Active Filter Network - Page 2

richie00boy · 15th March 2005, 09:30 AM

Quote:

Originally posted by Matttcattt
The buffers, or all the opamps?

Quote:

Originally posted by richie00boy
output of each op-amp that will drive a cable

So that would be the buffers then.

Quote:

Originally posted by Matttcattt
Which filters? The lowpass?

Quote:

Originally posted by richie00boy
for your sub low-pass as well instead of using a 0.22uF

It would seem so.

Matttcattt · 17th March 2005, 08:45 PM

I dont apear to have read you reply very well.

Thank you for your advice.

I'd better get on with building them...

[edit]: I've updated the diagram to check i've got the right idea.

carlosfm · 17th March 2005, 09:55 PM

Quote:

Originally posted by Matttcattt
I've updated the diagram to check i've got the right idea.

For the summing op-amp I would use lower value resistors (like 22k).
You have an input buffer now.
Also, you will optimize dc-offset if instead of connecting NI directly to ground you use a resistor.
That resistor value should be the parallel combination of the other three resistors.

richie00boy · 18th March 2005, 07:13 AM

Agree with that. Also I'd put the 100 ohm resistors on the outputs of the left and right lines as well. 22k would also be a good value of input impedance for your new input buffers.

Matttcattt · 23rd March 2005, 12:28 AM

Ok, i've made some changes, and ringed them as the diagram is quite large... Is everything i've changed ok?

[edit]:forgot the image...

richie00boy · 23rd March 2005, 07:29 AM

Looks good but those 10k resistors on the output to ground are redundant.

carlosfm · 23rd March 2005, 06:02 PM

Quote:

Originally posted by richie00boy
Looks good but those 10k resistors on the output to ground are redundant.

No, they are not redundant.

The chips need a path to ground when there's nothing connected on their outputs.

richie00boy · 23rd March 2005, 06:08 PM

Why is that Carlos? In the dozens of such circuits I have built it has yet to appear a problem. Sure the input if floating needs them to provide bias current, but I don't see why the output needs them.

carlosfm · 23rd March 2005, 06:34 PM

Quote:

Originally posted by richie00boy
Why is that Carlos? In the dozens of such circuits I have built it has yet to appear a problem. Sure the input if floating needs them to provide bias current, but I don't see why the output needs them.

The output should not be floating, as it will if there's no device connected.
It needs a return path.
Just try what happens when an op-amp has it's output(s) floating. Touch the op-amp with your finger and feel the heat.

pinkmouse · 23rd March 2005, 06:37 PM

What heat? I've never noticed any.

18th March 2005, 07:13 AM	#14
richie00boy Did it Himself diyAudio Member Join Date: Nov 2003 Location: Gloucestershire, England, UK	Agree with that. Also I'd put the 100 ohm resistors on the outputs of the left and right lines as well. 22k would also be a good value of input impedance for your new input buffers. __________________ www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more

23rd March 2005, 07:29 AM	#16
richie00boy Did it Himself diyAudio Member Join Date: Nov 2003 Location: Gloucestershire, England, UK	Looks good but those 10k resistors on the output to ground are redundant. __________________ www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more

23rd March 2005, 06:08 PM	#18
richie00boy Did it Himself diyAudio Member Join Date: Nov 2003 Location: Gloucestershire, England, UK	Why is that Carlos? In the dozens of such circuits I have built it has yet to appear a problem. Sure the input if floating needs them to provide bias current, but I don't see why the output needs them. __________________ www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more

23rd March 2005, 06:37 PM	#20
pinkmouse diyAudio Moderator Join Date: Apr 2002 Location: Chatham, England	What heat? I've never noticed any. __________________ Al I conceive of nothing, in religion, science or philosophy, that is more than the proper thing to wear, for a while. Charles Fort

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