USB Battery Charger for Lithium Ion Battery

USB Battery Charger for Lithium Ion Battery circuit diagram

This schematic diagram is used for charging lithium ion battery. The power source is from a computer's USB port. With this circuit, you do not need to build power supply circuits for charging your battery.

A USB port is a great power source for charging a single cell li-on battery. It is capable of supplying maximum 5.25V and 500 mA. The circuit above is a USB powered single cell li-on battery charger. LM3622 is used as the controller. This special purpose IC has a precise end-of-charge control and low battery leakage current about 200nA.

Simple Battery Charger using LM350

Simple Battery Charger using LM350 circuit diagram

The schematic diagram can be used for charging the 12V lead acid batteries.

The circuit is designed as a constant voltage source with a negative temperature coefficient. The transistor Q1 (BD 140) is used as the temperature sensor. The transistor Q2 is used to prevent the battery from discharging through R1 when the mains power is not available. The circuit is designed based on the voltage regulator IC LM350. The output voltage of the charger can be adjusted between 13-15 V by varying the POT R6.

The LM350 will try to keep the voltage drop between its input pin and the output pin at a constant value of 1.25V. So there will be a constant current flow through the resistor R1. Q1 act here as a temperature sensor with the help of components R6/R3/R4 which more or less control the base current of Q1. As the emitter/base connection of transitor Q1, just like any other semiconductor, contains a temperature coefficient of -2mV/°C, the output voltage will also show a negative temperature coefficient. That one is only a factor of 4 larger, because of the variation of the emitter/basis of Q1 multiplied by the division factor of P1/R3/R4. This results in approximately -8mV/°C. The LED will glow whenever the mains power is available.

The transistor Q1 must be placed as close as possible to the battery.
Use a 20 to 30 V / 3A DC power supply for powering the circuit.
This circuit is not possible for charging GEL type batteries as it draw large amounts of current.

Here the LM350 pin layout:
 Here the LM350 pin layout

100 Watt Inverter 12V DC to 220V AC

Electronic schematic diagram for 100 Watt Inverter 12V DC to 220V AC.

100 Watt Inverter 12V DC to 220V AC circuit diagram

The IC1 Cd4047 wired as an astable multivibrator produces two 180 degree out of phase 1/50 Hz pulse trains.These pulse trains are are preamplifes by the two TIP122 transistors. The out puts of the TIP 122 transistors are amplified by four 2N 3055 transistors (two transistors for each half cycle) to drive the inverter transformer. The 220V AC will be available at the secondary of the transformer. Nothing complex just the elementary inverter principle and the circuit works great for small loads like a few bulbs or fans. If you need just a low cost inverter in the region of 100 W, then this is the best.


  • A 12 V car battery can be used as the 12V source.
  • Use the POT R1 to set the output frequency to 50Hz.
  • For the transformer get a 12-0-12 V, 10A step down transformer. But here the 12-0-12 V winding will be the primary and 220V winding will be the secondary.
  • If you could not get a 10A rated transformer , don’t worry a 5A one will be just enough. But the allowed out put power will be reduced to 60W.
  • Use a 10 A fuse in series with the battery as shown in circuit.
  • Mount the IC on a IC holder.
  • Remember, this circuit is nothing when compared to advanced PWM inverters.This is a low cost circuit meant for low scale applications.

Design Tips:

The maximum allowed output power of an inverter depends on two factors. The maximum current rating of the transformer primary and the current rating of the driving transistors.

For example ,to get a 100 Watt output using 12 V car battery the primary current will be ~8A ,(100/12) because P=VxI. So the primary of transformer must be rated above 8A.

Also here ,each final driver transistors must be rated above 4A. Here two will be conducting parallel in each half cycle, so I=8/2 = 4A .

These are only rough calculations and enough for this circuit.

Bidirectional Power Inverter

Bidirectional Power Inverter circuit diagram
Figure 1

If you want to swap charge in either direction between unevenly loaded positive and negative battery buses, you need an inverting dc transformer. One implementation is the symmetrical flyback converter shown in Figure 1. The circuit can generate a negative output from a positive supply or a positive output from a negative supply. When the circuit starts up, the substrate diode of the output FET bootstraps the output voltage to the point where synchronous switching takes over. When the gate-switching signal is symmetrical, the output voltage is approximately -95% of the input voltage, and the efficiency is greater than 80%. You can obtain voltage step-up or step-down by adjusting the switching ratio.

When I used the circuit between two 4V lead-acid batteries, a comparator adjusted the switch ratio to drive charge in the desired direction. The circuit automatically replaces charge drained from one battery to the other. In a short-battery-life application, the 2.5-mA standby current from each battery may be negligible. Using lower-gate-capacitance, FETs can reduce losses. Alternatively, you can add gates to the drive circuit to turn off both FETs whenever the battery voltages balance. The minimum input voltage is a function of the gate thresholds of the FETs. The ±9V rating of the CMOS 555 timer sets the maximum voltage. My prototype supplies approximately 100 mA.


