What is difference between two circuits

LoveVirus · 16th November 2011, 12:54 PM

toprepairman · 16th November 2011, 12:59 PM

In the first circuit you will have only 50uF decoupling between pins 4 and 8.

LoveVirus · 16th November 2011, 01:07 PM

If so, is it better the second circuit, the circuit capacity is also simple.

janneman · 16th November 2011, 01:29 PM

In the second circuit you can still have supply ripple and noise on the supply lines that can get into the circuit. You can also still have coupling via the supply that can under circumstances lead to oscillations.
So you should always use the circuit 1, and then add circuit 2 if you want.
But it is important to get clean supplies referenced to the signal reference, and that normally is ground.

jan didden

DF96 · 16th November 2011, 03:00 PM

The second circuit does not deal with common-mode noise on the supply rails, but only differential-mode noise.

sreten · 16th November 2011, 03:36 PM

Quote:

Originally Posted by toprepairman

In the first circuit you will have only 50uF decoupling between pins 4 and 8.

Hi,

I can see that appears to be case but surely that is not the point if
the purpose of the decoupling is to decouple voltage rails to ground,
which it is I believe, rather than to each other, which it usually isn't.

As DF implies the second circuit has effectively 0uF for common mode.
The first circuit doesn't care about common / differential signals, and
as I understand it should always be used to guarantee stability.

I can't see the point of the second circuit.

rgds, sreten.

CBS240 · 16th November 2011, 07:09 PM

Since the PS supply caps, input, and output of the op-amp are referenced to gnd, so must the de-coupling caps or the circuit is not completed. IOW, the supply pins of the op-amp must have AC reference to gnd via the de-coupling along with the rest of the IC or instability may take place.

LoveVirus · 17th November 2011, 02:20 AM

Unfortunately I do not have equipment, which have the equipment to an experiment, the results made up better, I think just a noise to provide a capacitor discharge circuit diarrhea, do not know that understanding correct?

16th November 2011, 01:29 PM	#4
janneman diyAudio Member Join Date: May 2002 Location: Where Germany, The Netherlands and Belgium meet Blog Entries: 6	In the second circuit you can still have supply ripple and noise on the supply lines that can get into the circuit. You can also still have coupling via the supply that can under circumstances lead to oscillations. So you should always use the circuit 1, and then add circuit 2 if you want. But it is important to get clean supplies referenced to the signal reference, and that normally is ground. jan didden __________________ /Another new issue: Linear Audio Volume 3!

16th November 2011, 07:09 PM	#7
CBS240 diyAudio Member Join Date: Aug 2005 Location: K-town	Since the PS supply caps, input, and output of the op-amp are referenced to gnd, so must the de-coupling caps or the circuit is not completed. IOW, the supply pins of the op-amp must have AC reference to gnd via the de-coupling along with the rest of the IC or instability may take place. __________________ All the trouble I've ever been in started out as fun......

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16th November 2011, 12:59 PM	#2
toprepairman diyAudio Member Join Date: Nov 2010	In the first circuit you will have only 50uF decoupling between pins 4 and 8.

16th November 2011, 01:07 PM	#3
LoveVirus diyAudio Member Join Date: Jul 2010	If so, is it better the second circuit, the circuit capacity is also simple.

16th November 2011, 03:00 PM	#5
DF96 diyAudio Member Join Date: May 2007	The second circuit does not deal with common-mode noise on the supply rails, but only differential-mode noise.

17th November 2011, 02:20 AM	#8
LoveVirus diyAudio Member Join Date: Jul 2010	Unfortunately I do not have equipment, which have the equipment to an experiment, the results made up better, I think just a noise to provide a capacitor discharge circuit diarrhea, do not know that understanding correct?

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