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schematic

simulate this circuit – Schematic created using CircuitLab

I am testing an active lowpass filter based on the LM833 Opamp. Basically I am testing different values of power supply to see how they affect the output.

I first tried the 5V from Arduino, all ok except the signal gets distorted.

In an attempt to improve the output signal I connected the opamp with a 9V external DC power supply. I thought it should work, since 9V is far below the Max VCC accepted by the LM833. Well I was wrong. The device started to smell very bad. It's because of the current? The power supply can supply up to 1A. What am I doing wrong?

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  • \$\begingroup\$ Crystal ball error. To get a meaningfull answer you must give us all details, like the circuit diagram, and preferrably also a photo of how you realised it. \$\endgroup\$ – Wouter van Ooijen Sep 15 '15 at 11:40
  • \$\begingroup\$ If your circuit is correct (show us!) then 9V should not pose any problems. Maybe you connected the supply in reverse ? When experimenting without a current-limited lab supply there is always a chance that you blow up your components. \$\endgroup\$ – Bimpelrekkie Sep 15 '15 at 11:43
  • \$\begingroup\$ On a 5V supply you will get poor signal quality and note that the signal needs to be centred at 2.5 volts and not 0V. This includes any loads on the output. In fact cancel that - it needs a minimum supply of 10V to work reliably and within spec with inputs and output loads centred at +5V. \$\endgroup\$ – Andy aka Sep 15 '15 at 11:43
  • \$\begingroup\$ You made an error. See here, * points * and here, and this there. Also you need to connect that to that, and here you have this the other way round. \$\endgroup\$ – PlasmaHH Sep 15 '15 at 11:48
  • \$\begingroup\$ I added an image of my circuit. \$\endgroup\$ – Enrico Sep 15 '15 at 12:00
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Well I think you have most of the answers now so try this: Use a split rail supply i.e. +/- 5V or greater (not less) with the centre point connected to the arduino ground. This means the op-amp receives signals that are centred to its power rails. Disconnect the sound card input and check that it isn't warming up. If it is throw it in the trash and fit another IC if you are confident it is wired correctly.

When you are happy with this stage connect the ouput to the sound card via a 1kohm resistor and hopefully, it'll be fine.

Don't try running it with a total supply rail less than 10V because there is no guarantee it will work. I might also be tempted to put a 1uF capacitor in series with R1 (on the arduino side) just to prevent any DC getting into the input. If you do do that you'll need a 10k resistor down to ground straight after the 1uF.

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  • \$\begingroup\$ Thanks for your solution. I think my error was I was powering it with the wrong polarity. Is there a way to use a singe supply configuration? The input signal has already a 2.5V DV component, and it spans from 0 to 1V \$\endgroup\$ – Enrico Sep 15 '15 at 19:46
  • \$\begingroup\$ Just try it and see but keep the AC signal voltage levels low to avoid clipping and distortion. I think on a 5V supply it might just not work at all. Pot luck really. \$\endgroup\$ – Andy aka Sep 15 '15 at 21:19
  • \$\begingroup\$ I decided to use +12V as power supply. The Arduino board accepts it without problems, and trough the Vin pin I can power the opamp. \$\endgroup\$ – Enrico Sep 15 '15 at 21:51

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