Audio Pre-Amplifier

Simple Audio Pre-Amplifier

This simple circuit provides good gain to too audio singnals . Use it in main of an RF oscillators to make an RF transmitter that is very sensitive to sound

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Simple Dual Audio-Signal Tracer Circuit Diagram

The circuit described here is of a dual audio-signal tracer. An audio-signal tracer is a simple device used to troubleshoot for audio signals in radio and other electronic circuitry.

The device is a battery-powered stereo amplifier with two loudspeakers, packaged into a small handheld unit with test probes. An optional diode detector can be incorporated for the detection of amplitude-modulated signals. A test signal (audio) is injected into the tracer at CON1/CON2 from various points of the circuit under test. So long as the signal is heard, the circuitry up to that point is (at least minimally) functional. However, if the signal disappears, a fault can be assumed to be present in the stage of the circuit just preceding it.

Fig. 1: Circuit diagram of the dual audio-signal tracer

The simple external diode detector is not only sensitive to amplitude modulation but even circuits that are normally used for other modulation schemes (such as FM radios) can be tested in some cases.

Circuit and working
Fig. 1 shows the circuit diagram of the dual audio-signal tracer. It is built around LM358 (IC1) and TDA2822M (IC2). LM358 has two independent, high-gain, internal-frequency-compensated operational amplifiers, which are designed specifically to operate from a single power supply over a wide range (3V to 32V) of voltages.


TDA2822M is a low-power stereo amplifier. Its outputs can be directly coupled with the speakers through decoupling capacitors. The tracer is sensitive enough to capture signals from most microphones.

The relatively-high input resistance of 1-mega-ohm (VR1 and VR2) makes it possible to capture audible signals from many tone-control circuits and filters. Input signals are applied to connectors CON1 and CON2 and amplified by the two amplifiers in IC1.

Both amplifiers (channels) are completely independent. Resistor R3 and diodes D2 and D3 protect the input of the first amplifier. Similarly, resistor R4 and diodes D4 and D5 protect the input of the second amplifier. Resistors R1 and R2, diode D1 and capacitor C1 provide the necessary bias DC voltage for the operational amplifiers in IC1.

Potentiometers VR1 and VR2 adjust the volume for the first and second channel, respectively. Op-amps of IC1 are configured as non-inverting amplifiers with gain fixed at ten. Voltage gains can have any values starting from one, depending on the need. However, it is not a good idea to have voltage gains higher than 30 because then the circuit becomes too sensitive to electromagnetic fields and may produce a lot of noise in the loudspeakers.

IC2 works as a dual-channel output amplifier. Each amplifier works with internally-fixed gain of around 100. The amplifier can drive loudspeakers and headphones with resistance equal to or higher than 8-ohm.

Fig. 2: An actual-size, PCB layout of the dual audio-signal tracer

Fig. 3: Component layout of the PCB

Construction and testing
An actual-size, single-side PCB of the dual audio-signal tracer is shown in Fig. 2 and its component layout in Fig. 3. After assembling the circuit on a PCB, enclose it in a suitable plastic box.

The circuit works well off 6V battery; the preferred power supply is 6V and above. The circuit is appropriate for the signal tracer, as general-purpose dual audio amplifier and as low-power stereo amplifier. The output power can reach 1W over 4-ohm with 9V power supply, which is more than enough for listening to the produced sound in a small room.

Sourced By: EFY Author

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Audio Compressor circuit components Liabilities

We have seen here on the blog a very interesting audio compressor circuit, the audio compression is the process that adjusts the level of an audio signal, reducing the volume of loud sounds or amplifying low sounds by narrowing or dynamic range compression an audio signal.

The audio compression is used for sound recording, playback, radio and amplifiers for musical instruments, among other utilities. This circuit presented here is a single audio compressor that uses only passive components, or any semiconductor such as transistor, diode or integrated circuit.

