Dynamic microphone Amplifier for earphones

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I decided to make this circuit so that I could listen to faint noises. It is a simple two-stage transistor amplifier design. The circuit was designed to use the input from a dynamic microphone but I am sure that with some modifications it would be possible to use an electret microphone. The 2N3053 transistors used in the design don’t have a particularly high gain so other types could probably be used as long as they are NPN.
source: eleccircuit.com


Computer Microphone

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      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. original article soruse: eleccircuit.com



How to make 3V from one battery AA 1.5V

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How to make 3V from one battery AA 1.5V



LM4910 Stereo Headphone Amplifier

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Circuit description:    

      LM4910 belonging to the Boomer series of National Semiconductors is an integrated stereo amplifier primarily intended for stereo headphone applications. The IC can be operated from 3.3V ans its can deliver 0.35mW output power into a 32 ohm load. The LM4910 has very low distortion ( less than 1%) and the shutdown current is less than 1uA. This low shut down current makes it suitable for battery operated applications. The IC is so designed that there is no need of the output coupling capacitors, half supply by-pass capacitors and bootstrap capacitors. Other features of the IC are turn ON/OFF click elimination, externally programmable gain etc.

Circuit diagram:  

     Circuit diagram of the LM4910 stereo headphone amplifier is shown above.C1 and C2 are the input DC decoupling capacitors for the left and right input channels. R1 and R2 are the respective input resistors. R3 is the feed back resistor for left channel while R4 is the feed back resistor for the right channel. C3 is the power supply filter capacitor. The feedback resistors also sets the closed loop gain in conjunction with the corresponding input resistors.

The IC is available only in SMD packages and care must be taken while soldering. 
The circuit can be powered from anything between 2.2V to 5V DC. 
The load can be a 32 ohm headphone. 
Absolute maximum supply voltage is 6V and anything above it will destroy the IC. 
A logic low voltage at the shutdown pins shut downs the IC and a logic high voltage at the same pin activates the IC. Original aritcle sourse circuitsproject.com

Battery-powered Headphone Amplifier

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   Some lovers of High Fidelity headphone listening prefer the use of battery powered headphone amplifiers, not only for portable units but also for home "table" applications. This design is intended to fulfil their needs and its topology is derived from the Portable Headphone Amplifier featuring an NPN/PNP compound pair emitter follower output stage. An improved output driving capability is gained by making this a push-pull Class-B arrangement. Output power can reach 100mW RMS into a 16 Ohm load at 6V supply with low standing and mean current consumption, allowing long battery duration. The single voltage gain stage allows the easy implementation of a shunt-feedback circuitry giving excellent frequency stability.

Battery-powered Headphone Amplifier Circuit diagram
     For a Stereo version of this circuit, all parts must be doubled except P1, SW1, J2 and B1.  Before setting quiescent current rotate the volume control P1 to the minimum, Trimmer R6 to maximum resistance and Trimmer R3 to about the middle of its travel.  Connect a suitable headphone set or, better, a 33 Ohm 1/2W resistor to the amplifier output.  Switch on the supply and measure the battery voltage with a Multimeter set to about 10Vdc fsd.  Connect the Multimeter across the positive end of C4 and the negative ground.  Rotate R3 in order to read on the Multimeter display exactly half of the battery voltage previously measured.  Switch off the supply, disconnect the Multimeter and reconnect it, set to measure about 10mA fsd, in series to the positive supply of the amplifier.  Switch on the supply and rotate R6 slowly until a reading of about 3mA is displayed.  Check again the voltage at the positive end of C4 and readjust R3 if necessary.  Wait about 15 minutes, watch if the current is varying and readjust if necessary.  Those lucky enough to reach an oscilloscope and a 1KHz sine wave generator, can drive the amplifier to the maximum output power and adjust R3 in order to obtain a symmetrical clipping of the sine wave displayed. 

