Simple Hybrid Audio Amplifier Circuit

Here’s an amplifier circuit that based on the BUZ11 can be replaced by an IRFZ34N and an ECC83 can be used instead of the ECC88. In that case the anode voltage should be reduced slightly to 155 V. The ECC83 (or its US equivalent the 12AX7) requires 2 x 6.3 V for the filament supply and there is no screen between the two triodes, normally connected to pin 9. This pin is now connected to the common of the two filaments. The filaments are connected to ground via R5. If you’re keeping an eye on the quality, you should at least use MKT types for coupling capacitors C1, C4 and C7. Better still are MKP capacitors. For C8 you should have a look at Panasonic’s range of audio grade electrolyts. P1 is used to set the amount of negative feedback. The larger the negative feedback is, the flatter the frequency response will be, but the smaller the overall gain becomes. This is the figure of the circuit;

With P2 you can set the quiescent current through T2. We have chosen a fairly high current of 1.3 A, making the output stage work in Class A mode. This does generate a relatively large amount of heat, so you should use a large heat sink for T2 with a thermal coefficient of 1 K/W or better. For L1 we connected two secondary windings in series from a 2x18V/225 VA toroidal transformer. The resulting inductance of 150 mH was quite a bit more than the recommended 50 mH. However, with an output power of 1 W the amplifier had difficulty reproducing signals below 160 Hz. The distortion rose to as much as 9% for a signal of 20 Hz at 100 mW. To properly reproduce low-frequency signals the amplifier needs a much larger coil with an iron core and an air gap. This prevents the core from saturating when a large DC current flows through the coil.

22W Amplifier for 12V Power Supply Systems Circuit

Here’s a circuit for 22-W Amplifier circuit that is designed for or 12-V DC power supply Systems. There are many application for  this circuit,  such as in car audio  application. In car electrical power supply system, the 12V power supply will be provided by the host vehicle’s battery. The capacitor C3 is used to give ripple rejection, since noisy power supply voltage is common in automotive electrical system. This is the figure of the circuit; 

The power supply noise signal on car power supply is decoupled by the capacitors C2 and C1.  Smaller capacitor C2 is needed to decouple the high frequency noise, since the larger cap (C1) usually has high equivalent series inductance that prevent the high frequency noise  (such as glitch or spike) to be bypassed. The capacitors C5 couple the incoming audio signal to IC1 while decoupling static DC offset. For better bass response, this circuit prevent rolling off of the low audio frequencies by choosing a relatively large capacitance for small signal, 10μF capacitors. This circuit prevent power supply pop noise by muting the amplifier at the power-up. The mute input (pin 14) is fed by capacitor C6 and Resistor R1, giving delay on power-up which prevent  turn-on pop. This  R/C time constant gives about 1.4s delay to keep the output muted,  enough to make sure the amplifier reach the stable state after powered up.  About how this muting works, the amplifier will be ON if pin 14 has at least 8.5 V. The chip will remain in muted condition if the voltage at this pin is below 3.3V.  This input pin need very low current consumption, only about 100 pA for standby (muted)  and around 40 pA when active. The R1 values must be no larger than 100,000  Ω. The R1/C6 constant should be on the second order. If time constant is too short, the turn-on pop will still be heard, but too long  time constant will give unpleasant delay.

Complementary Pair Vertical Deflection Pre-Amp Circuit

This is a design circuit for Complementary Pair Vertical Deflection Pre-Amplifier circuit. This circuit is modification circuit of Vertical Deflection Pre-Amplifier for 100MHz scope. This circuit remove few resistor-capacitor combination from the original circuit. That components can be removed because they tweaked the response of the amplifier at high frequencies, so no problem. The second two transistors receive +2V from the two 1N4733 5.1V zener diodes. But the two 1N4733 5.1V zener diodes can be replaced with 10V zener. This is the figure of the circuit;

 

This circuit use a complementary pair of an npn and a pnp transistor. In other words coupling capacitors are not needed. This circuit has low output impedance about 2.6R. This circuit has small AC agin of 2.0, because of strong series-shunt feedback between the two transistors. The most of the bias current of the npn transistor, flows not through the emitter capacitor but through the feedback to ground. The basic amplifier is loaded by the feedback network.