Audio Compressor circuit

This compressor dynamic audio with passive components reduces the high signal to a lower signal, but more constant. If you look at this circuit will realize that has no power supply because it only reduces the input signal.

The basic operation is simple in its exit from the compressor will have a constant audio signal of approximately 70mV, so when the input voltage is between 100mV and 10Volts. The reduction control is made by the variable resistor P1 which may be a potentiometer or trimpot.

The diodes of this circuit should be germanium, because this type of diode has limits below the forward bias silicon diodes. Despite being simple this compressor circuit should work well, the drawback is its great attenuation, which makes it unfeasible for most audio applications.

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Simple Low-Power Audio Amplifier

The small-signal amplifier is generally referred to as a voltage amplifier because it usually converts a small input voltage into a much larger output voltage. The audio power amplifier works on the basic principle of converting low-power audio signal to a suitable level to be delivered to the load.

This low-power amplifier circuit is useful for the amplification of sound from small-signal devices such as mobile phones, laptops or desktops.

Circuit and working
As shown in Fig. 1, this circuit is built around a step-down transformer (X1), bridge rectifier BR1, regulators 7809 (IC1) and 7909 (IC2), dual op-amp TL072 (IC3), low-power amplifier LM386 (IC4) and some other components.

The circuit can be divided into two sections—dual power supply section and amplifier section. The dual power supply section is built around step-down transformer X1 (230V ac primary to 12V-0-12V, 1A secondary) and two voltage regulators 7809 and 7909. IC 7809 is a positive voltage regulator, while 7909 is a negative voltage regulator. Diodes D1 and D2 are used to protect IC1 and IC2 against reverse voltages from capacitors connected to the regulators. These regulators provide ±9V regulated output for the operation of the circuit.

Use suitable heat sinks with the regulator ICs because they get hot during operation. In case of overheating, there is provision for a thermal shutdown.

The amplifier section is built around TL072 (IC3) and a low-power amplifier LM386. The op-amp A1 of IC3 operates as a low-noise preamplifier. Capacitor C8 is used in order to pass low frequency. The op-amp A2 of IC3 operates as a low-pass filter. For changing the cut-off frequency, you have to change the values of capacitors C11 and C12.

 Simple Low-Power Audio Amplifier circuit Diagram

LM386 is a low-power amplifier IC with built-in biasing and inputs that are referred to the ground. It has a gain of 20 and can drive a speaker of 8-ohm impedance.

The circuit is simple to use. You have to simply feed the output from a mobile phone, or any other low-volume device, into RCA1 socket on the PCB. The amplified sound can be listened-to through the speaker (LS1). Potentiometer VR1 is used for volume control.
 
Construction and testing
An actual-size, single-side PCB for the simple low-power amplifier is shown in Fig. 2. Its component layout is shown in Fig. 3. After assembling the circuit on the PCB, enclose it in a suitable plastic box.

Fix RCA1 socket on the front side of the box for an audio-in signal. Fix a three-pin connector on the PCB for connecting secondary terminals (12V-0-12V) of transformer X1 and to two-pin connector on the rear side for mains 230V AC, 50Hz. Fix the transformer firmly on the cabinet with screws or nuts and bolts. Connect the speaker affixed on top of the box or placed at a distance. Use a shielded cable for connecting to the RCA socket.


Before inserting IC3 and IC4 into their respective IC bases, verify that all the connections have been made properly.

Sourced By : EFY  Author :  S.C. Dwivedi

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Simple Interface for Digital Sound Synthesis

You can make a digital sound synthesizer, for experimentation with sound equipment or with peripheral devices, using special integrated circuits or digital-to-analogue converters (DACs). But here is a simple 8-input digital sound-synthesis circuit for producing audio from digital codes that can be easily interfaced with microcontroller or microprocessor boards having up to eight TTL/CMOS-level digital output pins.

