[SOLVED] TL082 preamp: help please!

[runaway_pancake]

Is the original circuit wrong?

The one from openmusiclabs ?

"do what I tell you to do and just shut up, I know what I'm talking about while you don't".

I didn't tell you to "shut up". 
The part about "just doing what you're told" was in quotes, to take the sting out.
You might want to consider just playing along - for the present.

I'm going to provide supply from Arduino +5V

OK

and bias from an Arduino digital pin,

Why? What's wrong with "+5V"?

I haven't powered the circuit yet as I've done no calculation on current draw and I wish to avoid to burn out the Uno: is there anything wrong on my wiring?

Why do you have to re-render the schematic as a 2600x3300 PNG (huge)?
Why can't you edit the smaller drawing, if you must change values, etc, and make it easier on everyone [everyone else]?

How will you know if the circuit works?

[rlogiacco]

ALL op amps need a split supply.

Ok, got it!

Voltage is relative, in the circuit I posted this effect of the split supply is provided by input biasing by producing a virtual ground. What is important is the minimum voltage required to drive the amplifier, in the case of the TL082 this is =/- 5V. Down doad the data sheet of this amplifier.

I got the TL082 datasheet before posting here, I swear!

The other thing is how close the output can get to the rail, in the case of this amplifier it is not very good. Figure 10 in the data sheet shows you this. However it only shows this for a 30V supply ( +/- 15V ) and the output can not get within 2.5V of the rail at best with a 1K load. If the output could reach up to and down to the power supply this would be called a rail to rail amplifier.

Got it! I'd seen Figure 10 on datasheet and that's the reason I'm supplying 12V to the TL082.... Figure 10 reports 5V output for 6V supply....

Basically it is the wrong amplifier for the job you want it to do.

Yep, I guessed so when I understood I would have needed a 12V supply to use it, but I had already bought it (5€ at the local store!). My bad.

May I ask you which IC would you suggest for my case?

I would use a MCP602 it will work happily off +/- 2.5V which means you can simply power it from 5V and generate the virtual ground with resistors.

Great advice, thanks!

Biasing is the act of adding a fixed DC voltage to a signal. it applies to either inputs or outputs and there are various ways of doing it.

Yep, it took me three different readings to actually understand what you described so clearly, but them all described the biasing on op amp on the input, that's why I don't get the output biasing.... more reading awaits me...  

(is it correct to say ground biasing?)

No.

Right. And after re-reading my own sentence I understand "ground biasing" has no meaning (aka biasing to nothing).

I'm not debating your suggestions

You are doing a good job at pretending to then.

I don't know if I should be proud of   or ashamed  . Either way please trust me when I say I'm only trying to understand.

because I'm unable to apply them unless I understand them

You seem to be happy to implement the circuit you keep posting and you don't understand that.

I dumbly thought I did understand it. I needed a starting point.

Was my start a little complex?  

you gave me a diagram for an inverting amplifier with a grounded negative supply, which I already tried and it appeared non working for a TL082.

Then you must have done something else wrong then.

Ok, here is the circuit I have on my breadboard now: it should be the one you suggested with a little variation regarding one capacitor (a mylar 0.047nF instead of the electrolytic 0.1nF you suggested) and there's a missing 0.1nF capacitor (which I didn't have around).

If I understand your circuit, considering TL082 supply voltage requirements depicted in Figure 10 and the load resistance depicted in Figure 9 of the datasheet, this circuit should work only due to the 10R resistor.... Am I understanding it?

That 10R though will produce a 500mA load on my Uno power, but that should fry my Uno as it's capped at 200mA source and 400mA sink... which means I can't use this config with an external voltage source either as it can't be grounded with my Uno...

Are my calculations wrong?

[rlogiacco]

Is the original circuit wrong?

The one from openmusiclabs ?

No the one I started with http://www.instructables.com/id/Arduino-Audio-Input/?ALLSTEPS

"do what I tell you to do and just shut up, I know what I'm talking about while you don't".