Inverter 12 V DC to 120 V AC

Inverter 12 V DC to 120 V AC circuit diagram

This Inverter takes 12 volt d.c and steps it up to 120 volt a.c. The wattage depends on which transistors you use for Q1 and Q2, as well as the "Amp Rating" of the transformer you use for T1. This inverter can be constructed to supply anywhere from 1 to 1000 (1 KW) watts. If Q1, Q2 are 2N3055 NPN Transistors and T1 is a 15 A transformer, then the inverter will supply about 300 watts. Larger transformers and more powerful transistors can be substituted for T1, Q1 and Q2 for more power.

C1, C2 >> 68 uf, 25 V Tantalum Capacitor
R1, R2 >> 10 Ohm, 5 Watt Resistor
R3, R4 >> 180 Ohm, 1 Watt Resistor
D1, D2 >> HEP 154 Silicon Diode
Q1, Q2 >> 2N3055 NPN Transistor (see "Notes")
T1 >> 24V, Center Tapped Transformer
Wire, Case, Receptacle (for output)
Fuses, Heatsinks, etc.

Note: Don't try to run inductive loads (motors...) off this inverter.

Inverter 12V DC to 120-230V DC with IC 555

This DC-to-AC inverter schematic produces an AC output at line frequency and voltage. The 555 is configured as a low-frequency oscillator, tunable over the frequency range of 50 to 60 Hz by Frequency potentiometer R4.

Inverter 12V DC to 120-230V DC with IC 555 circuit diagram

Parts List:
R1 = 10K
R2 = 100K
R3 = 100 ohm
R4 = 50K potmeter, Linear
C1,C2 = 0.1uF
C3 = 0.01uF
C4 = 2700uF
Q1 = TIP41A, NPN, or equivalent
Q2 = TIP42A, PNP, or equivalent
L1 = 1uH
T1 = Filament transformer, your choice

The 555 feeds its output (amplified by Q1 and Q2) to the input of transformer T1, a reverse-connected filament transformer with the necessary step-up turns ratio. Capacitor C4 and coil L1 filter the input to T1, assuring that it is effectively a sine wave. Adjust the value of T1 to your voltage.

The output (in watts) is up to you by selecting different components.

Input voltage is anywhere from +5V to +15Volt DC, adjust the 2700uF cap's working voltage accordingly.

Replacement types for Q1 are: TIP41B, TIP41C, NTE196, ECG196, etc. Replacement types for Q2 are: TIP42B, TIP42C, NTE197, ECG197, etc. Don't be afraid to use another type of similar specs, it's only a transistor... ;-)

Multi tone alarm schematic diagram

electronic circuit diagram

This is a simple and easy to build multi tone alarm circuit that can be used in burglar alarms or sirens. The circuit is based on dual op-amp MC1458 and LM 380. The two op amps inside the MC 1458 are used to produce square and triangular waves.LM 380 is used to amplify the output.The first op amp IC1a is wired as an astable multi vibrator and second op amp IC1b is wired as an integrator, to make the square wave triangle.

The two output square ans sine can be selected using switch S1 to the input of IC2 which amplifies it to drive the speaker. POT R4 can be used for tone adjustment.

Notes .

0 to 3V Adjustable Output Power Supply

0 to 3V Adjustable Output  Power Supply circuit diagram

This is an LM317 based adjustable voltage regulator with a maximum output of 3V and 1.5A. The output voltage depends on the VIN, R1 and R2 values, so the circuit can be modified to use with a maximum output of greater than 3V. The maximum current output is also independent of the circuit design, it is related to the package options. In this circuit, LM317T, which is capable of transferring up to 1.5A, is used.

Since the internal reference voltage of the LM317 regulator is 1.25V, the output voltage can be also minimally 1.25V. One way to overcome this problem is using a reference voltage source built on two diodes. But this approach is mostly suitable for 1.5V to 15V regulators since the sensitivity becomes poor for the low voltage outputs less than 1.5 . On the other hand, diodes have temperature dependent forward voltages.

General Purpose Power Supply

General purpose power supply schematics:
General Purpose Power Supply circuit diagram

You can select the output voltage range by 0-30V or 0-40V of 0-60V. The component's value will be different depends the output range you choose.

Vout Iout
R4, R5 R9
0-30V 1.3A
0-40V 0.8A

Please check the output current since higher voltage output will decrease the current output.

Capacitor Explanation

A capacitor is a passive electrical component that can store energy in the electric field between a pair of conductors (called "plates"). The process of storing energy in the capacitor is known as "charging", and involves electric charges of equal magnitude, but opposite polarity, building up on each plate. A capacitor's ability to store charge is measured by its capacitance, in units of farads.