Circuit and working
Fig. 1 shows circuit diagram of the simple interface for digital sound synthesis. It is built around low-power audio amplifier LM386 (IC1), 9V voltage regulator 7809 (IC2) and a bridge rectifier (BR1).

Fig. 1: Simple interface for digital sound synthesis

The 8-bit digital code (representing audio signal) input is applied at connector CON4. Resistors R1 through R8 and potmeter VR1 work as a simple DAC circuit. The relationships to get approximate values of resistors in the DAC are:

R1 = 2R2 = 4R3 = 8R4 = 16R5 = 32R6 = 64R7 = 128R8
Value of VR1 can be from 10% of R8 to 20% of R8.

The minimum value of each resistor (R1 through R8) depends on digital output levels. Capacitors C14 and C15, with switches S1 and S2 closed, filter the sound signals, and can be omitted, if not needed.

Fig. 2: An actual-size PCB layout for the circuit

The audio input is amplified by LM386 low-power amplifier. The gain is set to 200. With 9V power supply, the circuit outputs around 0.5W. The loudspeaker can be 4-ohm, but 8-ohm or higher is preferred to avoid overloading LM386.

The power supply is built around voltage regulator 7809 which gives a 9V regulated output. You can use 4-9V DC as external supply at CON7 input when 230V AC mains is not available.

Diode D1 is used for reverse protection of the regulator.

Construction and testing
An actual-size, single-side PCB for simple interface for digital sound synthesis (excluding the dotted box shown in the circuit) is shown in Fig. 2 and its component layout in Fig. 3. After assembling the circuit on a PCB, enclose it in a suitable plastic box.

Fig. 3: Component layout for the PCB

For testing, generate 1kHz square-wave signal and connect it to any input line of CON4 (D0 through D7). You will hear sound in the speaker connected at CON5.

You can write a simple software code, burn it into the microcontroller, connect its port pins to CON4 and check output from the speaker. You may change the code to various audio frequencies and check the output for experimentation.

You can also use this circuit as a simple audio signal mixer by applying the audio signals (including square-wave signals) at inputs D0 through D8.

Before using the circuit, do verify that voltages at test points are as per table.
The author was a researcher and assistant professor in Technical University of Sofia (Bulgaria) and expert-lecturer in OFPPT (Casablanca), Kingdom of Morocco. Now he is working as an electronics engineer in the private sector Bulgaria


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Sourced By:  EFY: Author Petre Tzv Petrov

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Fast Symmetrical Zener Clipper Circuit Diagram

This is the simple Fast Symmetrical Zener Clipper Circuit Diagram. The problem with using two zeners back to back in series to get symmetrical clamping is that the knee of the zener characteristics is rather sloppy. Also, charge storage in the zeners causes speed problems and the zeners will have slightly different knee voltages, so the symmetry will not be all that good. 

 Fast Symmetrical Zener Clipper Circuit Diagram

This circuit overcomes these problems. By putting the zener inside a diode bridge, the same zener voltage is always experienced. The voltage errors caused by the diodes are much smaller than those caused by the zener. Also, the charge storage of the bridge is much less. By biasing the zener ON all the time, the knee appears to be much sharper.

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IC TL081 based 4 microphones mixer Circuit Diagram

This is the simple IC TL081 based 4 microphones mixer Circuit Diagram. A TL081 op amp is used as a high impedance to low. converter and a signal mixer. The input impedance is about 1 megohm and the output impedance is about 1 kohm. Two 9 volt batteries are used as power source. Battery must be several hundreds of hours with alkaline batteries.

IC TL081 based 4 microphones mixer Circuit Diagram

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Ic 555 Based 10 Note Sound Synthesizer Circuit Diagram

This is the simple Ic 555 Based 10 Note Sound Synthesizer Circuit Diagram. As shown, three ICs are used to produce the sounds. ICl is a 555 timer that generates clock pulses. It is configured as an astable multivibrator. The frequency of the clock pulses is set by trim: mer potentiometer PI. These clock pulses are coupled to the input of IC3 (a 4017 CMOS Johnson counter) on its clock input pin 14. 

