Oscillation and/or eventual clipping?
10 ohm load seems way too low for a 741.
Also do make sure the op-amp is unity gain stable. I could not find any information regarding that on the data sheet ...
Yeah its pretty low, what i found though, I went from 800, 100 and then 10.
While loading with 800 or 100, I seemed to get a very random oscillation that was actually not even a sine-wave, it was a squarewave.
So i must have messed up somewhere, but I do not really find with what
While loading with 800 or 100, I seemed to get a very random oscillation that was actually not even a sine-wave, it was a squarewave.
So i must have messed up somewhere, but I do not really find with what
Hello,
Yes, you can use 741 as long as you do go for high frequencies.
The TLxxx series have JFET in the input which gives a much higher impedance and also this opamp has much better bandwidth.
For this troubleshooting, working with 1kHz, it's ok the 741.
Are you building the opamp circuit in a protoboard?
I'm assuming you are first testing the opamp separated from the TDA, right?
If yes, you need to decouple the power supply with capacitors (try electrolytic and also film) as close as possible to the opamp (+V pin 7 and -V pin 4 for LM741).
Try 10uF, 100uF for electrolytic and 100nF for film.
And also try to choose a good or different ground connection (where the gnd from power supply connects to the protoboard).
Also try to connect scope GND lead closer to the power supply GND. You have to play around to find a good connection.
You need to get rid of these oscillations. I'm quite sure it's a matter of decoupling.
If you can take a picture of your wiring, I can suggest something.
In terms of load, 10 ohms is too low for 741. Try to test with 2.2kohm to 10kohm to start with.
It has been a long time I don't use 741. I searched here but I didn't find any 741 in my component box, so I will not be able to test it.
I was playing this afternoon with my TDA2003 and I connected a TL072 which worked fine without any 2nd harmonic distortion, but after some fight with oscillations too. I'm in a protoboard with full of wires.
When increasing the source impedance to drive the TDA2003, I do see some increase of 2nd harmonic distortion.
During these tests, I used an old cellphone to generate 1kHz. Since this is a headphone output, the impendance is very low and not distortion was observed if connected directly to the TDA. You may also try this setup to observe the 2nd harmonic instead of the opamp buffer.
Yes, you can use 741 as long as you do go for high frequencies.
The TLxxx series have JFET in the input which gives a much higher impedance and also this opamp has much better bandwidth.
For this troubleshooting, working with 1kHz, it's ok the 741.
Are you building the opamp circuit in a protoboard?
I'm assuming you are first testing the opamp separated from the TDA, right?
If yes, you need to decouple the power supply with capacitors (try electrolytic and also film) as close as possible to the opamp (+V pin 7 and -V pin 4 for LM741).
Try 10uF, 100uF for electrolytic and 100nF for film.
And also try to choose a good or different ground connection (where the gnd from power supply connects to the protoboard).
Also try to connect scope GND lead closer to the power supply GND. You have to play around to find a good connection.
You need to get rid of these oscillations. I'm quite sure it's a matter of decoupling.
If you can take a picture of your wiring, I can suggest something.
In terms of load, 10 ohms is too low for 741. Try to test with 2.2kohm to 10kohm to start with.
It has been a long time I don't use 741. I searched here but I didn't find any 741 in my component box, so I will not be able to test it.
I was playing this afternoon with my TDA2003 and I connected a TL072 which worked fine without any 2nd harmonic distortion, but after some fight with oscillations too. I'm in a protoboard with full of wires.
When increasing the source impedance to drive the TDA2003, I do see some increase of 2nd harmonic distortion.
During these tests, I used an old cellphone to generate 1kHz. Since this is a headphone output, the impendance is very low and not distortion was observed if connected directly to the TDA. You may also try this setup to observe the 2nd harmonic instead of the opamp buffer.
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Try 5532, TL07x series has a higher slew rate than 2003 can tolerate, needs to be max. 8 uV/sec, the TL07x series does 13.
741 has very low slew rate. Signal chip, not intended for audio use.
Put a socket there, easy to swap out op amps.
4558 will be just enough, I have tried the 358 also when I was building a phono pre amp.
Finally put TL072, it worked, as the slew rate of LPs is not as high as CDs.
In my experience, the 741 and 358 were terrible for audio use, 4558 was bad, 5532 not tried, and TL072 was best.
Put a socket there, easy to swap out op amps.
4558 will be just enough, I have tried the 358 also when I was building a phono pre amp.
Finally put TL072, it worked, as the slew rate of LPs is not as high as CDs.
In my experience, the 741 and 358 were terrible for audio use, 4558 was bad, 5532 not tried, and TL072 was best.
