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Basically, measure the input voltage and current, output voltage and current, and apply Ohm's Law.
Practically, you can apply a signal to an amplifier and measure its output. Then place a variable series resistor between the signal generator and adjust the resistor until the output drops to 50%. The resistor's value is the amp's input impedance, Zin.
While this will work OK at DC and audio frequencies, once you get to some hundreds of kilohertz and higher, you will need specialist equipment to measure Zin.
You might expect that you can put a variable resistor on the output and adjust the resistor until you get 50% of output. This will work with low-power amplifiers with substantial Zout.
Most audio amplifiers have *very low* Zout (less than an ohm), so trying this will probably blow the amplifier. You will need special test gear for (i) audio power amplifiers, even those in portable equipment, and (ii) anything above a few hundred kilohertz, as for Zin.
Wiki User
∙ 9y ago
Wiki User
∙ 11y agoHere comes help. The input impedance of an amplifier (load) works always together with the output impedance (source) of the device from where the audio voltage comes.
Scroll down to related links and look at "Input impedance - Wikipedia" and "Interconnection of two audio units".
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Input impedance of current shunt feedback amplifier?
The input impedance of a current shunt feedback amplifier is the open loop impedance of the amplifier divided by 1+(A*beta)
What are typical values of input impedance and outoput impedance of ce amplifiers?
Output of the power amplifier is smaller 0.1 ohms and input of the loudspeaker is more than 4 ohms.
What amplifier circuit is typically used as the input stage for an operational amplifier?
Differential amplifier ANSWER: A differential amplifier is an op amp. If any amplification is required a preamplifier is used mainly to cut the white noise and improve the input impedance
Why input impedance should be high for an amplifier?
The best way to answer this question might be to consider the consequences if the input impedance was low: with a low input impedance, (signifficant) current would start flowing, and the amplifier would draw energy from the signal sources. None of the typical signal sources is designed to deliver energy on its outputs (after all, this is where the amplifier itself comes in). It is certainly possible to think that some of these sources might be changed to deliver some energy, but this is not the case with present-time tuners, CD players, microphones, and so forth. Assuming that the energy supply was not the issue, just to ponder this theoretical scenario a little further, the fact that current would flow from the source to the amplifier would also make the signal more vulnerable to the characteristics of the cable that connects the two. The high impedance of an amplifier input draws no energy, thereby avoiding these issues. It is the amplifier's task to convert a very low energy, voltage-driven signal into an higher energy output signal (driving the speakers which themselves have a very low impedance). ---- The way I typically think about this is to consider connecting a load to a Thevenin equivalent circuit [1]. The voltage across the load is given by the voltage divider formula (Vload = Vsrc * Rload/(Rload+Rthevenin)). If there is a very low load impedance--this means the amplifier has a very low input impedance--most of the source voltage will drop over the Thevenin equivalent resistance. With a very high input impedance, however, the majority of the signal voltage will be transferred from the source to the load because in the above equation, if Rload >> Rthevenin, Vload is approximately equal to Vsrc. if an amplifier has low impedance input the f/b must be low impedance also which make it in practical to use. The hi impedance of a typical amplifier is because the input is one two diodes basically operating on it exponential curve. Making it virtual the same as the other diode. for a differential amplifier. Boltzmann constant will define the impedance of a single diode.
Why input impedance of operational amplifier is infinite?
Input impedance (Zin) is assumed to be infinite to prevent any current flowing from the source supply into the amplifiers input circuitry. Infinite Input impedance is one of the Ideal Characteristics of the Op-Amp. With an assumption of Infinite Input impedance, there is no Loading on the preceeding stage to the Op-Amp (i.e. Supply.) or The Op-Amp under test does not draw any current from the I/p Supply to it's internal Circuitry.
Input impedance of current shunt feedback amplifier?
The input impedance of a current shunt feedback amplifier is the open loop impedance of the amplifier divided by 1+(A*beta)
Input impedance of voltage amplifier?
In audio the input impedance of an amplifier is between 10 kiloohms and 20 kiloohms.
In a multistage amplifier input impedance is high and output impedance is low justify the statement?
no. input impedance is low & output impedance is high
What are the applications of fixed bias amplifier circuit?
low input impedance
Why a high input impedance?
A circuit (an amplifier) typically has a high input impedance so that it does not unduly load the input circuit. Any such load could cause distortion, and that is generally not desired.
What type of transformer configuration will you select to design a high input impedance and low output impedance amplifier?
main volage
Why the input resistance of opamp is high?
Because op amp consist differential amplifier and they posses high input impedance so that op-amp also posses high input impedance.
Why input resistance of voltage amplifier is infinity?
For the successful amplification of the input signal the opamp should have ideally infinite input impedance . It should act like a buffer amplifierBUFFER amplifier--------------------->1.input impedance infinity2.output impedance zerothe reason is thatAny signal source will have source impedancefor the signal not to get lost and dropped across source impedance we ideally insert infinite impedance in series with it which makes the whole drop across the infinite impedance but not across the sourcesimilarly at the output zero impedance is used where in no part of the signal should be left behind in the op amp as a drop
Why input impedance of any amplifier should very high?
To get all the audio voltage from a source to a target without loss you need voltage bridging, that is a relative low output impedance to a higher input impedance. Usualy the input impedance is at least ten times higher then the output impedance.An input impedance is called also a load impedance or an external impedance.An output impedance is called also a source impedance or an internal impedance.
What is bootstraping in darlington emitter follower?
Connecting a resistance btw the o/p and i/p of the amplifier to increase the i/p impedance is called bootstrapping..
What are typical values of input impedance and outoput impedance of ce amplifiers?
Output of the power amplifier is smaller 0.1 ohms and input of the loudspeaker is more than 4 ohms.
What amplifier circuit is typically used as the input stage for an operational amplifier?
Differential amplifier ANSWER: A differential amplifier is an op amp. If any amplification is required a preamplifier is used mainly to cut the white noise and improve the input impedance
