Supervisor: Xabier Izquierdo 7th group: Xabier De Diego

Imanol Gabarain Xabier Martinez

SOUND AMPLIFIER CIFP Don Bosco LHII - Electronics department

3-11-2017

1

ABSTRACT

In this memory we have listed all the parts of our project. First, an exhaustive

search for an amplifier was carried out and then its operation has been simulated on the

computer. Once we saw that the response was positive, we have designed and built the

plate that will hold the whole amplifier. Afterwards, we have placed the components in

the board and connected to the power supply and to some loudspeakers. Finally, the

corresponding adjustments, fixings and measurements were done.

LABURPENA

Memoria honetan anplifikagailuaren proiektua aurrera eramateko eman behar

izan diren pauso guztiak biltzen dira. Lehenik eta behin, anplifikagailuen eta haiei

buruzko informazio bilaketa bat egin da, jarraian haren funtzionamendua ordenagailuz

simulatuz. Emaitza baliozkoa eta positiboa dela ikusirik plakaren diseinua eta eraketa

egin da. Ondoren, osagaien muntaia eta elementuen konexioa egin da. Amaieran,

dagozkion doikuntza, konponketa eta neurketa garrantzitsuak egin dira.

RESUMEN

En esta memoria aparecen todas las partes llevadas a cabo en nuestro proyecto.

Primeramente, se ha llevado a cabo una búsqueda exhaustiva de un amplificador y

seguidamente se ha simulado su funcionamiento en el ordenador. Una vez visto que la

respuesta del mismo era positiva, la placa que sostendrá todo el amplificador se ha

diseñado y construido. Después, se han colocado los componentes necesarios y se ha

conectado a la fuente de alimentación y a unos altavoces. Finalmente, se le han hecho

los pertinentes ajustes, arreglos y mediciones correspondientes.

2

Index

1. Introduction ............................................................................................................... 5

2. Objectives ................................................................................................................. 6

3. Requirements ........................................................................................................... 7

4. Specifications ............................................................................................................ 8

4.1. Amplifier ............................................................................................................. 8

4.2. Constant current source ..................................................................................... 9

4.3. Differential amplifier ............................................................................................ 9

4.4. Driver ............................................................................................................... 10

4.5. Output stage ..................................................................................................... 11

4.6. Safety system ................................................................................................... 11

4.7. Power supply .................................................................................................... 12

4.8. Case ................................................................................................................. 13

4.9. Input ................................................................................................................. 15

4.10. Output ............................................................................................................ 15

4.11. Budget ............................................................................................................ 15

5. Alternatives ............................................................................................................. 16

6. Implementations ..................................................................................................... 18

6.1. Mounting procedure ......................................................................................... 18

7. Checking ................................................................................................................. 23

8. Start up and fixing ................................................................................................... 24

9. Problems and breakdowns ...................................................................................... 28

10. Improvements ....................................................................................................... 29

11. Conclusions .......................................................................................................... 30

12. Works for the future .............................................................................................. 31

13. References ........................................................................................................... 32

14. Annexes ................................................................................................................ 34

3

Image index

Image 1 - Blocks of the main circuit .............................................................................. 8

Image 2 - ARES of the main circuit ............................................................................... 9

Image 3 - Block of the constant current source ............................................................. 9

Image 4 - Block of the differential amplifier ................................................................. 10

Image 5 - Block of the driver ....................................................................................... 10

Image 6 - Block of the output stage ............................................................................. 11

Image 7 - Sevety system improvement ....................................................................... 12

Image 8 - Circuit of the power supply .......................................................................... 13

Image 9 - ARES of the power supply .......................................................................... 13

Image 10 - Mounting of the case of the power supply ................................................. 14

Image 11 - Power supply ............................................................................................ 14

Image 12 - First circuit alternative ............................................................................... 16

Image 13 - Second circuit alternative .......................................................................... 17

Image 14 - Third circuit alternative .............................................................................. 17

Image 15 - Selection of the CircuitCAM ...................................................................... 18