Capacitors are often used in electric and electronic circuits as energy-storage devices. They can also be used to differentiate between high-frequency and low-frequency signals. This property makes them useful in electronic filters. Practical capacitors have series resistance, internal leakage of charge, series inductance and other non-ideal properties not found in a theoretical, ideal, capacitor.

The capacitor is used in almost every electronic circuit. It is a very important component and it does many different things, depending on where it is placed.

A capacitor is basically a device that stores a charge of electricity.
It has two or more plates that are separated by air or a non conducting medium such as plastic.

A basic capacitor is shown in the diagram below with the corresponding circuit symbol.

Capacitor Explanation

Capacitors can be large or small and the size is the result of the value of the capacitor as well as the voltage it is capable of withstanding.

There is a lot to learn about capacitors and we will only be discussing the very basics.
There are many types of capacitors, here are 5 of the most common types:

AIR - such as a tuning capacitor in a radio.

GREENCAP - a polyester capacitor.

CERAMIC - a ceramic insulating material that produces a very compact

MONOBLOCK - also called monolithic - a multi-layer ceramic capacitor

ELECTROLYTIC - aluminium plates with a moist insulating medium. This type of capacitor has a very high capacitance in a small space.

The diagram below shows a single-ended electrolytic, suitable for mounting on a printed circuit board and the symbol.

electrolytic capacitor

The unit for capacitance is the FARAD. But one Farad is an enormous value and we don't use values this large in electronics. The value we use is the micro-farad. A microfarad is one-millionth of a farad.

For some circuits we need capacitors of more than 1 microfarad capacitance and for others we need less than 1 microfarad.

For a power supply we need electrolytics of 10 microfarad, 100 microfarad, 1,000 microfarad and even 10,000 microfarad. The letter to signify microfarad is "uF" or simply "u". Thus 1microfarad is 1u, 10 microfarad is 10u etc.

For audio work we need smaller values such as .1microfarad and .01 microfarad.
In electronics, we try and avoid using the decimal point as it can be rubbed off components and omitted from photocopies of circuit diagrams.

To get around this we use sub-multiples and the sub-multiple of microfarad is nanofarad.

1,000 nanofarad = 1 microfarad.
Thus .1u = 100 nanofarad.
The letter to represent nanofarad is "n".
Thus .01u = 10n

For radio frequency work, even smaller values of capacitance are needed.

The nanofarad is divided into 1,000 parts called picofarad. Thus 1,000 picofarad = 1nanofarad.

The picofarad is written pF or simply "p."
Thus 1,000p = 1n.

Some capacitors are physically very small and there is very little space to write the component value. To get around this, manufacturers have produced a numbering system using 3 digits.

It is based on picofarads. A 100 picofarad capacitor is written as 101, A 1,000 picofarad capacitor is written 102, A 10 nanofarad capacitor is written 103 and 100 nanofarads is written 104. The third digit represents the number of zero's.

For example: 1n = 1,000p = 102.
10n = 10,000 = 103
100n = 100,000 = 104

Capacitors do lots of things and it depends where they are positioned in a circuit, the value of the surrounding components and the value of the capacitor.

One of the things that makes the study of a capacitor complex is the current flowing into it starts off very high and gradually reduces as the capacitor charges.

In addition, the voltage across the capacitor does not increase evenly, it rises rapidly at first then gradually slows down. Some of these facts have already been covered and at this stage it only important to know that the charging is not linear.

The capacitor can also be used as a timing component. This has been covered in the oscillator circuits where the value of the capacitor determines the frequency of the oscillator.

The capacitor is basically a device that stores a charge of electricity, but depending on where it is placed in a circuit, it can be used as a reservoir device, a blocking device or a device to pass AC signals. It can be used for filtering, stage separation, decoupling, timing, and even amplifying! (In a tuned circuit it creates amplification when connected to a coil - but this is mainly due to one of the incredible properties of a coil).

It will take a lot more projects to cover all these features.

You can hear the result of a time delay circuit in the Simple Siren project (Project 4) and if you think of the electrolytic as a miniature rechargeable battery, charging and discharging as we have shown in the animations, you will be a little closer to "seeing" how the circuit operates.

Resistor Explanation

A resistor is a two-terminal electronic component designed to oppose an electric current by producing a voltage drop between its terminals in proportion to the current, that is, in accordance with Ohm's law: V = IR. The resistance R is equal to the voltage drop V across the resistor divided by the current I through the resistor.

Resistors are characterized primarily by their resistance and the power they can dissipate. Other characteristics include temperature coefficient, noise, and inductance. Practical resistors can be made of resistive wire, and various compounds and films, and they can be integrated into hybridprinted circuits. Size, and position of leads are relevant to equipment designers; resistors must be physically large enough not to overheat when dissipating their power. Variable resistors, adjustable by changing the position of a tapping on the resistive element, and resistors with a movable tap ("potentiometers"), either adjustable by the user of equipment or contained within, are also used.

