Auto-off for Audio Gear

A good way to spend a relaxing afternoon is to be in a quiet place with just the right amount of sun or shade, drinks within reach and listening to your favourite songs on MP3 or CD. You doze off and by the time you wake up again the audio equipment has dropped silent due to flat batteries. What a pity!

The simple circuit shown can prevent this embarrassing situation by de-actuating a relay when no audio signal is detected for about two seconds.

Auto-off for Audio Gear Circuit Diagram

The circuit consists of a sensitive LM358 based comparator, IC1A, which keeps monostable IC2A (a 4538) triggered as long as an audio signal is detected at the input. Via coupling capacitor C1 the circuit takes its input signal from the ‘hot’ side of the loudspeaker or headphones in your audio gear. The monostable will time out 2 s after being triggered, the delay being deter-mined by R6 and C3.

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1W Audio Amplifier Circuit Using NCP2830

This 1w audio amplifier circuit is designed using NCP2830 audio IC manufactured by ON Semiconductor. This audio power amplifier ic designed for portable communication device applications and require few external electronic components.
1W Audio Amplifier Circuit Diagram

NCP2830 is capable to provide 1W continuous output power in 8 ohms load. NCP2830 audio power amplifier main features are : high quality audio (THD+N = 0.04%) , low noise: SNR up to 100 dB, overall system efficiency optimization: up to 89% , Superior PSRR (−88 dB): Direct Connection to Battery , Very Low Quiescent Current 7 mA , Optimized PWM Output Stage: Filterless Capability , Selectable gain of 2 V/V or 4 V/V .

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Sound Effects Generator 2

This circuit uses the Holtek HT2884 IC to produce 8 different sound effects. All sound effects are generated internally by the HT2884 IC. Power is a 3 Volt battery, but the IC will work with any voltage between 2.5 and 5 Volts. Switch S1 is the on / off switch.

Sound Effects Generator 2 Circuit Diagram:

The output at pin 10 is amplified and drives a small 8 ohm loudspeaker. Pressing S3 once will generate all the sounds, one after another. S2 can be used to produce a single sound effect, next depression gives the next sound effect. There are 2 lazer guns, 1 dual tone horn sound, 2 bomb sounds, 2 machine gun sounds and a rifle shot sound. Standby current is about 1 uA at 3 Volt, so battery life is very economical. The IC may be obtained from Maplin Electronics order code AZ52G.Link

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Simple Sound-to-Light Converter Schematic

Figure 1 shows a simple ambit for converting an audio arresting (such as one that comes from the apostle terminals of a CD player). The ambit basically consists of a buffer/amplifier date and three clarify circuits: a high-pass filter, a mid-pass filter, and a low-pass filter. The achievement of anniversary clarify ambit drives a light-emitting diode of altered color.

Simple Sound-to-Light Converter Schematic Circuit Diagram:

 

The ascribe arresting is fed to the absorber date through C1. The ethics of RF and RV1 should be called so that the absorber is able to drive the three filters absorbed to its output. The low-frequency, mid-frequency, and high-frequency apparatus of the ascribe arresting are alone accustomed to canyon through the low-pass clarify (bottom filter), the mid-pass clarify (middle filter), and the high-pass clarify (topmost filter), respectively, appropriately amid them from anniversary other.

Changes in the achievement of a clarify account its agnate achievement LED to about-face on and off. In effect, agriculture a connected audio arresting to the ascribe of this ambit causes the LED's to 'dance'.

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A Headphone Monitoring Switch

In any recording situation, monitoring is critical to make sure you're getting what you want on tape. This is just as true in field recording, but in most cases, one's monitoring options are severely limited--stereo headphone is the only choice.

Headphone Monitoring Switch  :

Since I often use dual-mono mics, hearing a stereo feed of the two is not always convenient. I wanted the option to hear JUST the left mic in BOTH ears, or just the right mic in both ears, as well as a normal stereo signal. This is simple enough to do with a big rotary switch. When completed, you can create a little box that your headphones plug into, which in turn is plugged into the stereo phone output of your deck. Then, by turning the knob on the switch box, you can hear normal stereo, left-only mono, right-only mono, left+right mono and even left-right reversed stereo (or normal stereo again).

Note the use of summing resistors in the left+right mono section. This was an attempt to prevent the two outputs from "fighting" each other if there were very different voltages in left and right outputs. I used 8 ohm resistors here, but a higher value might be better. Maybe ~20 ohms? Also, I initially decided to put normal stereo on both ends of the switch's travel so I'd always be able to find it without looking. However, I sometimes wish to have left-right reversed. If you'd like to try this, simply swap the leads on one of the "normal stereo" connections.

One final caveat: The left only/right-only mono positions are -6dB down, since only one half of the deck's headphone amp is driving your phones when the switch is in those positions.