Image 16 - Different mounting steps ........................................................................... 18

Image 17 - First step of the CircuitCAM ...................................................................... 19

Image 18 - Contour edge ............................................................................................ 19

Image 19 - Contour the routes .................................................................................... 20

Image 20 - First checking of the plate ......................................................................... 25

Image 21 - Input of altern signal .................................................................................. 26

Image 22 - Final amplificator ....................................................................................... 27

Image 23 - Main circuit + improvement ....................................................................... 29

4

Table index

Table 1 – Requirements of the project .......................................................................... 7

Table 2 - Characteristics of the amplifier ....................................................................... 8

Table 3 - Characteristics of the power supply ............................................................. 12

5

1. Introduction

In order to satisfy the highly demanding music lovers market, we have been hired

by a new company that wants to expand their sales into the high fidelity (Hi-Fi) audio

world. This company aims to enter into the market with really high-quality products and

taking into account this objective, the company has allocated part of its budget to the

R&D area, where we have been working as R&D technicians.

With this in mind, we have built a low cost and high fidelity 40 W power amplifier.

An audio power amplifier is an electronic amplifier that strengthens low-power, inaudible

electronic audio signals such as the signal from radio receiver or electric guitar pickup to

a level that is strong enough for driving loudspeakers. As a group of former technicians,

we have been learning the basis of the audio and we have applied our knowledge to the

project, designing and building the previously mentioned amplifier.

6

2. Objectives

The main objective of this project is to elaborate a detailed analysis of a high-fidelity

sound amplifier, with its consequent design, developing a scale model. We can divide

this main objective down into some partial objectives considering the product that has to

be delivered and the knowledge we have to acquire at the end of the project:

1. Configure and design a high fidelity 40 W amplifier.

2. Complete the challenge in approximately 5-6 weeks.

3. Acquire basic knowledge about microphones, amplifiers, loudspeakers and audio

machinery in general.

4. Learn how to design boards on the PC and make them with a milling machine.

5. Be able to explain the functioning our project and answer any questions the

teachers may have.

7

3. Requirements

Table 1 – Requirements of the project

RMS 40 W – 4 Ω (1 kHz)

Heat

dissipation It is for inside use, so would not need an extra dissipation

Dimensions A small compact amplifier to fit in any place.

The amplifier plate must be smaller than 130x90 mm or 120x100 mm

Quality High fidelity. Best sound quality as possible. High S/N relation. Low

distortion.

Input The line level obligatory, mic level optional.

Output Mono audio signal.

Low cost The price must be low to be very affordable.

Transformer

Toroidal

230 V / 2x24 V 3,3 A – 160 VA

⍉ 115 mm - high 66 mm

2.30 kg

8

4. Specifications

Size of the full project: 229x166x12 mm

4.1. Amplifier

Table 2 - Characteristics of the amplifier

Size 95x122 mm

Supplying Symmetrical (positive and negative) DC supply. ±33 V

Class AB

Amplification 34.15 dB

Distortion 2.041 %

Dissipation 130ºC

RMS 40 W – 4 Ω (1 kHz)

*The corresponding planes of the circuits are added in the annexes.

Image 1 - Blocks of the main circuit

9

Image 2 - ARES of the main circuit

4.2. Constant current source

This configuration provides a constant intensity to a load despite the changes in

the voltage, working as an active load. Both transistors adjust the polarization of each

other, providing that they are on the working point. When a transistor is on the working

point the change of the intensity is near 0.

Image 3 - Block of the constant current source

4.3. Differential amplifier

The differential amplifier is a part composed by two identical transistors and a

constant current source system. Its function is to compare the input signal with the output

signal (attenuated by a resistor to make similar to the input’s amplitude) and correct

possible distortions produced in the circuit, as well as amplifying the voltage of the signal.

But even if both signals are equal there is going to be a little distortion, but if we have a

good constant current source we will have a better, lower, common mode rejection ratio

which means less distortion.