We will now explain how to work out resistance values by using the colour bands. Hold the resistor so the fourth band is GOLD. The first two bands of colour provide the two digits in the answer and the third band provides the number of zeros. The answer will be in OHMS.
Here are the resistors used in the projects and their colour bands:

resistor color band

In a moment we will show how the colours are worked out but first we will discuss resistors in general.

The value of a resistor is measured in ohms. A low value resistor may be 10 ohms or 22 ohms. A high value resistor may be 100,000 ohms, 330,000 ohms 1,000,000 ohms or even higher.

This is an enormous range and we need this range for electronics. If we had a resistor of each value from 1 ohm to 5 million ohms we would need 5 million types! This is impractical and the designers of circuits have found that in most cases, the value of a resistor can be 10% higher or lower than a specified value and the circuit will work perfectly ok. So the manufacturers of resistors worked out a range of values to provide designers with a complete coverage without the need for too many types.

This is called the range of PREFERRED VALUES and starts at 10 ohms (there are also lower values). The next value is 12 ohms, then 15 ohms, 18 ohms, 22 ohms, 27 ohms 33 ohms 39 ohms 47 ohms 56 ohms 68 ohms and 82 ohms. This is the first 12 values and they may seem like unusual values but each value has been worked out on a 10% tolerance scale. The next values are 100ohms, 120 ohms, 150 ohms, 180 ohms and you can see a pattern emerging - they follow the first group except they are ten times greater. Each group is called a decade and the next decade is 1000ohms, 1200 ohms, 1500 ohms, 1800 ohms etc.

In the old days, when a manufacturer made a batch of resistors, he could not control the final value. So he simply made resistors and tested them just before adding the bands of colour. He did not want to throw any resistors away so when making 100 ohm resistors, for example, he had some at 100 ohms, some at 101 ohms, some at 125 ohms, some at 80 ohms and lots of other values.

Every resistor between 90 ohms and 110 ohms would be banded as 100 ohms. Resistors from 111 ohms to 133 ohms would be banded 120 ohms and in this way the value of any resistor would be either the exact value or only 10% away from the exact value. In electronics, most circuits will work perfectly ok with a resistor that is slightly higher or lower than the stated value. Electronics is not that critical. We are really talking about the old days of radio and the use of valves - where the resistor values were not very critical. Modern electronics (digital electronics) is somewhat more critical and resistors are much more accurate as you will see by the gold band on the resistors in the kit. Gold represents a tolerance of 5%.

Resistors have always been the most difficult component to identify in electronics and that's why they need a lot of study. Once you master the colour code you will feel much happier.

To the casual observer, any circuit board is a mass of "little coloured things" called resistors, with no indication of what value they represent. Once you know the resistor colour code you will be able to work out the values and relate them to a circuit diagram.

That's why it is so important to master this part of electronics. The resistors required for the experiments in this section are contained in a kit of parts and must be separated from the rest of the components and correctly identified.

This is the first thing you will be doing so you don't fit the wrong value in any of the projects.
If you fit the wrong value, the circuit may not work and some of the other components may be damaged. Later on you can experiment with changing resistor values but at this stage you should only fit the specified values.

Separate the resistors from all the other components and place them on the bench so that the gold band is to the right.

The gold band indicates the resistors have a tolerance of 5%. In other words they are more accurate than older-style 10% types. This gold band does not concern us in this course but it DOES tell us which way around to hold the resistor so that the colour bands can be read correctly. Only 10 different colours are used for ALL resistors.

The following table shows these 10 colours and the number given to each:

resistor color

Hold the resistor so that the 3 colour bands are to the LEFT and the right hand band is either gold or silver.

The first colour gives the first DIGIT of the resistance. The second colour give the second DIGIT in the answer. The third colour gives the number of zero's in the answer. There are only 12 resistors in each decade and they have the following first two colours:

resistor color

All you have to do is add the number of zero's to get the resistance. Use this table to give the number of zero's:

identifying resistor

For example, what is the value of a resistor with colour bands:
red red black
2 2 Ohms

22 ohms. This is written 22R

What is the value of a resistor with colour bands:
red red red
2 2 00

2,200 ohms. This is written 2k2

A resistor with colour bands:
yellow purple orange
4 7 ,000

This is written 47k.

A resistor with colour bands:
orange white brown
3 9 0

This is written 390 ohms or 390R.

To make it easy to recognise the value of a resistor, it is important to present the value in a STANDARD FORM - an easily recognised form. This involves using the letters: R, k and M to represent ohms, kilo ohms and Meg ohms (instead of writing lots of ,000's).

For example a 4,700,000 ohm resistor is 4.7 Meg and the decimal point is replaced by the letter M to give 4M7.

A 2,200 ohm resistor is 2.2k and this is written as 2k2. A 100,000 ohm resistor is written as 100k. A 10 ohm resistor is written as 10R, as the letter R represents ohms. The letter R was possibly chosen as a short form of "Resistance."

A 2.2 ohm resistor is written as 2R2. A 1,000 ohm resistor is written as 1k, and so on.

