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Author Topic: [SOLVED] TL082 preamp: help please!  (Read 8381 times)
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Roma - Italy
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Ok, I got a little forward step here, I believe.

First of all I managed to identify the mains pick up source by observing changes in the input wave reported in my software oscilloscope (I'm proud of that little piece of software  smiley-cool). I've replaced my voltage supply to fix this, I believe my transformer cables where acting as antenna (about 1m/3' wire lenght)

Now I have an almost flat input with no signal, but I still have some sort of reasonance/disturbance: my best guess this is caused by signal interferences due to the breadboard/wiring.

Does it sound?

Note: green wave is picked before amplification, blue wave after amplification.

UPDATE: I've added another attchment referring to a 33Hz sine wave: it seems clearer the interference going on


* 20Hz.png (9.29 KB, 1000x400 - viewed 23 times.)

* 33Hz.png (9.72 KB, 1000x400 - viewed 14 times.)
« Last Edit: December 01, 2013, 01:15:16 pm by rlogiacco » Logged

Manchester (England England)
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I believe my transformer cables where acting as antenna (about 1m/3' wire lenght)
Sounds plausible.

Well done on the progress.  smiley
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Roma - Italy
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Well, I found the cause of the interference, including the previous one: it was the other channel as my audio connector and cable is delivering two stereo channels and I had another frequency on that one.

Is it normal for the two channels frequencies to interfere each other? Is it a consequence of bad wiring? If that is normal behavior then my entire project might get blown away...

Anyway I want to thank all those that helped me with this: you guys are amazing!

I will add the final circuit diagram and an example output trace for the records ASAP.

I'll switch to a different opamp in a couple of days: get ready for another flow of issues and questions  smiley-grin
« Last Edit: December 01, 2013, 05:05:45 pm by rlogiacco » Logged

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Is it normal for the two channels frequencies to interfere each other?
Yes it is called cross talk, you can minimise it but you can never get rid of it all. Two circuits running so close to each other are bound to give you problems. One way to minimise it is to have good supply decoupling, using inductors in a Pi filter like I show for a motor on this page.
http://www.thebox.myzen.co.uk/Tutorial/De-coupling.html
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