I didn't tell you to "shut up". 
The part about "just doing what you're told" was in quotes, to take the sting out.
You might want to consider just playing along - for the present.

Apologies, I might have over-reacted. I wasn't referring to your specific words anyway, it was more about the average answer type...

and bias from an Arduino digital pin,

Why? What's wrong with "+5V"?

Arduino current draw... Please read the reply to Mike I wrote right after you posted this... Apparently the only way I can turn the TL082 into operating mode with such a low voltage is by using a load current....

I haven't powered the circuit yet as I've done no calculation on current draw and I wish to avoid to burn out the Uno: is there anything wrong on my wiring?

Why do you have to re-render the schematic as a 2600x3300 PNG (huge)?
Why can't you edit the smaller drawing, if you must change values, etc, and make it easier on everyone [everyone else]?

Arghh, totally unintended, I didn't verify the diagram size, I thought it was decently sized.... Apologies 

How will you know if the circuit works?

I found two options, may be not the best ones and I'm open for improvements and suggestions:

• check datasheets and do some maths using ohm's law


• use a SPICE based circuit simulator like http://www.partsim.com/ and check current and voltages at critical nodes (sadly partsim doesn't list a TL082 part, but they do list other op-amps)

[runaway_pancake]

With regard to the Instructables - he's using two batteries (a TRUE split/double-ended supply); it is different.

The 10? resistor, with the "preferred" circuit, is part of a filter.
I don't want to debate its merit/s, but if you were to omit it the world would not end.

With regard to SPICE etc: - on a certain level, "an op-amp is an op-amp is an op-amp."

In any event, please understand that the op-amp's output (level) cannot be greater than its supply.
With a 5V supply there's no risk of overloading anything.
If you had/have a "non-Arduino" 5V source/supply, you could relax [a little  (: ].

For "true gain", if I may call it that, I would use a pot/rheostat in place of the "100K" between the output and the non-inv input)
If we stay, basically, with the "preferred" circuit, the only modification I would make would be with regard to the output (lose the pot and place there a diode with its anode to Gnd - that may seem backward but it is "dc restoration").

If you had an oscilloscope then we could all breathe again.   (:[/b}

[Grumpy_Mike]

Are my calculations wrong?

Yes about as wrong as it is possible to be. It shows that you understand even less than I thought you did.

That 10R though will produce a 500mA load on my Uno power,

Only if the other end is connected to ground not the power input to an amplifier.

Figure 10 reports 5V output for 6V supply....

No it does not. Not even close. Figure 10 is the output swing you will get under different values of load on the amplifier's output. This graph only applies when you have a power supply of +15 and -15 volts.

The data sheet shows that the MINIMUM supply voltage is +5V and -5V so you can not run this amplifier directly from the 5V of the arduino because that will only give you +/- 2.5V half the minimum value you need.

That circuit you posted.
1) Why post an SVG file these are hard to view.
2) The file again is a massive picture - you have been told about this quite a few times. Now it is verging either on stupidity or malicious.
3) The circuit is total CRAP

You have to decide if :-
1) You want to stick to this amplifier and power it off 12V
or
2) You want to use a more modern amplifier and power it off the 5V from the arduino.

Tell me what and I will post a diagram you can use.

but I had already bought it (5€ at the local store!)

Sorry but you have been totally ripped off.
 

[rlogiacco]

Are my calculations wrong?

Yes about as wrong as it is possible to be. It shows that you understand even less than I thought you did.

And in which way this should help me understand where I was wrong?

That 10R though will produce a 500mA load on my Uno power,

Only if the other end is connected to ground not the power input to an amplifier.

I admitted my ignorance on op-amps. I don't know how the supply line influences the circuit current, but I believe questioning myself is a good way to learn.

Figure 10 reports 5V output for 6V supply....

