OTL

PROJECT NAME: OTL Sound Amplifier

Members: 1. Nguyen Duc Minh<20081736>< Leader>2. Nguyen Duc Minh<20081737>3. Tran Minh Quan4. Le Hong Nam5. Dam Tien Long

18/11/2011

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Project Name: Sound Amplifier Electrical Engineering – Advanced ProgramReport 1

OTL sound amplifier

ContentsOBJECTIVE........................................................................................................................................3

ACKNOWLEDGEMENTS................................................................................................................3

ABSTRACT.........................................................................................................................................4

I. Project requirements and parameters:......................................................................................4

II. Block Design.............................................................................................................................5

1. Pre-amplifier............................................................................................................................5

a. Functional..............................................................................................................................5

b. Requirement...........................................................................................................................5

c. Parameter..............................................................................................................................6

2. Push-pull...................................................................................................................................6

a. Functional..............................................................................................................................6

3. Power amplifier........................................................................................................................6

a. Functional..............................................................................................................................6

b. Parameter..............................................................................................................................6

4. Other blocks.............................................................................................................................6

a. Microphone............................................................................................................................6

b. Speaker..................................................................................................................................6

5. Block diagram..........................................................................................................................7

III. Detail Design............................................................................................................................7

1. Analysis the circuit :................................................................................................................7

a. Pre-amplifier.........................................................................................................................7

b. Push-pull................................................................................................................................8

c. Power amplifier.....................................................................................................................8

d. The circuit..............................................................................................................................9

2. Calculation...............................................................................................................................9

IV. List of device............................................................................................................................9

V. PCB layout.................................................................................................................................11

VI. Real circuit.............................................................................................................................11

Hanoi University of Science and Technology, 2023

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VII. Test case..................................................................................................................................11

a. Frequency range of input signal.............................................................................................11

b. Voltage range of input signal..................................................................................................11

OBJECTIVEDesign and make a sound amplifier circuit that use for amplify the sound from the electrets microphone or from the jack 3.5mm of laptop or mobile phone. The output of circuit will be a speaker to release the sound.

ACKNOWLEDGEMENTS Using the properties of the BJT transistor to amplify the signal.


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Design the circuit base on the block diagram.

Using Orcad capture software to draw the circuit and simulate the circuit.

Using the Orcad layout software to make the PCB.

ABSTRACTOTL stands for Output Transformer-Less. It is a term used to describe amplifiers, particularly tube amplifiers that do not have an output transformer. Such amplifiers are commonly called OTL tube amplifiers. The advantages of OTL are reducing the noise and the output resistor in order to match with the speakers, which commonly have the resistance, are about 8 ohms. However, the sound which is created by OTL circuit is quite good, and the very good OTL circuit is very expensive, and particularly integrated in high quality tube-speaker.

I. Project requirements and parameters:

Requirement :


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- Voltage input is low sin AC voltage and it comes from the electrets microphone or 3.5mm jack from mobile phone or computer.- The source can take from the battery or accumulator- The speaker has the resistor R = 8 ohm and have the small power.- The sound is average quality, with low noise, and high volume.- Small size and light.

b. Parameter:

- Voltage input: 150mV-AC

- Microphone connection: 3.5mm jack

- Source: 24V

- Speaker resistance: 8 Ω

-Speaker power range: 0.8W to 3W

- Frequency response range: 30Hz to 15 kHz

- Size: 0.4dm2 to 0.5dm2

- Weight: 50g.

II. Block Design

1. Pre-amplifier

a. Functional

Amplify the small audio signal (voltage) from the microphone

b. Requirement

i. The voltage gain is high enough to hear the sound without too many noises

ii. The input is the audio signal from laptop

iii. The output go to the “Push - pull” block


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c. Parameter

i. Input voltage :from 0.01V to 0.19V

ii. Input frequency : vary from 30Hz to 15kHz

iii. The gain is 40

2. Push-pull

a. Functional

i. Class A amplifier

ii. Correct the error generated from distortion

iii. Balances amplitude of output

iv. Preventing the circuit from unexpected oscillation.