10

Image 4 - Block of the differential amplifier

4.4. Driver

Is a stage which increases notoriously the voltage for the output (or power) stage.

It also controls the polarization voltage of the output stage and the crossover distortion

with it, transistors with the potentiometer.

Image 5 - Block of the driver

11

4.5. Output stage

This is the stage where the intensity is raised to amplify the power to move the

loudspeaker. The two transistors are configured in push-pull position. To avoid the

crossover distortion, it uses a resistance of the driver stage. It has a resistor and a

capacitor connected in serial to protect the circuit if the output load is not connected.

Image 6 - Block of the output stage

4.6. Safety system *Not implemented in the physical circuit

It is a system to protect the output stage MOSFET transistors from an

overcurrent, polarizing the BJT transistor when the intensity increases to the double of

the nominal value. When this transistor is polarized in the working point it will reduce the

current flow in the gates.

12

Image 7 - Sevety system improvement

4.7. Power supply

Table 3 - Characteristics of the power supply

Size 68x52 mm

In ±230 V AC

Out ±33 V DC

Transformer

Toroidal

230 V / 2x24 V 3,3 A – 160 VA

⍉ 115 mm - high 66 mm

2.30 kg

The amplifier requires a DC voltage supply with positive and negative symmetric

supply, so as a battery or the electric wall socket did not give that required power we

need a power supply.

This power supply is formed by three main blocks. The transformer, is a toroidal

double secondary winding which turns the 250 V from the socket to 2x24 V. The rectifier

consists in a diode bridge, which rectifies the full wave into the same polarity. The filter

is going to act as a filter and regulator leaving a very little ripple factor and then making

it nearly nule with the second capacitor, this is known as passive filter.

13

Image 8 - Circuit of the power supply

Image 9 - ARES of the power supply

4.8. Case

The case is going to be built in aluminium to be light and resistant without

increasing the costs notoriously. It is going to have a rectangular form base of 229x166

mm with holes to hold the elements. Also, two sides will have a side cover of 10 mm high

which will have holes for the sockets, control potentiometer and the heat sink.

As it t is designed for an inner use we don’t take care of closing all the case.

14

Image 11 - Mounting of the case of the power supply

Image 10 - Power supply

15

4.9. Input

This amplifier uses an external audio player (such as a cassette player, CD

reproduce, MP3 reproductor…) to receive line level audio signal. If we input a mic level

signal the output would be too small.

4.10. Output

The output connected must be a 4 Ω impedance and at least 40 W loudspeaker.

In the testing case, it was an electrodynamic 40 W loudspeaker reflex box with a woofer,

a squeaker and a tweeter.

This is the type of output we recommend for this type amplifier.

4.11. Budget

After looking to the components on internet in some dealers pages we made an

estimation of the budget, 122.74 € would be our price approximation.

https://docs.google.com/spreadsheets/d/1lZn_zb9HMelXKD1UqpabzJAQPSY9X8k9Kv

VErDFJsJw/edit?usp=sharing

16

5. Alternatives

First of the alternatives was a 100 W subwoofer made with BJT and MOSFET

transistors. In this case we see that the differential amplifier is in a Darlington

configuration. The second pair of transistors, also, are part of the driver, amplifying more

the voltage.

This was discarded due to its excessive power (for our requirements), the driver

part seems quite messy and the constant current source could be improved.

Image 12 - First circuit alternative

The next alternative was a subwoofer made entirely with BJT transistors. The

main characteristic of this circuit is that in the output stage are used BJT transistors

(complementary) as in a Darlington configuration, forming a Sziklai pair or

complementary-feedback pair. As a single BJT is not powerful enough for this stage we

have to attach another one; the main difference with the normal Darlington configuration

is that the dropout voltage or the turn on voltage is smaller. While 1.4 V is the dropout of

the diodes in the Darlington, in the complementary-feedback that dropout is of 0.7 V.

This helps reducing the possible crossover distortion.