This is not an easy question to answer because a resistor is able to do many things, depending on where it is placed in a circuit, its value and the surrounding components. Every resistor carries out a particular task, and sometimes it does more than one task.
To keep things simple we will cover only a few tasks. In future pages we will cover more features.

We have already shown that resistors are marked with coloured bands to show the value of the resistance in OHMs and they have a value from .22 ohm (actually from zero ohms - a zero ohm resistor is used as a LINK on a PC board and the purpose of this component may be to act as a bridge to jump over other tracks on the board or it may be a temporary component that can be removed and changed at a later date. It can also be a "test point" where the resistor (link) is removed for testing or calibration.

Resistors can be as high as 10M or greater, depending on the purpose.
This is an enormous range and depending on the value of the resistor and the other component(s) around it, so its function will be determined.

Whenever a resistor is placed in a circuit, the current flow through that part of the circuit will be less when the resistor is fitted.

Some components, such as Light Emitting Diodes, will take too much current if they are connected directly across a battery or power supply.

To prevent them burning out, a resistor must be connected in series with one of the leads.
This has already been covered in previous pages.

The resistor can also act as a voltage divider. When two resistors are placed in series, the voltage at their join is a percentage of the voltage across them. The actual voltage can be determined by mathematics or experimentation. For example, If two equal-value resistors are connected in series to a 12v supply, the voltage at their mid point will be 6v. The value of the resistors can be adjusted so that the "pick off" voltage is 9v, or 11v or any voltage up to 12v.

The resistor can also be used to create a TIMING CIRCUIT by combining it in series with a capacitor. This will be covered later in the course.

The resistor limits the current into the capacitor so that it takes a PERIOD OF TIME to charge. Whenever you see a resistor and capacitor in series you can be fairly certain they form a timing circuit. There are lots of other functions for a resistor including a fusible resistor that is simply designed to burn out if the current through it gets too high, and these will be covered in future pages.

Basic Analog Flip Flop Schematics

This schematics is a basic analog flip flop. As we know, there are analog flip flop which built using analog components like ordinary transistor and digital flip flop build using digital logic IC (integrated circuit) like TTL IC.

Basic Analog Flip Flop Schematics diagram

and here the result:

Flip Flop Schematics

To control the speed of light's "on" and "off" in another word "control the flash rate", you can replace the Resistor 10K with variable resistor 20K or replace the electrolytic capacitor 100uF with other value.

Flip flop PCB layout:
Flip Flop Schematics

Dancing Lights

Dancing Lights circuit diagram
This circuit is very simple... you can use this circuit for decoration purposes or as an indicator. Flashing or dancing speed of LEDs can be adjusted and various dancing patterns of lights can be formed.

The circuit consists of two astable multivibrators. One multivibrator is formed by transistors T1 and T2 while the other astable multivibrator is formed by T3 and T4. Duty cycle of each multivibrator can be varied by changing RC time constant. This can be done through potentiometers VR1 and VR2 to produce different dancing pattern of LEDs.

Flashy christmas light

electronic circuit diagram

This simple and inexpensive circuit built around a popular CMOS hex inverter IC CD4069UB offers four sequential switching outputs that may be used to control 200 LEDs (50 LEDs per channel), driven directly from mains supply. Input supply of 230V AC is rectified by the bridge rectifiers D1 to D4. After fullwave rectification, the average output voltage of about 6 volts is obtained across the filter comprising capacitor C1 and resistor R5.

LED light flasher

LED light flasher circuit diagram
This is a very basic circuit for flashing one or more LEDS and also to alternately flash one or more LEDs.

It uses a 555 timer setup as an astable multivibrator with a variable frequency.
With the preset at its max. the flashing rate of the LED is about 1/2 a second. It can be increased by increasing the value of the capacitor from 10uF to a higher value. For example if it is increased to 22uF the flashing rate becomes 1 second.

Just a minute scoring board circuit

Just a minute scoring board circuit diagram
You can use this circuit for quiz contests wherein any participant who presses his button (switch) before the other contestants, gets the first chance to answer a question. The circuit given here permits up to eight contestants with each one allotted a distinct number (1 to 8). The display will show the number of the contestant pressing his button before the others. Simultaneously, a buzzer will also sound.

Gate Alarm Circuit

electronic circuit diagram
Image Description:
Figure 1 represents a cheap and simple Gate Alarm, that is intended to run off a small universal AC-DC power supply.

Figure 2 shows how an ordinary reed switch may be converted to close (a "normally closed" switch) when the gate is opened. A continuity tester makes the work easy. Note that many reed switches are delicate, and therefore wires which are soldered to the reed switch should not be flexed at all near the switch. Other types of switches, such as microswitches, may also be used.