3. Power amplifier

a. Functional

i. Amplify power of the circuit to match with speakers

ii. Create the output resistance to match with speaker

b. Parameter

i. Speaker power : 0.8 to 3W

ii. Speaker resistance : 8 Ω

4. Other blocks

a. Microphone

i. A transducer which convert sound to voltage

ii. Connection : 3.5mm jack

iii. Source : Human voice or laptop

b. Speaker

i. A transducer which converts the audio signal to sound


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ii. Resistance : 8 Ω

iii. Power 1.5W

5. Block diagram

Figure 1: Block Diagram

III. Detail Design

1. Analysis the circuit :a. Pre-amplifier

i. Schematic - Q1 is amplifying stage, using pnp transistor. R1 and

R2 are used to polarizing Q1's Base. R3 and capacitor C2 supply voltage for this stage. With this kind of filter, the Boating effect is neglected. C1is coupling capacitor and RV1 is for adjusting the volume. The negative feedback is formed by R, R11 and C4

- Current through R2 is the most important current. Without this current, other polarizing currents will disappear.

- Increasing R8 enhances the effect of negative feedback and decrease gain. However, sound quality will be improved. In contrast, decreasing RF decline the quality.

ii. DC-analysis


Push-Pull PowerAmplifier

SpeakerPre-Amplifier

Microphone

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iii. AC-analysis - The gain is 37

b. Push-pulli. Schematic

- Q2 is push-pull stage. Output signal from Q1's collector is directed to Q2's base. Diodes D1, D2, D3 are used to polarize this stage and immense signal distortion Output signal is taken with resistor R7. Feedback network with C3, R6 balances amplitude of output signal. C5 acts as feedback, preventing the circuit from unexpected oscillation.

ii. DC-analysis iii. AC-analysis

c. Power amplifieri. Schematic


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- Q3 and Q4 form a power push-pull stage. When output signal from Q2's C is at positive phase, Q3 on and Q4 offs, and vice-versa. These mechanisms improve productivity of the circuit to 78%. R8 and R9 compensate heat for transistors. D4 is used for impedance compensation at output channel of Q4 and Q6 at positive phase and of Q3 and Q4 at negative phase.

- Q5 and Q6 are power transistors, supplying high current for the speaker. At positive phase, while Q3 and Q5 on and Q4 and Q6 off, charging current to C6 is pushed to speaker. At negative phase, Q4 and Q6 on, Q3 and Q5 off, discharging current from C3 is pushed to speaker. Hence, signal through Q5 and Q6 vibrate the membrane of the speaker, creating sound.

- C7, R10 compensate speaker for its impedance, so that sound distortion is neglected. Impedance of the speaker is 8 ohm at low frequency region and increase when frequency becomes higher. At this time, Zobel filter keep the impedance stable, avoiding power distortion effect.


d. The circuiti. Schematic


- The gain is 27.52. Calculation

IV. List of device

ComponentsDescription

Quantity PriceTotal Price

30.950VND

Resistor


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9C04021A1502FLHF3 (15k Ohm)

RES 15K OHM 1/16W 1% 0402 (1105 METRIC) SMD 2 50VND/Unit 100VND

9C04021A4702FLHF3 (47k Ohm)

RES 47K OHM 1/16W 5% 0402 (1005 METRIC) SMD

2 50VND/Unit 100VND

ERA-3YEB152V (1.5k Ohm)

RES 1.5K OHM 1/16W .1% 0603 SMD

1 50VND/Unit 50VND

ERA-3YEB472V (4.7k Ohm)

RES 4.7K OHM 1/10W .1% 0603 SMD

2 50VND/Unit 100VND

ERA-3YEB102V (1k Ohm)

RES 1.0K OHM 1/10W .1% 0603 SMD

1 50VND/Unit 50VND

9C04021A3300FLHF3 (330 Ohm)