Technical data:

Output power (1KHz sinewave):
16 Ohm: 100mW RMS
32 Ohm: 60mW RMS
64 Ohm: 35mW RMS
100 Ohm: 22.5mW RMS
300 Ohm: 8.5mW RMS

Sensitivity: 160mV input for 1V RMS output into 32 Ohm load (31mW)
200mV input for 1.27V RMS output into 32 Ohm load (50mW)
Frequency response @ 1V RMS:
flat from 45Hz to 20KHz, -1dB @ 35Hz, -2dB @ 24Hz
Total harmonic distortion into 16 Ohm load @ 1KHz:
1V RMS (62mW) 0.015% 1.27V RMS (onset of clipping, 100mW) 0.04%
Total harmonic distortion into 16 Ohm load @ 10KHz:
1V RMS (62mW) 0.05% 1.27V RMS (onset of clipping, 100mW) 0.1%
Unconditionally stable on capacitive loads

Class-A Headphone Amplifier

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     This circuit is derived from the Portable Headphone Amplifier featuring an NPN/PNP compound pair emitter follower output stage. An improved output driving capability is gained by making this a push-pull Class-A arrangement. Output power can reach 427mW RMS into a 32 Ohm load at a fixed standing current of 100mA. The single voltage gain stage allows the easy implementation of a shunt-feedback circuitry giving excellent frequency stability.

     The above mentioned shunt-feedback configuration also allows the easy addition of frequency dependent networks in order to obtain an useful, unobtrusive, switchable Tilt control (optional). When SW1 is set in the first position a gentle, shelving bass lift and treble cut is obtained. The central position of SW1 allows a flat frequency response, whereas the third position of this switch enables a shelving treble lift and bass cut.
     Before setting quiescent current rotate the volume control P1 to the minimum, Trimmer R6 to zero resistance and Trimmer R3 to about the middle of its travel. 
Connect a suitable headphone set or, better, a 33 Ohm 1/2W resistor to the amplifier output. 
Connect a Multimeter, set to measure about 10Vdc fsd, across the positive end of C5 and the negative ground.  Switch on the supply and rotate R3 in order to read about 7.7-7.8V on the Multimeter display. 
Switch off the supply, disconnect the Multimeter and reconnect it, set to measure at least 200mA fsd, in series to the positive supply of the amplifier.  Switch on the supply and rotate R6 slowly until a reading of about 100mA is displayed.  Check again the voltage at the positive end of C5 and readjust R3 if necessary.  Wait about 15 minutes, watch if the current is varying and readjust if necessary.
P1          : 22K  Dual gang Log Potentiometer 
R1          : 15K 
R2          : 220K
R3          : 100K
R4          : 33K 
R5          : 68K 
R6          : 50K 
R7          : 10K 
R8,R9       : 47K 
R10,R11     : 2R2 
R12         : 4K7
R13         : 4R7
R14         : 1K2
R15,R18     : 330K
R16         : 680K
R17,R19     : 220K
R20,R21     : 22K
C1,C2,C3,C4 : 10µF/25V 
C5,C7       : 220µF/25V
C6,C11      : 100nF
C8          : 2200µF/25V
C9,C12      : 1nF
C10         : 470pF
C13         : 15nF
D1          : LED
D2,D3       : 1N4002 
Q1,Q2       : BC550C 
Q3          : BC560C  
Q4          : BD136   
Q5          : BD135   
IC1         : 7815
T1          : 15CT/5VA Mains transformer
SW1         : 4 poles 3 ways rotary Switch 
SW2         : SPST slide or toggle Switch

Stereo Amplifier Circuit Diagram with TDA7052

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BTL Stereo Amplifier Circuit Diagram with TDA7052



Amplifier Circuit 2W

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Amplifier description:

     This amplifier was designed to be self-contained in a small loudspeaker box. It can be feed by Walkman, Mini-Disc, iPod and CD players, computers and similar devices fitted with line or headphone output. Of course, in most cases you will have to make two boxes to obtain stereo. The circuit was deliberately designed using no ICs and in a rather old-fashioned manner in order to obtain good harmonic distortion behavior and to avoid hard to find components. The amplifier(s) can be conveniently supplied by a 12V wall plug-in adapter.Closing SW1 a bass-boost is provided but, at the same time, volume control must be increased to compensate for power loss at higher frequencies. In use, R9 should be carefully adjusted to provide minimal audible signal cross-over distortion consistent with minimal measured quiescent current consumption; a good compromise is to set the quiescent current at about 10-15 mA. To measure this current, wire a DC current meter temporarily in series with the collector of Q3.

