Author Topic: Connecting right and left output on amplifier board  (Read 2328 times)

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Offline dclevy1

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Connecting right and left output on amplifier board
« on: March 06, 2018, 06:33:24 am »
I bought a TDA7492P amplifier board from AliExpress and I was planning on making a custom Bluetooth speaker out of a speaker enclosure and just stuff everything inside of the speaker enclosure. But I'm trying to figure out a safe to connect the right and left output channels together to a mono input for the speaker. Do I have to build a circuit and if so how do I do this and if there is a small board on the market that I can use where is it? The speaker is a small 67 watt Max and 5 ohm . The description said the amplifier board can withstand any resistance from 4 all the way to 16 ohms


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Offline Jwillis

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Re: Connecting right and left output on amplifier board
« Reply #1 on: March 06, 2018, 07:50:21 am »
-R and -L tie together  +R and +L tie together so you have one channel  + and -
 

Offline dclevy1

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Re: Connecting right and left output on amplifier board
« Reply #2 on: March 06, 2018, 07:54:53 am »
-R and -L tie together  +R and +L tie together so you have one channel  + and -
I've read that tying two of the outputs together to one speaker is not particularly safe for the amplifier chip. I also came across this diagram for a stereo to Mono circuit but I can't make sense of this.


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Offline paulca

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Re: Connecting right and left output on amplifier board
« Reply #3 on: March 06, 2018, 07:55:01 am »
Be aware that any phase difference between left and right will cause cancellation and reduced in volume.  Any in phase signals left and right will be increased in volume.  Simply adding L and R signals together never sounds as good as you hoped.  It's often better to just listen to left or right.  To achieve that you would connect the Left (or Right) input to both Left and right inputs.
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Online BrianHG

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Re: Connecting right and left output on amplifier board
« Reply #4 on: March 06, 2018, 08:02:32 am »
Be aware that any phase difference between left and right will cause cancellation and reduced in volume.  Any in phase signals left and right will be increased in volume.  Simply adding L and R signals together never sounds as good as you hoped.  It's often better to just listen to left or right.  To achieve that you would connect the Left (or Right) input to both Left and right inputs.
Unfortunately, tying the left and right output together wont work like that.  In phase mono audio going into the amp will come out at normal volume.  Mute one channel going into the amp, and at the output, 1 output be trying to drive the no sound 0v, and the other channel trying to drive sound, creating a short circuit, to such an extent that you will burn up the amp chip, or draw too much current from your power supply as 1 channel with sound fights the other which is trying to stop the sound.  With out of phase stereo audio going into the amp, this effect gets even 4x worse.  And then the magic smoke might come out.

The easiest way is at the input of the amp, just use a series of two 1k resistors connected from your left and right audio source, with the center going to 1 input channel on the amp.  EG: use the left.  That channel will now have a mono sound.  Now, tie the left output to your speaker.  Just ignore the right channel.
« Last Edit: March 06, 2018, 08:06:20 am by BrianHG »
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Offline tooki

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Re: Connecting right and left output on amplifier board
« Reply #5 on: March 06, 2018, 08:10:54 am »
I bought a TDA7492P amplifier board from AliExpress and I was planning on making a custom Bluetooth speaker out of a speaker enclosure and just stuff everything inside of the speaker enclosure. But I'm trying to figure out a safe to connect the right and left output channels together to a mono input for the speaker. Do I have to build a circuit and if so how do I do this and if there is a small board on the market that I can use where is it? The speaker is a small 67 watt Max and 5 ohm . The description said the amplifier board can withstand any resistance from 4 all the way to 16 ohms


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Just use one channel of the amp and forget the other altogether.


Stereo class-D amps normally have differential outputs for the channels. Because of this, you cannot simply bridge the channels.

Indeed, you cannot even bridge, say, the two output negatives to share a ground (for example, to create a headphone output.) Each speaker must be wired totally independently. To get around this, you must add a circuit like described here: https://www.edn.com/design/analog/4313726/Add-headphones-to-a-Class-D-amplifier
The downside is some loss of channel separation.

