It’s time to look at the input stage of how a modern car audio amplifier works. The input stage is responsible for interfacing with your radio and provides features like the gain control, crossovers, bass boost, remote level control and signal summing that your installer will use to make your stereo system sound great and function reliably. While we don’t need to get into the specifics of the components in this part of your amp, understanding the importance of the features is crucial in picking the right solution for your applications.

RCA Preamp and Speaker Level Inputs

Your amplifier can’t amplify an audio signal if you can’t connect the amp to your radio. Almost every amplifier on the market has RCA input jacks that allow your installer to connect an aftermarket radio quickly and easily. We say “almost” because some amplifiers are designed exclusively for integration with factory-installed audio systems. These amps may have a set of wires on a pigtail harness to accept signals.

In most cases, speaker-level signals are no different than a preamp signal other than they are usually higher in voltage and, because they have already passed through an amplifier stage (in the factory-installed radio or amp), may contain a little more distortion.

Whether the amp uses preamp or speaker-level signals, it should have a feature called Balanced Differential Inputs, or a variation of those words. This simple circuit compares the signal (or noise) on the center conductor and the shield of an RCA interconnect and uses an Op-Amp (a small integrated circuit that can be configured to compare or combine two signals into a single output) to remove anything common to both conductors. If you are using twisted-pair interconnects, EMI or RFI noise should be common to both conductors and thus will be reduced or eliminated by this circuit. When shopping for an amp, Balanced Differential Inputs are one of the first things you should ask the salesperson about.

Signal Processing Features

The next important feature in any amplifier is the sensitivity or gain control. This adjustment allows your installer to configure the amp to produce maximum power for a specific voltage that matches the maximum undistorted output of your source unit, or your power requirements based on the design of your audio system. The gain control is something that should be set once using an oscilloscope and a real-time analyzer (RTA), then not touched again unless the design of the system changes.

Most modern amplifiers include some form of electronic crossover that limits the range of frequencies that pass from the inputs to the outputs. A high-pass crossover only allows frequencies higher than the crossover point to pass and would be used on midrange and high-frequency speakers. A low-pass crossover allows audio signals lower in frequency than the crossover point to pass through the amp. This type of crossover would be used for woofers and subwoofers. Depending on the design of your audio system and the features of your amplifier, your installer may choose to combine high- and low-pass crossovers to create what is known as a band-pass crossover. This crossover would be used on midrange or midbass drivers to cut out low- and high-frequency information.

Many amplifiers have a bass boost control. This control operates as a single-band equalizer that the technician installing your sound system can use to reinforce a narrow band of frequencies being sent to a subwoofer. In reality, adding a narrow-bandwidth boost to your audio signal, from a purist perspective, makes no sense. Most systems sound better with proper DSP equalization to deliver smooth and predictable response across the entire operating range from 20 Hz to the upper limit of your sub around 60 or 70 Hz. A peak at any particular point will sound unnatural.

Remote Level Controls

Most high-quality subwoofer amplifiers come with a remote level control or remote bass boost control that can be installed in the front of the vehicle. This control allows the driver to turn the bass up or down to suit the music he is listening to or his mood. When shopping for an amp, look for units that offer a level control as opposed to a bass boost. As we mentioned above, adding emphasis to a narrow band of frequencies doesn’t sound as natural as turning as adjusting the overall output of the subwoofer.

Amplifiers with Integrated DSP

A friend of ours was in charge of developing a series of high-end amplifiers for one of the well-known head-unit manufacturers. The goal was to include as much flexibility as possible in terms of crossovers and signal summing. The complexity of the amp grew to a point where it was becoming difficult to fit all the switches and adjustments on the side of the amp. To provide their clients with the features they wanted, the company decided to remove all the controls and implement a digital signal processor (DSP) to handle everything. Now, the installer could combine signals from multiple sources, set crossovers very accurately and equalize the signal to deliver a smooth and predictable response from the speakers. Sure, your technician will need to connect a computer to the amp, but the results will be fantastic!

Great Features and Great Design

As important as the features of the amplifier you choose are, the design and component layout of the input stage of a car audio amplifier can have a huge effect on the performance of the amp. Keeping these components away from noisy sections of the amp like the power supply and output stage can dramatically reduce the signal-to-noise ratio of the amp. For this reason, larger amplifiers often sound and perform better than their compact counterparts. As with any design, the electronics engineers and technicians who develop the circuits and lay out the components have to balance performance, features, cost and size.