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Audio Processor Circuit using IC SSM2045

This audio processor circuit features the SSM2045 IC which was developed specially for electronic music applications and the 741 opamp IC. The circuit is configured as a low pass filter with a DC voltage control for gain. The input signal is set to a working level of 150mVpp through the resistor R1.

Audio Processor Circuit Diagram :

The filter has 2 buffered outputs: the 2-pole output at pin 1 and 4-pole output at pin 8. Internally, the outputs are connected to 2 voltage-controlled-amplifiers (VCA). The R15 and R16 are connected to these outputs to achieve optimum offset and control voltage suppression. P4 is the volume control. The current that flows to the pins 15 and 16 should not go beyond the maximum of 250 µA. The balance of the two VCAs and the entire filter is being controlled be a voltage range of -250 mV to + 250 mV at pin 14. This voltage can be set by P2.

The input can be driven with source impedances up to a maximum of 200 Ω. With an input level of 0dBm, the VCA weakens by 6 dB. The bias current needed at pin 17 is between 120 µA and 185 µA. The cutoff frequency can be shifted between 20 Hz and 20 kHz with a variable voltage at pin 5. This can be varied through P1. The capacitor values were selected to give the filter its Butterworth characteristics.

The output current of the SSM2045 IC is converted to a voltage output by the 741 opamp. Any sybsequent circuit must be DC decoupled from IC2. The noise-voltage ration is about 80 dB.

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Simple Bass Treble Tone Control

The LM1036 is a DC controlled tone (bass/treble), volume and balance circuit for stereo applications in car radio, TV and audio systems. An additional control input allows loudness compensation to be simply effected. Four control inputs provide control of the bass, treble, balance and volume functions through application of DC voltages from a remote control system or, alternatively, from four potentiometers which may be biased from a zener regulated supply provided on the circuit.

Circuit diagram :

Bass Treble Tone Control Circuit Diagram

Each tone response is defined by a single capacitor chosen to give the desired characteristic.

Features:

• Wide supply voltage range, 9V to 16V
• Large volume control range, 75 dB typical
• Tone control, ±15 dB typical
• Channel separation, 75 dB typical
• Low distortion, 0.06% typical for an input level of 0.3 Vrms
• High signal to noise, 80 dB typical for an input level of 0.3 Vrms
• Few external components required

Note:

Vcc can be anything between 9V to 16V and the output capacitors are 10uF/25V electrolytic

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3 Transistor Audio Amp (80 milliwatt)

This circuit is similar to the one above but uses positive feedback to get a little more amplitude to the speaker. I copied it from a small 5 transistor radio that uses a 25 ohm speaker. In the circuit above, the load resistor for the driver transistor is tied directly to the + supply. This has a disadvantage in that as the output moves positive, the drop across the 470 ohm resistor decreases which reduces the base current to the top NPN transistor. Thus the output cannot move all the way to the + supply because there wouldn't be any voltage across the 470 resistor and no base current to the NPN transistor.

Circuit diagram :

3 Transistor Audio Amp Circuit Diagram

This circuit corrects the problem somewhat and allows a larger voltage swing and probably more output power, but I don't know how much without doing a lot of testing. The output still won't move more than a couple volts using small transistors since the peak current won't be more than 100mA or so into a 25 ohm load. But it's an improvement over the other circuit above.  In this circuit, the 1K load resistor is tied to the speaker so that as the output moves negative, the voltage on the 1K resistor is reduced, which aids in turning off the top NPN transistor. When the output moves positive, the charge on the 470uF capacitor aids in turning on the top NPN transistor.

The original circuit in the radio used a 300 ohm resistor where the 2 diodes are shown but I changed the resistor to 2 diodes so the amp would operate on lower voltages with less distortion. The transistors shown 2n3053 and 2n2905 are just parts I used for the other circuit above and could be smaller types. Most any small transistors can be used, but they should be capable of 100mA or more current. A 2N3904 or 2N3906 are probably a little small, but would work at low volume.

The 2 diodes generate a fairly constant bias voltage as the battery drains and reduces crossover distortion. But you should take care to insure the idle current is around 10 to 20 milliamps with no signal and the output transistors do not get hot under load.  The circuit should work with a regular 8 ohm speaker, but the output power may be somewhat less. To optimize the operation, select a resistor where the 100K is shown to set the output voltage at 1/2 the supply voltage (4.5 volts). This resistor might be anything from 50K to 700K depending on the gain of the transistor used where the 3904 is shown.

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Simple Sound Effects Generator

A Simple Sound Effects Generator Circuit uses a UM3561 IC to produce four different sound effects.

Circuit diagram :

Simple Sound Effects Generator Circuit Diagram

Notes:

Nothing too complicated here. The IC produces all the sound effects, the output at Pin 3 being amplified by the transistor. A 64 ohm loudspeaker can be substituted in place of the 56 ohm resistor and 8 ohm loudspeaker. The 2 pole 4 way switch controls the sound effects. Position 1 (as drawn) being a Police siren, position 2 is a fire engine sound, 3 is an ambulance and position 4 is a machine gun effect. The IC is manufactured by UMC and was available from Maplin electronics code UJ45Y. At the time of writing this has now been discontinued, but they have have limited stocks available.

