Amplifier Circuit

Home Stereo Amplifier Using STK4241V

2009-12-23T15:45:00.000-08:00

This home stereo amplifier circuit using STK4241V. This home stereo amp is equiped with STK4241V wich is a thick film hybrid IC, AF Power Amplifier (Split Power Supply) (120W+120W min, THD = 0.08%).

Some features of STK4241V

Muting circuit built-in to isolate all types of shock noise.
Current mirror circuit for low 0.08% total harmonic distortion

For this 2×120W home stereo power audio amplifier we use a single monochip STK4241V to obtain up to 120W for each channel.

Printed Circuit Board (PCB) of Home Stereo Amplifier STK4241V

STK4241V Stereo Amplifier Parts List
R6, R22 – 560 ohm / 0.125W
R1, R24 – 1K / 0.125W
R9, R10 – 1K / 0.5W
R7, R18 – 4.7K / 0.25W
R8, R19 – 4.7K / 0.5K
R2, R5, R21, R23 – 56K / 0.125W
C7, C17 – 3pF ceramic
C2, C20 – 470pF ceramic 50V
C6, C16 – 1nF 100V
C11, C12 – 100nF 100V
C1, C19 – 2.2uF 50V
C5, C15 – 1uF 63V
C4, C10, C13 – 10uF 63V
C9, C14 – 47uF 63V
C8, C18 – 100uF 16V

Source: STK4241V Home Stereo Amplifier

Simple Microphone Preamplifier

2009-12-23T15:28:00.000-08:00

This simple microphone preamplifier circuit can use between your microphone and stereo amplifier. This amplifier microphone suitable for use with normal home stereo amplifier line/CD/aux/tape inputs. This microphone preamplifier can take both dynamic and electret microphone inputs (preamplifier provides power foe electret microphone elements).

This circuit idea is to keep the design as simple as possible to be easy to build. That was my goal when I needed a simple external microphone preamplifier for my mixer. The performance of the circuit is nothing superior but can be used with many not so serious projects.

Microphone Preamplifier Circuit Features

Brief description of operation: Simple microphone preamplifier
Circuit protection: No special protection circuits used
Circuit complexity: Very simple one transistor circuit
Circuit performance: Amplification 35 dB, flat frequency response from 20 Hz to 20 kHz, quite poor distortion performance figures, a little bit noisy
Availability of components: Uses common and easily available components
Design testing: I have built few microphone preamplifiers based on this circuit and theu have worked without problems.
Applications: Interface dynamic or electret microphone to a line level audio input in HIFI amplifier or computer soundcard.
Power supply: 9V battery, takes less than 10 mA current
Estimated component cost: Electronics components than $10
Safety considerations: No special electrical safety considerations.

The circuit is a simple one transistor amplifier with amplification of about 30-40 dB (depends on transitor, temperature and voltage). The dynamic mic input is just a simple one transistor amplifier circuit with nothing special in it. LED D1 is in the circuit to show that the circuit operates. The voltage drop caused by LED (around 1.8V for RED led) has been taten in account when designing the amplifier circuit built around Q1. Resistor R4 and capacitor C5 make a filter to filter out possible noise from battery or other power source which is used to feed this circuit. Capacitors C1, C2 and C3 are used to block the DC bias on Q1 base to flow out of microphone input to microphone (the polarity of all capactors is straigh line = + and curved line = -).

Electret microphone input has a resistor R1 fo feeding current through electret microphone capsule when it is connected to the electret microphone input. Electret microphone needs some current (about 1 mA) flowing through it to operate, because there is a small amplifier circuit inside the microphone capsule. This circuit is suitable for all typical cheap electret capsules which available from any electronic component shop. Because electret microphones have higher signal level output, it is quite easy to overdrive the amplifier when you shout to electret microphone.

The circuit is bet to build to a small metal box like in the picture above. Put the 9V battery inside the case too. Battery power and metal box keep external noise and interference sources away. I used standard 6.3 mm jack for dynamic microphone and 3.5 mm mono jack for electret micrphone both installed to from, panel of the metal box. The LED and power switches are also installed to front panel.