Graphic Equalizer 3 Band

Graphic Equalizer 3 Band circuit diagram
Very simple and cheap 3 band Equlizer for your home made sound system :D

Vinyl Pre-Amplifier

This is old pre amplifier circuit, but still...this is very good and cheap analog circuit...
Vinyl Pre-Amplifier circuit diagram
1) A moving magnet pick-up cartridge is an inductive transducer that must be resistively damped and reactively tuned to optimise reproduction.
Hence I fitted a sub-miniature twin gang 500pF variable and screen earthed twin gang potentiometers directly to the input circuitry
It is only *after* you have actually used these input damping and tuning controls whilst music listening to optimise your own equipment line-up, that you can understand just how much mind distracting spin has been repeated about fractional 'dB' variation with respect to an ideal RIAA characteristic.
Cartridge to pre-amplifier matching has a much more significant effect upon reproduction than does the achievement of perfect RIAA equalisation !!!

(2) Another factor greatly affecting reproduction relates to NFB loop controlled gain stage interactions and terminations.
For example, it is possible to build a moving magnet stage using just one or two gain stages per channel, and they can measure near ideal under steady sinewave examination, but this cannot guarantee that they will actually sound good when coping with highly dynamic music waveforms. NFB loop controlled equalisation stages should be buffered at input as well as output. The input terminal of a stage that is called upon to output current not retaining a linear relationship with voltage at all frequencies, will itself not respond with amplitude linearly if fed at high impedance, and this is especially so with bipolar input circuitry.
(Stage interaction often arises, and this is why some power amplifier plus pre-amplifier combinations can reproduce less cleanly than expected.)
Interconnects are not the only cause of audible degradation, thus a separate additional NFB loop controlled line output driving stage that does not load previous circuitry whilst providing a lower output impedance can further improve rather than degrade the final sound by its own presence.

(3) The components used for upper and lower RIAA equalisation characteristics are better separated, as in this circuit.
Passive (non distorting) 750 ohm (or 2x 1k5 in //) plus 100nF close tolerance components not only perform the RIAA hf cut between stages three and four, but they also reduce higher audio frequency noise and distortion from the earlier stages.
Here the line driver stage is already operating at good input signal level with falling input input impedance as frequency increases, and the resulting improvement in sound reproduction becomes instantly recognisable.
Additionally, the uncompensated series feedback unity gain error seen on some other vinyl pre-amplifier circuits is automatically covered.

(4) The original RIAA characteristic was, *is*, sub-bass weak, with a low frequency roll-off that introduces notable bass phase distortion.
For this reason I extended the low frequency equalisation to 25Hz instead of 50Hz, with a switchable option for 'standard' reproduction.
Do not try to use the extended bass response for loud real-time playback (via a computer is okay) unless you have solid floors or your turntable is brick wall mounted.
The 22uF capacitors then introduce multi-pole passive roll-off below 20Hz to more sharply cut turntable and pressing rumbles.

(5) At high live playback levels the extended bass response can set up feedback via differentially energised room resonances. This was easily remedied by connecting the primary of a subminiature transistor radio output transformer between channels, thereby mono-ing the sub-bass without affecting other stereo reproduction. Thus this pre-amp offered a new method for bass feedback reduction that has minimal impact upon the overall bass reproduction level, yet which allows higher 'pop-party' sound levels in undamped rooms.

Don't just look at this circuit and think 'Yeah ?' or 'Sure ?' and say to yourself 'Look at all those capacitors !'.
This analogue pre-amp is a tested design providing not just both a cleaner and quieter background to the music we are meant to hear, but also an optimisable clarity of reproduction that few are likely to have heard before, or even imagined could ever have become a realisable experience.

Today there are many internally compensated audio integrated circuits to choose from, several offering fet input devices. Remotely power your construction with at least four 470uF or 1mF capacitors per 15V rail, and place it beside the tone arm with no more than two feet of screened interconnect.
Do please let me know how you can get on, and let me know which ICs performed well so that they can be mentioned here for other constructors.

MP3 Car Amplifier 150 Watts

MP3 Car Amplifier 150 Watts circuit diagram
This car amplifier schematics is quite simple and cheap for car audio system.
For complete tutorial and schematics, please go to this page

Amplifier 24 Watts Class A

This is very good and low cost Amplifier for your medium indoor sound system. A 24 Watt Class A Amplifier made from discrete semiconductors, built and tested by Marc Klynhans from South Africa.
electronic circuit diagram

Marc's website may be found at:

Simple Line Mixer and Patchbay

Here the finished circuit include the box:
Simple Line Mixer and Patchbay

And here the schematic diagram:
Simple Line Mixer and Patchbay circuit diagram

100 to 150 Watt Amp

Amplifier Schematics:
100 to 150 Watt Amp circuit diagram

Power Supply Schematics:
power supply circuit diagram

Peak Reading Audio Level Meter

electronic circuit diagram
This simple circuit will indicate peak audio response on an analogue meter, similar to a tape recorders meter. The circuit uses an opamp as a non inverting amplifier, but with one addition - a diode in the feedback loop. The circuit has a fast response time and slow decay time to indicate peak readings. The 1N4148 diode provides half wave rectification of the input signal, the dc output being smoothed by the 22u capacitor. the capacitor will charge to the peak value of the input waveform, and then discharge via the meter and 18k resistor. I used a meter with a FSD of 150uA, but any meter with a FSD in the range 50-250uA may be used. The discharge time is around a quarter of a second. Increase the 22uF cap for a longer discharge time, or omit altogether to make an instantaneous reading level meter.