This was not a bad choice of implementation. The main downside was that the

constant current source is not very efficient to soften the common mode rejection ratio.

17

Image 13 - Second circuit alternative

The last discarded option was a 50 W circuit based on MOSFET transistors, in

fact is the most similar alternative to the definitive design, with the difference that in the

output we have a coil (like the resistor in our design) linked to the loudspeaker to filter

the range of frequencies in the output.

That frequency filter with the coil in the output and the fact of having a quite basic

constant current source were the definitive reasons to discard this option and choose our

design.

Image 14 - Third circuit alternative

18

6. Implementations

6.1. Mounting procedure

As we had the scheme on ISIS, we had to transfer it to the ARES program to

design the printable PBC. Some of the encapsulations had to be changed to make

connections easier (decomposing, moving, making a new package and substituting the

old package). Some of the tracks were connected manually and mitre them all

individually, though we tried to make as similar as possible as de schematic. Some of

the pads also have to be widened to make soldering easier.

After finishing all the design we had to generate as output .GBR (Gerber) files,

which are files of each layer of our PBC design. The layers which are most important are

top copper, bottom copper, top paste, edge, mech1 and drill.

Image 15 - Selection of the CircuitCAM

Those .GBR files will be used in the CircuitCAM program, which is the program

to make a printable format for the LPKF, exporting file by file, layer by layer to create

this. In this process need to use only these buttons:

Image 16 - Different mounting steps

19

With the first one is to import and design .GBR files from ARES to the program

and create the main parts of the plate.

Image 17 - First step of the CircuitCAM

The second button is to contour the edge of the board with little gaps to keep

attached our design to the plate.

Image 18 - Contour edge

20

The third button is inactive and the fourth one is one that we don’t need it for our

task. With the fifth button we are going to contour the routes isolating the cooper from

the tracks and the ground.

Image 19 - Contour the routes

The last selector is going to export all the design transferred and adapted to .LMD

and .cam files. That first extension file is going to tell the LPKF machine how to work by

using the Master Board program.

In the Master Board program (the software which enables the communication

between the PC and the LPKF machine) the first thing to do is to open the milling

machine and open the .LMD file. We feel the tip of the machine and see if there are any

tools in use. In case it is not we press OK; in affirmative case, we introduce the free

position of the toolbar (counted from right to left).

BUTTONS

(Pause) It stops the machine

(House) x=0, y=0 coordinates

Moves the head wherever we want

Moves to the point we want

Turns the head

21

Lowers the drill bit

Moves the plate of place

Selects all

(Toolbox) When the tool is selected it goes straight

for it. If we want another one, we choose it, the machine leaves the old one and goes for

the new one. The tool is left in place with the right button on the frame.

(Machining operations box) Writing, drilling, serigraphy, milling,

cutting....

Step 1

- Make sure that the plate is not concave; in affirmative case bend it by hand.

- Remove the pistons of the driller (the rounded part is always placed upwards)

- Make the reference holes to hold the plate with the 3 mm drill bit. (x=15 and

x=280).

Step 2

Open the file:

Files

Import

.LMD (choose the file from the PC or flash drive)

Step 3

Open the operations box and see if the ordered tools and the ones placed in the

driller are the same; if not, change them manually. Is very important to take into account

that we have heads of different metric and type. There are heads for drilling holes (only

vertically - the green ones) and a sort of heads for milling (contour router, universal cutter

and end mill).

Process:

Drilling plated (holes)

All+

START

22

Milling bottom (furrows) *x2

All+

START

Milling top (silkscreen printing) *turn over the plate

All+

START

Cutting outside

All+

START

When finally the plate was printed we had to check that all the tracks were

completely isolated measuring it with the multimeter in ohms. The result between the

ground of the plate and the track must be bigger than 20 MΩ.

Once we are sure that the plate is perfectly made we can solder the components

in the plate taking into account the polarity of the capacitors and the configuration of the

transistors helped by the ISIS scheme and the ARES plan. As we want to be sure that

we didn’t make or produce any error while soldering we are going to review the isolation

of the tracks with the multimeter in ohms, ensuring that they still have a resistance bigger

than 20 MΩ.