358 doesn’t even have enough slew rate to use as a phono preamp. Unequalized the signal has enough HF content to overload one. Horribly - it sounds as bad as stylus mistracking. Doing the gain all in one stage with low pass in the feedback doesn’t even seem to help. That’s even after the crossover distortion fix. Stick with TL07x, TL08x. 5532 has lower noise and more drive capability, neither of which is needed. And costs more mA of supply current.
I was playing...just put different chips in the socket of the phono preamp I was making.
I think the 741 is even slower than the 358 in terms of slew rate.
My hint to 2nd harmonic problem was that the op amp may not properly match the chip amp...so try another!
I think the 741 is even slower than the 358 in terms of slew rate.
My hint to 2nd harmonic problem was that the op amp may not properly match the chip amp...so try another!
Alright,
Thanks everyone for chipping in.
So first off. I did try feeding it (TDA2004R, not opamp) with 2 different mp3-players and lately a more modern mobilephone via the headphone jack. It is the same 2nd harmonic, unfortunately.
Later I did pull out a TL081 instead that i found, moved it over to a "new" circuit with a soldered protoboard instead. With the exact circuit as the one posted above, including values.
Unfortunately results are very poor anyway. This time around i get my sine-wave, but output has a very very low amplitude compared to the input for some reason.
Turns out this op-amp adventure was way more finicky than i thought 😵
I need to tripple check this also of course, but looks like this op-amp thing might introduce more errors then its helping right now, especially since its being very very delicate if I understand correctly.
When I get more time I will see if I can redo the whole thing again!
Thanks everyone for chipping in.
So first off. I did try feeding it (TDA2004R, not opamp) with 2 different mp3-players and lately a more modern mobilephone via the headphone jack. It is the same 2nd harmonic, unfortunately.
Later I did pull out a TL081 instead that i found, moved it over to a "new" circuit with a soldered protoboard instead. With the exact circuit as the one posted above, including values.
Unfortunately results are very poor anyway. This time around i get my sine-wave, but output has a very very low amplitude compared to the input for some reason.
Turns out this op-amp adventure was way more finicky than i thought 😵
I need to tripple check this also of course, but looks like this op-amp thing might introduce more errors then its helping right now, especially since its being very very delicate if I understand correctly.
When I get more time I will see if I can redo the whole thing again!
Hi!
It's not easy when in protoboard or in untested PCB.
See below, what my setup looks like while we were discussing since the begining so you can compare with yours.
In the protoboard, I added the opamp with single voltage, the same of the TDA2003 following the schematics I suggested.
Note that there is no ground high current flowing in the protoboard.
Ground goes directly to the heatsink and from there to the speaker.
High current only in a single connection from TDA to the output capacitor and the +V rail, which only feeds the TDA and the opamp.
This way, I don't create spurious GND voltages along the protoboard connections.
This setup has less than 0.3% of THD as seen in the picture.
But if I play around with decoupling capacitors, move the GND connections, move speaker connections or put big resistor (>47k) in series with TDA input, the 2nd harmonic shows up at around 1% same as yours.
It's not easy when in protoboard or in untested PCB.
See below, what my setup looks like while we were discussing since the begining so you can compare with yours.
In the protoboard, I added the opamp with single voltage, the same of the TDA2003 following the schematics I suggested.
Note that there is no ground high current flowing in the protoboard.
Ground goes directly to the heatsink and from there to the speaker.
High current only in a single connection from TDA to the output capacitor and the +V rail, which only feeds the TDA and the opamp.
This way, I don't create spurious GND voltages along the protoboard connections.
This setup has less than 0.3% of THD as seen in the picture.
But if I play around with decoupling capacitors, move the GND connections, move speaker connections or put big resistor (>47k) in series with TDA input, the 2nd harmonic shows up at around 1% same as yours.
Alright! So third times the charm. Now at least I got a signal, about the same in as out, and this is what is intended I hope? As we are aming for this as a buffer.
However, In my first measurements I got some really disappointing results. Its even noisier in the output than the TDA, please see the attached screenshot.
Clear 2nd harmonic is still there, plus a lot of other stuff going on I think it looks like?
Now some observations on tonight's tests:
Since the circuit feels pretty noisy and we hunt a pretty small issue on the "real" problem, i guess a attempt to move the circuit to a soldered stripboard would be next course of action?
Just one "click" below when 2nd harmonic dissapears:
However, In my first measurements I got some really disappointing results. Its even noisier in the output than the TDA, please see the attached screenshot.
Clear 2nd harmonic is still there, plus a lot of other stuff going on I think it looks like?
Now some observations on tonight's tests:
- I did dab around a bit with decoupling capacitors, however it did not really make a difference.
