly.

 

If you would like to hear what the 5.1K can do then please feel free to call into our shop on Sunderland Street in Macclesfield and I would be pleased to demonstrate it in our Discovery or on the demonstration stand in store. If you would like any more information on amplifiers in general please call me on 01625 432707.

 

 

Gain An Advantage: Amplifier

Anyone who has dabbled in car audio will have come across an amplifier at some point. They come in many shapes, sizes, and outputs but from the cheapest eBay special to eye wateringly expensive European exotica they all have one purpose, to get the musical signal to the speakers. The amplifier is, therefore, sat between the CD player and the speakers accepting the low-level input signal and converting it to a high power speaker output. I don’t want to get too bogged down in technicalities but let’s discuss the different types available and the controls we are given.

The JL Audio RD900.5 is a perfect example. This 5 channel, D class amplifier is capable of running a complete car audio system with front speakers, rear speakers, and a subwoofer. Alternatively, it could run a pair of front speakers bridged for enormous power plus a subwoofer once again. So, the RD900.5 is a very high performance, a flexible amplifier with a pretty small footprint making it easy to install.

The input stage is on the far left of this amplifier and comprises the usual red and white RCA connectors. There are 3 pairs that equate to the front, rear and sub input. Above these are three switches that allow for hi or low-level input, auto turn on mode and input channel selection (2, 4 or 6). Not all amplifiers are equipped with these selectors but these add to the RD900.5 flexibility.

The next stage is what interests us here, the frequency filter and the gain controls. The RD 900.5 is nonsymmetrical meaning that all channels are not identical. Channels 1 to 4 are for main speakers while 5 and 6 are for subwoofers. Therefore there is a variable high pass filter for 1 to 4 and a low pass filter for 5 and 6.

What is the filter for you ask? It is used to remove frequencies that are not required by the speaker on that channel. If we know we have a subwoofer fitted then it makes no sense to send the very low frequencies to the door speakers. Sub frequencies require a speaker cone to move a great distance and most door speakers simply cannot achieve this without distortion, I’m sure you have all heard a speaker trying too hard causing the classic ‘burping’ sound. In extreme cases, the speaker coil can be heard crashing into the back plate creating a clapping noise. Either situation is undesirable so to prevent these from occurring the frequency filter is applied to restrict the low tones.

The cutoff frequency is variable to suit different speakers and installations and setting it correctly requires the use of a signal generator. If you do not have access to one of these then it is possible to do roughly by ear, simply play music and slowly raise the filter frequency until there are no very low sounds in the speaker. The result will be a much clearer sound with no distortion. The mid definition should be greatly improved meaning vocals will cut through better. Typically the filter control is graduated and a very rough initial setting for a typical door speaker would be around 80Hz but you should experiment either side of this to find the best setting.

The subwoofer (low-pass) filter is the opposite of the high pass filter as it removes the higher frequencies sent to the sub. This ensures it only gets useful frequencies and we do not waste amplifier energy trying to make it play the higher tones.

Again the cutoff frequency is variable but what we want is to blend the sub with the main speakers so it is important to find a filter point that complements the high pass filter for the speakers.

So now we come to the input sensitivity, perhaps one of the most misunderstood controls. First and foremost it is not a volume control. Sure, it does increase the volume as you turn it but that does not mean it is increasing the amplifier power. Let’s consider what an amplifier is doing, it is taking a small signal and making it bigger. That signal is very dynamic meaning it is made up of loud and quiet parts, an extreme example could be Tchaikovsky’s 1812 Overture. Not something we listen to every day but it serves our example very well. If you are not familiar with the piece it starts very quietly and builds to a crescendo of orchestra and cannons. A more modern piece would be Warriors Dance by Prodigy but with fewer cannons!

The most important thing to consider when setting the sensitivity is that the amplifier only has a finite amount of power, let’s say 100Watts. That is represented by the upper dotted line on the graphs above. Our goal is to get the maximum, undistorted output.

If we look at a typical input sound wave it is obvious that there are loud and quiet parts. As we stated the amplifier is there to make this signal louder. Now let’s add the maximum amplifier power to the input signal graph.

As we increase the sensitivity we increase the size of the input signal at the input stage to the amplifier and remember there is a finite amount of power available. So what happens if we go too far?