Find the Latest Car Audio Amplifiers at Your Local Car Stereo Shop

When it’s time to shop for a new amplifier for your car, truck, motorcycle or boat, make some notes about why you need an amp and what you want it to do. Armed with that information, the product specialists at your local stereo shop can help you find a solution that will meet your requirements quickly and efficiently and ensure that your mobile audio system sounds magnificent.

This article is written and produced by the team at www.BestCarAudio.com. Reproduction or use of any kind is prohibited without the express written permission of 1sixty8 media.

We’ve talked about car audio amplifier features and specifications at great length, but up to this point, we haven’t discussed how a car audio amplifier works. In this article, we’ll provide a simple overview of how the power supply in your mobile amplifier can take the 12 volts supplied by your electrical system and convert it into a much higher voltage to drive your speakers.

Making Power for Your Speakers

To supply enough power to your speakers to produce music at realistic listening levels, we need a lot of voltage. For standard 4-ohm speakers, it takes a peak-to-peak voltage of almost 60 volts to deliver about 100 watts to your speaker. In most amplifiers, this voltage is configured as +30V and -30V, relative to the ground reference voltage of your vehicle chassis. So, how in the world do we get plus and minus 30 volts from 12? That’s the job of the power supply.

How a Transformer Works

Power supplies couldn’t be created with any reasonable amount of efficiency without a transformer. A transformer is a simple device that increases or decreases alternating current (AC) voltages using two coils of wire wrapped around a magnetically conductive iron core. If you have a 1:2 transformer and feed 12V of AC signal into the primary, you get 24 volts on the output. The big green boxes out on your curb or the cylinders on the power poles near your house are step-down transformers that convert the 16kV feed that enters your neighborhood into 120- and 240-volt feeds to your home.

How Do We Get AC Voltage in a Car?

As you may (or should) know, the power supplied by the battery and alternators in our cars and trucks is direct current (DC). Left in that state and fed into a transformer, we’d see a small voltage spike when the signal was first connected, then nothing. The steady current flowing through the primary winding would simply heat it up and not produce anything on the output side of the transformer.

Since we need an AC signal, modern amplifiers use a pulse-width modulator to create a series of square waves that turn on a bank of MOSFETs (electrically controlled high-current switches) that pulse the supply voltage on and off very quickly. Many high-quality amplifiers have power supplies that switch at more than 300kHz.

In the simplest of terms, by switching the connection from the battery to the input of the transformer on and off very quickly, we create an alternating current signal. The voltage of the pulsed signal is increased through the transformer and then fed into a set of diodes and capacitors to smooth it back out to what we call the rail voltage. The rails are the positive and negative power supply sections of the amp that are connected to the output devices.

In application, the circuit is far more complex, but this is the basic operation of the system.

Energy Storage and Power Delivery

As the output voltage of a car audio amp increases, so to does the amount of current flowing to the speaker. The pulse-width modulation controller that manages the power supply can change the relative “on” to “off” time in order to increase the current supplied by the amp. More “on” time means that more current is fed to the transformer, which results in more voltage being produced on the output. Regulated back down to the required rail voltage, this extra voltage ensures that we maintain stable rail voltages.

If you look inside an amp, you will almost always see a toroidal transformer and a bank of energy storage capacitors. These large capacitors help smooth the output of the transformer and diode rectifier stage, and store large amounts of energy so that the amp can keep up with the current demands of the audio signal.

Learn How a Car Audio Amplifier Works

You should now have a basic understanding of how your car audio amp converts the 12V feed from your alternator into much higher voltages for the rails. In the next article, we’ll talk about the front end or input stage of a car audio amplifier and discuss crossovers, gain controls and the features and functions that make it easier for your installer to configure your car audio amplifier for optimum performance in your car or truck.

This article is written and produced by the team at www.BestCarAudio.com. Reproduction or use of any kind is prohibited without the express written permission of 1sixty8 media.

Unlike buying and setting up a basic home audio system, having a new amplifier and speakers installed in your car or truck requires proper setup and tuning. At home, you can adjust the placement of the speakers and how much they are toed in to affect the focus of the soundstage and the bass response. In a car, your installer needs to mount the amplifier, wire it, then adjust the crossover and sensitivity controls to work with your source unit and the design of the system. Getting these settings wrong can have an audibly detrimental effect on the performance of your mobile audio system. Let’s look at why proper amplifier setup and tuning are so important.