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Car-Stereo LED Power (VU) Meter

This circuit senses AC audio voltage supplied to the car-radio loudspeakers and displays it as power using a LED bar graph, achieving at the same time an attractive visual effect. It is designed to cover common car-radio output power ranges, but can easily be modified to suit different needs. It is supplied from the 12 V car electrical system and is suitable for classical CC (Capacitor-coupled) as well as BTL (Bridge Tied Load) types of amplifier with no changes to the circuitry or connections at all. In fact, only the meaning of the LEDs changes — with BTL, the LED increments equal four times the CC value on the same load. CC-type amplifiers have the loudspeaker connected via a DC-decoupling capacitor at the output and ground (negative). BTL-type amplifiers, on the other hand, have the loudspeaker DC-coupled and ‘stretched’ between two equal, parallel, but phase-reversed outputs.

Project image :

Stereo LED Power (VU) Meter Image

The result compared to ‘CC’ is twice the voltage swing, hence quadrupling the power being fed to the same loudspeaker load. It is necessary to know to which of the two types this circuit is connected to only in order to correctly assign power levels (W) to the LEDs. CC-type have no DC voltage to ground at the outputs and return wires. The return wires are actually connected to the common ground (negative). BTL-type have approximately Vcc/2 at outputs and on the return wires too, explaining at the same time why no DC-decoupling capacitors are needed.

Circuit diagram :

Stereo LED Power (VU) Meter Circuit Diagram

The LM3915N integrated circuit used in this circuit has been the subject of numerous publications in this magazine so will not will not be discussed again. In this application, the two LM3915Ns are configured as a LED bar graph drivers (pin 9 connected to pin 3), The ICs share the same power supply section. The audio input signal is fed via network C1/C2, R1, R2 (C3/C4, R5, R6) to pin 5 of IC1 (IC2). Only positive half-waves are processed by the ICs. Internally, the buffered input voltage is compared using comparators to the voltages along a resistor ladder network.

The nominal +1.25 V reference source voltage (between pins 7 and 8) is applied across R3 (R7) to program the LED current. The programming current flows through R4 (R8) to achieve the desired reference voltage between pin 7 and ground. Here, only 2.0 V is developed, allowing this circuit to be used with low power amplifiers too. This voltage is applied to the ‘top’ of the on-chip resistor array (pin 6) and so determines the threshold at which the LED connected to the L10 output comes on. The other (low) side of the array (pin 4) is connected to ground. So, for an input voltage equal to or greater than the voltage at pin 6, all LEDs are on.

At input voltages below the threshold set up for the lowest LED (89.3 mV or –27dB below the top LED) all LEDs are off. In order to limit power dissipation of IC1 and IC2, the LED voltage is stepped down to +5 V using IC3, C6 and C7. Diode D1 protects the circuit against reversed polarity. If a ‘dot’ mode graph is preferred pins 9 of IC1 and IC2 should be left open circuit. Using the listed value for R1 (R5), the indicator range covers audio power levels of 10 W into 4 Ω (CC) or 40 W into 4 Ω (BTL). Each ‘lower‘ LED indicates half the power of the previous ‘higher’ LED Only R1 (R5) needs to be redimensioned for different power levels. The value can be calculated from R1 = [R2 √(PO ZL) / (k * VRefOut)] – R2 where PO = maximum output power to be indicated (LED D2 or D12) ZL = loudspeaker impedance R2= R6 VRefOut = 2.0 V k = constant; 2 for BTL, 1 for CC The condition √ (PO ZL ) / (kVRefOut) ≥ 1 must be met. A small printed circuit board has been designed to allow a stereo version of the power indicator to be built.

The board is cut in two to separate the channels. The boards may be assembled in a sandwich construction with three inter-board connections A-A’, B-B’ and C-C’ made in stiff wire. IC3 should be secured to a small heatsink (10 K/W). Rectangular-face LEDs are recommended for this circuit. If on the other and 3mm dia. LEDs are used, these may have to be filed down a bit to be able to fit them in a straight row. The connection to the car radio should not present any problems. The audio signal is taken from the (+) loudspeaker connector for each channel and ground. The power supply leads to the indicator circuit are connected in parallel with car radio power supply. At a supply voltage of 14.4 V, the maximum and quiescent current consumption of the circuit was measured at 171 and 22 mA respectively.

