For our project we decided to disassemble and understand a Memphis 1 Channel Mono Block Amplifier. First we started by disassembling the amp down to the main circuit board. From there we assigned ourselves different components to understand what they were and how they worked inside the amp. We all researched our components and got back together to discuss and figure out the flow of power and operations of the amp worked.
A general idea of what the amp does is as follows. Power comes into the inputs from the positive side of the car battery. A negative source comes from the car’s chassis to the negative terminal. The remote wire comes in from the head unit or source of sound to the remote input. When the source turns on, power runs from the remote wire to a relay inside that allows power to run through. Power then runs to various capacitors to store up power before running to the inductor that converts the power to usable power for the MOSFETs. As the power runs through the circuit, it eventually comes to resistors which slow up the current flow. Sound comes in through the inputs and to the MOSFET amplifiers. Then sound goes to the sound dampeners to clean the sound waves up before going to the sound outputs. To better understand the amp and its components we will branch off and explain each of the components and what they do. When a relay receives power, power runs through a set of coils and creates a magnetic field that actuates an arm inside and closes the circuit. Relays are used as switches to control larger circuits with more power. Since a relay is able to control an output circuit of higher power than the input circuit, it can be considered to be a form of an electrical amplifier. When using a relay in a dc current, diodes are put in across the coil to dissipate energy from the collapsing magnetic field at deactivation, which would cause a spike in voltage and damage components if not there. In a single channel mono block amplifier like the one our group disassembled, capacitors were used throughout the circuit for both reasons. Due to the size of the amp and the amount of power required to properly run it, a large number of capacitors were needed. A capacitor is an electrical device that can store energy in the electrical field between a pair of closely spaced conductors. When voltage is applied to the capacitor, electrical charges of equal magnitude, but opposite polarity, build up on each plate. The capacitor stores some of the energy inside of it and keeps the amp from getting too much power and overheating. After the power from the outlet goes through the capacitors and the resistors, it travels to the main inductor. A voltage is applied to the wire, and a current is created which produces a magnetic force (MMF). MMF is a force that pushes a flux through a magnetic circuit. This also occurs in an opposing wire with the current going in the opposite direction. In an ideal transformer the MMFs of both wires and currents would cancel out and there would be no flux.

The math behind it is…

and where * vP and vS are the voltages across the primary winding and secondary winding, * NP and NS are the numbers of turns in the primary winding and secondary winding, * dΦP / dt and dΦS / dt are the derivatives of the flux with respect to time of the primary and secondary windings. * The current is inversely proportional to the number of turns in the coil. So if there are more turns there is higher the voltage, and a lower the current. The voltage from the first wire creates the current in the second wire. This is how the opposing MMF is created. As the voltage from the first wire is being drained into the second wire, the current is increasing in the first wire. Also, the current in the second wire is going down and the voltage is going up. So, if the power going into the first wire was 50 Watts, with 2V and 25A, the transformer would make it 25V and 2A, as it is proportional to the number of turns in the coil.
Another use for capacitors is to shave off some of the power in the circuit to prevent too much from spreading throughout the rest of device for many reasons. In the pictures are several examples of modern capacitors used throughout all types of devices.

The transformer in our amp is in a circular shape. This is different from other transformers that normally take the shape of a rod. The reasons why it is shaped like a circle are… * This shape allows for less wire to be physically in the transformer * No air gaps in the cross section which could add to unwanted resistively * Screens electromagnetic interference by minimizing the core’s magnetic field * So basically, less weight, less mass, and most of all, less hum which is essential in an amplifier