10.7-MHz IF Amplifier Circuit

This is a design circuit for 10.7-MHz IF amplifier circuit. This circuit is used in many application such as cell phone base station receivers (final IF) and FM broadcast receivers. The ceramic filter that is used in this circuit is cheap and available in a variety of insertion losses and bandwidths. This circuit uses a 230-kHz bandwidth filter SFELA10M7GA00-B0 and the gain stage. This is the figure of the circuit;

 

The second figure shows the circuit response. The insertion loss of this circuit is 4 dB. However, actually the insertion loss is slightly more than 4dB. In the pass band, the slight nonlinearity  has more to do with the ceramic filter’s characteristics than with the op amp. The circuit’s impedances are different from a nominal load of 50 Ohm, so the response should be corrected. Actually, a 280-Ohm resistor and the 50-Ohm instrument as the load that is configured in series connection measures the response. The voltage divider in this circuit is used to compensate that effect.

Op Amp Based Sound Detector Circuit

This is a circuit that can be used for detecting sounds and providing an output signal when a sound is detected.  This output signal may be fed to another circuit that sets off an alarm when the signal is received.  This circuit is therefore useful in security applications. This is the figure of the circuit;

   
The circuit uses a condenser microphone to pick up sounds from the environment. This is a powered microphone, which makes it more sensitive than ordinary microphones. The microphone transforms the sound waves into an electronic signal that is fed to the 741 op amp. 
   
The 741 op amp in this circuit is configured as a single-supply inverting amplifier. Adjust R1 to maximize the sensitivity of your circuit.  C1 and C2 are used to block the DC component of the signals, so that only the AC component carrying the sound information reaches the output transistor Q1. Note that the output, which is taken from the collector of Q1, is inverted with respect to the output of the 741 amplifier.
 

Digital Voltmeter Circuit

This is a design circuit for digital voltmeter circuit. The integrated circuit ICL7107 is a 3-1/2 digit LED A/D convertor. It contains an internal voltage reference, high isolation analog switches, sequential control logic, and the display drivers. The auto-zero adjustment mechanism ensures zero reading for 0 volts input. The circuit is classic design and you can be sure that it will work fine. However, for better result, it is recommended to design a proper PCB for minimum voltage drift and noise. This is the figure of the circuit;

Connect the positive and negative probes PLG1 and PLG2 to two points of the electric circuit you would like to know their electric potential difference or simply voltage. You have to set the selector switch S2 to proper voltage range you expect those two points would have. To calibrate the volt-meter, use the potentiometer P1. Adjust it to read correct voltage on the display by connecting probes to a known voltage source. You may need to use another calibrated volt-meter in this case.

60W Guitar Amplifier Circuit
This is a circuit for the power amplifier, using a single-rail supply of about 60V and capacitor-coupling for the speaker. This is the figure of the circuit;

 

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 implements a two-transistor gain-block capable of delivering about 20V RMS output. This provides a very high input overload capability. 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. 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.

Part Amplifier:
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

Part Pre Amp:
1,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

Guitar Pre Amp Circuit

This is a circuit for guitar pre amp that has a few interesting characteristics that separate it from the “normal” – assuming that there is such a thing. This is simple but elegant design, that provides excellent tonal range. The gain structure is designed to provide a huge amount of gain, which is ideal for those guitarists who like to get that fully distorted “fat” sound. This is the figure of the circuit;

However, with a couple of simple changes, the preamp can be tamed to suit just about any style of playing. Likewise, the tone controls as shown have sufficient range to cover almost anything from an electrified violin to a bass guitar – The response can be limited if you wish (by experimenting with the tone control capacitor values), but I suggest that you try it “as is” before making any changes.