Parts List :

Resistors:

• R1,R5 = 22kΩ
• R2,R6 = 10kΩ
• R3,R7 = 820Ω
• R4,R8 = 470Ω

Capacitors:

• C1-C4 = 470nF, lead pitch 5mm
• C5,C6,C7 = 10µF 63V radial

Semiconductors:

• D1 = 1N4001
• D2-D21 = LED, 3mm dia. or rectangular-face
• IC1,IC2 = LM3915N-1 (National Semiconductor)
• IC3 = 7805

Miscellaneous:

• Heatsink for IC3 (10 K/W)

 

Author : R. Lali´c - Copyright : Elektor

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Microphone Preamplifier for Radio Amateurs

The technical demands on microphones used with radio equipment are not stringent in terms of sound quality: a frequency response from around 50 Hz to 5 kHz is entirely adequate for speech. For fixed CB use or for radio amateurs sensitivity is a more important criterion, so that good intelligibility can be achieved with-out always having to hold the microphone directly under your nose. Good micro-phones with extra built-in amplifiers can be bought, but, with the addition of a small preamplifier, an existing micro-phone will do just as well.

Circuit diagram :

Simple Microphone Preamplifier for Radio Amateurs Circuit Diagram

The project described here uses only a few discrete components and is very undemanding. With a supply voltage of between 1.5 V and 2 V it draws a current of only about 0.8 mA. If you prefer not to use batteries, the adaptor circuit shown, which uses a 10 kΩ resistor, three series-connected diodes and two 10 µF electrolytic smoothing capacitors, will readily generate the required voltage from the 13.8 V supply that is usually available. There is little that need be said about the amplifier itself. Either an ordinary dynamic microphone or a cheaper electret capsule type can be connected to the input. In the latter case a 1 kΩ  resistor needs to be connected between the 1.5 V supply volt-age and the positive input connection. The impedance of the microphone and of the

following stage in the radio apparatus are not of any great importance since the available gain of 32 dB (a factor of 40) is so great that only in rare cases does P1 have to be set to its maximum position. With a frequency range from 70 Hz to about 7 kHz, low distortion, and small physical size, the preamplifier is ideal for retrofitting into the enclosure of the radio equipment or into the base of a micro-phone stand.

In case you are concerned about our somewhat cavalier attitude towards distortion: for speech radio the ‘fi’ does not need to be ‘hi’. Quite the reverse, in fact: the harmonics involved in a few percent of distortion can actually improve intelligibility  it’s not a bug, it’s a feature!

Author : Ludwig Libertin - Copyright : Elektor

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Simple Automatic Loudness Control

( Simple add-on module Switchable "Control-flat" option )

In order to obtain a good audio reproduction at different listening levels, a different tone-controls setting should be necessary to suit the well known behaviour of the human ear. In fact, the human ear sensitivity varies in a non-linear manner through the entire audible frequency band, as shown by Fletcher-Munson curves. A simple approach to this problem can be done inserting a circuit in the preamplifier stage, capable of varying automatically the frequency response of the entire audio chain in respect to the position of the control knob, in order to keep ideal listening conditions under different listening levels. Fortunately, the human ear is not too critical, so a rather simple circuit can provide a satisfactory performance through a 40dB range.

Circuit diagram :

Simple Automatic Loudness Control Circuit Diagram

The circuit is shown with SW1 in the "Control-flat" position, i.e. without the Automatic Loudness Control. In this position the circuit acts as a linear preamplifier stage, with the voltage gain set by means of Trimmer R7. Switching SW1 in the opposite position the circuit becomes an Automatic Loudness Control and its frequency response varies in respect to the position of the control knob by the amount shown in the table below. C1 boosts the low frequencies and C4 boosts the higher ones. Maximum boost at low frequencies is limited by R2; R5 do the same at high frequencies.

Parts:

P1_________________10K   Linear Potentiometer (Dual-gang for stereo)

R1,R6,R8__________100K   1/4W Resistors
R2_________________27K   1/4W Resistor
R3,R5_______________1K   1/4W Resistors
R4__________________1M   1/4W Resistor
R7_________________20K   1/2W Trimmer Cermet

C1________________100nF   63V Polyester Capacitor
C2_________________47nF   63V Polyester Capacitor
C3________________470nF   63V Polyester Capacitor
C4_________________15nF   63V Polyester Capacitor
C5,C9_______________1µF   63V Electrolytic or Polyester Capacitors
C6,C8______________47µF   63V Electrolytic Capacitors
C7________________100pF   63V Ceramic Capacitor

IC1_______________TL072 Dual BIFET Op-Amp

SW1_____DPDT Switch (four poles for stereo)

Notes:

• SW1 is shown in "Control flat" position.
• Schematic shows left channel only, therefore for stereo operation all parts must be doubled except IC1, C6 and C8.
• Numbers in parentheses show IC1 right channel pin connections.
• R7 should be set to obtain maximum undistorted output power from the amplifier with a standard music programme source and P1 rotated fully clockwise.

Technical data:

Frequency response referred to 1KHz and different control knob positions:

Total harmonic distortion at all frequencies and 1V RMS output: <0.01%

Source :redcircuits

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Simple Color Organ Circuit

Three Lamp-Channels Output Built-in Electret Microphone

A simple, satisfactory Color Organ can be built with a handful of cheap components. This design features: no mains supply transformer, built-in microphone and three widely adjustable frequency bands obtained by means of very simple, passive filters for Bass, Middle and Treble.

