OTL

PROJECT NAME: OTL Sound Amplifier

Members: 1. Nguyen Duc Minh<20081736>< Leader> 2. Nguyen Duc Minh<20081737> 3. Tran Minh Quan 4. Le Hong Nam 5. Dam Tien Long

18/11/2011

Project Name: Sound Amplifier

Electrical Engineering – Advanced Program

Report 1

OTL sound amplifier Contents OBJECTIVE ......................................................................................................................................... 3 ACKNOWLEDGEMENTS ................................................................................................................. 3 ABSTRACT ........................................................................................................................................... 4 Project requirements and parameters: ....................................................................................... 4

I.

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

II.

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

1. a.

Functional............................................................................................................................... 5

b.

Requirement ............................................................................................................................ 5

c.

Parameter ............................................................................................................................... 6

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

2. a.

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

3. a.

Functional............................................................................................................................... 6

b.

Parameter ............................................................................................................................... 6

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

4. a.

Microphone............................................................................................................................. 6

b.

Speaker .................................................................................................................................... 6

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

5.

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

III.

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

1.

2. IV. V. VI.

Functional............................................................................................................................... 6

a.

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

b.

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

c.

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

d.

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

Calculation ................................................................................................................................. 9 List of device .............................................................................................................................. 9 PCB layout ................................................................................................................................... 11 Real circuit ............................................................................................................................... 11 Hanoi University of Science and Technology, 2012

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VII.

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

a.

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

b.

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

OBJECTIVE Design 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. Hanoi University of Science and Technology, 2012

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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.

ABSTRACT OTL 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 tubespeaker.

I.

Project requirements and parameters: 

Requirement : Hanoi University of Science and Technology, 2012

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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 2

2

- Size: 0.4dm to 0.5dm - 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 Hanoi University of Science and Technology, 2012

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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 Hanoi University of Science and Technology, 2012

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ii. Resistance : 8 Ω iii. Power 1.5W 5. Block diagram

Microphone

PreAmplifier

Push-Pull

Power Amplifier

Speaker

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 Hanoi University of Science and Technology, 2012

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iii. AC-analysis - The gain is 37 b. Push-pull i. 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 amplifier i. Schematic

Hanoi University of Science and Technology, 2012

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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. ii. DC-analysis iii. AC-analysis d. The circuit i. Schematic ii. DC-analysis iii. AC-analysis - The gain is 27.5 2. Calculation

IV. List of device Components

Description

Quantity

Price

Total Price 30.950VND

Resistor Hanoi University of Science and Technology, 2012

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9C04021A1502FLHF3 (15k Ohm) 9C04021A4702FLHF3 (47k Ohm) ERA-3YEB152V (1.5k Ohm) ERA-3YEB472V (4.7k Ohm) ERA-3YEB102V (1k Ohm) 9C04021A3300FLHF3 (330 Ohm) 9C04021A1600FLHF3 (160 Ohm) 9C04021A1200FLHF3 (120 Ohm) ERJ-1WRQJ1R0U (1 Ohm) 325W-1-503LF (50k Ohm) Capacitor HITEMP2200U25V (2200uF) ZL220U25V (220uF) T510E107M025A E050 (100uF) B45197A5476K409 (47uF) 06032F104Z8B20D (10uF) PHYC0805X7R100N2 5 (0.1uF) C0402C101J3GACTU (100pF)

RES 15K OHM 1/16W 1% 0402 (1105 METRIC) SMD RES 47K OHM 1/16W 5% 0402 (1005 METRIC) SMD RES 1.5K OHM 1/16W .1% 0603 SMD RES 4.7K OHM 1/10W .1% 0603 SMD RES 1.0K OHM 1/10W .1% 0603 SMD RES 330 OHM 1/16W 1% 0402 SMD RES 160 OHM 1/16W 1% 0402 SMD RES 120 OHM 1/16W 1% 0402 SMD RES 1.0 OHM 1W5 5% 2512 (6432 METRIC) SMD POT 50K OHM 1/2 INCH SQ CERM SL MT 2200u 25V HIGH TEMP RADIAL CAPACITOR 220u 25V RADIAL ELECTROLUTIC CAPACITOR CAP TANT 100uF 25V 20% SMD CAP TANT 47uF 25V 10% LOESR SMD CAP 10uF 25V CERAMIC Y5V 0603 100pF 25V NICKEL BARIER SMT CERAMIC CAPACITOR CAP CERMIC 100pF 25V NP0 042

2

50VND/Unit

100VND

2

50VND/Unit

100VND

1

50VND/Unit

50VND

2

50VND/Unit

100VND

1

50VND/Unit

50VND

2

50VND/Unit

100VND

1

50VND/Unit

50VND

1

50VND/Unit

50VND

1

50VND/Unit

50VND

1

5000VND/Unit

5000VND

1

2500VND/Un it

2500VND

1

500VND/Unit

500VND

1

50VND/Unit

500VND

1

50VND/Unit

500VND

1

30VND/Unit

100VND

1

30VND/Unit

100VND

1

30VND/Unit

100VND

Transistor

Q2SC1815

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

TIP41C

SILICON NPN POWER O TRANSISTOR 65W 150 C

Q2SA1015

2 2 2

3000VND/Un it 3000VND/Un it 3000VND/Un it

6000VND 6000VND 6000VND


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Diode 1N4148WS-7

DIODE SWITCH 75V 200MW SOD-323

4

500VND/Unit

2000VND

3.50mm (0.141", 1/8") -25°C ~ 85°C 1A

2

500VND/Unit

1000VND

In/Output Jack Audio 3.5mm

V. PCB layout VI. Real circuit VII. Test case a. Frequency range of input signal Purpose Requirement

Expected result Test conditions

Implementation steps

Test the circuit’s working under the varying frequency -Board circuit -Software PIANO SINGER -The circuit works stably -The sound quality is good in the frequency range of 30Hz-15kHz -Room temperature(25 Celsius degree) -Vin = 0.15V AC -Source: 24V -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 Tester Note

The frequency range varies from 30Hz to 12kHz Lê H ồng Nam Tr ần Minh Quân Đàm Tiế n Long -The parameter “frequency” doesn’t match the specification (expected 15kHz)

b. Voltage range of input signal


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Purpose Requirement

Expected result Test conditions

Implementation steps

Test the circuit’s working under the varying input AC voltage -Board circuit -Software Pspice -The circuit works stably -The sound quality is good in the voltage range of 0.05V to 0.2V -Room temperature(25 Celsius degree) -Frequency : 1kHz -Source: 24V -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

The voltage range is 0.01V to 0.19V

Result Tester Note

Nguyễn Đức Minh (1736) Nguyễn Đức Minh (1737) -The parameter “input AC- voltage” matches the specification (expected 0.01V to 0.19V) -The gain is 37 (expected 40)


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OTL

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