Milivolt Meter Circuit Using Op Amp LM11

This circuit is design for milivolt meter circuit. This circuit is using LM11. This circuit has requirements analogous to those discussed for the ammeter. This is the figure of the circuit;

In the most-sensitive position, the range resistor is zero and the input resistance equals R1. As voltage measurement is desensitized by increasing the range resistor, the input resistance is also increased, giving the maximum input resistance consistent with zero stability with the input open. Thus, at full-scale, the source will be loaded by whatever multiple of the noise current is required to give the desired open-input zero stability.

[Schematic circuit source: National Semiconductor Notes]

A Precision DC Amplifier Circuit with a 100 MHz Gain Bandwidth

This is a design circuit for precision of DC amplifier circuit. This circuit has reasonable recovery

(~7 μs) from a 100% overload; but beyond that, AC coupling to the fast amplifier causes problems. This circuit is based on LM11. This is the figure of the circuit;

Alone, the gain error and thermal feedback of the LH0032 are about 20 mV, input referred, for ±10V output swing. Adding the LM11 reduces this to micro volts. An ammeter should read zero with no input current and have no voltage drop across its inputs even with full-scale deflection. Neither should spurious indications nor inaccuracy result from connecting it to low impedance. Meeting all these requirements calls for a DC amplifier, and one in which both bias current and offset voltage are controlled.

[Schematic circuit source: National Semiconductor Notes]

50 W Amplifier Circuit Using Transistor

This is a design of circuit that is very rugged and reasonably power amplifier circuit that can be used for any audio applications. The circuit is designed such that most of the components are not critical and can be easily replaced by nearest values. This is makes it ideal to assemble from your electronics junk box. This is the figure of the circuit for the amplifier;

The operation of the amplifier is the amplifier produces 60W rms at 50V supply on a 8 Ohm load. The capacitor C1 controls low frequencies and capacitor C2 controls high frequencies. The circuit is basically a class B amplifier. The transistors 2N 3055 serves the function of driving the speaker. The other transistor functions as pre amplifiers for the driver stage. This is the basic scheme of the circuit. The maximum power level of amplifier can be set by adjusting the 500 Ohm POT connected with the BC107 transistor.

The are some notes for this circuit. The circuit can be powered using a 50 V DC power supply with 5A current rating. It is up to 60 V can be given to the circuit. Any way the power supply must be well regulated and filters to avoid noise. The amplifier is adjusts the 500 ohm POT to obtain optimum performance. Volume control can be attained by connecting a 10 K POT in series to the input of the amplifier.

3 W Mono Class-D Audio Power Amplifier Circuit

This is a design circuit for audio power amplifier. This circuit uses SA58672 as main controller in this circuit. This is the figure of the circuit;

The SA58672 is a mono, filter-free class-D audio amplifier which is available in a 9 bump WLCSP (Wafer Level Chip-Size Package) and 10-terminal HVSON packages. The SA58672 features shutdown control. Improved immunity to noise and RF rectification is increased by high PSRR and differential circuit topology. Fast start-up time and very small WLCSP package makes it an ideal choice for both cellular handsets and PDAs. The SA58672 delivers 1.7 W at 5 V and 800 mW at 3.6 V into 8 W. It delivers 3.0 W at 5 V and 1.6 W at 3.6 V into 4 W. The maximum power efficiency is excellent at 90 % into 8 W and 84 % to 88 % into 4 W. The SA58672 provides thermal and short-circuit shutdown protection.

[Circuit source: NXP Semiconductor Notes]

Wide Voltage Range 1.8 Watt Audio Power Amplifier Circuit with Short Circuit Protection

This is a design circuit for power amplifier using wide voltage range. This circuit is based on LM4951 single op-amp circuit. This is the figure of the circuit;

The LM4951A is an audio power amplifier designed for applications with supply voltages ranging from 2.7V up to 9V. The LM4951A is capable of delivering 1.8W continuous average power with less than 1% THD+N into a bridge connected 8Ω load when operating from a 7.5VDC power supply. Boomer audio power amplifiers were designed specifically to provide high quality output power with a minimal amount of external components. The LM4951A does not require bootstrap capacitors, or snubber circuits. The LM4951A features a low-power consumption active-low shutdown mode. Additionally, the LM4951A features an internal thermal shutdown protection mechanism and short circuit protection.