- At least now this 2nd harmonics or the others does not reflect on the player side, so that's a good start?
- There are a very distinctive difference in the 2nd harmonics if I go above 50% volume on the player
Since the circuit feels pretty noisy and we hunt a pretty small issue on the "real" problem, i guess a attempt to move the circuit to a soldered stripboard would be next course of action?
Just one "click" below when 2nd harmonic dissapears:
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Oop, should add that the above measurement is still just the op-amp stand-alone. Only the 4.7kohm resistor and then the oscilloscope hooked up,
I would use a pot to adjust line in level to the chip, or electronically.
I use the Winamp player on my computer as the input signal, and the wrong signal level can have issues with the sound quality.
I use the volume control on the computer program, the 'sound mixer' in the computer main settings has all levels maxed out, and the circuit I am testing is then checked.
Winamp is the player I am most familiar with, it has many competitors, with different levels of complexity..that is your choice, I have no ties to Winamp or their competition.
I use the Winamp player on my computer as the input signal, and the wrong signal level can have issues with the sound quality.
I use the volume control on the computer program, the 'sound mixer' in the computer main settings has all levels maxed out, and the circuit I am testing is then checked.
Winamp is the player I am most familiar with, it has many competitors, with different levels of complexity..that is your choice, I have no ties to Winamp or their competition.
Hello!
Ok, at least some buffering function we are getting - there is no 2nd order harmonic reflected to the source.
I understood that when opamp is disconnected from the TDA, it is clear (2nd screenshot) and when you connect it to the TDA, you get all the noise signal (1st screenshot).
With this amount of noise, I would first look at the time domain to make sure we see a clear sinewave form. Looking in time domain, we may see if it is an oscillation, distortion, clipping etc. Looking only at the frequency domain, we are unable to see what is causing the harmonics/noise.
Before you go to a soldered opamp solution, if you want to show a picture of your setup, I may try to give you some suggestions.
It should work in a solder less breadboard ans it is working here at home. I started with a lot of problems too. but got them resolved.
I'm curious about how the power supply leads are being connected to TDA and to opamp protoboard.
When building things before PCB, there are some tricks or workarounds here and there that can be made to resolve oscillation issues.
Since this player might not be super high quality (you may tell me), as you set different volumes it might distort the signal a bit.
I noticed the same with the old smartphone I was using if I max the volume - was no clipping, but distortion increased.
So everytime I checked the TDA output for harmonics, I also checked if the input was clear from harmonics. You have to be digilent to check and recheck everything. I know you are doing that, since you discovered that at sometime the 2nd harmonic was present in the input.
Hey! Thanks.
So lets back up a little bit, I might not have been as clear as i thought i was 😀
I still have not tried the op-amp with the TDA, all measurements so far is a standalone circuit, before involving the TDA.
The two different measurement you see, is with only oscilloscope and the 4.7kohm resistor from the circuit.
The measurement with distortion is when i go above like 50% or 60% volume on the player, and the one without is just one "click" down from it in volume.
So, Maybe the op-amp needs to be loaded down more or something of that sorts? I wanted to get the op-amp as good as possible before messing with the TDA again, just so we can know we are not introducing even more errors.
However it is still true that the 2nd harmonic observed on the output of the opamp does not "taint" the input of the opamp, as the situation is with the TDA currently.
So lets back up a little bit, I might not have been as clear as i thought i was 😀
I still have not tried the op-amp with the TDA, all measurements so far is a standalone circuit, before involving the TDA.
The two different measurement you see, is with only oscilloscope and the 4.7kohm resistor from the circuit.
The measurement with distortion is when i go above like 50% or 60% volume on the player, and the one without is just one "click" down from it in volume.
So, Maybe the op-amp needs to be loaded down more or something of that sorts? I wanted to get the op-amp as good as possible before messing with the TDA again, just so we can know we are not introducing even more errors.
However it is still true that the 2nd harmonic observed on the output of the opamp does not "taint" the input of the opamp, as the situation is with the TDA currently.
Hello!
Ah ok, now I understood the "one click down" difference. 🙂
You're right, first clean up the opamp and later on connect it to TDA.
Just to make myself clear, first circuit analysis or visualization is always best done looking in time domain, so looking at the waveform.
Once the waveform looks good, then you move to frequency analysis (spectrum analysis) to get the minimum details (THD <2%, <1% etc).
For example: 1% THD cannot be checked visually in a waveform. But, if you see 10% THD in spectrum analysis, you are not able to see where that distortion comes from - it might be clipping, crossover distortion, noise, oscillations etc. We can see 10% distortion in waveform and we will see whats going on.
Maybe when you crank up the player volume, there might be some saturation (clipping) right at the output or saturation in the opamp that you can see in the waveform.