Source: Simple Microphone Amplifier

Photodiode Amplifier Circuits with OPA128

2009-11-22T09:01:00.000-08:00

The OPA128 ultra-low bias current operational amplifier achieves its 75fA maximum bias current without compromise. Using standard design techniques, serious performance
trade-offs were required which sacrificed overall amplifier performance in order to reach femtoamp (fA = 10E–15 A) bias currents.

Unique Design Minimizes Performance Trade-Offs
Small-geometry FETs have low bias current, of course, but FET size reduction reduces transconductance and increases noise dramatically, placing a serious restriction on performance when low bias current is achieved simply by making input FETs extremely small. Unfortunately, larger geometries suffer from high gate-to-substrate isolation diode leakage (which is the major contribution to BIFET® amplifier input bias current).

Replacing the reverse-biased gate-to-substrate isolation diode structure of BlFETs with dielectric isolation removes this large leakage current component which, together with a noise-free cascode circuit, special FET geometry, and advanced wafer processing, allows far higher Difet ® performance compared to BIFETs.

How To Improve Photodiode Aplifier Performance
An important electro-optical application of FET op amps is for photodiode amplifiers. The unequaled performance of the OPA128 is well-suited for very high sensitivity detector designs. A few design tips for photodiode amplifiers may be helpful. Please download How To Improve Photodiode Amplifier Performance. Source: Texas Instruments Incorporated

40-900 MHz TV Signal Amplifier

2009-11-21T03:32:00.000-08:00

Here's a small signal amplifier circuit which covers the broad band frequencies from 40 to 900 MHz. These frequencies include TV in VHF and UHF and also the radio broadcasting frequencies in the 88 - 108 MHz FM band. It is connected between the antenna and the input of your receiver and boosts the signals by up to 20 dB.

Technical Specifications -Characteristics
Frequency response: 40 - 900 MHz
Gain: . 20 dB
Maximum output level: 90 uV
Input - output impedance: 75 ohm

The signal amplifier circuit is built around a single transistor a UHF low signal device, the BFW 92. This transistor can operate in frequencies as high as 1.6 GHz, and has a gain of 23 dB. The signal from the antenna is applied to the input of the circuit and through C5 is fed to the base of the transistor. It is amplified and from the collector of the BFW 92 through C2 and C1 is taken to the input of the radio or TV receiver.

The circuit operates off a small 9 V battery which, because of the very low power consumption of the circuit, is going to last for a very long time.

TV Signal Amplifier Printed Circuit Board
Printed circuit board dimensions (4,3cm x 5,4cm)

TV Signal Amplifier Parts List
R1 = 120 Ohm
R2 = 1,5 KOhm
R3 = 270 Ohm
R4 = 82 KOhm
C1,C5 = 100pF (ceramic)
C2,C3 = 1nF (ceramic)
C4 = 2,2pF (ceramic)
D1,D2 = 1N4148 diode
Transistor = BFR90, BFR91, BFW92
Misc = PCB, 6pins, solder, 9V battery clip

L1,2 -= diameter : 5mm, wire thickness : 0,5mm, turns : 8

Source: TV Signal Amplifier

MAR-6 CATV Amplifier Circuit

2009-11-21T03:06:00.000-08:00

This Cable TV amplifier design has 5 outlets. This amplifier boosts the TV cable signal with 18dB before the signal is split into 5. The design is based around a MAR-6 MMIC. This Integrated Circuit amplifies DC to 2GHz with about 18dB.

The CATV distribution amplifier circuit is built on a piece of double sided circuit board with one trace cut out with a sharp hobby knife. It is housed in a standard metal housing, that holds the 6 F-connectors for the HF. A 7805 is used to stabilise the electrical power.

