Sorry i don't understand. I am using a 741 op-amp in the simulation. Also when the input is 200mv pk-pk then i require voltage rails of at least +/-2.2v for a gain of +2. So it appears the minimum required voltage rails to get no clipping, reduces as the input signal reduces in magnitude.

I do believe that you have encountered the minimum rail voltage for which the 741 opamp can operate.

As for Millman's Theorem, I have not found a circuit problem that can be solved with the more common circuit analysis methods that Millman's cannot solve with less algebraic manipulation.

hgmjr

 

I do believe that you have encountered the minimum rail voltage for which the 741 opamp can operate.

hgmjr

But this minimum rail voltage if that is the case, varies with respect to the input signal or gain required...

 

How about trying another opamp from the component library just to see how other devices behave?

hgmjr

 

The 741 cannot fluctuate its output at the edges of its power supply. I was using 0-12V to power it up in a radio amplifier project and it couldn't get the signal higher than 10V or lower than 2V.

However, I don't know which field in the datasheet describes this behaviour.

 

What was the homework assignment, as assigned by the instructor?

You've mentioned 200 mV pk-pk inputs, 400 mV pk-pk inputs, gains of 10, et al.

 

What was the homework assignment, as assigned by the instructor?

You've mentioned 200 mV pk-pk inputs, 400 mV pk-pk inputs, gains of 10, et al.

Hey thanks for the support, but i finally had my labs today and we have got the amplifier working, all three stages (pre-amp, tone control & output amp).

To answer the questions, we are just told to build an mp3 player amplifier with those above stages, using a recommended voltage source of 3 AA batteries. As for the input, it is just from research i have seen that mp3 players output anywhere from 200mv-2v pk-pk, so i was just testing at various values in that range, but ideally it should support all input voltages in that range, hence the gain of 2. The gain of 10 was just for research purposes on the 200mv-400mv pk-pk input.

 

I am in the same class as James

I have no respect for the 741 after this lab! It couldnt even amplify (simple 1k / 5k inverting) a 5kHz sine wave at +/-3V without some distortion.

 

741 is a very old amplifier, but it works adequately with correct design and handling. The assessment of the results depends on the initial expectations.

 

well we are limited to around three op-amps for this particular project (I guess we could put orders in, but that's not in the spirit of things is it?)

I'm using the LM358 (or 385?) dual op-amp. Works best for me at these rail voltages. What comes out of the speaker almost sounds like music! I kid, it's not bad at all just not Sennhauser quality.

 

The 1k in your circuit should be from the negative input terminal to ground.

hgmjr

that's the way

 

The LM358 has crossover distortion and a full output bandwidth to only 2kHz.
I use the MC33172 dual opamp to replace it and the MC33171 single opamp and the MC33174 quad opamp. They all have exactly the same low power supply current per opamp and 3V minimum supply voltage. But the Motorola opamps have no crossover distortion and a full output bandwidth to 35kHz.

 

If I thought we would get any extra credit for researching the best performing amplifiers I would consider getting them on order, but I know we won't so will stick to what they have in the lab.

We have at least learned an important lesson in what's suitable equipment for the job in hand.

 

If I thought we would get any extra credit for researching the best performing amplifiers I would consider getting them on order, but I know we won't so will stick to what they have in the lab.

We have at least learned an important lesson in what's suitable equipment for the job in hand.

We will get marked on the quality of the output, and the battery consumption/input voltage. But i don't think we will be able to purchase op-amps though. However i read they have a store of old ICs from past projects which we can use, so maybe theres some higher quality ones in there.

We have to compromise really, but it doesn't mean we won't get extra marks for research.

 

You will probably get extra marks if you explain that the buzzing caused by the lousy old LM358 opamp (an LM324 quad opamp uses the same opamps) is caused by its crossover distortion then explain about what causes crossover distortion and show a sine waveform with crossover distortion like this:

 

I think audioguru has a good point. If you can convince your instructor that you are acquainted with the concept of crossover distortion, he/she will be impressed.

hgmjr

 

You might get more extra marks by eliminating the crossover distortion of the lousy old LM358 opamp with a switch then explain that its crossover distortion is caused by the output operating in low-current class-B and your switch adds a DC load (pullup resistor) so that the output operates in class-A.