This is the circuit diagram of 24 Watt class A linear audio amplifier, built and tested by Marc Klynhans from South Africa. The supply voltage can be between 34V and 46V and the quiescent current should be set to 1.7A measured through R25 (a voltage of 0.75V must be measured over R25 for a quiescent current of just under 1.7A). R23 is a trimmer and must be set to maximum resistance (10kOhm) when powering up. Then the resistance of R23 must be decreased until the the quiescent current is achieved. If the amplifier is mounted on a big enough heatsink ( 0.6K/W at most) then the amplifier is very safe from thermal runaway. Intelligence must be used when choosing power and voltage ratings of resistors and capacitors.

24W Audio Amplifier (Class A) Specifications:

• 24W Class A into 8 Ohm
• 100mHz – 100kHz flat
• 305mV input for 24W into 8 Ohm (33dB gain)

Dynamic microphones are versatile and ideal for general-purpose use. They use a simple design with few moving parts. They are relatively sturdy and resilient to rough handling. They are also better suited to handling high volume levels, such as from certain musical instruments or amplifiers. They have no internal amplifier and do not require batteries or external power.

Schematic diagram:

Circuit Notes:

• This dynamic microphone amplifier circuit has a total gain of 200 times.
• If you use 200? microphones R4 must be 220? and C1 is 4.7uF.
• For the best performance, use metal film resistor, MKM type for unpolar capacitor and tantalum type for bipolar capacitor. Use stabled and regulated power supply.

With a 3mVpp input signal the output will be 800mVpp. The maximum output voltage was 10Vpp when the input is 50mVpp. The frequencies domain is between 50Hz and 100KHz.

There are possible alternative input stage transistors, the Toshiba 2SA970BL and 2SC2240BL, which appear to be good substitutes for the Hitachi 2SA1085E and 2SC2547E. The ‘BL’ suffix is the high gain group. Alternatives for the Sanyo 2SC2911 and 2SA1209 are the Toshiba 2SC3423 and 2SA1360.

This 70W power amplifier is designed for quality rather than quantity, and if much higher power is really needed there are other more suitable design approaches.

This is an awesome amplifier circuit, and this is the older version?(MJR7-Mk3). There is new version released (MJR7-Mk5) for better quality and performance, just go to THIS PAGE for complete circuit explanation.

This circuit is quite simple but will give you high quality audio output. Take a note that above diagram designed for single input and single output (mono system). For stereo system, you need to build two similar circuits.

The input stage is an LF351 op amp which provides most of the open loop gain as well as stabilizes the quiescent dc voltage. This feeds a level shift stage which references the voltage swing to the (-) rail. The transconductance stage is a darlington, to improve high-frerqency linearity. The 2SC2344 by itself has a rather large collector-base capacitance which is voltage dependent. The MPSA42 presents this with a low-z and has a C(ob) of only a few pf that is effectively swamped by the 33pF pole-splitting cap. The stage is supplied by the 2SA1011 active load (current source) which is about 20 ma. The current to the stage is limited by the 2N3094 to about 70 ma under worst case.

The output is a full complementary darlington with paralleled outputs. Although you could “get away with” only one if only 8 ohm easy-to-drive loads are used, this is not recommended. The use of parallel devices increases the ability to drive reactive loads (which can pull a significant current while the voltage waveform crosses zero and puts a high voltage and a high curent across the transistor simultaneously), gives the amp a higher damping factor, and reduces the maximum current each transistor has to supply to peaks (remember, the gain of a power transistor drops as the current increases).

Compensation is two-pole and one zero. The op-amp’s pole and the pole generated by the 33pf cap and the 470 ohm bias resistor of the MPSA42 dominate. (the 33pF gets multiplied by the stage gain.) The 22 pf feedback capacitor provides lead compensation, and is taken from the output of the tranconductance stage rather than the output itself. In this way, the phase lag introduced by the output transistors is not seen by the high-frequency feedback. This intorduces a closed-loop pole which limits the high-frequency response. The two compensation capacitors must be type 1 creamic (NPO) or silver mica – with ZERO voltage coefficient.

The 100W RMS audio amplifier circuit was designed to run 2 channels off a +/- 55 volt unregulated supply, reducing to +/- 48 volts under full load. It used a 40-0-40 volt, 5 amp toroid transformer, a bridge rectifier, and 10,000 uf of filter cap per side. If a standard EI transformer is used, a 6-amp rated unit should be used. With this power supply, it produces 100 watts continuous, both channels driven into 8 ohms resistive with no clipping. Dynamic headroom is about a db and a half. For more headroom, unloaded voltages to +/- 62 volts can be used with no circuit modification.

Read detail explanation about this 100W RMS audio amplifier HERE
Download large schematic diagram in PDF format HERE

This amplifier can be used for practically any application that requires high power, low noise, distortion and excellent sound. Examples would be Sub-woofer amp, FOH stage amplifier, One channel of a very high-powered surround sound amplifier etc.

For detail explanation about how this circuit works include the large schematic diagram, power supply schematic diagram and complete component listing, download this complete article

This is the scheme diagram of 20 Watt stereo audio amplifier which use dual IC TDA2005, one IC for left channel and the another one for right channel. Each IC will give you 20 watt output, so the output will be 2×20 Watt. The supply voltage for this circuit is 8VDC to 18VDC, use regulated power supply for better audio output performance.

Use a good quality transformer (of course it wiil be more expensive) to get less noise. It will be another good way to use a sufficient battery to power the circuit. Keep the supply wires as short as possible. Input source should be isolated from the external noises too. It is recommended to use coaxial cable to connect the input audio.

Bottom PCB Layout:

Top PCB Layout and Component Placement:

20 Watt Stereo Audio Amplifier Technical Data:

• Performance of TDA2005M: (for this circuit); At 14.4 V supply voltage: 2 x 20 watts (stereo) into 4 Ohms.
• Distortion: Approx. 0.2% at 4 Watts into 4 ohm load.
• Frequency Range: Approx. 20 Hz to 22 KHz.
• Input Sensitivity: Approx. maximum 150 mV rms.
• Power supply: + 8 to 18 volts, approx. maximum 3.5 Amps per channel.

This is 20 watt audio amplifier circuit design which use IC LM1875 as main component. This circuit is simple and very easy to built. For stereo channel, you need to build the two same circuits which will amplify the both of audio channels (right and left channel). Dual polarity / symmetrical power supply required for this kind of amplifier.

The LM1875 is a monolithic power amplifier offering very low distortion and high quality performance for consumer audio applications.

The LM1875 delivers 20 watts into a 4 ohm or 8 ohm load on 25V supplies. By using an 8 ohm load and 30V supplies, over 30 watts of power may be delivered. The amplifier is designed to operate with a minimum of external components. Device overload protection consists of both internal current limit and thermal shutdown.

The LM1875 design takes advantage of advanced circuit techniques and processing to achieve extremely low distortion levels even at high output power levels. Other outstanding features include high gain, fast slew rate and a wide power bandwidth, large output voltage swing, high current capability, and a very wide supply range. The amplifier is internally compensated and stable for gains of 10 or greater.

Download LM1875 datasheet for 20 Watt audio amplifier reference project:

LM1875 Datasheet

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