Amplifier circuit diagram:

Amplifier circuit partlist:

R9----------100R-1/2W Trimmer Cermet
C1 ----------10µF-63V
C2 ----------10µF-63V
SW1---------SPST switch
SPKR--------3-5 Watt Loudspeaker


Mini Portable Guitar Amplifier

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Guitar Circuit description:

     This small amplifier was intended to be used in conjunction with an electric guitar to do some low power monitoring, mainly for practice, either via an incorporated small loudspeaker or headphones. The complete circuit, loudspeaker, batteries, input and output jacks can be encased in a small box having the dimensions of a packet of cigarettes, or it could be fitted also into a real packet of cigarettes like some ready-made units available on the market. This design can be used in three different ways: Loudspeaker amplifier: when powered by a 9V alkaline battery it can deliver about 1.5W peak output power to the incorporated loudspeaker.  Headphone amplifier or low power loudspeaker amplifier: when powered by a 3V battery (2x1.5V cells) it can drive any headphone set type at a satisfactory output power level or deliver to the incorporated loudspeaker about 60mW of output power. This configuration is useful for saving battery costs. Fuzz-box: when powered by a 3V battery (2x1.5V cells) and having its output connected to a guitar amplifier input the circuit will behave as a good Fuzz-box, showing an output square wave with marked rounded corners, typical of valve-circuits output when driven into saturation. 

Guitar amplifier circuit diagram:

Guitar amplifier partlist:
  • R1__________22K 1/4W Resistor
  • C1__________10µF 25V Electrolytic Capacitor
  • C2__________100nF 63V Polyester or Ceramic Capacitor
  • C3__________220µF 25V Electrolytic Capacitor
  • IC1_________TDA7052 Audio power amplifier IC
  • J1,J2_______6.3mm Stereo Jack sockets (switched)
  • SPKR_______8 Ohm Loudspeaker (See Notes)
  • B1_________9V PP3 Battery or 3V Battery (2 x 1.5V AA, AAA Cells in series etc.)
  • Clip for PP3 Battery or socket for 2 x 1.5V AA or AAA Cells

Technical data:

  • Max output power: 1.5W @ 9V supply - 8 Ohm load; 60mW @ 3V supply - 8 Ohm load
  • Frequency response: Flat from 20Hz to 20kHz
  • Total harmonic distortion @ 100mW output: 0.2%
  • Max input voltage @ 3V supply: 8mV RMS
  • Minimum input voltage for Fuzz-box operation: 18mV RMS @ 3V supply
  • Current consumption @ 400mW and 9V supply: 200mA
  • Current consumption @ 250mW and 9V supply: 150mA
  • Current consumption @ 60mW and 3V supply: 80mA
  • Quiescent current consumption: 6mA @ 9V, 4mA @ 3V supply
  • Fuzz-box current consumption: 3mA @ 3V supply

Crowbar Speaker Protection

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Crowbar circuits are so-called because their operation is the equivalent of dropping a crowbar (large steel digging implement) across the terminals. It is only ever used as a last resort, and can only be used where the attached circuit is properly fused or incorporates other protective measures.

A crowbar circuit is potentially destructive - if the circuitry only has a minor fault, it will be a major fault by the time a crowbar has done its job. It is not uncommon for the crowbar circuit to be destroyed as well - the purpose is to protect the device(s) attached to the circuit - in this case, a loudspeaker.

There's really nothing to it. A resistor / capacitor circuit isolates the trigger circuit from normal AC signals. Should there be enough DC to activate the DIAC trigger, the cap is discharged into the gate of the TRIAC, which instantly turns on ... hard. A TRIAC has two basic states, on and off. The in-between state exists, but is so fast that it can be ignored for all intents and purposes.

The BR100 DIAC (or the equivalent DB3 from ST Microelectronics) is rated for a breakdown voltage of between 28 and 36V - these are not precision devices. Needless to say, using the circuit with supply voltages less than around 40V is not recommended, as you will have a false sense of security. The supply voltage must be higher than the breakdown voltage of the DIAC, or it cannot conduct. Zeners cannot be used as a substitute for lower voltages - a DIAC has a negative impedance characteristic, so when it conducts, it will dump almost the full charge in C1 into the gate of the TRIAC. This is essential to make sure the TRIAC is switched into conduction.