Circuit diagram :

Simple Color Organ Circuit Diagram

Due to the very low current consumption of this circuit, the mains supply can be conveniently reduced with no heat dissipation by the reactance of C1; then rectified by D1 and D2 and clamped to 24V by the Zener Diode D3. The music diffused by the loudspeaker(s) of any type of media player, is picked-up by the built-in microphone and the resulting signal is greatly amplified by a two-stage transistor audio amplifier Q1 and Q2.

At the output of the second stage, the audio signal is filtered and split into three fully adjustable frequency bands by means of a simple (though effective) passive filter formed by P1, P2, P3, R7, R8, C6 and C7, thus avoiding the complexity of op-amp based active filters. Transistors Q3, Q4 and Q5 are the drivers for the Triacs D4, D5 and D6 respectively, but can be omitted if high sensitivity Triac devices are used.

Parts:

P1,P2,P3_____10K   Linear Potentiometers

R1_____470R   1/2W Resistor
R2_____100K   1/4W Resistor
R3_____1M   1/4W Resistor
R4_____22K   1/4W Resistor
R5_____220K   1/4W Resistor
R6_____15K   1/4W Resistor
R7_____1K5  1/4W Resistor
R8_____4K7  1/4W Resistor

C1_____330nF  400V Polyester Capacitor
C2_____470µF   35V Electrolytic Capacitor
C3,C4,C6_____100nF   63V Polyester or Ceramic Capacitors
C5_____1µF   63V Electrolytic Capacitor
C7_____4n7   63V Polyester or Ceramic Capacitor

D1,D2_____1N4007 1000V 1A Diodes
D3_____BZX79C24   24V 500mW Zener Diode
D4,D5,D6_____TIC206M  600V 4A TRIACs

Q1 to Q5_____BC547   45V 100mA NPN Transistors

MIC1_____Miniature Electret Microphone Capsule

SW1_____SPST Toggle Switch 250V 10-15A (See Notes)

PL1_____Male Mains Plug

SK1,SK2,SK3_____Female Mains Sockets

Notes :

• sing the Triac types suggested in the Parts List, each channel can drive several incandescent lamp bulbs, up to about 800W, but in this case a separate heatsink must be used for each Triac.
• Due to the absence of a mains transformer, avoid to connect this circuit to other appliances (e.g. to the output of an amplifier by means of a cable). Please use only the microphone enclosed into the main case to pick-up the music.
• For 110-120V mains operation, C1 value must be doubled: use two 330nF capacitors wired in parallel or one 680nF 250V capacitor. No further modification is required.
• SW1 must be a high voltage, high current switch, as it must withstand the total amount of current drawn by all bulbs wired to the three outputs of the circuit.

Warning! The device is connected to 230Vac mains, then some parts in the circuit board are subjected to lethal potential! Avoid touching the circuit when plugged and enclose it in a plastic or wooden box.

 

Source : redcircuits

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Valve Sound Converter

‘Valve sound’ is not just an anachronism: there are those who remain ardent lovers of the quality of sound produced by a valve amplifier. However, not everyone is inclined to splash out on an expensive valve output stage or complete amplifier with a comparatively low power output. Also, for all their aesthetic qualities, modern valve amplifiers burn up (in the full sense of the word!) quite a few watts even at normal listening volume, and so are not exactly environmentally harmless. This valve sound converter offers a cunning way out of this dilemma. It is a low cost unit that can be easily slipped into the audio chain at a suitable point and it only consumes a modest amount of energy.

A valve sound converter can be constructed using a common-or-garden small-signal amplifier using a readily-available triode. Compared to using a pentode, this simplifies the circuit and, thanks to its less linear characteristic, offers even more valve sound. For stereo use a double triode is ideal. Because only a low gain is required, a type ECC82 (12AU7) is a better choice than alternatives such as the ECC81 (12AT7) or ECC83 (12AX7). This also makes things easier for home brewers only used to working with semiconductors, since we can avoid any difficulties with high voltages, obscure transformers and the like:the amplifier stage uses an anode voltage of only 60 V, which is generated using a small 24 V transformer and a voltage doubler (D3, D4, C4 and C5).

Since the double triode only draws about 2mA at this voltage, a 1 VA or 2 VA transformer will do the job. To avoid ripple on the power supply and hence the generation of hum in the converter, the anode voltage is regulated using Zener diodes D1 and D2, and T1. The same goes for the heater supply: rather than using AC, here we use a DC supply, regulated by IC1. The 9 V transformer needs to be rated at at least 3 VA. As you will see, the actual amplifier circuit is shown only once. Components C1 to C3, R1 to R4, and P1 need to be duplicated for the second channel.