As can be seen the nice smooth curves at the top and bottom of the loud spikes have been flattened which is clipped distortion. So yes we have a loud sound but it will be fuzzy and unpleasant. It will also damage speakers as the flat tops of the wave are a DC signal that will only induce heat into the voice coils. So if we take our example, the 1812 Overture, with the sensitivity set as above the quiet passages will sound good but the loud sections will be badly distorted and this will get worse the louder we play it.

For the best sound and maximum output, it is imperative that the loudest sounds are not clipped. Normally this would be set up with an oscilloscope but it can also be done with a voltmeter by measuring the output for maximum unclipped voltage as long as you know the true output power.

Fortunately, the JL Audio RD amplifiers have a brilliant feature, a clip indicator. This will light up if the signal is distorted by over ambitious sensitivity meaning setting up is made much easier.

At Car and Home Stereo, we want all our installations to give the best possible sound and that is why we carefully set up each and every one.

If you would like to have your system checked for any problems and to find solutions to these we would love to measure your car using our state of the art test equipment. These can highlight deficiencies in the sound stage that are difficult to locate just by listening.

As usual, I have run out of space so I’ll leave amplifier types and their best application for another time. But please don’t hesitate to call on 01625 432707 if you have any questions.

Why Does Installation Matter?

At Car and Home Stereo we have been installing exceptional car audio for over 40 years, in fact, when we started there were barely the beginnings of in-car entertainment. Over those years we have seen a tremendous amount of change in the products we use to create outstanding audio experiences. From 8 track cartridge to CD to full digital audio, graphic equalisers to digital signal processors and all the other innovations that have come along we have embraced and utilised these to realise the best possible sound for our customers.

All these fabulous products are available to everybody, there has never been so much choice but all this technology will not guarantee a great sound. That will only be possible with the correct installation and careful setup. Many times I have had a car in that has had a lot of money spent on it yet still sounds bad. From buzzing door panels to downright dangerous wiring I’ve seen it all. Usually from DIY installations but not always. It’s not necessarily the fault of the equipment but rather a combination of poor choice and skimped installation.

It is true that the majority of my work is completely invisible but makes such a massive difference to either the finished sound or the reliability of the whole system.  Application of sound deadening material inside doors will improve the acoustic performance, soldering all connections may take longer but will improve reliability, looming cable runs with fleece tape is expensive but will eliminate any cable rattles and retain the OE look.

It is also important that equipment and wiring are installed to the highest standards to maintain vehicle warranties and safety standards. I have seen microphone cables wrapped around airbags, power cables attached to car batteries without a fuse and any amount of speaker wires dangling over brake pedals. At Car and Home Stereo, we take installation very seriously and we never rush. The best results are not achieved by racing to finish and I would rather spend an extra hour or two to get the best possible sound. After all, you would want your £1000 Rainbow speakers to sound their best.

Of course the same care and attention is applied whether we install top of the range JL Audio speakers or entry level Audison upgrades and in fact, the performance boost from proper door treatment at the lower price range is more apparent.

We will always recommend appropriate enhancements and best installation practices are rigorously followed which may take a little longer and cost a little more but will ultimately lead to a far better sound and is that not what we all really want?

coil

Practicing Safe Sound

There are many ways to upgrade your car audio system and let’s face it, most cars need it. I’m looking at you BMW, VW and Porsche in particular! It is not always possible to upgrade the head unit but it is always possible to improve the speakers. At Car and Home Stereo, we carry speakers by JL Audio, Audison, Hertz, Rainbow and others. This means we can choose the right speaker to suit the car and the customer. We will carefully install your speakers with custom built collars and fittings as well as add sound deadening in the door to improve its acoustic properties. The end result will be a vastly better sound without any cosmetic changes to your car.

And that is where we are finished but before you leave, a word of warning. Please take the time to run your new speakers in. The running in period varies for different speakers but generally, we recommend around 10 hours play time. Running in means keeping the volume at a sensible level without any large bass settings and we will always advise what should be the maximum volume for this period.

If this procedure is not followed your speakers may not fail but they will not reach their full potential, let me explain why.