The TRIAC is a common type, and may be substituted if you know the specifications. It's rated at 12A, but the peak current (non-repetitive) is 95A, and it only needs to sustain that until the fuse (or an output transistor) blows. A heatsink is preferred, but there is a good chance that the TRIAC will blow up if it has to protect your speakers, so it may not matter too much. The 0.47 ohm resistor is simply to ensure that the short circuit isn't absolute. This will limit the current a little, and increases the chance that the TRIAC will survive (albeit marginally). Feel free to use a BT139 if it makes you feel better - these are rated at 16A continuous, and 140A non-repetitive peak current.

The peak short circuit current will typically be about 90A for a ±60V supply, allowing ~0.2 ohms for wiring resistance and the intrinsic internal resistance of the TRIAC, plus the equivalent series resistance of the filter capacitors. That's a seriously high current, and it will do an injury to anything that's part of the discharge path. Such high currents are not advised for filter caps either, but being non-repetitive they will almost certainly survive.

Construction & Use

Apart from the obvious requirement that you don't make any mistakes, construction is not critical. Wiring needs to be of a reasonable gauge, and should be tied down with cable ties or similar. C1 must be polyester. While a non-polarised electrolytic would seem to be acceptable, the circuit will operate if the capacitor should dry out over the years. This means it will lose capacitance, and at some point, the crowbar may operate on normal programme material. This would not be good, as it will blow up your amplifier!

Make sure that all connections are secure and well soldered. Remember that this is the last chance for your speakers, so it needs to be able to remain inactive for years and years - hopefully it will never happen. The circuit doesn't have to be mounted in the amplifier chassis - it can be installed in your speaker cabinet. Nothing gets hot unless it operates, at which point no-one really cares - it just has to save the speakers from destruction once to have been worthwhile.

Remember that the crowbar circuit absolutely must never be allowed to operate with any normal signal. A perfectly good amplifier that triggers the circuit because of a high-level bass signal (for example) will very likely be seriously damaged if the crowbar activates. To verify that no signal can trigger it, you may want to (temporarily) use a small lamp in place of R2, and drive the amp to maximum power with bass-heavy material.

A speaker does not need to be connected. If the lamp flashes, your amp would have been damaged. If this occurs, you may want to increase the value of C1. Note that bipolar electrolytics should never be used for C1, because they can dry out and lose capacitance as they age. This could cause the circuit to false-trigger.
Origianl article sourse learningelectronics.net

70 Watt Guitar Amplifier

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Guitar Amplifier description:

Guitar Amplifier parts list:

R1______________18K 1/4W Resistor
R2_______________3K9 1/4W Resistor
R3,R6____________1K 1/4W Resistors
R4_______________2K2 1/4W Resistor
R5______________15K 1/4W Resistor
R7______________22K 1/4W Resistor
R8_____________330R 1/4W Resistor
R9,R10__________10R 1/4W Resistors
R11,R12_________47R 1/4W Resistors
R13_____________10R 1W Resistor
C1_______________1µF 63V Polyester Capacitor
C2_____________470pF 63V Polystyrene or Ceramic Capacitor
C3______________47µF 25V Electrolytic Capacitor
C4______________15pF 63V Polystyrene or Ceramic Capacitor
C5_____________220nF 100V Polyester Capacitor
C6_____________100nF 63V Polyester Capacitor
 D1,D2,D3,D4___1N4148 75V 150mA Diodes 
Q1,Q2________BC560C 45V 100mA Low noise High gain PNP Transistors
Q3,Q4________BC556 65V 100mA PNP Transistors
Q5___________BC546 65V 100mA NPN Transistor
Q6___________BD139 80V 1.5A NPN Transistor
Q7___________BD140 80V 1.5A PNP Transistor
Q8__________MJ2955 60V 15A PNP Transistor


Mosfet Audio Amplifier 25W

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General description:

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 in series with Q8 Drain) with no input signal. A correct grounding is very important to eliminate hum and ground loops. Connect in the same point the ground sides of R1, R4, R9, C3 to C8. Connect C11 at output ground. Then connect separately the input and output grounds at power supply ground.