RES 330 OHM 1/16W 1% 0402 SMD

2 50VND/Unit 100VND

9C04021A1600FLHF3 (160 Ohm)

RES 160 OHM 1/16W 1% 0402 SMD

1 50VND/Unit 50VND

9C04021A1200FLHF3 (120 Ohm)

RES 120 OHM 1/16W 1% 0402 SMD

1 50VND/Unit 50VND

ERJ-1WRQJ1R0U (1 Ohm)

RES 1.0 OHM 1W5 5% 2512 (6432 METRIC) SMD

1 50VND/Unit 50VND

325W-1-503LF (50k Ohm)

POT 50K OHM 1/2 INCH SQ CERM SL MT 1 5000VND/Unit

5000VND

Capacitor HITEMP2200U25V (2200uF)

2200u 25V HIGH TEMP RADIAL CAPACITOR

1 2500VND/Unit

2500VND

ZL220U25V (220uF) 220u 25V RADIAL ELECTROLUTIC CAPACITOR

1 500VND/Unit 500VND

T510E107M025A E050 (100uF)

CAP TANT 100uF 25V 20% SMD

1 50VND/Unit 500VND

B45197A5476K409 (47uF)

CAP TANT 47uF 25V 10% LOESR SMD

1 50VND/Unit 500VND

06032F104Z8B20D (10uF)

CAP 10uF 25V CERAMIC Y5V 0603

1 30VND/Unit 100VND

PHYC0805X7R100N25 (0.1uF)

100pF 25V NICKEL BARIER SMT CERAMIC CAPACITOR

1 30VND/Unit 100VND

C0402C101J3GACTU (100pF)

CAP CERMIC 100pF 25V NP0 042

1 30VND/Unit 100VND

Transistor Q2SA1015 TRANS PNP 50V 150MA TO-92

400mW 80MHz2 3000VND/

Unit6000VND

Q2SC1815 TRANS NPN 50V 150MA TO-92 400mW 80MHz

2 3000VND/Unit

6000VND

TIP41C SILICON NPN POWER TRANSISTOR 65W 150OC

2 3000VND/Unit

6000VND


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Diode

1N4148WS-7DIODE SWITCH 75V 200MW SOD-323 4 500VND/Unit 2000VND

In/Output

Jack Audio 3.5mm3.50mm (0.141", 1/8") -25°C ~ 85°C 1A 2 500VND/Unit 1000VND

V. PCB layout VI. Real circuit VII. Test case

a. Frequency range of input signal

Purpose Test the circuit’s working under the varying frequency

Requirement-Board circuit-Software PIANO SINGER

Expected result-The circuit works stably-The sound quality is good in the frequency range of 30Hz-15kHz

Test conditions-Room temperature(25 Celsius degree)-Vin = 0.15V AC-Source: 24V

Implementation steps

-Using software PIANO SINGER on IPhone to simulate the variable frequency. Each note represents a different frequency-Check whether if the note with respective frequency creates the good sound or not

Result The frequency range varies from 30Hz to 12kHz

TesterLê Hồng NamTrần Minh QuânĐàm Tiến Long

Note -The parameter “frequency” doesn’t match the specification (expected 15kHz)

b. Voltage range of input signal


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Purpose Test the circuit’s working under the varying input AC voltage

Requirement-Board circuit-Software Pspice

Expected result-The circuit works stably-The sound quality is good in the voltage range of 0.05V to 0.2V

Test conditions-Room temperature(25 Celsius degree)-Frequency : 1kHz-Source: 24V

Implementation steps

-Using software PSpice to simulate the variable input AC voltage. -Check whether if the output wave with respective input AC-voltage has distortion or not

ResultThe voltage range is 0.01V to 0.19V

TesterNguyễn Đức Minh (1736)Nguyễn Đức Minh (1737)

Note -The parameter “input AC- voltage” matches the specification (expected 0.01V to 0.19V)-The gain is 37 (expected 40)


Date post:	17-Oct-2014
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