Power amplifier electronic circuits-tube audio rf amplifiers

Electronic Amplifier Circuits-Power amplifier, audio amplifier designs and circuits

April 21st, 2008

Low cost Audio level meter circuit.

About the circuit.
An audio level meter is a must in the workbench of an amplifier specialist and if it this audio level meter circuit then it will be more fine.You will like this because of its simplicity and of course effectiveness.
The circuit depicted here is designed to get a steady frequency response over the audio frequency range.The circuit has an input sensitivity of 100mV to get a full scale deflection on the meter.Two common emitter amplifiers form the heart of this circuit.The preset R3 in the first stage can be adjusted to get a full scale deflection on the meter.For getting maximum AC voltage deflection the second stage is kept biased at half the supply voltage.Capacitors C1,C2 and C3 act as filters.The diode bridge will covert the signal at the collector of Q1 to a varying DC voltage and this voltage will be proportional to the input signal level.The meter will show this voltage as reading.That’s all about the circuit.

Circuit diagram & Parts list.



  1. This circuit will give only the instantaneous reading and peak readings will not be available.
  2. The calibration can be done in one step.Feed the input with a 1Khz 100mV peak to peak sine wave and adjust R3 to get a FSD on the meter.
  3. The circuit can be powered from  a 12 V DC supply.I recommend a 12V battery for a noise free operation.
April 21st, 2008

3Watt stereo ampliifer

About the circuit.

Here is a small but effective mini stereo amplifier circuit based on the MAX 7910 IC.The circuit can deliver a 3W power to a 4 Ohm load .The main feature is that the circuit can be operated from a single power supply.All these makes the circuit ideal for a mini box amplifier.Since only 3W is handled the IC doe snot need a heat sink .In addition the IC MAX 7910 has a built in  thermal overload protection which makes it quite difficult to be destroyed.

Circuit diagram & Parts list .



  1. Use a well regulated and filtered 5V DC power supply to power the circuit.
  2. For hand held applications a 6V battery with a IN 4007 diode in direction and  series to the  positive terminal of the battery can be used.The diode drops 0 .7 volts to give the IC ,the rated 5V supply.This is an adjustment for additional safety.
  3. The circuit can be assembled on a good quality Vero board.