The LM4951A contains advanced pop & click circuitry that eliminates noises which would otherwise occur during turn-on and turn-off transitions. The LM4951A is unity-gain stable and can be configured by external gain-setting resistors.

[Schematic circuit source: National Semiconductor Notes]

High-Performance 56W Audio Power Amplifier Circuit with Mute

This is a circuit schematic for basic design of power amplifier circuit. This circuit is based on LM3876 as a controller and op amp this circuit. This is the figure of the circuit;

The LM3876 is a high-performance audio power amplifier capable of delivering 56W of continuous average power to an 8 load with 0.1% THD+N from 20Hz-20kHz. The performance of the LM3876, utilizing its Self Peak Instantaneous Temperature (°Ke) (SPiKe™) protection circuitry, puts it in a class above discrete and hybrid amplifiers by providing an inherently, dynamically protected Safe Operating Area (SOA). SPiKe protection means that these parts are completely safeguarded at the output against overvoltage, under-voltage, overloads, including shorts to the supplies, thermal runaway, and instantaneous temperature peaks. The LM3876 maintains an excellent signal-to-noise ratio of greater than 95dB (min) with a typical low noise floor of 2.0µV. It exhibits extremely low THD+N values of 0.06% at the rated output into the rated load over the audio spectrum, and provides excellent linearity with an IMD (SMPTE) typical rating of 0.004%.

[Circuit schematic source: National Semiconductor Notes]

RF Power Amp Bias Circuit

This is a design circuit for power amps bias circuit. This circuit can be used to temperature compensate the gate voltage of an LDMOS. The output voltage of this circuit is equal to twice the DS4303's VOUT plus the PNP's VBE. The doubled DS4303 voltage is a low temperature-coefficient voltage source. The PNP's VBE will change approximately +2mV/°C, providing temperature compensation for the LDMOS. This circuit can provide good temperature compensation for the LDMOS, assuming that the PNP is thermally coupled to the LDMOS. This is the figure of the circuit;


This circuit is based on LDMOS DS4303 from MAXIM. To calibrate this circuit, place the expected DS4303 output voltage on the VIN pin, and pull the Adjust signal low to trigger the DS4303 to update its output voltage. Once the DS4303 completes its update, measure the quiescent current using the current sense amplifier, and iterate until the proper bias is reached. The input to the DS4303 should be held static while it is converging to ensure it reaches the proper value.

[Circuit schematic source: MAXIM Application Notes]

SA58672 Small Class-D Audio Amplifier Circuit for Mobile Device

This is a circuit of SA58672 Small Class-D Audio Amplifier. This circuit is suitable for mobile device. It has maximum output power of 3.0 W for a 4ohm load and 1.7W for 8ohm load with power supply of 5V. If we uses 3.6 V power supply, the maximum output power is 900mW with 8ohm load. This is the figure of the circuit;


Using 9-bump Wafer Level Chip Scale Package (WLCSP), the SA58672UK save space in portable designs, because it measures only 1.66 x 1.71 x 0.6 mm.

This circuit produces better overall audio performance because it has improved RF rectification and immunity to noise. The SA58672UK is suitable for cellular handsets or wireless and other portable audio application because it has fast start-up time of 7 ms eliminates pop-on sounds.

