Urgent Question About Op-Amps from the Newbie

[gaddargaddar]

Maybe it looks an idiotic question but Could someone show me how to make a working circuit with an op-amp...I've got lots of schematics but when I tried to built them something goes wrong and I cannot get out of the circuit...Especially could anybody show me how to give power to an op-amp with a single 9V battery???Really could anybody explain it to me like explaining a totally dumb person...There had to be some specific rules!!!
I tried lots of things and read lots of things I know about inverting and non-inverting, circuits etc...But none of the scmetaics show how to give power to the chip...Here's what I do in that situation:
I build the circuit and directly connect the battery to the 7th and 4th pin of the op-amp (it's a 741)...I got nothing as a result...
In short Could anybody show me a simple circuit made with an op-amp and produces any type of sound...

Thnaks anyway

[RDV]

This is the easiest I know of because the IC(741) is numbered and everything. http://www.generalguitargadgets.com/diagrams/dist_250_sc.gif

RDV

[petemoore]

i don't know what you know so
 ill just say 'socket the opamp so you don't burn it>

[The Tone God]

The easist opamp amp circuit I can think of is a non-inverting unity gain buffer. I don't have a schematic handy but here are the quick wiring instructions:

Pin 2 - connect to Pin 6. Becomes output
Pin 3 - input
Pin 4 - ground
Pin 7 - power

You may need a cap on the input and output. Other then that you should be able to get something out of it. It won't amplify the signal, just serve as a buffer.

As for how to power the opamp(s) in different situations you can read this:

http://www.geocities.com/thetonegod/opamp/opamp.html

Andrew

[RLBJR65]

Most opamps need a a bipolar supply or a voltage devider to work, usualy the circuits have a V. devider built into them. Check out this link //www.runoffgrove.com/bb-pwr.html it has a simple devider circuit you can build and use when experimenting.

Also you might down load the spec. sheets for the opamps you have, some of them will have example circuits and lots of other usefull information.

[Transmogrifox]

I think the schematic that RDV posted is pretty fool-proof unless there is something fundamentally wrong with your ground connection to the rest of the circuit or if your op amp is toasted.  

If that DOD circuit that RDV posted doesn't work, try a different op amp.  I have toasted some IC's by soldering them too hot.  I actually have a DOD death metal pedal that I replaced some IC's in and one of them has gone unstable at 2 kHz and I wouldn't be at all surprised if it has something to do with me having soldered it too hot...it sucks I have to take it out and replace it--few things worse than wasting a perfectly good MC33078 chip.

[gaddargaddar]

First thank for all of you but I still can't get  an op-amp work...This situation makes me mad..but I still can't get it work..For two days I've been working on this...Anyway I tried everything...I'd like to ask the where am I making a mistake...

Firs I read the text which it's link has be given by the Tone god..And try to build lokks like the  schematic called "figure 5"... For the power supply resistors (at the bottom  left corner of the figure with a cap) I used 100k and I used a 100mF(micro Farad) so I got nearly 3,9V whic goes to non-invertin pin of the op-amp(I measured this with respect to the earth witouht connecting it to the op-amp)...
Ihad a 10k resistor that goes from pin2 to pin 6 and a 1k resistor from pin 2 to the input...I gave +Vcc at pin7 and ground from pin 4. pin 6 is my ouput...I connect it to my amplifier(I'm sure that all the connections between my bass and between the amp are correct)
And then I measured every pins potential difference with respect to my ground...Here are the results
      For 741 ..................            for  TL071
pin1 0v ................                         0,10
pin2 0v ................                         0,86
pin3 0v ................                         0,83
pin4 0v ................                         0
pin5 0v ................                         0,08
pin6 +7.05v .........                  2,11
pin7 +7.65v .........                  2,75
pin8 0v.................                          0

I'm sure that I'm making something wrong,but I couldn't figured it out yet and it drives me crazy...I used a pair of each op-amp on the circuit. Could all of them might be burned??? and I get a sound from the circuit but if I ripped the op-amp out of the circuit I still can hear exactly the same voice,I mean the op-amp doesn't make a work in the circuit I think...
Any way I also would like ask the Tone God a question...What does buffer mean??? Why is it so important??? I mean I read some writings about the theory but I still couldn't understand what it is??? If you could help me I would be really glad...

Anyway Thanks for everybody in tihs  for their patience...

[The Tone God]

Firs I read the text which it's link has be given by the Tone god..And try to build lokks like the  schematic called "figure 5"... For the power supply resistors (at the bottom  left corner of the figure with a cap) I used 100k and I used a 100mF(micro Farad) so I got nearly 3,9V whic goes to non-invertin pin of the op-amp(I measured this with respect to the earth witouht connecting it to the op-amp)...

Ihad a 10k resistor that goes from pin2 to pin 6 and a 1k resistor from pin 2 to the input...I gave +Vcc at pin7 and ground from pin 4. pin 6 is my ouput...I connect it to my amplifier(I'm sure that all the connections between my bass and between the amp are correct)

And then I measured every pins potential difference with respect to my ground...Here are the results
      For 741 ..................            for  TL071
pin1 0v ................                         0,10
pin2 0v ................                         0,86
pin3 0v ................                         0,83
pin4 0v ................                         0
pin5 0v ................                         0,08
pin6 +7.05v .........                  2,11
pin7 +7.65v .........                  2,75
pin8 0v.................                          0

I'm sure that I'm making something wrong,but I couldn't figured it out yet and it drives me crazy...I used a pair of each op-amp on the circuit. Could all of them might be burned??? and I get a sound from the circuit but if I ripped the op-amp out of the circuit I still can hear exactly the same voice,I mean the op-amp doesn't make a work in the circuit I think...