23

7. Checking

Before starting connecting elements to the amplifier circuit we are going to ensure

that all the components are in the correct place and polarization, that all the pads are

correctly soldered, that the dissipating elements are correctly installed and that there is

no shortcuts or derivations. Is also a good idea to test the connectivity between the

components that should be linked.

Once we have everything in order, we are going to start making the main

connections before turning on. The output passive loads, two resistors of 8 Ω each,

connected in parallel (instead of the loudspeaker), two connections (in this case the

polarization is not relevant) and the symmetric DC power supplies three connections

from a laboratory power supply, +33 V, -33 V and GND. In the Laboratory power supply,

we have to make a bridge between the positive socket of one source and the negative

socket of the other source, as well as connecting this bridge as the ground of the circuit.

24

8. Start up and fixing

As everything is connected and checked we are going to open a minimum

intensity and rise the voltage till ±10 V in both laboratory sources and check that the

intensity is not bigger than 500 mA. If this happens we are going to reduce it turning the

timer and revise the polarization (base-emitter voltage, 0.6 V) of the transistors to identify

where is the problem.

If everything stays properly, we will open the current completely and rising the

tension up to ±33 V checking again that the intensity is not bigger than 500 mA.

Turning the timer, we are going to set the difference between the gates of the MOSFETs

in 7 V (3.5 volts per MOSFET).

Next, we are going to connect the sine wave creator in the input in a frequency

of 1000 Hz and 10 mV amplitude, the signal analyser in the 0.22 Ω resistor, the

temperature probe on the drain feet of the MOSFET and the voltmeter in the middle (one

in the positive and the other in the negative) of the two 8 Ω resistors in parallel and

increase the amplitude of the input wave till 12.65 V which is the tension that must have

the output of the circuit at full capacity.

Specifically in our case, in the beginning, after connecting the coming from the

output correctly, with a very little current (limited) and 10 V the output part gets

overheated and a bit of smoke comes out from a resistor connected to the output stage,

R15. So, looking for the reason for that failure, the first thing we check was the position

of that transistors, which were in the wrong place, so we had to put it in the correct place.

Starting up again after that disparage, the wrong values were not so big, but still have to

be modified.

As the smoke came out from a resistor a possible reason for that over current

could be that the resistor broke. To check that we used the ohmmeter and measure the

component. Definitely, its resistance was null and it must be replaced.

When we switch on the supply again in the same level again the same resistor

get burnt due to a high intensity again in the output stage after few seconds in a good

level, so still with a limited current we look to the BJT transistors polarization. Q2, Q5

and Q7 transistors polarization was too low. Following the scheme, the problem could

be in the feedback. To find the problem we looked to the copper circuit to find any

derivation. Using the dremel we isolate the tracks from the ground of the plate. We had

to replace again the resistor.

Restarting again we could reach a higher voltage (20 V) and a non limited current

flow, however after 22 V the intensity increases suddenly. As it looks like the same failure

that we had previously, because the symptoms were so similar, we looked if any metal

25

grain was in other track. Surprisingly we found that as consequence of standing on the

table and making pressure to make measurements a couple feets of a component get

together, touching and causing a shortcut. All feets (long and shorts) were cut again to

the minimum level and we tested the isolation again just in case.

Continuing with the start-up we could reach the acceptable values (31.4 V and

0.11 A) in DC so we could start introducing the sine wave signal to analyze its behaviour.

Image 20 - First checking of the plate

Connecting the sine wave creator to the input pins and the analyzer machine to

the R16 (0.22 Ω) and the output pin which is connected (this is because as the resistor

is on the copper side there was shortcut danger). We started with a 10 mV sine wave

and the output wave correct.

