would it be possible to amplify a signal with this resistor circuit?


i put 'signal in/out' because i mean, if any works.

the theory question is basically, this circuit would present a voltage divider, so if a signal comes in at v2/v1, would this voltage result in a change in the voltage at v1/v2 , and in this configuration (or an alternate resistor organization) would it be possible to result in an amplification of the signal?

 

Nope. At signal frequencies (i.e., above the cutoff frequencies imposed by the coupling capacitors), the gain is essentially the voltage divider action of the top two resistors. It will actually be less due to the interaction of the bottom resistor with the output impedance of the signal source, but if that impedance is low enough in relation, that can be neglected.

Don't try to spitball the analysis -- actually analyze the circuit.

 

Nope. At signal frequencies (i.e., above the cutoff frequencies imposed by the coupling capacitors), the gain is essentially the voltage divider action of the top two resistors. It will actually be less due to the interaction of the bottom resistor with the output impedance of the signal source, but if that impedance is low enough in relation, that can be neglected.

Don't try to spitball the analysis -- actually analyze the circuit.

i still don't know how to do that

 

Here is a simulation of the circuit. It does not amplify.



Remove the .txt extension if you want to use the plot settings file (Passive_Attenuator.plt) in LTspice

 

You can amplify a signal without active components using a transformer.

 

You can amplify a signal without active components using a transformer.

Respectfully - I disagree.

If you have a 500mV signal at 2W you can transform that voltage (and lets assume 100% efficiency) if you transform that voltage from 500mV to 1V you still get 2W. The voltage is higher but the volume remains the same. The amperage gets cut in half. Again, in a perfect world.

10V @ 10A is 100W. Transform that to 20V it's 5A. And that still works out to 100W.

 

Respectfully - I disagree.

If you have a 500mV signal at 2W you can transform that voltage (and lets assume 100% efficiency) if you transform that voltage from 500mV to 1V you still get 2W. The voltage is higher but the volume remains the same. The amperage gets cut in half. Again, in a perfect world.

10V @ 10A is 100W. Transform that to 20V it's 5A. And that still works out to 100W.

If amplification means increasing the power, then that is not possible because it defies the law of conservation of energy.

 

You can amplify a signal without active components using a transformer.

To change the voltage of a signal using a transformer, would you need to overcome the resistance of the inductors, meaning there would be a threshold minimum voltage to pass the signal?

when initially thinking about this resistor line and wondering if there was a way to amplify using only resistors, i was looking at common-base amplifiers. These amplifiers are good at taking weak small signals and increasing the voltage of the signal (according to the description i read on the net) so that it can be passed to another form of amplifier for power amplification. So, would a transformer work in this kind of way as well, or would it be better suited for an already quite powerful signal?

 

define what is that you wish to gain... usually amplification is referring to voltage gain Av=Vo/Vi. this ignores any currents, so transformer can be used to increase AC voltage...
similarly it can also be used to increase output current but not both voltage and current at the same time. to increase both, means increasing power and energy needs to come from somewhere - batteries or PSU

 

in simple single transistor amplifier, transistor works as variable resistor which is part of voltage divider.

so maybe try replacing transistor with some other resistor that can change value. for example use photoresistor or carbon microphone etc. and drive it with something suitable.

 

You can amplify a signal without active components using a transformer.

NO!!! You CAN NOT "AMPLIFY" A SIGNAL WITH A TRANSFORMER!!! What you CAN DO is increase the voltage, AND match the output to an external load impedance ! THAT is entirely possible,!
HOWEVER, if we accept the standard definition of the term "amplify" to mean "increase the power level" of the signal, that action MUST include the addition of POWER from an external source. Certainly there are tricks to mislead those who do not fully understand what amplification actually is.

Of course, POWER TRANSFER to aload can be improved by correct impedance matching, but that does not meet the definition of Amplification.

There does exist the possibility that some writer has decided that the meaning is different, for reasons that we are not given.


The unfortunate reality is that WISHING SOMETHING WERE TRUE DOES NOT MAKE IT TRUE!!! This applies no matter how intense the result is wished for.
ACTUALLY, that reality has saved humanity from awhole lot of serious problems. BUT that is off topic for this discussion.

 

NO!!! You CAN NOT "AMPLIFY" A SIGNAL WITH A TRANSFORMER!!! What you CAN DO is increase the voltage, AND match the output to an external load impedance ! THAT is entirely possible,!
HOWEVER, if we accept the standard definition of the term "amplify" to mean "increase the power level" of the signal, that action MUST include the addition of POWER from an external source. Certainly there are tricks to mislead those who do not fully understand what amplification actually is.

Of course, POWER TRANSFER to aload can be improved by correct impedance matching, but that does not meet the definition of Amplification.

There does exist the possibility that some writer has decided that the meaning is different, for reasons that we are not given.


The unfortunate reality is that WISHING SOMETHING WERE TRUE DOES NOT MAKE IT TRUE!!! This applies no matter how intense the result is wished for.
ACTUALLY, that reality has saved humanity from awhole lot of serious problems. BUT that is off topic for this discussion.

in my original post, i showed a voltage divider. what percent of change in v2 would occur from a change in v1?

 

If you look at Papabravo's simulation in post #4 you can see that with the resisor values he had chosen, there will be a REDUCTION of the output voltage of 50% (-6dB). A resistor alone, without an active element like a transistor, will always reduce the voltage, never increase. It is like the brake in a car, you can't accelerate by pressing the brake.

 

With equal 10KΩ resistors, an input, Vi, consisting of a 2 V P-P sinewave with an offset of +5 VDC; the output will be a 1 V P-P sinewave with an offset of +10V DC.



As in the previous example, drop the .txt extension from the plot settings file to apply the plot settings.

 

RF300 has it RIGHT!! While the DC bias voltage is greater, that does not constitute amplification! At the OUTPUT of the circuit the SIGNAL VOLTAGE will be reduced from the SIGNAL VOLTAGE on the other side.

This looks like an exam test question for a final exam in an "AC Circuit Theory" class. The arithmatic is a little bit tricky but the circuit is reasonable.
So we get back to the original definition of "AMPLIFY", which is to increase the signal power level of a signal. No quantity of weasel words can change that.
To provide some additional clarification here, altering the DC bias level of a signal voltage does not change the magnitude of the POWER level of that signal voltage.

 

And after sufficient time any DC offset at the output will be removed by C1.

 

If amplification means increasing the power, then that is not possible because it defies the law of conservation of energy.

I recall a definition of "amplifier" I read in an electronics dictionary when I was in college. I think it was "a circuit used to control the flow of power through a load".

 

I recall a definition of "amplifier" I read in an electronics dictionary when I was in college. I think it was "a circuit used to control the flow of power through a load".

That implies that external energy is introduced into the system.

 

Actually it's more like a circuit that modulates a power supply to produce a voltage which is a larger copy of the input signal.

 

To change the voltage of a signal using a transformer, would you need to overcome the resistance of the inductors, meaning there would be a threshold minimum voltage to pass the signal?

No, there is no minimum voltage a transformer can transform (until you get down to the intrinsic thermal noise of the system).
For example, RF transformers can work in the microvolt range.