Basic Car Audio Amplifier Setup

Once the power, ground and remote turn-on connections are made, and new speaker wires have been run to each location in the car, the last step is to connect your amplifier to the source unit in the system. Depending on the design of your audio system, you may have a very basic CD player with low-voltage preamp outputs, a premium multimedia receiver with 5-volt preamp outputs or you might be using a factory radio with or without an amplifier. The sensitivity (gain) control on your amplifier exists to ensure that your new amp can reach its full potential from any of these sources. Many shops use an oscilloscope or a distortion detecting device to ensure that the system is configured accurately and efficiently.

If you are adding a subwoofer to your vehicle, the basic process is the same, but your installer now has to balance the output of the sub to the other speakers in the car. He or she will also have to set the crossovers on the amp so that the output of the sub blends with the output of the smaller speakers. Many high-end shops use a real-time analyzer (RTA) to perform this task to ensure the output of the speakers blends perfectly. Setting up crossovers also needs to take into account the physical capabilities of a speaker. A small 4-inch midrange certainly can’t produce the same amount of low-frequency information as a 6.5-inch woofer and needs to be adjusted accordingly.

What if Things Aren’t Set Up Properly?

If the sensitivity setting is wrong, you may experience a lot of background noise or hiss in your system. At the opposite end of the scale, you may not be able to reach full volume. If the crossovers aren’t right, you run the risk of damage to small speakers or experience unwanted dips and peaks in the frequency response of the system around the crossover point.

Setting Up a Digital Signal Processor

The goal of adding a digital signal processor (DSP) to a mobile audio system is to produce accurate imaging and realistic frequency response at the listening position. Setting up a DSP properly requires training and an investment in tools. Beyond that, your installer needs to use a real-time analyzer to measure the acoustic performance of the system. While there are a variety of processes used to set parameters like signal delay and different theories on whether to boost or cut EQ bands, the person tuning the system needs to have a full and detailed understanding of how the adjustments he or she makes affect the amplifiers, the speakers and the resulting acoustic performance of the system.

What if Your DSP Isn’t Set Up Properly?

In the simplest of scenarios, your audio system may not be as optimized as it could be. There may still be frequency response, imaging or staging issues. If the settings are really far off, you run the risk of damaging speakers permanently, or the performance of your sound system might have been better off with no processing at all.

Choosing the Right Retailer to Setup Your Mobile Audio System

The easiest way to choose a shop to set up your mobile audio system is to ask to listen to one of their demo vehicles. If you like the sound of the system, it offers excellent imaging and staging and plays at a volume level that suits your listening preferences, they should be qualified to recreate something very similar in your vehicle. If you aren’t happy with the way the vehicle sounds, ask to listen to a client vehicle. If you still aren’t satisfied, look for another shop to work on your car or truck.

When a car audio system is set up and tuned properly, it can rival some of the best home audio and studio reference systems on the planet. Don’t short yourself on getting the most performance possible from your upgrade – make sure it’s installed and configured properly.

This article is written and produced by the team at www.BestCarAudio.com. Reproduction or use of any kind is prohibited without the express written permission of 1sixty8 media.

If you are in your late 40s or older, then you likely grew up with a turntable or tape player in your home as a way of listening to store-bought music. Between 1982 and 1983, the compact disc entered the market and forever changed the way music was stored and transported. In this article, we are going to look at how digital audio works and dispel some of the myths around the conversion between the analog and digital domains.

What Is Digital Audio?

In the simplest of terms, a digital audio file is a representation of an analog signal using a series of digital words. In the digital domain, i.e., a computer, information can be stored as a 1 or a 0.

Computers can combine strings of 1s and 0s to represent characters in a text document, colors in a photograph, commands in a program or voltage levels in an audio file.

For decades, the standard for storing audio in the digital domain has been the Red Book Compact Disc Digital Audio (CD-DA) standard of a 44.1kHz sampling rate with a depth of 16 bits.

The sampling rate describes how often a voltage level is measured and stored. To capture the entire audible spectrum of sound, the Nyquist-Shannon sampling theorem states that the sampling rate needs to be at least twice as high as the highest frequency you want to record for it to be recreated with accuracy.