The inset valve symbol in the circuit diagram and the base pinout diagram show how the anode, cathode and grid of the other half of the double triode (V1.B) are connected. Construction should not present any great difficulties. Pay particular attention to screening and cable routing, and to the placing of the transformers to minimise the hum induced by their magnetic fields. Adjust P1 to set the overall gain to 1 (0 dB). The output impedance of 47 kΩ is relatively high, but should be compatible with the inputs of most power amplifiers and preamplifiers.

For a good valve sound, the operating point of the circuit should be set so that the audio output voltage is in the region of a few hundred millivolts up to around 1.5 V. If the valve sound converter is inserted between a preamplifier and the power amplifier, it should be before the volume control potentiometer as otherwise the sound will change significantly depending on the volume. As an example, no modifications are needed to an existing power amplifier if the converter is inserted between the output of a CD player and the input to the amplifier.

 

Author : Stefan Dellemann - Copyright : Elektor

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Laptop Audio Amplifier-IC LA 4440

This is the best IC LA 4440 Laptop Audio Amplifier circuit diagram, the audio output from the laptop’s built-in loudspeakers is low. A energy amplifier is needed to obtain a high volume. This is a simple circuit to amplify the laptop’s audio output. The circuit is made around energy amplifier IC LA 4440 (IC1) along with a couple of other components. LA4440 is really a dual funnel audio energy amplifier.

Circuit diagram :

Laptop Audio Amplifier Circuit Diagram

It’s low distortion over an array of low to high wavelengths with good funnel separation. Built-in dual channels enable it for stereo system and bridge amplifier programs. In dual mode LA4440 gives 6 w per funnel as well as in bridge mode 19- watt output. It’s ripple rejection of 46 dB. The audio result can be recognized by utilizing two 6-watt loudspeakers.

Connect hooks 2, 6 and ground of IC1 towards the stereo system jack which is combined with laptops. Assemble the circuit on the general-purpose PCB and enclose inside a appropriate cabinet. The circuit works off controlled 12V power supply. It’s suggested to make use of audio input socket within the circuit board. Make use of a proper warmth-sink for LA4440.

 

Copyright : EFY

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Guitar Effect Pedal Power

A small box is fitted to the rear of the amplifier providing a 9V output for the effect pedal. The amplifier section gets 9V through a pedal switch. This power output and guitar signal input lines are combined into a single unit with multi-way cable connecting points as shown in the following figure.

Circuit diagram :

Guitar Effect Pedal Power Circuit Diagram

The circuit can be divided into two sections: power supply and signal handling. The power supply section is built around transformer X1, regulators 7805 and 7905, bridge rectifier comprising diodes D1 through D4, and a few discrete components. The signal-handling circuit is built around two OP27 op-amps (IC3 and IC4). The power supply of about 9V for the effect pedals is derived from step-down transformer X1. MOV1 is a metal-oxide varistor that absorbs any large spike in mains power.  IC 7905 (IC1) is a -5V low-power regulator. By using a 3.9V zener diode (ZD1) at its ground terminal, you get -8.9V output. The same technique is also applied to IC 7805 (IC2)-a +5V regulator to get 8.9V. Use good-quality components and heat-sinks for the regulators. This supply is more than enough for the five effect pedals.

The greater the voltage drop across the regulator, the lower the output current potential. Resistors R1 and R2 provide a constant load to ensure that the regulators keep regulating. Capacitors C3 through C8 ensure that the supplies are as clean as possible. It is very important to use proper heat-sinks for IC1 and IC2. Otherwise, these could heat up.

Working of the circuit is simple. The input signal stage uses a basic differentiation amplifier to accept the incoming signal and a voltage follower to buffer the output to the power amplifier. The differential amplifier is built around IC3. It works by effectively looking at the signals presented to its inputs. If the input signals are of different amplitudes, IC3 amplifies the difference by a factor determined by R4/R3 (where R4=R6 and R3=R5). If the input signals have same amplitudes, these are attenuated by the common-mode rejection ratio (CMRR) of the circuit. The value of CMRR is determined by the choice of the op-amp the auxiliary components used and circuit topology. You can use standard resistors. With the values shown, you get an overall gain of unity.

The combination of resistor R7 and C13 serves as a passive low-pass filter, progressively attenuating unwanted high-frequency signals. The second op-amp (IC4) forms a simple voltage follower (its output follows its input), providing a low output impedance to drive into the standard power amplifier.  Assemble the circuit on a general-purpose PCB and fit it to the rear of an amplifier. The unit must be compact, yet robust. So use a very sturdy aluminium extrusion for the cabinet in order to neatly house the assembled PCB.

To ensure simple operation, there are only three connections to the unit. First, mains power is tapped from the transformer. The second lead carries the 9V output to the amplifier. The third is the guitar signal input at the five-way socket for connection to the effect pedal.

 

Author : Raj K. GoRKhali – Copyright : EFY

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20W Rangkaian Audio Amplifier TDA7240

Here is an audio amplifier based on the TDA7240 IC from ST Microelectronics. The LM1875 is a monolithic power amplifier offering very low distortion and high quality performance for consumer audio applications.

