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 Post subject: LM741 Band Pass Filters
PostPosted: 20 Jan 2018, 23:59 
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Joined: 20 Jan 2018, 23:24
Posts: 5
Hello All;

This is my first post. I did a bit of searching and I wasn't able to find my topics in the previous topics here.
I am building a desktop clock radio with 2.1 sound. I'd like to build everything but the power supply from the ground up.

Currently, I am in the design phase of the band pass filters.
I found this terrific guide from TI: http://www.ti.com/lit/an/sloa093/sloa093.pdf
From the introduction:
Quote:
This document is intended for designers that do not have the time to check filter theory in old
college textbooks—and try to translate transfer equations into something that can be put into
production.

Which means it's perfect for me.

I intend to use a total of 4 filters, all using the LM471 http://www.ti.com/lit/ds/symlink/lm741.pdf op amp:
1) low pass filter with a transition frequency of 16,384 Hz
2) high pass filter with a transition frequency of 16.35 Hz
*) Split signal and run the last two on parallel channels
3a) low pass filter for the bass channel with a transition frequency of 261.63 Hz
3b) high pass filter for the full range channel with a transition frequency of 130.81 Hz

If this is a good plan I can easily follow the guide, do the math, and build it.

I have a few questions before I get to all that:
1) Have I made any major errors in my plan? I'm new to this
2) Will I need a second set for stereo sound?
3) If so, how can I ensure that sound from both left and right channel make it to the one bass speaker?
4) Is the LM741 a good op amp, or is there a better choice for a similar price?

Thank you for any help
I look forward to your responses :)


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PostPosted: 21 Jan 2018, 00:16 
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Joined: 08 Aug 2009, 03:11
Posts: 2225
Location: Chilliwack, BC
Hi, welcome!

BubbaGump wrote:
I am building a desktop clock radio with 2.1 sound. I'd like to build everything but the power supply from the ground up.


My first clock radio when I was young was a larger unit, stereo and dang, it had good sound! So this is a cool idea :up:

Quote:
I intend to use a total of 4 filters, all using the LM471 http://www.ti.com/lit/ds/symlink/lm741.pdf op amp:
1) low pass filter with a transition frequency of 16,384 Hz
2) high pass filter with a transition frequency of 16.35 Hz
*) Split signal and run the last two on parallel channels
3a) low pass filter for the bass channel with a transition frequency of 261.63 Hz
3b) high pass filter for the full range channel with a transition frequency of 130.81 Hz

If this is a good plan I can easily follow the guide, do the math, and build it.


Overkill from the description, maybe work out a block diagram so this old goat can visualize better? :D

Quote:
I have a few questions before I get to all that:
1) Have I made any major errors in my plan? I'm new to this
2) Will I need a second set for stereo sound?


After we see the diagram, maybe we can answer better (unless someone here is going, "OH! I know!")

Quote:
3) If so, how can I ensure that sound from both left and right channel make it to the one bass speaker?


A simple summing amplifier.

Quote:
4) Is the LM741 a good op amp, or is there a better choice for a similar price?


It has its uses, but is dated for audio circuitry. The dual 4558 superceeded it and you can get the TL072 for even cheaper and it's better yet.

Cheers!

_________________
-= Gregg =-
* Ratings are for transistors - tubes have guidelines*
Home: GeeK ZonE
Work: Classic Valve Design


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PostPosted: 21 Jan 2018, 00:34 
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Joined: 20 Jan 2018, 23:24
Posts: 5
Geek wrote:
Hi, welcome!

maybe work out a block diagram so this old goat can visualize better? :D

A simple summing amplifier.

you can get the TL072 for even cheaper and it's better yet.

Cheers!


Thank you
I will research the TL072 and the summing amplifier and make a block diagram and band graphs.

Overkill, yes quite possible. I'm known for that, in fact :)
I have hearing hearing issues and I really have to push the clear sound to enjoy my TV and music. I figure this will put it a lot closer and let me make something that's clear as a bell. I'm integrating an MCU to make a live spectrogram and display that and info on an 8 X 32 5050 RGB LED display. Bluetooth, WiFi, Kitchen Sink. Why, Why not? But I am concerned about those comms and 12V @ 16A causing issues, so I'd like to get ahead of them.

Time to put on some coffee :yumcoffee:


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PostPosted: 21 Jan 2018, 00:56 
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Joined: 20 Jan 2018, 23:24
Posts: 5
Image
This is the target function
I will get to the diagrams directly.


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