Noob trying to get started

[pwoolcoc]

Hello, I'm trying to learn and have immediately run into a problem that I just can't seem to figure out. I'm trying to build a simple buffer circuit but all I get is a loud buzzing. I'm using a TL071 for the opamp, and all the other parts are the same as they say in the schematic. I've included a picture of my breadboard, I apologize for the bad lighting.

When I take the opamp out of the circuit and basically make the lead that would have gone into pin 3 on the IC go to the + of the output coupling cap instead, it works fine, I hear a very clear signal. But as soon as I put the opamp in there, I just get the loud buzzing. I thought maybe I had a bad IC so I tried a couple more, with the same result. I didn't want to try too many because I was afraid that I'd done something wrong and just putting the IC in there was causing them damage.

Apologies for the noob post, I was hoping this would be an easy win to start out with and have been getting very frustrated that it isn't working.

[r080]

The colors are confusing me. Is it possible you have +9V going to both pins 7 and 4?

For a circuit this size, I learned some surefire troubleshooting techniques in school:
1. Turn power on
2. Connect power
3. Take it apart and start over
Repeat as necessary.

[r080]

Another thing that could possibly help is to use the breadboard rails. I noticed you have a line coming down from the top that appears to be power, and it crosses the middle line. If you set up your breadboard rails, say, with +power at the top and -power at the bottom, it might allow you to set up this circuit more like the schematic, making building and troubleshooting more intuitive.

[r080]

It may also help to come up with a color scheme you like and stick with it. For instance, I try to always have my inputs yellow and my outputs blue; + power always red, and green or black for ground.

[r080]

Okay, I took a closer look at your pictures. You have two red or orange wires plugged into your power rail. It looks like they both are on the same row. What are they connected to? I believe one of them should be connected to your positive power supply, and the other one should be connected to your negative power supply and the ground pins of both your input and output jacks.

[PRR]

What are you using for power?

That simple input biasing wants to inject *half* of all the crap from the power supply into the amplifier. If cheap wall power, mostly buzz. When you bypass this stage you also bypass the bias, so no trouble then. Try a battery?

[antonis]

A rough bias supply remedy..

[pwoolcoc]

Thanks all, I'm going to try a couple of the suggestions after work today and will post with an update.

I agree that the color scheme is confusing, unfortunately i soldered a couple wires to my jacks and only realized after that I should have swapped the colors.

As for inputs and outputs, I have the tips of each jack connected to the "Input" and "Output" points on the schematic, and the sleeves of both jacks are at ground.

The tip to put ground on one of the rails on the other side of the breadboard makes a lot of sense, thanks.

[r080]

Paul brings up a good question. Were you getting any signal through?

[pwoolcoc]

I couldn't hear any signal, even with the amp turned up all the way. I'm using a 1Spot for DC power, but I will try a 9v instead.

[antonis]

I'm afraid you'll have to take some DC measurements..

pin 7 should be +9V
pin 4       //         0V and shorted to power supply GND
pins 6, 2 & 3 should be 4.5V
(pin 3 might be lower..)
IN & OUT jack GNDs should be shorted to power supply GND

[PRR]

> I couldn't hear any signal, even with the amp turned up all the way.

Follow-up question. Any hum, buzz, hiss, crickets, police radio....?

The universal hiss, and ubiquitous hum/buzz, and computers and radio, are expected "turned full up". UTTER silence is a big clue.

[pwoolcoc]

Yea, "could hear any signal" was a bad choice of words, what I meant was "couldn't hear the guitar at all." I did hear signal, it was just a big buzz!

I tried with the 9v battery instead of the wall power and then the guitar came through loud and clear, so I expect it was just too much interference from the wall power. I'm going to go looking for another buffer schematic with similar input impedance but better DC isolation.

Thanks for your help everyone, I really appreciate it!

[MG]

Yea, "could hear any signal" was a bad choice of words, what I meant was "couldn't hear the guitar at all." I did hear signal, it was just a big buzz!

I tried with the 9v battery instead of the wall power and then the guitar came through loud and clear, so I expect it was just too much interference from the wall power. I'm going to go looking for another buffer schematic with similar input impedance but better DC isolation.

Thanks for your help everyone, I really appreciate it!

I doubt that this was about 'DC isolation.'  It should not have been saturated with buzz simply due to an external -DC- power supply, unless there was something odd with the supply.  But in any case, starting simple = 9v battery.

When you move on to a possibly less filtered supply: Antonis showed a circuit that will work for biasing the (+) input.  I've often used a small device from TI called a 'rail splitter.'  It was available in a TO92 package, like a small transistor.  But I'm not sure if that's still available.

[pwoolcoc]

Sooooo I found the problem, apparently sometime between when I plugged it in and when I started this project, one of my kids unplugged the 1Spot to make room for charging something else, and I hadn't looked under the workbench where it was all plugged in 

So I have it working fine with wall power as well, thanks to everyone again for being patient with me and helping out, I can now check that boneheaded mistake off the list.

[MG]

Now that's funny.  I was wondering how bad a DC supply would need to be in order to buzz without passing any signal.

Always nice to have a voltmeter.   

[PRR]

....I was wondering how bad a DC supply would need to be in order to buzz ....... .......

https://www.diystompboxes.com/smfforum/index.php?topic=127566.msg1223943#msg1223943

Assume 9V, with 1% ripple (a happy 1 Spot will be much less). 0.090V or 90mV ripple on the rail. 45mV at the half rail. Compare with typical guitar 20mV to 200mV. It is quite easy to have a LOT of buzz.

The rail-splitter chip will not help. It still splits the crap on the rail in half, whereas we may want 1/100 or 1/1000.

Yes, Antonius' scheme is good. R.G. has a whole page on it. For historical reasons called "noiseless biasing" but it is not about the hiss.

[antonis]

one of my kids unplugged the 1Spot to make room for charging something else,

Commiting infanticide should be added as preventive conservation into troubleshooting guide..

[r080]

Sooooo I found the problem, apparently sometime between when I plugged it in and when I started this project, one of my kids unplugged the 1Spot to make room for charging something else, and I hadn't looked under the workbench where it was all plugged in 

It looks like I need to modify my surefire breadboard troubleshooting steps slightly:

1. Turn power on Plug power supply into outlet
2. Connect power
3. Take it apart and start over
Repeat as necessary.

Of course, this is assuming you are starting from a schematic you know should work.

[MG]

....I was wondering how bad a DC supply would need to be in order to buzz ....... .......

The rail-splitter chip will not help. It still splits the crap on the rail in half, whereas we may want 1/100 or 1/1000.

8-pin TI Rail-Splitters have a noise reduction pin.  But I personally use the TO92 version cause I make sure the supply is stable.
Any time that you need to be concerned about noise on the supply being propagated into the splitting circuit, there's a deeper problem.

That's not the only reason that I suggested the circuit that was posted above.  If a second opamp was added to the original circuit, you'd need to duplicate the splitter.