When we start increasing the input signal amplitude to reach the maximum power

40 W. Applying the ohm and power law, V=√(P*R )→ V = √(40 W*4 Ω) → V=12.6 V at

maximum power in the output load at full performance. At that output voltage level the

input was of 140 mV but we saw that the distortion was quite big (looking the THD+N

and the SCOPE in the minilyzer machine).

To solve that excessive distortion, we decided to change the MOSFET

transistors, as in the start-up phase may get damaged by that over current, heating and

touches.

After changing the output stage, when we test again the sine input, we saw that

the distortion was not so big, but still haves a distortion, but we consider that it’s still in

the parameters of a Hi-Fi amplifier.

In the second plate, after applying some voltage, the current on the positive part

increases very little, as it should, but in the negative one the currents raises more than

expected. As we increase a bit more the voltage, the 10 Ω resistor thatis conected to 33

26

V burns so we can deduct that most of the current is going through this resistor and it is

not dividing as it should. We changed the resistor and see if there are any derivations

down the plate. They are, so with the dremel we start separating the ground with the

tracks in order to eliminate all derivations. Now the current of the positive is raising

correctly so we can increase the voltage to 33 V; we have now the small current we

need.

It is time to measure if the transistors are well polarized. We take the polimeter

and measure the voltage on the base and emitter. Both the BJTs of the left (the 3 of

them) are not well polarized or simply not polarized, so we can deduct that the failure

must be in the constant current generator of the differential amplifier. We look more

carefully and we see that the left transistor of the constant current generator is wrong

placed, with the emitter in the collectors place and vice versa. The transistor is changed

and the voltage differential starts to give 0.6 V more or less, the amount of voltage that

we were looking for.

At this point we introduce the altern sign and we measure the distortion; even

though it is more than expected we take it as a good result.

Image 21 - Input of altern signal

In the power supply to check the functioning, we have to connect the

transformer's secondary wires to the circuit. We have to connect and check the yellow

and the blue wires together to set as ground, the red wire to the positive AC pole of the

plate and the grey to the negative AC pole of the board input. Then, carefully, we are

going to connect the two black wires from the primary winding to the 230 V socket.

Finally, using the polymeter we checked the signal at the outputs obtaining +33.4 V and

-34.2 V, few decimals more than we wanted but still an acceptable value.

27

Image 22 - Final amplificator

28

9. Problems and breakdowns

When we started soldering we realize that the R16 was going to be a problem

because during the design we didn’t realize that in that part on the top of the plate we

had to place the aluminium piece, so the solution was to solder that resistor in the copper

side.

The first problem we've had in the start-up was that the MOSFET transistors were

exchanged with each other, so the amplifier doesn’t amplify correctly. The intensity was

very high, theoretically the intensity must be 500 mA or less when we amplify the voltage

to 10 V. We've solved the problem by putting the transistors back in place.

As in the previous step we had a too big intensity and the R15 resistance gets

overheated and burnt, as a consequence the circuit was cut so we had to replace this.

After rising the voltage we realise that the current increases a lot suddenly. We looked

to the connections and we found that there were little derivations in a couple of tracks

and a shortcut due to the long feets of the components. To solve that we cut all the long

feets of the components and go over the tracks with the dremel.

In the second plate, the negative one the currents raises more than expected and

the 10 Ω burns, so we change the resistor and see if there are any derivations down the

plate. As they are, we separate the part with derivations

We take the polimeter and measure the voltage on the base and emitter. Both

the BJTs of the left (the 3 of them) are not well polarized or simply not polarized, so we

we look more carefully and we see that the left transistor of the constant current

generator is wrong placed, with the emitter in the collectors place and vice versa. The

transistor is changed.

29

10. Improvements

The improvement we made to the original circuit was to add a safety system

connected to the MOSFET transistors. The collector of a BJT is connected to the gate of

the MOSFET, the emmiter is connected to the speaker load and the base is connected

to the drain and a 0.11 Ω* (is calculated to have a 0.7 V drop if the current exceeds 6.3

A) resistor which is connected to the speaker load. With this, we protect the MOSFETs

from the excessive current.