So, check the time domain waveform and post here if you prefer that I take a look on that.
Ah ok, now I understood the "one click down" difference. 🙂
You're right, first clean up the opamp and later on connect it to TDA.
Just to make myself clear, first circuit analysis or visualization is always best done looking in time domain, so looking at the waveform.
Once the waveform looks good, then you move to frequency analysis (spectrum analysis) to get the minimum details (THD <2%, <1% etc).
For example: 1% THD cannot be checked visually in a waveform. But, if you see 10% THD in spectrum analysis, you are not able to see where that distortion comes from - it might be clipping, crossover distortion, noise, oscillations etc. We can see 10% distortion in waveform and we will see whats going on.
Maybe when you crank up the player volume, there might be some saturation (clipping) right at the output or saturation in the opamp that you can see in the waveform.
So, check the time domain waveform and post here if you prefer that I take a look on that.
Alright! New measurements incoming. These are a pair, normal time domain in one and FFT view in the other!
What do we think about it? I dont think its a matter of clipping at least, but today one can clearly see that we even got a 3rd harmonic now even 4th maybe?
So it got more unstable over night 😀
FFT:
And finally the nightmare itself:
What do we think about it? I dont think its a matter of clipping at least, but today one can clearly see that we even got a 3rd harmonic now even 4th maybe?
So it got more unstable over night 😀
FFT:
And finally the nightmare itself:
Hi! Ok, THD is -40dB (1%), so the sinewave looks clear. This is the point where we really need spectrum analysis to check harmonics.
In this case, is the input real clear from harmonics? Cause the opamp looks quiet and the signal is small (100mV), thus way far from clipping.
One thing I missed is the bias decoupling RC as shown below. In single ended like this, it is a must.
If you don't do that, any noise from power supply, including ripple, will be injected to the opamp input.
Values are not critical, but use an RC with fc way below 1Hz (fc=1/(2*PI*R*C))
I'm not seen all that oscillations you got the other day, but, in case you come across with that again, you can decouple the power supply right in the protoboard as shown below to avoid any power supply problem.
Sometimes I put film 100nF, sometimes electrolityc 100uF, 220uF etc.
You may try different values and positions in the protoboard while observing the spectrum analysis (the harmonics).
In this case, is the input real clear from harmonics? Cause the opamp looks quiet and the signal is small (100mV), thus way far from clipping.
One thing I missed is the bias decoupling RC as shown below. In single ended like this, it is a must.
If you don't do that, any noise from power supply, including ripple, will be injected to the opamp input.
Values are not critical, but use an RC with fc way below 1Hz (fc=1/(2*PI*R*C))
I'm not seen all that oscillations you got the other day, but, in case you come across with that again, you can decouple the power supply right in the protoboard as shown below to avoid any power supply problem.
Sometimes I put film 100nF, sometimes electrolityc 100uF, 220uF etc.
You may try different values and positions in the protoboard while observing the spectrum analysis (the harmonics).
Great! Okey, I see now that I missed to put back the 470uF capacitor at the 4.7kohm resistor, I tried to clean the circuit up a bit, and forgot that of course.
Will attempt your suggested improvements and see what I can find! 👍
BTW I see also now when checking my own picture that I might have confused something.
In the schematic, is offset N2 directly connected to V+? If so, I see I made a major mistake 😀 😵💫
Will attempt your suggested improvements and see what I can find! 👍
BTW I see also now when checking my own picture that I might have confused something.
In the schematic, is offset N2 directly connected to V+? If so, I see I made a major mistake 😀 😵💫
Hello!
So, in the datasheet for the TL081, they call the "Input offset adjustment" pins "offset N1" & "offset N2"
I must confirm some concepts here, because I really cannot seem to get this one right 🤯
I will redo this circuit one last time, because I think i got some things very wrong, surprised i even got a signal out tbh 😀
Also, is it really a dead short between out and -? No resistor there?
In your schematics for example, if i read it correctly, Offset N1 (Pin1) should be directly shorted to ground, and Offset N2(Pin 5) directly shorted to V+?
Do we still feed the chip on VCC+/VCC-?
So, in the datasheet for the TL081, they call the "Input offset adjustment" pins "offset N1" & "offset N2"
I must confirm some concepts here, because I really cannot seem to get this one right 🤯
I will redo this circuit one last time, because I think i got some things very wrong, surprised i even got a signal out tbh 😀
Also, is it really a dead short between out and -? No resistor there?
In your schematics for example, if i read it correctly, Offset N1 (Pin1) should be directly shorted to ground, and Offset N2(Pin 5) directly shorted to V+?
Do we still feed the chip on VCC+/VCC-?