Circuit diagram :

20W Rangkaian Audio Amplifier  Circuit Diagram

This circuit of audio amplifier based IC TDA7240 can deliver 20 watts of audio output power into a 4ohm load. The IC has minimum external parts count and is available in the 7 pin compact Heptawatt package. The IC also has a lot of good features like loud speaker protection, short circuit protection, low noise, low distortion etc. The circuit can be operated from a 12V DC single power supply and this makes it very useful in car audio application.

Notes :

• Use 4 ohm, 20W speaker.
• S1 is the standby switch and S2 is the ON/OFF switch.
• LED D2 is a power ON indicator.
• give good cooling at TDA7240 IC.

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50W audio amplifier LM3876

LM3876 is a high performance audio power amplifier IC from National Semiconductors. The LM3876 can deliver 50watts of output power into an 8 ohm loudspeaker. LM3876 has excellent signal to noise ratio and has wide supply voltage range. Other features of LM3876 are output to ground short circuit protection, input mute function, and output over voltage protection, etc. Applications of LM3876 are component stereo, compact stereo, surround systems, self powered speakers, etc.

Circuit diagram :

50W audio amplifier Circuit Diagram

The 50 watt audio amplifier  circuit shown below is designed based on the application diagram from the data sheet of LM3876. Some modifications are made on the original circuit for improving the performance. The bipolar electrolytic capacitor C7 is the input DC decoupling capacitor. R4 is the input resistance. R2 & R1 and bipolar electrolytic capacitor C5 forms a feedback circuit. C2, C1 are filter/by-pass capacitors for the positive supply rail. C4 & C3 are the filters/by-pass capacitors for the negative supply rail. The feedback resistor R2 sets the gain of the amplifier. L1 provides high impedance at high frequencies so that R7 may decouple capacitive loads. R3 is the mute resistance which allows 0.5mA to be drawn from pin8 to turn the mute function OFF. S1 is the mute switch. Resistor R6 and capacitor C8 forms a Zobel network which improves the high frequency stability of the amplifier and prevents oscillations.

Notes :

• The LM3876 can be operated from a supply voltage range of +/-12V to +/-49V DC.
• I recommend +/-35V DC for powering the IC.
• LM3876 requires a proper heat sink.
• Quiescent current of LM3876 is around 70mA

Source : Circuits today

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60W Guitar Amplifier

Bass, Treble, Harmonic modifier and Brightness controls Output power: 40W into 8 Ohm and 60W into 4 Ohm loads

This design adopts a well established circuit topology for the power amplifier, using a single-rail supply of about 60V and capacitor-coupling for the speaker(s). The advantages for a guitar amplifier are the very simple circuitry, even for comparatively high power outputs, and a certain built-in degree of loudspeaker protection, due to capacitor C8, preventing the voltage supply to be conveyed into loudspeakers in case of output transistors' failure. The preamp is powered by the same 60V rails as the power amplifier, allowing to implement a two-transistors gain-block capable of delivering about 20V RMS output. This provides a very high input overload capability.

Circuit Diagram :

60W Guitar Amplifier Circuit Diagram

 

Amplifier parts:

R1__________________6K8    1W Resistor
R2,R4_____________470R   1/4W Resistors
R3__________________2K   1/2W Trimmer Cermet
R5,R6_______________4K7  1/2W Resistors
R7________________220R   1/2W Resistor
R8__________________2K2  1/2W Resistor
R9_________________50K   1/2W Trimmer Cermet
R10________________68K   1/4W Resistor
R11,R12______________R47   4W Wirewound Resistors

C1,C2,C4,C5________47µF   63V Electrolytic Capacitors
C3________________100µF   25V Electrolytic Capacitor
C6_________________33pF   63V Ceramic Capacitor
C7_______________1000µF   50V Electrolytic Capacitor
C8_______________2200µF   63V Electrolytic Capacitor (See Notes)

D1_________________LED    Any type and color
D2________Diode bridge   200V 6A

Q1,Q2____________BD139    80V 1.5A NPN Transistors
Q3_____________MJ11016   120V 30A NPN Darlington Transistor (See Notes)
Q4_____________MJ11015   120V 30A PNP Darlington Transistor (See Notes)

SW1_______________SPST Mains switch

F1__________________4A Fuse with socket

T1________________220V Primary, 48-50V Secondary 75 to 150VA
                  Mains transformer (See Notes)

PL1_______________Male Mains plug

SPKR______________One or more speakers wired in series or in parallel
                  Total resulting impedance: 8 or 4 Ohm
                  Minimum power handling: 75W

Circuit diagram :

Preamplifier Circuit Diagram

Preamplifier parts:

P1,P2______________10K   Linear Potentiometers
P3_________________10K   Log. Potentiometer