[Schematic diagram source: NXP Application Note]

High-Side Current Sense Amplifier Coverts 4-20mA Signal to 0-5V

This is a circuit that can be used to convert a 4-20mA signal to a 0V to 5V analog voltage. It is ideal conversion to digital with an analog-to-digital converter (ADC). In this circuit, a current-sense amplifier (IC1) is used to monitor the loop current. To generate a ground-referenced output that ranges from 0V at 4mA to 5V at the full-scale loop current (20mA), a reference/op-amp/comparator device (IC2) is employed. This is the figure of the circuit;


Using the resistor values shown (R2-R6), the output of IC at pin 8 is approximately 6.25V at 20mA and 1.25V at 4mA. An output range of 0.05V to 5.045V is generated by IC2 that is configured as unity-gain difference amplifier. Beside that, IC2 comparator can be used to flag a pre-set loop current or monitor input voltage.

Using 1% resistors, this circuit will perform well. The worst-case output error is 5% based on Monte Carlo analysis. However, the performance with unmatched components was better than 1% at full-scale. The accuracy of this circuit is better than 1% across the operating range that can be done by compensating for the dominant error. [Circuit Schematic Source: maxim-ic.com]

The Big E Stereo Parabolic Microphone Circuit

This is a design circuit for a stereo amplifier for a high sensitivity stereo parabolic microphone. This circuit can be used for listening to distant sounds. Typical parabolic microphones are mono phonic, this unit has a stereo audio path that helps produce more realistic sounding audio. This is the figure of the circuit.


The mini condenser microphone converts sounds into an electrical signal. Resistor R1 provides bias for the condensor microphone's internal amplifier transistor. The 2N3906 PNP transistor acts as a low noise microphone input amplifier. The 10K gain potentiometer is used for adjusting the audio signal level. A stereo 10K audio taper potentiometer can be used for adjusting both channels simultaneously, or individual 10K trimmers can be used for fixed gain applications. The preamp output signal is fed into the 1458 op-amp, which boosts the audio to a level that is sufficient for driving an 8-ohm headphone or a tape recorder input. The 1458 amplifier stage is fixed gain (10X) in the inverting configuration, it drives the headphone speakers. Capacitor C9 provides DC isolation from the 1458 op-amp output, which sits at half of the supply voltage. Resistor R13 provides impedance protection for the op-amp output and reduces audio distortion when driving low impedance headphones. DC bias for the 1458 op-amps is set at half of the supply voltage by the R16/R17 voltage divider. Capacitors C13 and C14 filter the DC power supply for the op-amp stage. The DC is further filtered for the input preamp transistors through resistor R15 and capacitor C11. Diode D1 and resistor R18 protect the circuit from reverse battery polarity.

18W Amplifier Circuit With Audio Single Chip IC HA13118

This is a circuit diagram for power amplifier. This circuit is a design for mini audio amplifier that can generated power only in 18Watt. This audio amplifier circuit is control by single chip audio IC HA13118. This is the figure of the circuit.


This amplifier has main types is a amplifier bridges as the output lines isn’t grounded. This circuit is supplied the voltage for the power supply is in 8 – 18 VDC and the current circuit is at least 1 – 2 Amperes. The maximum output power amplifier is obtained with 18V power supply with a greater than 2 Amps and using 4 ohm impedance of speakers. Power supply has filtered for reducing the main noise impedance using regulated supply for reduced noise. This amplifier can operate using battery.

AM RF Amp for Internal Antenna Circuit

This is a circuit for amplifier antenna. This circuit is work based on transistor. This is the figure of the circuit.


Any NPN transistor can be used. The author used a 2N3904, but a 2N2222A should work just as well. A good, low noise transistor would be even better. Some radios only have three connections to their ferrite bar antenna: the antenna connection to the tuning capacitor, ground (two wires twisted together) and secondary (the smaller number of turns). In this case, treat the twisted wires as ground, and the secondary wire as the base connection to the transistor. The transistor will then receive its base bias from the radio. R1 changes with the supply voltage. If your radio is 9V, use 56K. If it is 6V, use 47k. If it is 3V, use 33k. The goal is to bias the collector of the transistor to one half the supply voltage. The schematic shown is for a negative ground radio. For a positive ground radio, substitute a PNP transistor.