Amplifier circuit diagram:

25 Watt Amplifier

Part list:

R1,R4 = 47K 1/4W Resistors
R2 = 4K7 1/4W Resistors
R3 = 1K5 1/4W Resistors
R5 = 390R 1/4W Resistors
R6 = 470R 1/4W Resistors
R7 = 33K 1/4W Resistors
R8 = 150K 1/4W Resistors
R9 = 15K 1/4W Resistors
R10 = 27R 1/4W Resistors
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 45V100mA Low noise High gain PNP Transistors
Q6 = BD140 80V 1.5A PNP Transistor
Q7 = BD139 80V 1.5A NPN Transistor
Q8 = IRF532 100V 12A N-Channel Hexfet Transistor
Q9 = IRF9532 100V 10A P-Channel Hexfet Transistor

Power supply circuit diagram:

Part list:

R1 = 3K3 1/2W Resistor
C1 = 10nF 1000V Polyester Capacitor
C2,C3 = 4700µF 50V Electrolytic Capacitors
C4,C5 = 100nF 63V Polyester Capacitors
D1 200V 8A Diode bridge
D2 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


Detail of subwoofer

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Variations in the anatomy of a subwoofer dramatically changes their performance characteristics. An increase in voicecoil size coupled with a stronger cone material yields a higher power handling and increased output. By combining quality materials with Rockford’s proprietary acoustic technologies, our subwoofer lineup is sure to meet your system’s demands.

Basket - Also referred to as the frame or chassis, this is the skeletal system of the speaker. Here to keep everything in its place.

Spider - Second part of the speakers suspension, connects the cone and voice coil to the basket and controls the travel of the cone assembly.

Voice Coil - The brains of the operation, directing the force from the magnet to push or pull based on the applied electrical signal.

Surround - First part in the speakers suspension, attached to the cone to maintain the centering of the voice coil in the magnetic gap.

Cone - A.K.A the diaphragm, this is the voice of the speaker. Shape and material dramatically change tonality.

Magnet - The heart of speaker, creating the force to push and pull cone assembly. Size, material, and design may differ, depending on performance goals.
Original sourse article rockfordfosgate.com

MAX98500 Amplifier circuit 1x2.2W

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MAX98500 general description:

The MAX98500 is a high-efficiency Class D audio amplifier that features an integrated boost converter, to deliver a constant output power over a wide range of battery supply voltages. The boost converter operates at 2MHz, requiring only a small (2.2µH) external inductor and capacitor. The automatic level control has a battery tracking function that reduces the output swing as the supply voltage drops, preventing collapse of battery voltage. The amplifier has differential inputs and an internal fully differential design. The MAX98500 also features three gain settings (6dB, 15.5dB, and 20dB) that are selectable with a logic input. The MAX98500 is available in a small, 0.5mm pitch 16-bump WLP package (2.1mm x 2.1mm). It is specified over the extended -40°C to +85°C temperature range.

MAX98500 applications:

Active Speaker Accessories
Cell Phones
GPS Devices
Mobile Internet Devices
Data Sheet

MAX98500 features:

Boosted Class D Output
Integrated Automatic Level Control
Output Power
2.2W into 8Ω, 10% THD+N
1.7W into 8Ω, 1% THD+N
Wide 2.5V to 5.5V Supply Voltage Range
Undervoltage Lockout Protection
High Total Efficiency of 87%
High Step-Up Switching Frequency (2MHz)
Active Emission Limiting for Low EMI 

MAX98500 circuit diagram:

MAX98500 circuit diagram


LA3600 Equalizer 5 band

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  • Portable component stereos, tape-recorders, radio-cassette recorders, car stereos.


  • On-chip one operational amplifier.
  • 5-band graphic equalizer for one channel can be formed easily by externally connecting capacitors and variable resistors which fix fo (resonance frequency).
  • Series connection of two LA3600’s makes multiband (6 to 10 bands) available.
  • Highly stable to capacitive load.

LA3600 Circuit diagram:

LA3600 Circuit diagram
 LA3600 pcb:
LA3600 pcb