 Ic 555 Based 10 Note Sound Synthesizer Circuit Diagram

Each clock pulse causes IC3 to shift a high to each of its output pins in sequence. A trimmer resistor, which can be adjusted to set a different frequency for each note, is connected to each of IC3`s output pins. One side of each of the trimmers is connected to pin 5 (the control voltage pin) of IC2. IC2, another 555 timer IC, creates the tone; the overall pitch of the tone can be varied by P2. 

As the output sequences from the 4017, that tone, which is changed in frequency by each output shift is applied to a small speaker from pin 3 of IC2. An LED, which flashes with each clock pulse, is connected to pin 3 of ICl. Switch S2 is used to vary the sound between flowing and distinct notes.

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Simple Light Audio Transmitter Circuit Diagram

This is the Simple Light Audio Transmitter Circuit Diagram. In the visible-light transmitter, a 7805 voltage regulator is connected in a variable-voltage configuration, and an audio signal is fed to the common input, to modulate the output voltage. The modulated output voltage is used to transmit intelligence via an incandescent lamp.

Simple Light Audio Transmitter Circuit Diagram

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Digital Volume Control Circuit Diagram

This circuit could be used for replacing your manual volume control in a stereo amplifier. In this circuit, push-to-on switch SW1 controls the forward (volume increase) operation of both channels while a similar switch SW2 controls reverse (volume decrease) operation of both channels. A readily available IC from Dallas semiconductor, DS1669 is used here.

Digital Volume Control Circuit Diagram

Digital Volume Control Circuit Diagram

Parts:

J1 = RCA Audio Input Socket
J2 = RCA Audio Input Socket
C1 = 0.1uF-16V Ceramic Disc Capacitor
C2 = 0.1uF-16V Ceramic Disc Capacitor
C3 = 0.1uF-16V Ceramic Disc Capacitor
IC1 = DS1669 (is available from Dallas SCo.
SW1 = Momentary Push Button Switch
SW1 = Momentary Push Button Switch

Notes:

• Replaces mechanical variable resistors.
• Electronic interface provided for digital as well as manual control.
• Wide differential input voltage range between 4.5 and 8 volts.
• Wiper position is maintained in the absence of power.
• Low-cost alternative to mechanical controls.
• Applications include volume, tone, contrast, brightness, and dimmer control.
• The circuit is extremely simple and compact requiring very few external components.
• The power supply can vary from 4.5V to 8V.
• The input signal should not fall below -0.2 volts.

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Build a LED Mini Audio Analyzer circuit Diagram

This analyst is, a sensitive instrument, in the frequency changes   and width of a acoustic signal. Thus the brightness of LED that turns on each moment of is proportional signal width, while the colour of proportionally frequency.

Mini Audio Analyzer Circuit Diagram

 

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The circuit input sensitivity is regulated with R2, in order that in powerful signals they turn on the red LED, in the middle the yellow LED and in the low green LED. The display unit, is constituted by 3 lines of 10 LED the every, what is checked by a counter decoder (IC2). Two gates ICa-b, function as the IC2, with the R6 regulate the frequency.

When does not exist signal in the input, then no one LED does not turn on. As soon as it will be applied signal, then the LED will begin to blink depending on the rythm and the intensity of signal. Can experiment with the prices of resistances R4, R5, so that you find the value that suits in like your. Initially it can they are placed trimmer 1KO, in the place of R4, R5 and after is found the suitable value, they are replaced with permanent resistances.

What it wants it can it adds also other LED, adding other a completed same press with the IC2. The particular circuit does not have the claim, the precision of measurement  input signal.