This circuit will only work with a MOSFET type op-amp, bipolar types i.e. 741 and J-FET op-amps such as LF351 will not work in this circuit.

Hi-Fi Pre Amplifier

Hi-Fi Pre Amplifier circuit diagram
It has an exceptionally fast high frequency response, as demonstrated by applying an 100kHz squarewave to the input.

Doorphone Intercom

Doorphone Intercom circuit diagram
In this doorphone circuit, an 8 ohm speaker is used both as a microphone and also an output device. The BC109C stage amplifies in common base mode, giving good voltage gain , whilst providing a low impedance input to match the speaker. Self DC bias is used allowing for variations in transistor current gain. An LM386 is used in non-inverting mode as a power amplifier to boost voltage gain and drive the 8 ohm speaker. The 10k potentiometer acts as the volume control, and overall gain may be adjusted using the 5k preset. The double pole double throw switch, reverses the loudspeaker positions, so that one is used to talk and the other to listen. Manually operating the switch (from inside the house) allows two way communication.

Microphone for Computer

Microphone for Computer circuit diagram
This circuit was submitted by Lazar Pancic from Yugoslavia. The sound card for a PC generally has a microphone input, speaker output and sometimes line inputs and outputs. The mic input is designed for dynamic microphones only in impedance range of 200 to 600 ohms. Lazar has adapted the sound card to use a common electret microphone using this circuit. He has made a composite amplifier using two transistors. The BC413B operates in common emitter to give a slight boost to the mic signal. This is followed by an emitter follower stage using the BC547C. This is necessary as the mic and circuit and battery will be some distance from the sound card, the low output impedance of the circuit and screened cable ensuring a clean signal with minimum noise pickup.

6 Input Mixer Schematics

6 Input Mixer Schematics diagram
The mixer circuit below has 3 line inputs and 3 mic inputs. The mic inputs are suitable for low impedance 200-1000R dynamic microphones. An ECM or condenser mic can also be used, but must have bias applied via a series resistor. As with any mixer circuit, a slight loss is always introduced. The final summing amplifier has a gain of 2 or 6dB to overcome this. The Input line level should be around 200mV RMS. The mic inputs are amplified about 100 times or by 40dB, the total gain with the mixer is 46dB. The mic input is designed for microphones with outputs of about 2mV RMS at 1 meter. Most microphones meet this standard.

Audio Notch Meter

Audio Notch Meter circuit diagram
Nice notch meter for your audio device. At first glance this circuit looks fairly complex, but when broken down, can be divided into high pass and low pass filter sections followed by a summing amplifier with a gain of around 20 times. Supply rail voltage is +/- 9V DC. The controls may also be adjusted for use as a band stop (notch) filter or band pass filter.

8 Watt Amplifier

8 Watt Amplifier circuit diagram
Actually, the TDA2030 can deliver 20 watts of output power, but the output power reduced to about 8 watts to supply 10 watt speakers. Input sensitivity is 200mV. Higher input levels naturally will give greater output, but no distortion should be heard. The gain is set by the 47k and 1.5k resistors. The TDA2030 IC is affordable and makes a good replacement amplifier for low to medium audio power systems. Incidentally, it is speaker efficiency that determines how "loud" your music is. Speaker efficiency or sound pressure level (SPL) is usually quoted in dB/meter. A speaker with an SPL of 97dB/m will sound louder than a speaker with an SPL of 95dB/m.

Audio Line Driver

Audio line driver schematics:
Audio Line Driver circuit diagram

This preamplifier has a low output impedance, and is designed to drive long cables, allowing you to listen to a remote music source without having to buy expensive screened cables. The very low output impedance of around 16 ohms at 1KHz, makes it possible to use ordinary bell wire, loudspeaker or alarm cable for connection. The preamplifier must be placed near the remote music source, for example a CD player. The cable is then run to a remote location where you want to listen. The output of this preamp has a gain of slightly less than one, so an external amplifier must be used to drive loudspeakers.

Tone Control Circuit

Based on the classic Baxendall tone control circuit, this provides a maximum cut and boost of around 10dB at 10K and 50Hz.

Tone Control Circuit diagram

ECM Mic Preamplifier

Here a microphone amplifier schematics that may be used with either Electret Condenser Microphone (ECM) inserts or dynamic inserts, made with discrete components:
ECM Mic Preamplifier circuit diagram

2 Watt Audio Amplifier

A 2 Watt audio amplifier made from discrete components.