No it does not. Not even close. Figure 10 is the output swing you will get under different values of load on the amplifier's output. This graph only applies when you have a power supply of +15 and -15 volts.

Is it possible we are looking at two different datasheets? I've extracted Figure 9 and 10 from the datasheet I'm referring to and attached here in a small version. My Figure 10 reports "Maximum peak output voltage vs Supply voltage".
My datasheet source is Texas Instruments web site (www.ti.com), PDF datasheet for TL082 integrated circuit.

The data sheet shows that the MINIMUM supply voltage is +5V and -5V so you can not run this amplifier directly from the 5V of the arduino because that will only give you +/- 2.5V half the minimum value you need.

I understood that a few posts back, that's why I stopped trying to provide the supply voltage from the Arduino. And yes, I understand using a voltage splitter I'm not magically multiplying my Arduino voltage, as much as I understand voltage is not absolute but ground relative.
Anyway, on my datasheet it reports a minimal supply voltage of something a little less than 4V (which I understand it means +/-4V).

That circuit you posted.
1) Why post an SVG file these are hard to view.
2) The file again is a massive picture - you have been told about this quite a few times. Now it is verging either on stupidity or malicious.
3) The circuit is total CRAP

1) What's hard to view in an SVG file? Double click and it opens up in the browser.
2) An SVG doesn't have a size, it's a vector file and as such it has the size YOU decide it to have. BTW, I've been told once and I switched to SVG files immediately and apologized: about IT I'm neither stupid nor ignorant.
3) Ok, once again that doesn't help me understand where or why and you could have used something a little less offensive, nonetheless I accept your critic and I'm ready to listen what's wrong in there.

In regards to diagrams, if you folks have a preferred size and format I'll do my best to suit your needs. Until now those massive pictures I've sent, they where max 250KB, less than a quarter of second download on modern connections. Neverthless if that's annoying you I apologize again.

You have to decide if :-
1) You want to stick to this amplifier and power it off 12V
or
2) You want to use a more modern amplifier and power it off the 5V from the arduino.

Until I get a different IC I don't have a choice. As I said I will switch to a LM386 as soon as I'll get my hands on it.
Because I have to power my opamp out of 12V, as we finally agreed in regards to TL082, do I need to protect the Arduino side from over voltage? If I do, as I believe, wasn't my wrong circuit doing that already?

Tell me what and I will post a diagram you can use.

This thread subject is "TL082 preamp"

but I had already bought it (5€ at the local store!)

Sorry but you have been totally ripped off.

That's why I'm not buying anything any more from that shop and I'm waiting to receive the new IC.
I might be ignorant on electronics, as I repeatedly admit, but I'm not stupid, as you repeatedly suggested above.

I've exhausted my good manners: if you want to help or explain I will appreaciate, otherwise leave me in my ignorance and find someone else to be grumpy with.

[rlogiacco]

With regard to the Instructables - he's using two batteries (a TRUE split/double-ended supply); it is different.

Ok.... I don't get why though... Can you point me to something that explains why using two separate batteries is different from using a single supply with a voltage divider? I understand the two batteries may discharge at different speed and have not exactly the same capacity, but by creating a virtual ground from a double sized AC source it should work... At least this is what my limited knowledge tells me in regards to the topic....

The 10? resistor, with the "preferred" circuit, is part of a filter.
I don't want to debate its merit/s, but if you were to omit it the world would not end.

Ok, got it.

With regard to SPICE etc: - on a certain level, "an op-amp is an op-amp is an op-amp."

I use it for testing macro conditions trying to avoid frying out pins and voltage suppliers... I understand it is just a simulator

In any event, please understand that the op-amp's output (level) cannot be greater than its supply.
With a 5V supply there's no risk of overloading anything.
If you had/have a "non-Arduino" 5V source/supply, you could relax [a little  (: ].