Part List

R1= 1K8Kohm    
R2= 100Kohm trimmer    
R3= 1Kohm    
R4= 100 ohm.....1Kohm    
R5= 100 ohm.....1Kohm
R6= 100Kohm trimmer
C1= 100nF 100V
D1....10= RED LED    
D11....20= YELLOW LED    
D21....30= GREEN LED    
IC1= LM3915
IC2= 4017
IC3= 4011

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10W Small Audio Amplifier

This is a simple 10W Small Audio Amplifier circuit diagram. You can use this powerful amplifier in any small audio project. It is very small (6.5 x 4.5 cm).It outputs 10W and uses a 9V battery.

10W Small Audio Amplifier

Component

 

PCB

Components List

R1 : 6 Ohm

R2 : 220 Ohm

R3 : nothing

R4 : 10 KOhm pontesiometer

C1 : 2200 uF / 25V

C2 : 470 uF / 16V

C3 : 470 nF / 63V

C4 : 100 nF

C5 : nothing

C6 : nothing

IC1 : TDA 2003

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Single -IC Dual-tones Siren Circuits Diagram

Double-tone Police sound Circuits Diagram

This circuit is intended for children fun, and can be installed on bicycles, battery powered cars and motorcycles, but also on models and various games and toys. With SW1 positioned as shown in the circuit diagram, the typical dual-tone sound of Police or Fire-brigade cars is generated, by the oscillation of IC1A and IC1B gates. With SW1 set to the other position, the old siren sound increasing in frequency and then slowly decreasing is reproduced, by pushing on P1 that starts oscillation in IC1C and IC1D. 

The loudspeaker, driven by Q1, should be of reasonable dimensions and well encased, in order to obtain a more realistic and louder output. Tone and period of the sound oscillations can be varied by changing the values of C1, C2, C5, C6 and/or associated resistors. No power switch is required: leave SW1 in the low position (old-type siren) and the circuit consumption will be negligible.

Single -IC Dual-tones Siren Circuits Diagram

Parts:

R1,R3___470K   1/4W Resistors

R2______680K   1/4W Resistor

R4_______82K   1/4W Resistor

R5______330K   1/4W Resistor

R6_______10K   1/4W Resistor

R7_______33K   1/4W Resistor

R8________3M3  1/4W Resistor

C1,C5_____10µF  25V Electrolytic Capacitors

C2,C6_____10nF  63V Polyester Capacitors

C3_______100nF  63V Polyester Capacitor

C4_______100µF  25V Electrolytic Capacitor

D1-D3___1N4148  75V 150mA Diodes

IC1_____4093   Quad 2 input Schmitt NAND Gate IC

Q1______BC337   45V 800mA NPN Transistor

P1______SPST Pushbutton

SW1_____DPDT Switch

SPKR____8 Ohm Loudspeaker

B1______6V Battery (4 AA 1.5V Cells in series)

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Precision Audio Milli volt meter Circuits Diagram

This electronic circuit is audio milivolt meter. It measures 10mV to 50Volt RMS in eight ranges.

Precision Audio Millivoltmeter Circuits Diagram

 Notes:

• Connect J2 and J3 to an Avo-meter set to 50µA range:
• Switching SW2 the four input ranges will be multiplied by 5
• Total fsd ranges are: 10mV, 50mV, 100mV, 500mV, 1V, 5V, 10V, 50V
• Set R11 to read 1V in the 1V range, with a sine wave input of 1V @ 1KHz
• Compare the reading with that of another known precision Millivoltmeter or with an oscilloscope.
• The oscilloscope reading must be a sinewave of 2.828V peak to peak amplitude
• Frequency response is flat in the 20Hz-20KHz range
• If you have difficulties in finding resistor values for R1, R2, R3 & R4, you can use the following trick:
  R1 = 10M + 1M in parallel
  R2 = 1M + 100K in parallel
  R3 = 100K + 10K in parallel
  R4 = 1K2 + 6K8 in parallel
  All resistors 1/4W 1% tolerance 

Parts:

R1_____909K    1/2W 1% Metal Oxide Resistor

R2______90K9   1/2W 1% Metal Oxide Resistor

R3_______9K09  1/2W 1% Metal Oxide Resistor

R4_______1K01  1/2W 1% Metal Oxide Resistor

R5_____100K    1/4W Resistor

R6_______2M2   1/4W Resistor

R7______82K    1/4W Resistor

R8______12K    1/4W Resistor

R9_______1K2   1/4W Resistor

R10______3K3   1/4W Resistor

R11____200R    1/2W Trimmer Cermet

C1_____330nF   63V Polyester Capacitor

C2,C3__100µF   25V Electrolytic Capacitor

C4_____220µF   25V Electrolytic Capacitor

C5______33pF   63V Polystyrene Capacitor

C6_______2µ2   63V Electrolytic Capacitor

D1-D4___1N4148 75V 150mA Diodes

IC1_____CA3140 Op-amp

IC2_____CA3130 Op-amp

SW1_____2 poles 5 ways rotary switch

SW2_____SPDT switch

J1______RCA audio input socket

J2,J3___4mm. output sockets

B1______9V PP3 Battery

Clip for PP3 Battery

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25 Watt Audio Amplifier Circuits Diagram

25 Watt Audio Amplifier Circuits Diagram

Parts:

R1,R4_________47K  1/4W Resistors

R2____________4K7  1/4W Resistor

R3____________1K5  1/4W Resistor

R5__________390R   1/4W Resistor

R6__________470R   1/4W Resistor

R7___________33K   1/4W Resistor

R8__________150K   1/4W Resistor

R9___________15K   1/4W Resistor

R10__________27R   1/4W Resistor

R11_________500R   1/2W Trimmer Cermet

R12,R13,R16__10R   1/4W Resistors

R14,R15_____220R   1/4W Resistors

R17___________8R2    2W Resistor

R18____________R22   4W Resistor (wirewound)

C1___________470nF  63V Polyester Capacitor

C2___________330pF  63V Polystyrene Capacitor

C3,C5________470µF  63V Electrolytic Capacitors

C4,C6,C8,C11_100nF  63V Polyester Capacitors

C7___________100µF  25V Electrolytic Capacitor

C9____________10pF  63V Polystyrene Capacitor

C10____________1µF  63V Polyester Capacitor

Q1-Q5______BC560C   45V 100mA Low noise High gain PNP Transistors

Q6_________BD140    80V 1.5A PNP Transistor

Q7_________BD139    80V 1.5A NPN Transistor

Q8_________IRF530  100V 14A N-Channel Hexfet Transistor

Q9_________IRF9530 100V 12A P-Channel Hexfet Transistor

Power supply circuit diagram

Parts:

R1____________3K3  1/2W Resistor C1___________10nF 1000V Polyester CapacitorC2,C3______4700µF   50V Electrolytic CapacitorsC4,C5_______100nF   63V Polyester Capacitors D1__________200V 8A Diode bridgeD2__________5mm. Red LED F1,F2_______3.15A Fuses with sockets T1__________220V Primary, 25 + 25V Secondary 120VA Mains transformer PL1_________Male Mains plug SW1_________SPST Mains switch

Notes:

• Can be directly connected to CD players, tuners and tape recorders. Simply add a 10K Log potentiometer (dual gang for stereo) and a switch to cope with the various sources you need.
• Q6 & Q7 must have a small U-shaped heatsink.
• Q8 & Q9 must be mounted on heatsink.
• Adjust R11 to set quiescent current at 100mA (best measured with an Avo-meter connected in series to Q8 Drain) with no input signal.
• A correct grounding is very important to eliminate hum and ground loops. Connect to the same point the ground sides of R1, R4, R9, C3 to C8. Connect C11 to output ground. Then connect separately the input and output grounds to power supply ground.
• An earlier prototype of this amplifier was recently inspected and tested again after 15 years of use.