A speaker is a transducer that converts electrical energy into sound and at the heart of the speaker is a coil of wire sitting inside a magnet. It is bright, shiny copper.

coil speakers good copper

It’s not necessary to know how it works but the important point is that when you pass electricity through a wire heat is generated and the higher the electrical current the more heat is generated. Now, this coil of wire is crucial to the accuracy of the speaker and it is protected by a thin coating of lacquer. This lacquer is quite soft when new and easily damaged by heat but if it is gently warmed over a number of hours the lacquer will harden.

I bet you can see where this is going! If a new speaker is subjected to a lot of power and played loud the voice coil lacquer will boil causing short circuits. Now while this will not necessarily cause the speaker to fail it will mean that the voice coil is not a single continuous wire which leads to a ‘lumpy’ effect within the magnetic gap. This, of course, means that the reproduction of sound is not linear and your investment will not reach its true performance capability. In extreme circumstances, the lacquer is burnt and expands into the magnetic gap which will cause a scratchy sound. These failures are non-reversible, cannot be repaired and are not covered under any warrantee.

 

coil bad burnt copper

burnt copper coil

So that is why we advise the running in period, to gently warm the voice coil lacquer causing it to cure. This hardened lacquer can now stand the heat of high power and your speakers will really perform as the designers intended.

I cannot overstate the importance of running in, a speaker is more likely to be damaged in the first few hours of use rather than over the rest of its life. At Car and Home Stereo, we want you to get the best possible sound from our expert installation so just hold back on the volume for a few hours, you’ll be glad you did.

 

Cutting Edge! with JL Audio

Today let’s look at the range of fantastic high performance products from JL Audio.

Formed in 1975, JL Audio are based in Florida USA and from the very start, their passion has always been to produce the best possible products. Originally they concentrated on sub-woofers and they quickly earned an enviable reputation for amazing power and performance. More recently JL Audio have expanded their range to include speakers and amplifiers with the emphasis once again firmly on quality and performance.

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It’s true to say that the JL Audio range of subs has something for everyone. From small, discreet custom enclosures to high output monsters to true Hi-Fi quality audiophile drivers. The engineering expertise at JL Audio means that even their least expensive sub still sounds amazing and will work in a relatively small enclosure.

Every in car system will benefit from the installation of the dedicated bass speaker and at Car and Home Stereo we will make sure that it is fitted and set up correctly.

 

 

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Of course a sub-woofer always needs an amplifier and so the logical step for JL Audio was to produce their own range. Car and Home Stereo is proud to be a JL Audio Signature dealer which means we carry a wide range of products. The XD range of amplifiers is a particular favourite of mine. They only take up a small amount of space but deliver an amazing performance! From the compact XD 200.2 to the immensely powerful XD 1000.1 they offer a level of flexibility and performance unparalleled to anything else.

Never a company to stand still, JL Audio have just upped their game and released a new range of amplifiers designated the RD series.

 

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These units are extremely good value for money and sound amazing as they are based on JL Audio’s NexD D class technology. Multiple input configurations are available making for pretty much universal compatibility while the small footprint means installation is straight forward.

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JL Audio speakers are some of the best around. Even the entry level TR series have a detail and clarity many other more expensive speakers cannot compete with. Taking a step up to the C2 series and we are well on the way to a true Hi-Fi performance. Where space is tight the C2 400 (a 10cm speaker) punches far above its weight for low frequency. This has become my first choice for the Land Rover Defender and is more than capable of overcoming the road noise while still producing a full range performance.

One speaker range stands out though, the C5. This speaker range has a natural and transparent sound that is simply breathtaking. OK they are not cheap but that is not the point, where high fidelity is the goal you have to go a long way to beat this speaker. The tweeter alone is one of the smoothest speakers I have heard with vocal and piano pieces a joy to experience.

And of course there are many more products in the JL Audio line up. There are processors that allow seamless integration with factory standard audio systems. These units can repair the poor performance of the standard head units found in BMW, Audi,  VW and others that can not be changed meaning you do not have to put up with the stock audio.

There is also a range of very high performance marine speakers used on the like of Sunseeker power boats. However at Car and Home Stereo we are land locked and there has never been a big demand for these here!

The most important point is that, with JL Audio, we have a range of products that can suit any application and any performance requirement. We have the experience and resources to make sure we offer and install the best possible sound at any budget.

 

Give Tim a call to discuss your requirements or, better still, call in to the shop in Macclesfield for a coffee and a chat.