Op amp issues

[Jaymucas]

Hi, I am brand new to building on breadboards. I've done quite a few pre-printed PCBs. I am trying to get my op amp to work. I've not added any caps or resistors yet cause I just want to get a signal through the op amp. Unfortunately it's dead. I've changed the op amp to make sure I wasn't using a dud. It's a tl072 op amp. Thanks

[Jaymucas]

[antonis]

HI & WELCOME..

Is there, by any chance, a schematic according to which you've populated your breadbord..??

[ElectricDruid]

Welcome!

Could you have another go at taking a photo of the breadboard please? That one is too fuzzy to really see what's going on.

It looks a lot like there aren't enough parts on the breadboard. You'd need a few resistors at minimum, and a cap or two, depending what you're trying to build. Have you got a link to the circuit you're trying to build?

[Transistor-Transistor]

Hi!
So like ElectricDruid said you'll need a few parts at minimum.

An input cap is necessary so that no dc voltage gets into your guitar.

You need to bias your op-amp. This is done with 2 resistors forming a voltage divider at your noninverting input so that you have a 4.5v reference voltage for the op-amp to know how much voltage its amplifying to.

And then you'll need an output cap so no DC is in your guitar signal.

I may be missing something. Someone else will tell you what that is 

[Matthew Sanford]

To expand on what transistor said:
do a 10k pair for the divider (one to V+, one to ground) joined together the other sides and a 1 Meg (or at least 100k) resistor to take that in to +input - after the cap! Caps block DC, keep it in the op amp and out of your guitar & amp, when using voltage bias like that you need them. Also, the other opamp should get some treatment, tie it's output to the -input like you've done but also it's +input to ground, that will keep the dual package more stable.

Voltage bias is very important so your AC signal has room to go above and below. Otherwise it is on the ground, and TL072 doesn't like you getting close to ground at all! I've been informed many times thanks to Duck, Antonis, and others here until it finally sunk in that the signal is between the two rails of the opamp and to not put it in the middle is just foolhardy, was for me, a lot of "why won't this work?!?!" while they already had told me...

[Jaymucas]

Thank you all, I shall have a go again the morning and if I get no result I'll add a better picture.

[Matthew Sanford]

One more thing, if you want gain add a smaller resistor to the input after the cap, and a larger one (or pot) to replace the feedback wire. This gives you gain on your signal and distortion once large enough gain clips the voltage rails.

[duck_arse]

also welcome, and what everyone else said, especially photos and circuit diagrams.


but ......

... the other opamp should get some treatment, tie it's output to the -input like you've done but also it's +input to ground, that will keep the dual package more stable.

.... Otherwise it is on the ground, and TL072 doesn't like you getting close to ground at all! I've been informed many times thanks to Duck, Antonis, and others here until it finally sunk in ...

finally, or one more time?

[antonis]

So you guys, are fond of guessing..

[Matthew Sanford]

finally, or one more time?

Finally. Enough times (I think...)



...or maybe one more time? No promises...

[GibsonGM]

The promise of a noob - sucks us in every time...

[ElectricDruid]

So you guys, are fond of guessing..

+1 agree. We really *do* need that schematic of what this thing is supposed to be...

[Matthew Sanford]

What I meant, in picture form.

[ElectricDruid]

What I meant, in picture form.

Not *yours*, OP's!!

I'm pretty sure you've got a schematic somewhere of what you're putting together. But what we need to know is what the OP is trying to do. Thus far, we don't even know if this is a buffer, an inverting amp, or a non-inverting amp. Antonis is right - we're all totally guessing...

[antonis]

@Jaymucas: Proceed to following schematics builds by verifying good working state of previous circuit..
(i.e. If (A) works OK then go to (B) and so on..)

[Transistor-Transistor]

Well I think the OP said he was just trying to get the amplifier to work with no other attached circuitry. I'm guessing he just didn't know that it needs other stuff to work. I was like that too for a while. He's just learning how to use op-amps

[Matthew Sanford]

I just meant I believe the top as blurry was what it seems he's got. The bottom was my thoughts on where to go, but Antonis has posted better on that end.

[duck_arse]

What I meant, in picture form.

Otherwise it is on the ground, and TL072 doesn't like you getting close to ground at all!

bottom right corner, pin 5, how far from ground is a happy TL0xx?

[Matthew Sanford]

Ah... so input to bias voltage on an unused op amp?