Unlike this headphone workaround, I couldn’t find any solutions for paralleling both channels to a single mono speaker.

I’d just use a more powerful amp and only use one channel.
 

Offline tooki

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Re: Connecting right and left output on amplifier board
« Reply #6 on: March 06, 2018, 08:12:40 am »
Be aware that any phase difference between left and right will cause cancellation and reduced in volume.  Any in phase signals left and right will be increased in volume.  Simply adding L and R signals together never sounds as good as you hoped.  It's often better to just listen to left or right.  To achieve that you would connect the Left (or Right) input to both Left and right inputs.
On class-D amps, it’s not just an issue of phase. It’s also that the outputs are differential, and the chip will fry (apparently) if you bridge the channels.

The link in my comment above shows the staggered pulse waveforms of a class-D amp.
 

Offline dclevy1

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Re: Connecting right and left output on amplifier board
« Reply #7 on: March 06, 2018, 08:23:13 am »
Be aware that any phase difference between left and right will cause cancellation and reduced in volume.  Any in phase signals left and right will be increased in volume.  Simply adding L and R signals together never sounds as good as you hoped.  It's often better to just listen to left or right.  To achieve that you would connect the Left (or Right) input to both Left and right inputs.
Unfortunately, tying the left and right output together wont work like that.  In phase mono audio going into the amp will come out at normal volume.  Mute one channel going into the amp, and at the output, 1 output be trying to drive the no sound 0v, and the other channel trying to drive sound, creating a short circuit, to such an extent that you will burn up the amp chip, or draw too much current from your power supply as 1 channel with sound fights the other which is trying to stop the sound.  With out of phase stereo audio going into the amp, this effect gets even 4x worse.  And then the magic smoke might come out.

The easiest way is at the input of the amp, just use a series of two 1k resistors connected from your left and right audio source, with the center going to 1 input channel on the amp.  EG: use the left.  That channel will now have a mono sound.  Now, tie the left output to your speaker.  Just ignore the right channel.
I bought a TDA7492P amplifier board from AliExpress and I was planning on making a custom Bluetooth speaker out of a speaker enclosure and just stuff everything inside of the speaker enclosure. But I'm trying to figure out a safe to connect the right and left output channels together to a mono input for the speaker. Do I have to build a circuit and if so how do I do this and if there is a small board on the market that I can use where is it? The speaker is a small 67 watt Max and 5 ohm . The description said the amplifier board can withstand any resistance from 4 all the way to 16 ohms


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Just use one channel of the amp and forget the other altogether.


Stereo class-D amps normally have differential outputs for the channels. Because of this, you cannot simply bridge the channels.

Indeed, you cannot even bridge, say, the two output negatives to share a ground (for example, to create a headphone output.) Each speaker must be wired totally independently. To get around this, you must add a circuit like described here: https://www.edn.com/design/analog/4313726/Add-headphones-to-a-Class-D-amplifier
The downside is some loss of channel separation.

Unlike this headphone workaround, I couldn’t find any solutions for paralleling both channels to a single mono speaker.

I’d just use a more powerful amp and only use one channel.
Thanks for your input I was afraid of this. By the way I am using Bluetooth audio which comes this with this board as well. So I guess there's definitely no way this will work.


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Offline MattHollands

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Re: Connecting right and left output on amplifier board
« Reply #8 on: March 06, 2018, 12:08:41 pm »
Be aware that any phase difference between left and right will cause cancellation and reduced in volume.  Any in phase signals left and right will be increased in volume.  Simply adding L and R signals together never sounds as good as you hoped.  It's often better to just listen to left or right.  To achieve that you would connect the Left (or Right) input to both Left and right inputs.
Unfortunately, tying the left and right output together wont work like that.  In phase mono audio going into the amp will come out at normal volume.  Mute one channel going into the amp, and at the output, 1 output be trying to drive the no sound 0v, and the other channel trying to drive sound, creating a short circuit, to such an extent that you will burn up the amp chip, or draw too much current from your power supply as 1 channel with sound fights the other which is trying to stop the sound.  With out of phase stereo audio going into the amp, this effect gets even 4x worse.  And then the magic smoke might come out.