Ok so it sounds like you built the circuit in Figure 3 with the resistor network in Figure 4. Looks like your 741 might be blown. Stick with the TL071 for now. Try building the circuit in Figure 5 as is with no resistors and report back the voltages. Lets see if the opamps are working first.

Any way I also would like ask the Tone God a question...What does buffer mean??? Why is it so important??? I mean I read some writings about the theory but I still couldn't understand what it is??? If you could help me I would be really glad...

A buffer basicly provides isolation between the input and output but no amplification or attenuation. In Figure 5 if the output were to be shorted the input from the resistor divider would not be affected. It would stay at 1/2 V+.

A good use for this is when you are feeding multiple opamps with the same 1/2 V+ as in Figure 10. If you were to feed multiple sources from a passive divider network (Figure 4) there could be loading causing a change in the actual voltage. If an active/buffered voltage source, in this case an opamp, is used to feed multiple source the opamp under load will adjust the output to make sure the output is matching the input. It acts like a mini voltage regulator.

An example of this in use is the Vanishing Point. The VP has a opamp voltage reference (Figure 7) feeding three other opamps performing different functions. This way the voltage reference is maintained.

Andrew

[niftydog]

you should be getting similar voltages for each op amp. The fact that you have

pin6 +7.05v ......... 2,11
pin7 +7.65v ......... 2,75

leads me to beleive there's something wrong with the TL071 op amp. In fact, there's something wrong with both of them. You say you're using a 9V battery, then there should be 9V (or there abouts) at pin 7 for both op amps.

Also, it would appear that the output is saturated. by that I mean it's at it's maximum positive voltage. You probably have too much gain.

Change the 10k resistor to a 1k, this should give you a gain of 1. This is effectively a buffer.

A buffer is a device that passes a signal without changing it at all. It's purpose is to "separate" one circuit from another so that they don't interact with each other. It has a high input impedance and a low output impedance. For now, you should just take it for granted that this is a good thing! You'll learn more about it later.

This is about as simple as it gets with a single supply;

Code Select Expand

                      ___ 1k
                   o-|___|-o
                   |       |
              1k   |  VCC  |
             ___   | |\|   |
 signal in--|___|--o-|-\   |
     ___     ___     |  >--o--signal out
VCC-|___|-o-|___|-o--|+/
     1k   o  500  |  |/|
          |       o   GND
         .-.      |
         | |     ---
       1k| |     ---0.1uF
         '-'      |
          |       |
         GND     GND

Getting mad at it won't help. Just go slowly, check and double check your work. We've all been there before, and we learnt from our mistakes.

[gaddargaddar]

Thanks everybody for all of your help...I made niftydogs schematic and it worked...so I'm quite happy now...But I still have questions...Where can I use that kind of a circuit and could I make another circuit whic has a bigger gain than 1 with an op-amp...Also why do we want our effects circuit to have high input empedance and low output empedance???I read something about it but I'm still confused...I understand fairly well what the empedance is but why do we want it high at the input and low at the output???

Thanks foa your patience( again  )

[niftydog]

Where can I use that kind of a circuit

anywhere you need a buffer! (will expand on this below!)

could I make another circuit whic has a bigger gain than 1

Make the 1k resistor at the very top of my schematic a larger value. the gain is set by the ratio of this resistor and the 1k from the signal input. I have it set at 1 for simplicity; 1k/1k = 1.

So, if you made it 2k, it would have a gain of 2k/1k =  2.
5k, a gain of 5 etc.

Be aware that there's several limitations on how much gain you can have. The main one being that the op amp can only generate so much voltage swing.

why do we want our effects circuit to have high input empedance and low output empedance???

It's to do with ohms law and the electrical limits of the devices we use.

Take my schematic as an example; lets say your guitar is hooked up to the signal input. Your guitars pickups can only provide a finite amount of power. If the input of the circuit trys to take MORE power, then the pickups don't work properly. We say that the pickups are "loaded down". If on the other hand, the input to the circuit only requires a fraction of what the pickups can produce, then the load on the pickups is very small and they have no problems providing the power.

A high input impedance is a sign that the input to a circuit does not consume very much power to do it's job. Hence, this is obviously desireable in most situations.

Now, output impedance is somewhat similar, but a bit more complex to explain. Are you familiar with voltage dividers? If you are, it makes this a little easier to understand.

Lets say my circuit has an output impedance of 600 ohms and it's output is 1VAC. Connected to the output is a second circuit with an input impedance of 1kohms. (this is quite low, but it illustrates my point.)

due to the voltage divider action, the actual voltage at the input to the second circuit is 1k/(1k+600) = 0.625VAC.

Now, say we changed my circuit, and it's output impedance is lowered to 300 ohms; 1k/(1k+300) = 0.77VAC. Better...

Now, say we change the second circuit, and it's input impedance becomes 10k; 10k/(10k+300) = 0.97VAC. Much closer to the original 1VAC.

So, you can see that low output impedance and high input impedance is a good thing in almost all circuits.

I hope this is sufficient for you to better understand what you have read on the subject.

[Travis]

ND, that is the most user-friendly explanation of impedance I've ever seen.

[niftydog]

I try.  

Problem being an engineer is that you can quickly glaze many an eye with tech speak. I always appreciated it when my teachers could get a concept accross without any technobable.