As we did not have time to implement in the real circuit we put it in the schematic.

Image 23 - Main circuit + improvement

*The value of the 0.11 Ω resistor is calculated to have a 0.7 V tension drop with a peak

bigger than the double of the nominal intensity, 2*3.16 A = 6.32 A (the nominal intensity

is calculated using the power and the resistor of the load and applying the power law,

I=√(P/R) → I=√(40 W/4 Ω) → I=3.162 A). Using the ohm’s law (R=V/I) we got the value

that we need to implement that protection system, R = 0.7 V/6.32 A → R=0.110 Ω.

30

11. Conclusions

After collecting information and building our first amplifier we realise of some

important technical and procedural aspects:

- It’s important to save space, but it is more important to have enough place to

mount the components and measure. So we have to optimize the space by

making a good disposition of the components and tracks.

- Is better to design the plate with big pads to make easier to solder and reducing

possible errors caused by derivations.

- It helps to solder if the holes of the pads are of a fair size, in order to maintain the

component hold while soldering upside down.

- To get as better sound as possible we have to put the best alternatives as we

could, that’s why that putting a resistor as a constant current source is not enough

efficient.

- The exceeding feets of the components have to be removed as much as possible

to avoid shortcuts caused by the deformation of those feets when that feets are

the support.

- Using MOSFETs in the output stage it is a better idea if we want to achieve a Hi-

Fi response because it’s behaviour is more linear and as a consequence we get

a clearer sound.

- Even the circuit should work perfectly, as a precaution adding a safety system in

the output should help avoiding some breakdowns and save money and time with

repairs.

- Would be recommendable to know if would be of the interest to the customer to

have a microphone entry.

31

12. Works for the future

This amplifier only works for CD players or some similar whose input is a line

level signal. Which means that if we want to amplify a signal coming from a microphone

(mic level) we need a pre-amplifying stage. So, that would be the work we should do in

the future, as an improvement of our amplifier. Depending on for what is going to use the

amplifier, there are different types of microphones. The best microphone price for value

is the dynamic one, it captures the voice very well and it work between 50 Hz and 18

kHz. Then if you are looking for is a really good quality of the audio is better to use a

capacitor microphone, but it is more fragile and more expensive. The bigger microphone

sensitive level the better definition we will have.

Revising the circuit to reduce the distortion at a full performance output sine signal

would be also an important aspect to work on in the future.

32

13. References

- Alternative nº1: A scheme of a 100 W subwoofer amplifier.

http://www.amplifiercircuits.com/2014/04/100-watt-subwoofer-for-home-circuit.html

- Alternative nº2: A university engineering project of a Hi-Fi audio amplifier.

https://www.ee.iitb.ac.in/uma/~wel/wel45/public_html/edl10a/Audio%20amplifier.pdf

-Alternative nº3: A little guide to make a 50 W power amplifier.

http://www.circuitsgallery.com/2012/10/50watt-MOSFET-amplifier.html

-Teachers notes: It is a PowerPoint where all the theory is written.

https://docs.google.com/presentation/d/10MyROykIdINbEwerhqrc5HsY-

wjM9squOAqYZJAdWRE/edit#slide=id.g134b479467_3_803

-University notes: Some theory about electroacoustics.

http://aholab.ehu.es/users/imanol/akustika/IkasleLanak/Amplificadores%20de%20audi

o.pdf

-Blocks of an audio amplifier: Parts of an audio amplifier are explained.

http://www.circuitstoday.com/practical-power-amplifier-stages-and-block-diagram

-Blocks of an audio amplifier: Functions of stages are explained.

http://www.ecircuitcenter.com/Circuits_Audio_Amp/Basic_Amplifier/Basic_Audio_Ampli

fier.htm

-Constant current source: Brief and simple explication about the CCS.

http://www.learningaboutelectronics.com/Articles/What-is-a-constant-current-

source.php

-Constant current source: A more detailed information about what a CCS is and how

does it work.