I get it, problem is I can't operate a TL082 from Arduino's voltage supply as it appears Mike and me have finally agreed.
Anyway I was concerned by the 10R resistor and the current flowing through it as I've no clue about current limitations on op amps supply line.... Apparently Mike says I shouldn't worry about that

For "true gain", if I may call it that, I would use a pot/rheostat in place of the "100K" between the output and the non-inv input)
If we stay, basically, with the "preferred" circuit, the only modification I would make would be with regard to the output (lose the pot and place there a diode with its anode to Gnd - that may seem backward but it is "dc restoration").

This might surprise you, but I believe I understood both your suggestions  XD

If you had an oscilloscope then we could all breathe again.   (:[/b}

You can start a crowd funding initiative to get me one  and save everybody time

[runaway_pancake]

With regard to the Instructables - he's using two batteries (a TRUE split/double-ended supply); it is different.

Ok.... I don't get why though... Can you point me to something that explains why using two separate batteries is different from using a single supply with a voltage divider?

The signal outputs from those "false ground" (virtual ground, et al.) designs are referenced to the "false ground", between the output and the "false ground" (as opposed to output and circuit ground/Vss).
You could use the output from a "false ground" design and put that through a transformer with a secondary referenced to circuit ground.
To eventually use this with your Arduino project, the signal must be (has to be) referenced to Arduino ground (circuit ground, Vss).

Look at it as two 1K resistors in series between 5V and Gnd.
If I call the junction of the resistors "virtual ground" and I put my ? voltmeter probe there then I will measure +2.5V across one resistor and -2.5V across the other.
If I then connect that "false ground" point to circuit ground (the rest of the circuit's ground) then what happens?

problem is I can't operate a TL082 from Arduino's voltage supply as it appears Mike and me have finally agreed.

Could you please go back to your original post and Modify it to include the "design objective"?
I'm sorry, but after so many posts, I think we've nearly lost the plot (that's not an indictment or a nasty aside - it's in the interest of clarity).

> > >  If I don't have a TL082, I probably have a TL072, so I may have rummage about and get something going here.

[Grumpy_Mike]

1) What's hard to view in an SVG file? Double click and it opens up in the browser.

Which then shows as a huge file and you can only see a tiny fraction of the circuit. there is no way to zoom out.

Quote from: Grumpy_Mike on Today at 09:30:05 am
Quote
Are my calculations wrong?
Yes about as wrong as it is possible to be. It shows that you understand even less than I thought you did.

And in which way this should help me understand where I was wrong?

In order to tell you what is wrong with a thing you need some of it to be partly right. Nothing about those calculations was right. The basic premiss was wrong, how you applied the formula was wrong the conclusions you reached was wrong. It is like being given a pile of Lego bricks put together by a child and the child insisting you tell him why it will not operate like the Large Hadron Collider. You have to know something before you can learn something more.
Things you have to know are
1) Ohms law
2) How currents flow through circuits
3) Basic electricity
Now you might think you know these things but you don't. And you never will if you persist with your attitude.

I admitted my ignorance on op-amps.

And basic electricity. The things you are misunderstanding are not specific to op-amps but apply to the whole of electronics.

but I'm here to learn and understand.

If only that were true we would all have a happier time. What you want is for some one to explain exactly why you have these ideas in your head that we are all saying are wrong. You want to know exactly why they are wrong - but in order to do this we need to be a mind reader or to be able to find out and understand the whole of your internal model for electronics. And then correct that.  Sorry that is not going to happen it is just impossible.
The way to learn is to look at and study correct circuits. If there is something you don't understand about these correct circuits then you can ask and it will be explained to you.

I have no idea why you thought that by connecting a 10R resistor in series with your OP- amp's would give you a 500mA load on your arduino. It is so far divorced from reality as to be totally incomprehensible. Therefore I can't explain what you are doing wrong except to say everything. Or would you like me to speculate on the three thousand you could have miscomprehended?

Is it possible we are looking at two different datasheets?

