Amplifier problem that no one understand

keeth

Joined Feb 17, 2018
6
Hello!
I found this place on google and thought this forum might be able to help me understand my homework.
We are 4 students who are studying abroad at San Diego State University and we need help to understand a simple
problem in our homework. Aparently language is a barrier for us after all, hehe.

The problem sound like this:

2.1 An amplifier with 40 dB of small-signal, open-circuit voltage gain, an input resistance of 1 MΩ, and an output resistance of 10 Ω, drives a load of 100 Ω.
(a) What voltage and power gains (expressed in dB) would you expect with the load connected?
(b) If the amplifier has a peak output-current limitation of 100 mA, what is the rms value of the largest sine-wave input for which an undistorted output is possible?
(c) What is the corresponding output power available?

There are no drawings or anything included in the paper what so ever.
We've are really confused as to what resistor is where. Is the input resistance the internal resistance? is there any feedback loop?

HW-nut

Joined May 12, 2016
97
I won’t answer the question directly but I can provide a few hints.

The load in combination with the output resistance forms a voltage divider which will reduce both the voltage and power output according.

For the gain calculations, you simply need to fill in the blanks on the log voltage/ power gain equations.

keeth

Joined Feb 17, 2018
6
The load in combination with the output resistance forms a voltage divider which will reduce both the voltage and power output according.
Ok so there is a feedback involved afterall? Because that is the only way i can get this to make sence.
Or is R output the internal resistance of the amplifier?

crutschow

Joined Mar 14, 2008
26,058
No feedback.
The input resistance is looking at the amp input.
The output resistance is looking into the amp output (internal resistance in series with an ideal zero impedance amp).

keeth

Joined Feb 17, 2018
6
No feedback.
The input resistance is looking at the amp input.
The output resistance is looking into the amp output (internal resistance in series with an ideal zero impedance amp).
Ok i see. I think we got it now

Papabravo

Joined Feb 24, 2006
14,876
Would it be impertinent of me to point out that an amplifier described in words is an insoluble problem. A schematic diagram is the language of electronics. No schematic equals no useful help or communication unless both side happen to be communicating in some non-obvious way. Telepathy and crystal balls come to mind.

keeth

Joined Feb 17, 2018
6
Would it be impertinent of me to point out that an amplifier described in words is an insoluble problem. A schematic diagram is the language of electronics. No schematic equals no useful help or communication unless both side happen to be communicating in some non-obvious way. Telepathy and crystal balls come to mind.
omg you express our feelings perfectly! Thank you! \o/

anhnha

Joined Apr 19, 2012
881
This is what it means:

2.1 An amplifier with 40 dB of small-signal, open-circuit voltage gain, an input resistance of 1 MΩ, and an output resistance of 10 Ω, drives a load of 100 Ω.

JoeJester

Joined Apr 26, 2005
4,390
why is AV gain 100?

anhnha

Joined Apr 19, 2012
881

JoeJester

Joined Apr 26, 2005
4,390
Nice ... I'm sure the thread starter appreciates your diagram since the four of them couldn't figure out one.

keeth

Joined Feb 17, 2018
6

JoeJester

Joined Apr 26, 2005
4,390
It is exactly how we imagined it to be. Or had to be like.
You could have posted what you imagined in the first thread and you wouldn't have had to wait till the 8th reply to confirm your "imagination" of the circuit.