The second consideration in converting an analog signal to the digital domain is the need to store an adequate amount of resolution to properly represent the original signal. The Red Book standard uses a digital word length of 16 bits. This means that there is a string of 16 1’s and 0’s that can be used to represent 65,536 voltage levels. If you are converting the output of a microphone to digital, and the maximum voltage is 1 volt, then a resolution of 16 bits means that the resolution is 0.000015258789 volts. That’s a lot of detail.

Finally, the Red Book standard states that two channels of audio will be sampled simultaneously to create a stereo recording.

Some Quick Math on CD Quality Audio

For those interested, it’s easy to calculate the effective bitrate of a CD-quality audio file. Since we sample the audio signal at 44,100 times a second, and each sample has a voltage level represented by a 16-bit word, and we do this for two channels, 44,100 times 16 times two is 1,411,200, or 1.411 kilobits per second.

To calculate how much space it would take to store a song like “Bohemian Rhapsody” by Queen, you can simply multiply 1,411,200 by the number of seconds in the song (in this case, 355 seconds) for a total of 500,976,000 bits, or about 60 megabytes of data.

How Are Digital Audio Files Created?

A device called an analog-to-digital converter (ADC) is responsible for taking the analog signal and converting it into a digitally represented value. These devices are commonplace and are found connected to the microphone in your smartphone or the Bluetooth microphone in your car. They are incredibly compact and, relative to when they were first introduced, inexpensive.

ADC work in several ways, but we’ll describe the basics. Imagine, if you will, a series of comparator switches, each stacked one atop the next and referenced to an ever-increasing voltage. We’ll keep the example simple and say that we have eight switches, each of which is triggered at

0.125-volt increments. If we feed an analog signal into our comparator switch tree with a level of 0.3 volts, the bottom two switches will turn on, and we get the digital word 0010 (which is 2). If we increase the voltage to 0.8 volts, we trigger all but the last two switches and get the word 0110 (which is 6).

Counting in Digital

Counting in digital is easy, once you understand how it works. Each space in a digital word represents a value of 2 to the power of the location. So, the first space is 2 to the power of 0, which is 1. The second space is 2 to the power of 1, which is 2, the next space is 2 to the power of 2 which is 4, and so on.

2^0 = 1 2^1 = 2 2^2 = 4 2^3 = 8

To encode a value using this format, we simply assign a 1 or a 0 to each placeholder such that the sum values represented by the placeholders with a 1 represent the original value.

0000 = 0 0001 = 1 0010 = 2 0011 = 3 0100 = 4

0101 = 5 0110 = 6 0111 = 7 1000 = 8

In our example above, we are using a very low resolution of 3 bits, which means we can show only eight different levels. This limited resolution, of course, introduces some error – known as quantization error. The math can get very complicated very quickly. Suffice it to say that in our example, our theoretical digitizer doesn’t know the difference between a voltage of 0.63 and 0.73 volts. This is a large error and would not work in an attempt to sample audio. Luckily, our 16-bit resolution gives us 65,536 levels from which to choose.

What About Those Crazy Stair-Step Graphs?

You have undoubtedly seen marketing images showing a comparison of CD-quality audio resolution versus high-resolution 96 kHz, 24-bit audio.

While the concept of having a higher sampling rate and more resolution is accurate, it doesn’t mean that the CD-quality audio signal suffers in any way.

To demonstrate this, we created two 20 kHz test tones in Adobe Audition. The first track has a 96 kHz sampling rate and a resolution of 24 bits.

As you can see, the waveform looks smooth and detailed and shows roughly five samples per cycle.

The second track is the same 20 kHz sine wave stored at a sample rate of 44.1 kHz and a resolution of 16 bits.

As you can see, there is no significant difference in the shape of the two waveforms. More importantly, they both look like sine waves and neither has any stepping in them.

Understanding Digital Audio

Storing audio signal in the digital domain offers distinct packaging and reliability benefits over analog storage media like vinyl records and magnetic tapes. Of course, digital files don’t degrade over time. Digital files are also impervious to playback speed issues. If your turntable or cassette deck is playing too slowly, the music won’t sound right.

In a future article, we’ll look at the file format options available for storing digital audio files. Until then, be sure to drop by your local specialist mobile enhancement retailer to see all the latest digital media-compatible source unit upgrades available for your car, truck or SUV.

This article is written and produced by the team at www.BestCarAudio.com. Reproduction or use of any kind is prohibited without the express written permission of 1sixty8 media.