Yes we were. I was looking at the one:- SNOSBW5C -APRIL 1998-REVISED APRIL 2013
No idea what one you were looking at because the link you provided did not point to a data sheet but just to the TI web site, therefore there is no way of knowing what one you were looking at.

As promised here is a diagram of what you need. It contains nothing you have not been told about before but it puts it into one diagram.

[runaway_pancake]

As promised here is a diagram of what you need. It contains nothing you have not been told about before but it puts it into one diagram.

Mike,
Is that diode between "A0" and Gnd the right way round?

[rlogiacco]

Could you please go back to your original post and Modify it to include the "design objective"?
I'm sorry, but after so many posts, I think we've nearly lost the plot (that's not an indictment or a nasty aside - it's in the interest of clarity).

Done!

About the other part of your post I'll take some time to re-read it until I get it  :~

[Grumpy_Mike]

Mike,
Is that diode between "A0" and Gnd the right way round?

Yes you are right - sorry. The post is now corrected. Thanks

[rlogiacco]

Things you have to know are
1) Ohms law
2) How currents flow through circuits
3) Basic electricity
Now you might think you know these things but you don't. And you never will if you persist with your attitude.

I admitted my ignorance on op-amps.

And basic electricity. The things you are misunderstanding are not specific to op-amps but apply to the whole of electronics.

Let me try, ok?

1) I = V/R and V = I*Z with many simplifications regarding temperature influences and other non linear factors. You can turn it around and bring in power, but that doesn't change much. There's a second law regarding wire resistance, something like "wire resistance is proportional to wire lenght and inversely proportional to wire section", but that's usually not considered as much important as the first one
2) Current always flows through the easiest path: with a great simplification a circuit is like a pipe full of water. Along this simplification voltage is a measure of height difference between the water source and the sink level (it doesn't matter at what height you are, 5m difference id always 5m), resistors are pipe thightenings, capacitors are tanks, diodes are directional valves, etc... At any pipe junction water will push into the with the outgoing pipes with the same force (measured in volts) but it will flow faster in the bigger pipes (lower resistance). If there's no resistance between the source and the sink then the water will flow at full speed (short circuit). When water flows it will heat up everything it encounters: consider it like a friction between water molecules and the pipes, faster the water flows more heat it generates. If the water flows too fast (high current) then the pipes might melt down breaking the circuit into pieces.
3) Like the atom structure, protons and electrons, the electron charge, the magnet field, principle of heisenberg and all that? Or Coulomb's Law, Farady Cage, Volt arch and stuff like that? Long time I don't touch all that stuff, but I believe I still have some memories here and there... I should be able to refresh and recall that when needed

How much do I get for the electronics basics test?

but I'm here to learn and understand.

If only that were true we would all have a happier time. What you want is for some one to explain exactly why you have these ideas in your head that we are all saying are wrong. You want to know exactly why they are wrong - but in order to do this we need to be a mind reader or to be able to find out and understand the whole of your internal model for electronics. And then correct that.  Sorry that is not going to happen it is just impossible.
The way to learn is to look at and study correct circuits. If there is something you don't understand about these correct circuits then you can ask and it will be explained to you.

If you say something like "hey dude, that R5 resistor there is too big and prevents enough current to flow into your source and that capacitor there is too small and will not smooth your current" I believe it would be a good source of directions.

Anyway, I'm not going to continue this sterile part of the conversation as I know I'm wasting your time other than mine and annoying everybody else who's reading this thread.

I have no idea why you thought that by connecting a 10R resistor in series with your OP- amp's would give you a 500mA load on your arduino. It is so far divorced from reality as to be totally incomprehensible. Therefore I can't explain what you are doing wrong except to say everything. Or would you like me to speculate on the three thousand you could have miscomprehended?