The electrical power (8..30 VDC - 50mA) enters the housing via a (1n) feedthrough-Capacitor. A single diode protects the circuit from reverse polarity voltage. A 7805 soldered to the housing (GND) stabilises the voltage at 5 Volt. Two 100nF capacitors prevent the generation of spurious signals and noise by the 7805

The HF signal enters via a F-connector. An optional attenuator (0,75 - 20 dB) gives the ability to decrease the signal strength in case you should experience interference by intermodulation products. In my situation, I ended up adjusting the attenuator at the maximum level…

After the attenuator, the signal passes through a 1nF capacitor to block DC voltages and goes into the MAR-6. The input to the MAR-6 is indicated by a dot on the body and a chamfer to the input leg.

Power is supplied to the output of the MAR-6 through a 100 Ohm resistor and a 6 hole ferrite choke (1uH). DC current will be about 15mA (3,5 Volt DC at the output of the MAR-6). Another 1 nF capacitor blocks DC and only HF signal is sent to a passive resistor splitter, made from 51 ohm carbon film resistors. Input impedance is 50 Ohm for the MAR-6. Output impedance will be a little less than 75 Ohm. The splitter is build as a 'spider web' floating over the circuit board. Each output is has a female F-connector. All F-connectors are soldered directly to the housing.

After closing the lid of the housing, the circuit should be reasonably immune to the 5 x 1.5 kW Digitenne (DVB-T) transmitters built less than 3 kilometre from my house L

Safety ground
I placed the amplifier right where the cable enters our house, and routed coax to all outlets. The housing is connected to safety-ground with a copper wire.

CATV Amplifier Power supply
For power supply, I use a non stabilised adapter. Unloaded, the output is 8,5 Volt DC, just enough for the 7805 to do its job.

Source: Cable-TV Amplifier with 5 Outlets

Boost Converter Circuit

2009-11-20T15:23:00.000-08:00

The completed board may be driven by voltages between .8 and 3 Volts. While the basic design goal was ‘candle like light from a single cell’, the values used were chosen to allow safe operation from 3 Volts so you can, for example, use it to ‘drain the last bit of energy’ out of used Lithium based cells from flashlights.

This means that you can also drive it from a fresh 123 cell at full brightness (for 16 hours or so) or two NiMH, alkaline or other cells in series. While the current consumption (and therefore light output) goes down with supply voltage, some light is produced even with very low inputs.

Above is the current schematic for the Boost converter. The negative power is connected to the emitters and LED cathode. With the values shown, the circuit draws about 18 mA and drives the LED to 5 mA or so. Higher input voltage, up to 3 volts assuming white LED use, pulls more current and therefore produces more light. Changes in values will change performance. Attention should be paid to the inductor, as it is the key in most cases. It needs to be capable of dealing with peak currents and not saturating.

Source: Boost Circuit Kit

Voltage Boost Circuit For A Battery Operated LED Lantern

2009-11-20T14:57:00.000-08:00

This circuit is a series connected voltage booster. It is designed around two blocking oscillators in parallel with a single inductor core in common. The oscillators are locked together by virtue of their using the same core. The PNP blocking oscillator connects and disconnect the positive power supply to the inductor and the NPN blocking oscillator connects and disconnects the negative supply to the inductor.

Voltage Boost Circuit

In order for the oscillators to run, a diode, D3, needs to be placed across the LED (D4) to power the circuit while current builds up in the inductor. When the transistors turn off, the inductor current flows through steering diodes D1 and D2, and LED D4. Diode D3 that conducted during the build up of current in the inductor is reverse biased while the inductor discharges. The 4.7k resistor across D3 and D4 is optional; it lowers startup voltage to below 1.2 volts, about 100 millivolts lower than the normal 1.3 volt startup voltage.

Voltage Boost Circuit 1

Somehow the transistors turn on (the startup of a blocking oscillator is covered in the other LED flashlight page on this site and also covered in many text books, so I'm not going to do it again here). I will point out that there is a 100k resistor to make sure something conducts when power is first applied. Without it, the oscillator relies on leakage currents to get started, and that really makes me uncomfortable. Yours will probably work fine without either the 100k or 4.7k resistors. Once the transistors are conducting, current builds up in the inductor until the transistors come out of saturation. The time it takes for the transistors to come out of saturation is determined by the largely characteristics of the inductor (initial inductance, core saturation characteristics, and in some cases, winding resistance). The current path is shown in Circuit 1, and is through D3, the inductor, the two transistors, and the 1.5 volt flashlight cell.

