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Old 5th February 2013, 10:17 PM   #1
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Default How to use TDA7439 for center and subwoofer

Hi,
I'm planning to build a 7.1 mixer & switch with TDA7439. For all the channnels I'm fine, but I'm not really good with the high pass and low pass filters. All channels will be connected according to the datasheet but I have a problem/question:
If I want to use one TDA7439 to mix center speaker and subwoofer, how can I change the highpass and lowpass filter on the IC that the highpass on one channel will be disconnected / won't have any gain and on the second channel the bass filter will be bypassed (won't have any gain).
Can I somehow modify the values of the capacitors and resistors of the treble and bass stage (and how) or do I have to put another high pass and low pass filter after the IC.
Basicly I don't want the basses to get into the center and trebles to go into the subwoofer.
The adjustment of the tone is linked, so both channel trebles and bass are being adjusted at the same time.
Or is it just easier to use two independent chips?
Datasheet: http://www.st.com/internet/com/TECHN...CD00004906.pdf
Thanks for any help or suggestions
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Old 5th February 2013, 10:23 PM   #2
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I would not use this chip as it is obsolete.
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Old 5th February 2013, 10:30 PM   #3
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Quote:
Originally Posted by Harleyjon View Post
I would not use this chip as it is obsolete.
What chip with tone control and input multiplexer would you recommend? I was looking for some alternative myself, but couldn't find anything. Would you know how to solve the the filters?
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Old 6th February 2013, 12:19 AM   #4
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Quote:
Originally Posted by buracek View Post
Hi,
I'm planning to build a 7.1 mixer & switch ...........
If I want to use one TDA7439 to mix center speaker and subwoofer, how can I change the highpass and lowpass filter on the IC that the highpass on one channel will be disconnected / won't have any gain and on the second channel the bass filter will be bypassed (won't have any gain).
maybe I am having a stupid day [quite likely] but I do not follow.

Could you rough out a diagram?
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Old 6th February 2013, 12:20 AM   #5
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Quote:
Originally Posted by Harleyjon View Post
I would not use this chip as it is obsolete.
Personally I detest it when some-one criticizes but offers no alternative.....
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Old 6th February 2013, 05:08 PM   #6
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Default Better explanation

I'll try to explain it better. Each channel has its own filters.
- If I adjust something (eg bass, both left and right will adjust together - I can't address left or right channel only). Only both at the same time
-I would like to use one half of the chip for center speaker and the second half for a subwoofer.
That mean that I have to somehow bypass or modify the:
-lowpass filter for the channel that will be used for the center speaker (as I don't want to feed the center speakers with bass)
-highpass filter for the subwoofer channel (as I don't want to feed the subwoofer with trebles)

The schematic is from TDA7440 (not 7439) to make it easier (7439 has an extra midpass filter, which is identical to the lowpass filter, only with different values of the capacitors)

The question might sound stupid, but if I remove the capacitor connected to the treble section, will the highpass filter stop working? (For the subwoofer channel) and if I remove the capacitors for the low pass filter and connect it with wire, will it work? (for the center speaker channel)

Or is it better leave it as it is and add another filters after (or before?) the TDA chip to filter the signal further (lowpass and highpass with op-amp)?
Thanks
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File Type: png TDA description.png (46.2 KB, 57 views)
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