Source was basic Ohm's law: 5V through a 10R resistor imply a 500mA current. Looking at the circuit I draw there was nothing other than that resistor and the opamp between the Arduino +5Vcc and the Arduino GND. If the op-amp impedence was going to be very low then the required current might have exceeded Arduino's current limit.

Does it make sense now? Not that it helps to solve the problem, but it might convince you I'm not completely out of my mind....

Is it possible we are looking at two different datasheets?

Yes we were. I was looking at the one:- SNOSBW5C -APRIL 1998-REVISED APRIL 2013
No idea what one you were looking at because the link you provided did not point to a data sheet but just to the TI web site, therefore there is no way of knowing what one you were looking at.

Actually I did not even try to link the datasheet because I was posting the figure excerpt and I didn't want to put a couple MB attachment when I got complaints about attachments of a few hundred KB.

Now, indipendently from the datasheet source, I now understand referring to figure numbers is going to always work as they get renumbered between datasheet versions.

With regards to the figure I posted, did I interpreted it correctly? Doesn't it say the TL082 will not work with less than +/-4V?
Shouldn't I be able to obtain about 5V swing (+/-2.5V) with a supply voltage of +/-4V?
Shouldn't I be able to obtain that +/-4V supply from a 9V source using a voltage divider (I should get +/-4.5V)?
If I take out of the equation my need to identify wave amplitude can't I use a very high gain to saturate the amplifier and get an almost square wave out of the sine wave?

As promised here is a diagram of what you need. It contains nothing you have not been told about before but it puts it into one diagram.

I'm starting to study it right now: thanks for it!  XD

[rlogiacco]

I've added labels for reference in my questions.

1) diodes D0 and D1 are there to protect arduino against inverse voltage, right?
2) what is the purpose of C2?
3) The op amp is biased at 6V (arduino gnd) thus it's output will swing between 0-10V (considering the datasheet), right?
4) C1 is there to smooth the input line, is C4 there to smooth the output?

Update I'm refreshing my knowledge about capacitors reactance  

5) is C4 R6 an high pass filter?

[Grumpy_Mike]

How much do I get for the electronics basics test?

About half out of three.

1) I = V/R

Yes half a mark

V = I*Z

No. If Z is impedance then you can't say this, it is a vector sum.

2) Current always flows through the easiest path:

No - total myth - current always flows through all possible paths

3) Like the atom structure,

Just rambling - no marks.

Source was basic Ohm's law: 5V through a 10R resistor imply a 500mA current.

Voltage does not go through anything, that is current. 5V across 10R would imply 500mA BUT then you would have zero volts across your amplifier, you are supposed to be powering that and if you had zero volts across it you wouldn't be.

f the op-amp impedence was going to be very low

What makes you think that. Did you look up the supply current for the amplifier in the data sheet?

Doesn't it say the TL082 will not work with less than +/-4V?

Well I would say it was 5V from the data sheet I read.

when I got complaints about attachments of a few hundred KB.

No it was the size of the picture that we moaned about not its data size.

1) diodes D0 and D1 are there to protect arduino against inverse voltage, right?

Right.

2) what is the purpose of C2?

To reduce the impedance of the power supply. This is known as power supply decoupling. That is what C3 is for with the virtual ground.

3) The op amp is biased at 6V

The input is yes.

(arduino gnd)

No this point is not the arduino ground, this is the same as your 12V power supply ground.

thus it's output will swing between 0-10V (considering the datasheet), right?

No, assuming you get a 5V swing, it will swing between 1V and 11V

4) C1 is there to smooth the input line,

No it is to protect the microphone from any DC voltage. This is known as AC coupling.

is C4 there to smooth the output?

No. C4 is used to provide AC coupling into the arduino. This removes the 6V DC bias of the output of the amplifier.
Both C1 and C4 determine the low frequency response, the bigger these capacitor the better the low frequency response.

5) is C4 R6 an high pass filter?

No, C4 see above R6 along with R5 provide the 2.5V DC bias on the arduino input.