I simulated the circuit using multisim and it works fine. However, when it is implemented on a breadboard it doesn't work.

Here is the result:
The active band-pass filter circuit shorts out the power supply I was using for some reason. The good thing is that the power supply has a protection and turns off automatically. I disconnected the the circuit from the power supply and tested only the power ampliffier part and I keep getting a 9 V DC voltage at the output as supposed to getting an AC signal.

I am just confused. I could really use some help.

IC Links:
Opamp: LM675: http://www.ti.com/lit/ds/symlink/lm675.pdf
Power amp: TL072: http://www.ti.com/lit/ds/symlink/tl074a.pdf

I have attached the circuit diagram and the implemented breadboard circuit pictures for you to see.


Thank you very much!

 

If the color coding ( and marking on the bread board ) on ur images are correct for RED (+Ve) and BLACK (-Ve), Then ur OPAMP Power pins are way wrong.

 

If OPAMP power pins are reversed, the OPAMP might short circuit

 

If the color coding ( and marking on the bread board ) on ur images are correct for RED (+Ve) and BLACK (-Ve), Then ur OPAMP Power pins are way wrong.

If you look at IMG-0997, the positive power supply is connected to the right-side (+) red colour and the the negative power supply is connected to the (-) black colour at the left side. pin 8 of the opamp is where the positive power should be connected to and the negative power to the pin 4 of the opamp according to the datasheet. I see that I connected pin 4 to the ground just before taking the picture but it was connected to the negative power source when testing. I will update the picture.

 

Remove the OPAMP and check PSU is shutting down.
Then use a DMM to check for polarity.
If OK and still shorting, replace the OPAMP

 

Remove the OPAMP and check PSU is shutting down.
Then use a DMM to check for polarity.
If OK and still shorting, replace the OPAMP

Yeah I did all that but it keeps shutting down the Power Supply. However, with the Opamp removed the power supply operates normally. Ok, I will test the active band-pass circuit with another opamp. The power amplifier problem is also another odd issue.

 

Some of the power amp (LM675T) connections seem wrong. It's hard to tell from the pic which way you've bent its leads, but it looks as though pins 1, 3 and 5 have been brought forward and pins 2 and 4 bent back. If that's so, then pin 1 is connected via a resistor to the +ve rail (not the -ve rail); pin 2 is connected to the negative rail; pins 3 and 5 go nowhere.

 

Some of the power amp (LM675T) connections seem wrong. It's hard to tell from the pic which way you've bent its leads, but it looks as though pins 1, 3 and 5 have been brought forward and pins 2 and 4 bent back. If that's so, then pin 1 is connected via a resistor to the +ve rail (not the -ve rail); pin 2 is connected to the negative rail; pins 3 and 5 go nowhere.

You are correct, that is how the pins of the amplifier are bent. If I have read the datasheet correctly, from top to bottom the pins are 1, 2, 3, 4 and 5. I have added another picture named FullSizedRender (2) to give you a close up look at the connections.
I can assure you that Pin 1 is connected to the ouput of the opamp circuit via the yellow capacitor. Pin 2 is not connected to the negative rail as it can be seen in the image named FullSizedRender (2). Pin 3 is connected to the negative voltage source and pin 5 is connected to the positive voltage source via the red wire as seen in the image named FullSizedRender (2).

 

Ah, that's much clearer. Having a negative rail marked with a red paint line is confusing.

 

I'd take some time with DVM to probe around the board to verify that voltages (or continuities) are what you expect. You may uncover a misplaced connection from that exercise. It can be hard to see a mistake when you keep looking at the same wires over and over. Changing your inspection technique – using a meter – can better help reveal a mistake.

 

I'd take some time with DVM to probe around the board to verify that voltages (or continuities) are what you expect. You may uncover a misplaced connection from that exercise. It can be hard to see a mistake when you keep looking at the same wires over and over. Changing your inspection technique – using a meter – can better help reveal a mistake.

Yeah that is a good suggestion but I actually did a continuity test and all seem to be fine. Also the breadboard is good when it comes to quality.

 

Ah, that's much clearer. Having a negative rail marked with a red paint line is confusing.

True! it is confusing to looking at the black colour as a power source indicator.

 

True! it is confusing to looking at the black colour as a power source indicator.

We don't buy and use rainbow coloured wires just to be pretty.
Consistency with colour coded wires will help to avoid making mistakes.

 

Power supply decoupling near a power opamp is *critical*. Audio power amp ICs are notorious for misbehaving due to poor decoupling. The 675 datasheet probably has examples, but start with a 0.1 uF ceramic and a 47 uF electrolytic in parallel for each rail, with the leads and connection paths as short as possible.

Do you know what the current limit or overcurrent shutdown on the PS is set to? Is it adjustable?

ak

 

Power supply decoupling near a power opamp is *critical*. Audio power amp ICs are notorious for misbehaving due to poor decoupling. The 675 datasheet probably has examples, but start with a 0.1 uF ceramic and a 47 uF electrolytic in parallel for each rail, with the leads and connection paths as short as possible.

Do you know what the current limit or overcurrent shutdown on the PS is set to? Is it adjustable?

ak

Ok I will add a 47 uF for each rail.
The supply current is adjustable but I am not sure about the maximum amount. I can check it tomorrow when I have access to the laboratory I work in.

 

We don't buy and use rainbow coloured wires just to be pretty.
Consistency with colour coded wires will help to avoid making mistakes.

hahahaha I know but the black coloured lines on the breadboard have (-) sings. I wanted to keep the (-) sign for the negative voltage source.

 

Your 4-Ohm load is insignificant. A short means power is going to the negative rail with little or no resistance in between. Your power-supply crowbars to protect itself, not your circuit, so be aware your parts can get damaged before it protects itself.

Find the path that is allowing a short. This is unlikely through an OpAmp unless it's damaged.

 

Your 4-Ohm load is insignificant. A short means power is going to the negative rail with little or no resistance in between. Your power-supply crowbars to protect itself, not your circuit, so be aware your parts can get damaged before it protects itself.

Find the path that is allowing a short. This is unlikely through an OpAmp unless it's damaged.

I put the 4-Ohm load in the circuit diagram for power simulation purpose. I did not actually put an actual 4-Ohm reistor at the ouput. As you may already know it will blow up unless it is capable of handling high power. The load will be replaced by an actuall 8 or 4-Ohm speaker driver that is capable of handling the measured output power.
I will change the opamp as well as the breadboard. I will also do another continuity test just to make sure everything goes right. First I will only test the active filter circuit and see if it shorts out again. Hopefully I will do all these tomorrow and let you all know the result.

 

I have a good news! The whole circuit works now. I changed the breadboard as well as the opamp. I added 47uf decoupling cap for each rail. I put the components closer to the ICs (this should also help with getting cleaner signal).

The active band pass filter works as it should. Also the power amp works as it is supposed to work. Unfortunately I didn't put back the prevouse opamp to see if it works. I am asking myself why I didn't do that.

I attached the picture of the working implemented circuit below with a file named img-1028. Red and black wires were not available in the laboratory so I just used the brown wire shown in the image.

In response to AnalogKid's question about the power supply: The power supply has a maximum current limit of 0.5A for its two adjustable power supply terminals. It also have a fixed power supply terminal with a fixed 5v and a 1A current limit.

Thank you all for your support!