The purpose of the transformer is to convert the high current and low voltage power into high voltage and low current power. This is done by having the power go around the inductor in several coils. The voltage in one wire is creating the current in the other wire, and vice versus. The proportion between the voltage and the current in both wires is directly related to the number of turns in the transformer. This particular design provides less wire that needs to be in the amp, which makes the amp lighter, as well as less complicated. Also the circular design minimizes the core’s magnetic field, which could create interference to components around it. Most importantly though, is the reduced humming.
So, basically, the audio transformer takes the input voltage from the capacitors, increases it, and sends it to the MOSFETS. This can be seen by looking at the underside of the amplifier, this where the path of the voltage can be seen. The MOSFETS are located at the top and bottom of the picture.
In our 1 Channel Mono Block Amplifier, we had many resistors throughout the circuit. A resistor is a two-terminal electrical or electronic component that resists an electrical current by producing a voltage drop between its terminals in accordance to Ohm’s Law. The relationship between voltage, current, and resistance through a metal wire, and some other materials, is given by a simple equation called Ohm's Law: V=IR where V is the voltage (or potential difference) across the wire in volts, I is the current through the wire in amperes, and R, in ohms, is a constant called the resistance. The electrical resistance is equal to the voltage drop across the resistor divided by the current through the resistor. Resistors are used as part of electrical networks and electronic circuits. In our amp we were working with axial resistors. Axial resistors use a color code to indicate the resistance of each resistor. As you can see from the diagram on the next page, the first color band represents the first digit for the resistance, the second band represents the second digit, and the third band represents the third digit. The next band is the multiplier band. It tells you how much to multiply the number by. The next band is the tolerance band and it gives you the tolerance of that resistor, and then the last band gives you the temperature coefficient of the resistor. That is how to read a 6-Band Color Code. The 5-Band Color Code doesn’t include a temperature coefficient band. The 4-Band Color Code has the first two bands represent the significant digit in the resistance, the third band as the multiplier band, and the fourth band as the tolerance band. The 4-Band resistor is the most commonly used resistor. The 4-Band and 5-Band resistors were used in our amplifier. The 6-Band resistors are used for higher tolerance resistors. There were different size resistors all along the circuit in our amplifier. As the head unit sent 12 volts to the remote wire terminal, power for our amplifier would travel through the wires from the head unit, and then when it came to a resistor, it would create a voltage drop and limit the current in that spot of the amplifier and slow everything up.

MOSFET stands for metal oxide semiconductor field effect transistor. The

MOSFETS are located around the edge of the amplifier. MOSFETS are the principle

component in the amplification process. After the power goes through the transistors and

capacitors, creating the right voltage and power, it goes to the MOSFETS.

Upon closer examination we see that the MOSFET chip has three leads. The one on the right in the “source”. The middle lead is the “gate”. The left lead is the
“drain”.
You can tell from the picture above that this amplifier has many MOSFET amplifier chips. They are all located around the edge of the circuit board. This is not an accident. MOSFET amplifier chips create a lot of heat as a by product.
Heat is the enemy of electronics. If the heat is not dissipated the MOSFETS will burn out and ruin the amplifier. That is why they are located at the edge of the board. The case that the circuit board is mounted in is aluminum and has fins across the front of it. This is called a heat sink. The MOSFETS are screwed to the aluminum heat sink with another piece of aluminum on top of it. There is also a white paste between them to aid in the heat transfer. The heat is transferred to the heat sink and away from the MOSFETS and other components. The aluminum fins are used to increase he surface area because the more surface area there is the more heat can be released.

MOSFETS are voltage controlled power devises. When there is not a voltage applied to the gate the MOSFET is non-conducting. Then we apply a voltage to the gate and the resistance between the drain and source decreases. This happens because there is an electrostatic field created between the gate and the rest of the chip. This will push away the gaps in the n type substrate and also attracts any movable electrons in the p type region under the drain and source. This creates a channel in which electrons can get into and move between the source and drain. So there is a direct relationship between the voltage applied to the gate and the resistance between the drain and source. The input form the pre-amp comes into the amplifier with a relatively low voltage. The MOSFET is a good chip to use because it can operate on very low voltages.
As the power from the battery comes in it eventually finds it way to the source lead of the MOSFET. Halted there by the resistance between the source and drain it waits on the input from the pre-amp. The input from the pre-amp comes in to the gate lead and controls the flow of electricity from the source to the drain. So the power from the transistors and capacitors can acquire the same pattern as the input from the pre-amp. This is how the amplifier actually amplifies the music. Sound dampeners have wire wrapped around them to create a coil that the amplified power and sound runs through before being sent to the outputs. Sound or power runs through these and when it does the small spikes in arcs of the lows or highs of the waves are smoothed out back to normal flowing waves before being sent to the outputs. If the waves weren’t corrected then there would be excessive spikes and overheat the amp and harm the subwoofer.
As the 12v runs from the car battery and head unit travel to the terminals, then to a relay, through the circuit to resistors and capacitors, then to MOSFETs and sound dampeners, we are able to amplify and enjoy our music and sound today. The process of taking the amplifier apart, determining all the parts that went into powering the amplifier, and then assigning parts to research for each group member worked out quite well for our group. Everyone did their part and it helped make this project run smoothly. By the end of our project we all could understand how the amplifier all worked. It turned out to be a great team building and learning experience.