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Active audio divider with LME49720 Dual
Active audio divider with LME49720 Dual
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Old 25th January 2020, 04:07 PM   #1
MilanAudio is offline MilanAudio  Czech Republic
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Question Active audio divider with LME49720 Dual

Hello to all,

I am working on audio divider using LME49720 Dual op amp. I am not experienced with making design dedicated to some op amp, but I guess there should be some resistor and at least one cap.

Any idea what resistors should be used? Or what should be added?

Thanks for help!

Milan

PS: I did some googling but some dividers has feedback resistor, some not... I am confused

I've done this... and the same will be for R ch. as I want dedicate 1 dual op amp to one channel because of separation.
Click the image to open in full size.

Datasheet: http://www.ti.com/lit/ds/symlink/lme49720.pdf

Last edited by MilanAudio; 25th January 2020 at 04:12 PM. Reason: added datasheet
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Old 25th January 2020, 04:50 PM   #2
Douglas Blake is offline Douglas Blake  Canada
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If you are simply wanting 2 identical outputs, you've just about got it covered except for biasing the + inputs, there you will need a resistor to ground, typically 100k works fine.

If you want unity gain you can eliminate R1 and R2 and simply connect the - inputs to the output pin.

If you are after some gain you will need to add a resistor from each - input to ground. The gain would then be the ratio of the values of the resistors.

R3 should be set to match the impedance of the previous stage, although in practice it's not actually needed if the unit is permanently connected.
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Old 25th January 2020, 05:55 PM   #3
MilanAudio is offline MilanAudio  Czech Republic
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Quote:
Originally Posted by Douglas Blake View Post
If you are simply wanting 2 identical outputs, you've just about got it covered except for biasing the + inputs, there you will need a resistor to ground, typically 100k works fine.

If you want unity gain you can eliminate R1 and R2 and simply connect the - inputs to the output pin.

If you are after some gain you will need to add a resistor from each - input to ground. The gain would then be the ratio of the values of the resistors.

R3 should be set to match the impedance of the previous stage, although in practice it's not actually needed if the unit is permanently connected.
Thank you, I hope I got it right...
No amplification, just two identical left channel outputs, most possible channel separation, this is why 1 LME will be for left channel and second one for right channel.

Here is edited version:
Click the image to open in full size.
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Old 25th January 2020, 06:02 PM   #4
as_audio is offline as_audio
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R2 is not required.
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Old 25th January 2020, 06:13 PM   #5
MilanAudio is offline MilanAudio  Czech Republic
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Quote:
Originally Posted by as_audio View Post
R2 is not required.
So yes, the device will be connect permanently, but it might be working without input/load for short time...

the 1 pair LR will go to 1 amp, second pair will go to second amp.

So like this? Looks really simple more than I thought.
Click the image to open in full size.
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Old 25th January 2020, 06:17 PM   #6
as_audio is offline as_audio
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You would call this splitter, not divider, I think.
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Old 25th January 2020, 06:20 PM   #7
MilanAudio is offline MilanAudio  Czech Republic
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Quote:
Originally Posted by as_audio View Post
You would call this splitter, not divider, I think.
I think it's the same - split or divide, no? In other words - it should make from 1 left ch two left channels. And from 1 right channel two right channels.

I did googling and people are using the both words.

Off topic - grammar: To split something it to cause it to divide, usually using some type of force that causes it to break. When someone says "split" they are essentially using a different way to say "divide". A country divided into 5 parts and a country SPLIT into 5 parts is virtually the same thing, however, saying "a country split into 5 parts" is more like saying "a country (that has been) broken into 5 parts". In everyday conversation or simplified explanation, it is more informal and casual to say "split" instead of saying "divide", but something that has been split was probably divided by force or broken into parts. or 'Divide' might suggest a more equal distribution between the parts, and it may also suggest a more careful, thought-out action than 'split'.

Last edited by MilanAudio; 25th January 2020 at 06:33 PM.
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Old 25th January 2020, 06:34 PM   #8
MilanAudio is offline MilanAudio  Czech Republic
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Back to circuit: is there something should be added please? isn't it too simple?
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Old 25th January 2020, 07:05 PM   #9
Douglas Blake is offline Douglas Blake  Canada
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If it is just feeding one pre-amp to two power amps, it's probably already too complex.

You don't actually need any electronics at all ... just a simple Y adaptor cord will do the job just fine.

In fact the cord might be better than your solution because a chunk of wire can't introduce hum, phase shift, crosstalk, distortion or propogation delays.

If you still want to go the active route... See the thumbnail (revisions in red)
Attached Images
File Type: jpg ad.jpg (245.7 KB, 99 views)

Last edited by Douglas Blake; 25th January 2020 at 07:17 PM.
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Old 25th January 2020, 07:24 PM   #10
MilanAudio is offline MilanAudio  Czech Republic
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Quote:
Originally Posted by Douglas Blake View Post
If it is just feeding one pre-amp to two power amps, it's probably already too complex.

You don't actually need any electronics at all ... just a simple Y adaptor cord will do the job just fine.

In fact the cord might be better than your solution because a chunk of wire can't introduce hum, phase shift, crosstalk, distortion or propogation delays.

If you still want to go the active route... See the thumbnail (revisions in red)
Thank you Douglas, so basically your attachment is like my last updated image:
Click the image to open in full size.

I would like to have two pairs outputs because I would like to connected one to main amp which has build in preamp and second output to external sound card, or tapedeck, etc. (it dependent what I will be doing, what combinations). And yes, I want channel separation, minimum distortion and so on, the LME49720 has nice specs.
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