Will this circuit work?

Kolloi · 25th February 2008, 10:06 PM

http://www.fileden.com/files/2007/9/...69/circuit.gif

Just a quick question about this circuit I designed.

The big idea is to take an audio signal, put it through second order low-pass and second order high-pass passive filters so that it's rolled off at 40hz and 15000hz, and then split the signal so that it goes into:

1) a combo of 2nd order low- and high-pass filters rolling off at around 60hz and 125hz; and
2) a combo of 2nd order low- and high-pass filters rolling off at around 2000hz and 4000hz.

After this, the mixed signal from (1) and (2) goes through an op-amp IC in differential configuration to increase the loudness. The feedback and potential divider resistors going to the op-amp are potentiometers i.e. variable resistors.

Please check that the connections are correct, and that the resistances I worked out are correct for the frequencies I want to obtain. The only silver mica capacitors I can obtain are 150pF, so all the caps in this circuit have this capacitance.

Any other comments about the circuit vis a vis its chances of success are welcome. Thanks

gootee · 25th February 2008, 11:08 PM

Hi Kolloi,

I can't say offhand if it will work as you intend for it to work. You might need to either use active filter (i.e. containing opamps) circuits, or, use opamps as unity-gain buffers in between some of your stages.

Note that there is a good 'automatic active filter design' program available, free, from Texas Instruments, at http://www.ti.com . You can go there and do a search for FilterPro, and download it. I have used it and it works very well. It gives a labeled schematic and plots the frequency response, given your specs, for any of the many types of standard filter responses, from which you can choose.

I strongly recommend that you download the free LTspice software, to simulate your circuit's operation.

You should be able to right-click on the following link and then select 'Save target As', to download the LTspice installation software:

http://ltspice.linear.com/software/swcadiii.exe

Have fun!

Leolabs · 26th February 2008, 12:34 AM

Just add an input buffer will do.Also the output buffer should be a JFET OPAMP.

Kolloi · 26th February 2008, 05:20 PM

Thanks gootee! Those programs look very useful and I will make some use of them in the future for sure.

Leolabs, thanks for your note about the op-amp type. I have added an input buffer stage as per your advice, and it looks like this now:

http://www.fileden.com/files/2007/9/...9/circuit2.gif

Hopefully this will ensure that the signal is strong enough for the passive filters to have a meaningful effect, and for the output to be at line level. At the moment the resistors around the 2 op-amps use pots, so that I have a realistic idea of the feasibility when I build it and play around with it.

25th February 2008, 10:06 PM	#1
Kolloi diyAudio Member Join Date: Dec 2007	Will this circuit work? http://www.fileden.com/files/2007/9/...69/circuit.gif Just a quick question about this circuit I designed. The big idea is to take an audio signal, put it through second order low-pass and second order high-pass passive filters so that it's rolled off at 40hz and 15000hz, and then split the signal so that it goes into: 1) a combo of 2nd order low- and high-pass filters rolling off at around 60hz and 125hz; and 2) a combo of 2nd order low- and high-pass filters rolling off at around 2000hz and 4000hz. After this, the mixed signal from (1) and (2) goes through an op-amp IC in differential configuration to increase the loudness. The feedback and potential divider resistors going to the op-amp are potentiometers i.e. variable resistors. Please check that the connections are correct, and that the resistances I worked out are correct for the frequencies I want to obtain. The only silver mica capacitors I can obtain are 150pF, so all the caps in this circuit have this capacitance. Any other comments about the circuit vis a vis its chances of success are welcome. Thanks

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25th February 2008, 11:08 PM	#2
gootee diyAudio Member Join Date: Nov 2006 Location: Indiana Blog Entries: 1	Hi Kolloi, I can't say offhand if it will work as you intend for it to work. You might need to either use active filter (i.e. containing opamps) circuits, or, use opamps as unity-gain buffers in between some of your stages. Note that there is a good 'automatic active filter design' program available, free, from Texas Instruments, at http://www.ti.com . You can go there and do a search for FilterPro, and download it. I have used it and it works very well. It gives a labeled schematic and plots the frequency response, given your specs, for any of the many types of standard filter responses, from which you can choose. I strongly recommend that you download the free LTspice software, to simulate your circuit's operation. You should be able to right-click on the following link and then select 'Save target As', to download the LTspice installation software: http://ltspice.linear.com/software/swcadiii.exe Have fun!

26th February 2008, 12:34 AM	#3
Leolabs diyAudio Member Join Date: Dec 2004 Location: Bukit Mertajam	Just add an input buffer will do.Also the output buffer should be a JFET OPAMP.

26th February 2008, 05:20 PM	#4
Kolloi diyAudio Member Join Date: Dec 2007	Thanks gootee! Those programs look very useful and I will make some use of them in the future for sure. Leolabs, thanks for your note about the op-amp type. I have added an input buffer stage as per your advice, and it looks like this now: http://www.fileden.com/files/2007/9/...9/circuit2.gif Hopefully this will ensure that the signal is strong enough for the passive filters to have a meaningful effect, and for the output to be at line level. At the moment the resistors around the 2 op-amps use pots, so that I have a realistic idea of the feasibility when I build it and play around with it.