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Topics => Robotics => Topic started by: zaciatok on Jun 14, 2013, 07:04 pm

Title: op-amp:Gain Tunning Problem
Post by: zaciatok on Jun 14, 2013, 07:04 pm
Hello,
I would like to ask you very kindly the following question:
I'm trying to make an active low pass filter, It consists of 3 parts. First one is to develop a bipolar symmetric source in order to connect a op-amp ua741, the second is to implement an active low pass filter using that op-amp. Up to this point everything is going well. But when I connect the second op-amp and put the suitable resistors. So there is starting a problem with the bipolar symmetric source, which is not symmetric anymore. So, I get more negative voltage than positive and I don't know why? Can somebody explain me why?
Thank you in advance for your response.
Best regards
Title: Re: op-amp:Gain Tunning Problem
Post by: retrolefty on Jun 14, 2013, 09:41 pm
Best to post a schematic drawing if you expect useful help. The use of 741 type opamps in this day and age is also questionable.

Lefty
Title: Re: op-amp:Gain Tunning Problem
Post by: AndiJay on Jun 15, 2013, 03:49 am
Whut?

Yea, you need to at least post some schematics of what you're trying to do.

What does "bipolar symmetric source" even mean? Are you talking about some sort of current mirror or something?
Title: Re: op-amp:Gain Tunning Problem
Post by: oric_dan on Jun 15, 2013, 06:09 am
If you do a google search, you'll probably find 1000 webpages that have the solution
to an opAmp active low-pass filter.

You will not get symmetrical outputs, either if your gain is too high and one of the
stages has a DC offset, or you're using a single-ended power supply.