Inverted GainClone question?

5150ed · 8th July 2006, 10:02 AM

What would happen if I remove R3 and .1mf cap and connect pin 7 to ground directly?
Is there any harm?

Greg Erskine · 8th July 2006, 12:09 PM

hi 5150ed,

I've made a few IGC, and all have NI input connected directly to ground. So I wouldn't expect you to have any significant problems.

I believe R3 is an attempt to reduce DC offset, I could be wrong. Why don't you try both and see what happens?

regards

jackinnj · 8th July 2006, 12:26 PM

yes, there are some microAmps flowing out of the opamps input pins --

that design uses unusually large resistance -- about 1/4 the magnitude would be better.

janneman · 8th July 2006, 01:00 PM

Yes, the input bias currents are flowing through the two balanced 220k resistors (the 10k on the inv input isn't there for DC) so unbalancing by deleting the one 220k will surely give gross DC output offset.

Cutting down the values on the 220k and 10k series R would be much better, also from a noise standpoint, but that would lower the Zin and you would need a lower vol control than 100k.
This is a major problem in inverting apps and also the reason why most would avoid it.

Jan Didden

5150ed · 8th July 2006, 02:15 PM

Thank you so much.
But I am very new here.

Can you Janneman can you explain in easier words?
I should keep 10K and reduce 220K to how many K?
Is this also reduce gain of my amp? [I am so confused. I am using OPA541AP chip, some said I should keep the gain at only 10, some said between 10 to 20 is ok. Do u have any idea?]

I only have 100K step, can I adjust it to 50K by parallel 100K resistor with the step output?

Nuuk · 8th July 2006, 04:11 PM

If you are new to all this, make things simple for yourself. Don't try to modifiy circuits that you come across with different chips!

Have a look at the circuits on my web site. There is a very basic IGC there and a fairly comprehensive FAQ section.

5150ed · 8th July 2006, 04:26 PM

Thank Nuuk.

Can you give me your web site's address?

Nuuk · 8th July 2006, 05:39 PM

Click on the www at the bottom of my posts.

Christer · 8th July 2006, 05:41 PM

Quote:

Originally posted by Nuuk
Click on the www at the bottom of my posts.

Hm, I can't see any URL there. But he can click on your name "Nuuk" instead, and find the link there.

Nuuk · 8th July 2006, 05:45 PM

There is a button with www on it. In the same place there is a button with email on it at the bottom of your post!

8th July 2006, 12:09 PM	#2
Greg Erskine diyAudio Member Join Date: Jan 2002 Location: Sydney/Australia	hi 5150ed, I've made a few IGC, and all have NI input connected directly to ground. So I wouldn't expect you to have any significant problems. I believe R3 is an attempt to reduce DC offset, I could be wrong. Why don't you try both and see what happens? regards __________________ Greg Erskine

8th July 2006, 01:00 PM	#4
janneman diyAudio Member Join Date: May 2002 Location: Where Germany, The Netherlands and Belgium meet Blog Entries: 6	Yes, the input bias currents are flowing through the two balanced 220k resistors (the 10k on the inv input isn't there for DC) so unbalancing by deleting the one 220k will surely give gross DC output offset. Cutting down the values on the 220k and 10k series R would be much better, also from a noise standpoint, but that would lower the Zin and you would need a lower vol control than 100k. This is a major problem in inverting apps and also the reason why most would avoid it. Jan Didden __________________ /Another new issue: Linear Audio Volume 3!

8th July 2006, 04:11 PM	#6
Nuuk diyAudio Member Join Date: Feb 2003 Location: Somerset, SW England	If you are new to all this, make things simple for yourself. Don't try to modifiy circuits that you come across with different chips! Have a look at the circuits on my web site. There is a very basic IGC there and a fairly comprehensive FAQ section. __________________ The truth need not be veiled, for it veils itself from the eyes of the ignorant.

8th July 2006, 05:39 PM	#8
Nuuk diyAudio Member Join Date: Feb 2003 Location: Somerset, SW England	Click on the www at the bottom of my posts. __________________ The truth need not be veiled, for it veils itself from the eyes of the ignorant.

8th July 2006, 05:45 PM	#10
Nuuk diyAudio Member Join Date: Feb 2003 Location: Somerset, SW England	There is a button with www on it. In the same place there is a button with email on it at the bottom of your post! __________________ The truth need not be veiled, for it veils itself from the eyes of the ignorant.


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8th July 2006, 12:26 PM	#3
jackinnj diyAudio Member Join Date: Apr 2002 Location: Llanddewi Brefi, NJ	yes, there are some microAmps flowing out of the opamps input pins -- that design uses unusually large resistance -- about 1/4 the magnitude would be better.

8th July 2006, 02:15 PM	#5
5150ed diyAudio Member Join Date: Jul 2005 Location: BKK	Thank you so much. But I am very new here. Can you Janneman can you explain in easier words? I should keep 10K and reduce 220K to how many K? Is this also reduce gain of my amp? [I am so confused. I am using OPA541AP chip, some said I should keep the gain at only 10, some said between 10 to 20 is ok. Do u have any idea?] I only have 100K step, can I adjust it to 50K by parallel 100K resistor with the step output?

8th July 2006, 04:26 PM	#7
5150ed diyAudio Member Join Date: Jul 2005 Location: BKK	Thank Nuuk. Can you give me your web site's address?

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