Voltage Boost Circuit 2

Once the transistors turn off, inductor current continues to flow, but since the transistors are off, the current flows through previously revers biased diodes D1, D2, and the LED D4. As shown in Circuit 2, the discharge current also flows through the 1.6 volt flashlight cell and of course, the inductor, which is the source of the current during this phase of operation.

It should be noted that all the inductor ripple current passes through the 1.5 volt flashlight cell. If this were to be a large current, I would be concerned about heating in the cell from I2R losses, where R is the internal resistance of the cell.

The inductor was made by a continuous winding of 45 turns of #32 single Beldsol magnet wire on various cores. The taps were made at 15 and 30 turns (each tap was 15 turns from its nearest end).

Here are some cores that I tried, and the results obtained

Ferroxcube TC8.2/3.7/4-3E7, This core gave the best performace of those tested. With this core, the supply started with less than 1.1 volts applied (with the 4.7k start up resistor). The oscilltion frequency was about 20 kHz with a 1.5 volt input. The core is an 8 mm diameter high permeability (ui = 15,000). This gave an inductance of about 1.7 mH in the 15 turns between the taps.
Very large high permeability toroid core, about 4 cm in diameter. Even better than the 9 mm core, but it was really too big for this kind of use.
Ferrite RF tuning slug 10 mm long: Very poor performance - needed about 1.8 volts before the LED would visibly start to light.
RF toroid abut 10 mm in diameter: Even worse than the slug for some reason. Needed about 2.0 volts to get a faint glow from the LED. It has a large enough winding window for a lot more wire, and it probably would have worked at a lower voltage if I had put more turns on it.

What these quick experiments with various cores confirmed is that this circuit worked best when operating with moderate inductance's (2 millihenry per winding) and operating in the tens of kilohertz. Perhpas faster transistors and maybe litz wire would make this work better at higher frequencies.

Source: Series Connected Voltage Boost Circuit for a Battery Operated LED Lantern

Simple Battery Booster Circuit

2009-11-20T14:25:00.000-08:00

Here's a simple battery booster circuit and it can be used in any battery compartment irrespective of the number of cells. The number of batteries (n) will then be replaced by n–1 rechargeable cells (with one cell position taken up by the booster) giving an output voltage the same as if n primary cells are fitted.

Battery Booster Schematic

The battery booster circuit described here can be used in applications requiring four to ten primary cells. With the booster fitted, only three to nine rechargeable cells would be required. The use of (more bulky) electrolytic capacitors with a 35 V rating would allow the booster to be used in applications of up to 20 batteries.

In principle almost any switching regulator IC can be used in this way. The power output from this circuit with a LT1172 regulator is around 500 mA but it can be increased to 2 A for example by using the LT1170 instead.

Source: Battery Booster Circuit

Cell Phone Antenna Booster Installation

2009-11-20T12:48:00.000-08:00

Tired of dropped cell phone incoming calls? The cause for your dropped calls are a lack of cell phone signal. Installing a cell phone antenna booster will increase your signal strength and stop dropped calls. This is how to install one now!

Cell Phone Antenna Booster Installation:

Remove your battery cover. Most have a small tab to push or they will simply slide off. You will need to remove this to install the cell phone antenna booster.
Remove your battery. With the battery removed, wipe down the battery compartment. Make sure that all dirt, dust and fingerprints are removed. Most antenna boosters are attached using an adhesive side.
Peel off the cover on the adhesive side to place the antenna booster on your phone. Place the booster on the side where the antenna is attached. Make sure that you do not put the cell phone antenna booster over any circuit boards or metal contacts on the phone.
Press the antenna booster down firmly to make sure that it is securely attached. Replace your battery and your battery cover.

Source: http://www.ehow.com/how_5174019_install-cell-phone-antenna-booster.html

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2009-11-20T09:59:00.000-08:00

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