http://www.radio-electronics.com/info/circuits/transistor/active-constant-current-

source.php

-Constant current source: Types of CCS.

https://sites.google.com/site/roelarits/home/current-sources-1

33

-Differential amplifier: General information about the differential amplifier.

https://en.wikipedia.org/wiki/Differential_amplifier

-Differential amplifier: Brief information about differential amplifier focused on audio.

http://unicrom.com/amplificador-diferencial/

-Differential amplifier: More general information about differential amplifiers.

https://www.ecured.cu/Amplificador_diferencial

-Differential amplifier: Extensive explanation about the operation of the differential

amplifiers.

http://mrelbernitutoriales.com/amplificador-diferencial/

-MOSFET transistor: Summary of what the characteristics of this transistors are.

https://es.slideshare.net/JCCG_1/transistores-mosfet-configuracion-y-polarizacion

-MOSFETs: Wide information about the operation of the MOSFET transistors.

http://hispavila.com/total/3ds/atmega/mosfets.html

-BJT transistor: Main idea and function of this type transistors.

http://www.electronics-tutorials.ws/transistor/tran_1.html

-Crossover distortion: What is the distortion which appears in B class amplifiers.

http://www.aikenamps.com/index.php/what-is-crossover-distortion

-Complementary feedback pair: Main characteristics of this type of Darlington.

https://en.wikipedia.org/wiki/Sziklai_pair

-Power supply: Extensive information about AC/DC power supplies, how it works and its

blocks.

https://www.electronicafacil.net/tutoriales/Fuentes-alimentacion.php

34

14. Annexes

Concept File

Budget https://drive.google.com/file/d/0B9bklUUZrvI2RlJrUjhKZF

ExWFU/view?usp=sharing

Datasheets https://drive.google.com/file/d/0B9bklUUZrvI2bVloVHJjN

1c4b2s/view?usp=sharing

Power

Supply

ISIS https://drive.google.com/file/d/0B43A93LH_Rd6UDhnLWt

Qc2VwdHc/view?usp=sharing

ARES https://drive.google.com/file/d/0B9bklUUZrvI2U2VISDNx

d1dzRkE/view?usp=sharing

CircuitCAM https://drive.google.com/file/d/0B9bklUUZrvI2bzBYQWVZ

cFQwM3c/view?usp=sharing

Main

circuit

ISIS https://drive.google.com/file/d/0B9bklUUZrvI2V0NwSEJS

UEdTNUU/view?usp=sharing

ARES1 https://drive.google.com/file/d/0B9bklUUZrvI2a0ZaRkxR

Y0pFVXM/view?usp=sharing

CircuitCAM1 https://drive.google.com/file/d/0B9bklUUZrvI2cUJaZVVJ

QUY1Rlk/view?usp=sharing

ARES2 https://drive.google.com/file/d/0Bx8ldQ_MS-

0zREFWUDJTOEpzLU0/view?usp=sharing

CircuitCam2 https://drive.google.com/file/d/0Bx8ldQ_MS-

0zdk1GczhKdllsWjQ/view?usp=sharing

ARES3 https://drive.google.com/file/d/0B9bklUUZrvI2bUlndm9N

VHNVSDA/view?usp=sharing

CircuitCam3 https://drive.google.com/file/d/0B9bklUUZrvI2M0ctMWZM

alZQVm8/view?usp=sharing

35

ISIS

improvements

https://drive.google.com/file/d/0B9bklUUZrvI2cFdUc1ZE

U0RHbVk/view?usp=sharing

Alternati

ves

Alternative1

ISIS

https://drive.google.com/file/d/0B9bklUUZrvI2Rl9UODZx

MGt4UG8/view?usp=sharing

Alternative2

ISIS

https://drive.google.com/file/d/0Bx8ldQ_MS-

0zSnFBTk1saVJ5Nms/view?usp=sharing

Alternative3

ISIS

https://drive.google.com/file/d/0B43A93LH_Rd6S1lvdFdE

c2gxblk/view?usp=sharing