R1,R2______________68K   1/4W Resistors
R3________________680K   1/4W Resistor
R4________________220K   1/4W Resistor
R5_________________33K   1/4W Resistor
R6,R16______________2K2  1/4W Resistors
R7__________________5K6  1/4W Resistor
R8,R21____________330R   1/4W Resistors
R9_________________47K   1/4W Resistor
R10_______________470R   1/4W Resistor
R11_________________4K7  1/4W Resistor
R12,R20____________10K   1/4W Resistors
R13_______________100R   1/4W Resistor
R14,R15____________47R   1/4W Resistors
R17,R18,R19_______100K   1/4W Resistors

C1,C4,C5,C6________10µF   63V Electrolytic Capacitors
C2_________________47µF   63V Electrolytic Capacitor
C3_________________47pF   63V Ceramic Capacitor
C7_________________15nF   63V Polyester Capacitor
C8_________________22nF   63V Polyester Capacitor
C9________________470nF   63V Polyester Capacitor
C10,C11,C12________10µF   63V Electrolytic Capacitors
C13_______________220µF   63V Electrolytic Capacitor

D1,D2____________BAT46   100V 150mA Schottky-barrier Diodes (see Notes)

Q1,Q3____________BC546    65V 100mA NPN Transistors
Q2_______________BC556    65V 100mA PNP Transistor

J1,J2___________6.3mm. Mono Jack sockets

SW1,SW2___________SPST Switches

Notes:

• The value listed for C8 is the minimum suggested value. A 3300µF capacitor or two 2200µF capacitors wired in parallel would be a better choice.
• The Darlington transistor types listed could be too oversized for such a design. You can substitute them with MJ11014 (Q3) and MJ11013 (Q4) or TIP142 (Q3) and TIP147 (Q4).
• T1 transformer can be also a 24 + 24V or 25 + 25V type (i.e. 48V or 50V center tapped). Obviously, the center-tap must be left unconnected.
• D1 and D2 can be any Schottky-barrier diode types. With these devices, the harmonic modifier operation will be hard. Using for D1 and D2 two common 1N4148 silicon diodes, the harmonic modifier operation will be softer.
• In all cases where Darlington transistors are used as the output devices it is essential that the sensing transistor (Q2) should be in as close thermal contact with the output transistors as possible. Therefore a TO126-case transistor type was chosen for easy bolting on the heatsink, very close to the output pair.
• R9 must be trimmed in order to measure about half the voltage supply across the positive lead of C7 and ground. A better setting can be done using an oscilloscope, in order to obtain a symmetrical clipping of the output wave form at maximum output power.
• To set quiescent current, remove temporarily the Fuse F1 and insert the probes of an Avo-meter in the two leads of the fuse holder.
• Set the volume control to the minimum and Trimmer R3 to its minimum resistance.
• Power-on the circuit and adjust R3 to read a current drawing of about 30 to 35mA.
• Wait about 15 minutes, watch if the current is varying and readjust if necessary.

Technical data:

Sensitivity:
    35mV input for 40W 8 Ohm output
    42mV input for 60W 4 Ohm output
Frequency response:
    50Hz to 20KHz -0.5dB; -1.5dB @ 40Hz; -3.5dB @ 30Hz
Total harmonic distortion @ 1KHz and 8 Ohm load:
    Below 0.1% up to 10W; 0.2% @ 30W
Total harmonic distortion @ 10KHz and 8 Ohm load:
    Below 0.15% up to 10W; 0.3% @ 30W
Total harmonic distortion @ 1KHz and 4 Ohm load:
    Below 0.18% up to 10W; 0.4% @ 60W
Total harmonic distortion @ 10KHz and 4 Ohm load:
    Below 0.3% up to 10W; 0.6% @ 60W
Treble control:
    +9/-16dB @ 1KHz; +12/-24dB @ 10KHz
Brightness control:
    +6.5dB @ 500Hz; +7dB @ 1KHz; +8.5dB @ 10KHz
Bass control:
    -17.5dB @ 100Hz; -26dB @ 50Hz; -28dB @ 40Hz

 

Source : red circuits

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Stereo Peak Indicator

The circuit diagram shows a low-cost, fast responding, peak holding, audio level indicator.

The sensitivity is determined by preset P1, which (sort of) DC-biases the input of Schmitt-trigger gate IC1a to a level close to the switching threshold. When the negative peaks of the audio signal cause the output of the first Schmitt trigger gate to go high, the capacitor on the input of the second Schmitt trigger gate rapidly charges via diode D1. The charge can only disappear via the 1-Mohm resistor, R2, so a fast attack, slow decay is the result. In this way, even the fastest peaks will be caught and indicated by LED D2. Four NAND gates in a single 4093 package make a stereo version. A multiturn quality trimpot will ensure easy adjustment and stable function over time.

Circuit Diagram :

Stereo Peak Indicator Circuit Diagram

The circuit is based on a standard CMOS IC and will work from any supply voltage between 5 and 15 V.

Author : F. Jensen - Copyright : Elektor

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