Technical data:

Output power:

well in excess of 25 Watt RMS @ 8 Ohm (1KHz sine wave)

Sensitivity:

200mV input for 25W output

Frequency response:

30Hz to 20KHz-1dB

Total harmonic distortion @ 1KHz:

0.1W 0.014% 1W 0.006% 10W 0.006% 20W0.007% 25W 0.01%

Total harmonic distortion @10KHz:

0.1W 0.024% 1W 0.016% 10W 0.02% 20W0.045% 25W 0.07%

Unconditionally stable on capacitive loads

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10W Stereo Audio Amplifier Using TDA2009A

This is a schematic of a 10W stereo audio amplifier using TDA2009A amplifier IC. TDA2009A is a good IC provides quality sound. It has built in features like output current protection and thermal protection etc. The circuit can be operate between 8 to 24V DC with 1 to 2 amphere.

10W Stereo Audio Amplifier Circuit Diagram :

If you want to operate this 10 watt amplifier circuit with watt amplifier circuit with mains supply then use a filtered and stable power supply to reduce mains hum. 10 watt out put power can be obtained by providing 20V 1.5A to the circuit. Use good and thick heatsink with the IC. 

Source By : Circuitsstream

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Audio Lm 3909 IC-conduction tester

This tiny conductivity tester works with LM 3909. The tester makes a beeping sound if the resistance between the test probes between 0 and 100 O lies. Due to the volume of the beep, the resistance between the test probes can be determined.

Audio Lm 3909 IC-conduction tester Circuit Diagram

Parts List

     R1 = 1 k
     C1 = 10 uF
     C2 = 100 nF
     LS = Loudspeaker 12 to 16 Ω
     IC1 = LM 3909

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Voice Scrambler

With this circuit you can modify how your voice sounds by changing the pitch of your voice. This circuit can be connected to a phone and with a duplicate circuit on the end of the phone line, you can have a scrambled voice communication. The way the circuit works is as follows: If we cut the circuit in half at the T2 transformer and include the LM324 on the left side, you will see that the LM324 portion of the circuit is a tone oscillator which shifts the frequency of all input signals to a new higher frequency. When the voice and the tone oscillator mix frequencies the voice is not recognized. The voice signal is then inputted to the second stage which again shifts the voice signal again. I recommend that the first stage be tuned to a frequency that is 100hz lower then the second stage.

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Equalising HEXFETs

When experimenting with audio output stages featuring multiple HEXFETs it quickly becomes apparent that the total power is not divided equally among the individual transistors. The reason for this lies in the wide part-to-part variations in gate-source voltage, which in the case of the IRFP240 (or IRFP9240) can be from 2 V to 4 V. Source resistors in the region of 0.22 Ω as commonly seen in amplifier circuits (see example circuit extract) help to counteract this, but usually not to a sufficient extent. One possible solution to this problem is to ‘select’ the transistors used so that their gate-source voltages match as closely as possible.


For building prototypes or very short production runs this is feasible, but requires additional manual effort in testing the components, and, of course, more transistors must be ordered than will finally be used. The circuit idea shown here allows differences in gate-source voltage between pairs of transistors to be compensated for by the addition of trimmer potentiometers: the idea has been tested in simulation using Simetrix. The second circuit extract shows the required changes.

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The Audio/Video Distribution Amplifier

With the amount of equipment in home entertainment centers today the need to be able to vary the gain of the audio or video signal is needed. I found this particular circuit helpful when used in conjunction with the Universal Descrambler and a Stabilizer circuit I built for making copies of video tapes. It not only allowed me the ability to fine tune the video strength it also helped me increase the recorded audio which typically becomes poor when making tape copies. Circuit operation is straight forward for amplifier circuits. The second channel for the audio amplifier is made up of the same components except the other half of IC1 is used. Pin 6 & 5 are inputs and 7 is the output.

Circuit Diagram

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