Picture of Voltage Amplifier
A voltage amplifier in simplest form is any circuit that puts out a higher voltage than the input voltage.  When you are forced to work with a set amount of voltage, these amplifiers are commonly used to increase the voltage and thus the amount of power coming out of a circuit. This is useful for reading and adapting small signals such as boosting an audio signal before sending it on its way to speakers. The voltage amplifier is a form of the common emitter amplifier, which relies on the transistor; the amplification of voltage is dependent on the ratio of resistors on the collector and emitter of this transistor.

The following materials are for an amplifier with a gain of 10. If you want to increase or decrease this factor, refer to step 2.


To build this circuit, you will need the materials listed below. Names of specific instruments used in this particular circuit are included in parentheses. 

 - function generator (BK Precision 4011A 5MHz Function Generator)
 - breadboard (Global Specialties Proto-Board PB-503)
 - DC power supply (15V, included in our breadboard) 
 - transistor (Q1 2N3904)
 - capacitor - 100nF
 - resistors - 56 kOhm, 5.6 kOhm, 6.8 kOhm, 680 Ohm

If you are using this circuit for practical purposes, you can use any DC power supply you desire; keep in mind that your output voltage can not be larger than the voltage provided by this DC power supply. Therefore I would recommend power supplies in the range of 9 to 15V DC. The sine input from the function generator is simply the input that you wish to be amplified. 

Additionally, you will likely want something to read or use the output voltage produced by this circuit, depending on your reasons for wanting to build a voltage amplifier. If you are simply looking to investigate the circuit, an oscilloscope can be used to read the output voltage.

Again, this circuit has an voltage gain of 10. For different values of gain, different resistors will be needed (see step 2). 
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DearN1 month ago

Hi, I would like to amplify a 100-200 mv pulse to 5v DC. The frequency of the pulse would vary between 20-600 per second. At lover frequency the pulse is 100-200 mv, So I would like to amplify it to 5 volt. But at higher frequency the pulse goes upto 30-50 volts. So I would like to maintain the pulse to 5 volts at all frequencies So I need the schematics for it.

allochthon made it!5 months ago

I just built this circuit to amplify a control voltage signal ( for a synthesizer) from a reference of 0V to 0.58V, and it was totally successful. However, that input CV voltage changes depending on the note (i.e., voltage) being sent. What this circuit does not do is change output voltage relative to input voltage. The output stays at ~0.58V no matter what the voltage in. Ideally, the voltage out would maintain that 0.58V increase for any input voltage (e.g., 1V = 1.58V, 2.36V = 2.92V, etc.) Any suggestions of the type of circuit that would do this, or if this circuit can be modified to do so?

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randoman2219 months ago

like this: alt+m=µ. then, just add cap. f. :)

halamka1 year ago

15 mhz --- then switch to grounded base

the emitter resistance is .025 / Ic ?? seems to make sense --- Va = Rc/Re = 5000/25 = 200 --- Carl Stancil is on facebook

Dear! if i replace this transistor with 2SC5200, what will be the maximum frequency that i can get from this circuit. your reply will be very helpful for me.
TeslaRox1 year ago
Will this be a good enough bump up in power to drive a Flyback transformer?
crudders1 year ago
Could you modify this to show the effect of adding an emitter bypass capacitor as well ?
Nice electronics 101 'Ible.