2 Watt Audio Amplifier circuit diagram

The amplifier operates in Class AB mode; the single 470R preset resistor, PR1 controls the quiescent current flowing through the BD139/140 complimentary output transistors. Adjustment here, is a trade-off between low distortion and low quiescent current. Typically, under quiescent conditions, current is about 15 mA rising to 150 mA with a 50 mV input signal. The frequency response is shown below and is flat from 20Hz to 100kHz:

12Volt to 9Volt DC Converter

12Volt to 9Volt DC Converter circuit diagram

Parts List:
R1 = 560 ohm
C1 = 1000uF/40V, Electrolytic
C2 = 10uF/25V, Electrolytic
C3 = 330nF, Ceramic
Z1 = 9.1V, 1watt zener
Q1 = ECG184, NTE184

To get a more precise output voltage, replace zener diode Z1 with 10V and R1 with a 1Kilo ohm potentiometer. A Coolrib for Q1 is optional but highly recommended. You can replace Q1 for a more robust type to get more output amps depending on your requirements. Simple circuit to power your 9 volt cassette recorder and other stuff.

Battery 9V Voltage Doubler

electronic circuit diagram

MAX1044 is a charge pump converter - it uses a capacitor as a "bucket" to pump charge from one place to another. Normally, there is a capacitor connected from pin 2 of the 1044 to pin 4. This capacitor is charged between +9V and ground, and then switched in parallel with a capacitor from pin 5 to ground in a way that makes a negative voltage on the second cap.

In this UPverting use, the 1044 still switches pin 2 between +9V and ground just as it would for a voltage inverter. However, we ignore the pin 4 and 5 connections that would make an inverter from it. Instead, we connect two capacitors and diodes as shown (D1, 2, and C1, 2). The voltage on pin 2 of the 1044 is switched from +9V to ground. When it switches to ground, C1 fills with voltage through D1. When it then switches to +9, it pulls the negative terminal of C1 up to +9V. D1 now blocks any flow of current back into the battery, so the charge in C1 flows through D2 into C2. So at C2, we now get almost 18V!

There's more. If we add another two diodes and capacitors (D3, D4 and C3, C4), we can add another 9V to it, as C3 charges to +18 through D3 when pin 2 is at ground, and is pulled up to +25 (+27 minus the voltage drops of the diodes) when pin 2 goes high. We can do it again with D5, D6 and C5, C6 to get +33V. The limit on all this is the losses in the diode voltages. Each time we add a section, we add two more diode drops that we can't take advantage of to charge capacitors. But +33 is not bad for a single 9V battery!

If you build this, you MUST take notice of the voltages on the capacitors. The caps can all be the same value, but C1, C2 need to be 25V units, C3, 4, 5, and 6 can be 35V units, and C5 and C6 might need to be 50V unit just for some safety margin. 1N400x diodes work and are cheap, but the losses are higher than they really need to be. For higher performance and lower losses, it's better to use something like the 1N5817 schottky diodes for low losses. But both will work.

This charge pumping is a very efficient way to convert voltages. The only power lost is that power dissipated in the resistances of the switches inside the 1044 and the series resistance of the capacitors and diodes, as well as the power to run the internal oscillator that flips the switches when needed.

All by itself, the 1044 runs at about 7-10kHz, so there will be ripple of that amount on the C2 output and on the +9V output from the battery as well. Audio equipment that uses this voltage could have a "whine" audible if you're not careful. However, the 1044 has a frequency boost feature. If you connect pin 1 to the power supply (shown by the little open switch) then the oscillator frequency goes up by about 6:1. The oscillator then works well above the audio region. Any whine is then going to be inaudible.

Unregulated Power Supply

This page come from, show you about circuit of un regulated powersupply:

A basic full wave rectified power supply is shown below. The transformer is chosen according to the desired load. For example, if the load requires 12V at 1amp current, then a 12V, 1 amp rated transformer would do. However, when designing power supplies or most electronic circuits, you should always plan for a worst case scenario. With this in mind, for a load current of 1 amp a wise choice would be a transformer with a secondary current rating of 1.5 amp or even 2 amps. Allowing for a load of 50% higher than the needed value is a good rule of thumb. The primary winding is always matched to the value of the local electricity supply.

Unregulated Power Supply circuit diagram

An approximate formula for determining the amount of ripple on an unregulated supply is:

Vrip = Iload * 0.007 / C

where I load is the DC current measured through the load in amps and C is the value of the capacitor in uF.The diagram below shows an example with a load current of 0.1 amp and a smoothing capacitor value of 1000uF.

electronic circuit diagram

The calculated value of ripple is (0.1 * 0.007) / 1000e-6 = 0.7 volts or 700mV. The value of peak-peak ripple measured from the graph is 628mV. Therefor, the equation is a good rule of thumb guide for choosing the correct value for a smoothing capacitor in a power supply.