The easiest way is at the input of the amp, just use a series of two 1k resistors connected from your left and right audio source, with the center going to 1 input channel on the amp.  EG: use the left.  That channel will now have a mono sound.  Now, tie the left output to your speaker.  Just ignore the right channel.
I bought a TDA7492P amplifier board from AliExpress and I was planning on making a custom Bluetooth speaker out of a speaker enclosure and just stuff everything inside of the speaker enclosure. But I'm trying to figure out a safe to connect the right and left output channels together to a mono input for the speaker. Do I have to build a circuit and if so how do I do this and if there is a small board on the market that I can use where is it? The speaker is a small 67 watt Max and 5 ohm . The description said the amplifier board can withstand any resistance from 4 all the way to 16 ohms


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Just use one channel of the amp and forget the other altogether.


Stereo class-D amps normally have differential outputs for the channels. Because of this, you cannot simply bridge the channels.

Indeed, you cannot even bridge, say, the two output negatives to share a ground (for example, to create a headphone output.) Each speaker must be wired totally independently. To get around this, you must add a circuit like described here: https://www.edn.com/design/analog/4313726/Add-headphones-to-a-Class-D-amplifier
The downside is some loss of channel separation.

Unlike this headphone workaround, I couldn’t find any solutions for paralleling both channels to a single mono speaker.

I’d just use a more powerful amp and only use one channel.
Thanks for your input I was afraid of this. By the way I am using Bluetooth audio which comes this with this board as well. So I guess there's definitely no way this will work.


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What Bluetooth module are you using? Is there anyway you can make it output mono audio instead of stereo?
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Offline Adhith

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Re: Connecting right and left output on amplifier board
« Reply #9 on: March 06, 2018, 02:35:44 pm »
hello dclevy1
I'm not a much experienced person to give suggestions but few months back i was working with the same question and I'm now working with the same amp module that you are using now..so just thought to mention something. I just used a resistor mixer back then to combine the left and right audio input to form a mono output and it had not much of a problem but it was just for an experimental setup and I have no idea about prolonged use .
I had a small discussion about it in two forums i'll leave you its link
https://www.eevblog.com/forum/beginners/converting-stereo-audio-input-to-mono/msg1226808/#msg1226808

https://forum.allaboutcircuits.com/threads/converting-stereo-audio-input-to-mono.135922/

 I also referred summing amplifier for it also

http://www.edaboard.com/showthread.php?t=315120

maybe this could help
Regards
Adhith
 

Online BrianHG

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Re: Connecting right and left output on amplifier board
« Reply #10 on: March 06, 2018, 04:52:41 pm »
Be aware that any phase difference between left and right will cause cancellation and reduced in volume.  Any in phase signals left and right will be increased in volume.  Simply adding L and R signals together never sounds as good as you hoped.  It's often better to just listen to left or right.  To achieve that you would connect the Left (or Right) input to both Left and right inputs.
Unfortunately, tying the left and right output together wont work like that.  In phase mono audio going into the amp will come out at normal volume.  Mute one channel going into the amp, and at the output, 1 output be trying to drive the no sound 0v, and the other channel trying to drive sound, creating a short circuit, to such an extent that you will burn up the amp chip, or draw too much current from your power supply as 1 channel with sound fights the other which is trying to stop the sound.  With out of phase stereo audio going into the amp, this effect gets even 4x worse.  And then the magic smoke might come out.

The easiest way is at the input of the amp, just use a series of two 1k resistors connected from your left and right audio source, with the center going to 1 input channel on the amp.  EG: use the left.  That channel will now have a mono sound.  Now, tie the left output to your speaker.  Just ignore the right channel.
Thanks for your input I was afraid of this. By the way I am using Bluetooth audio which comes this with this board as well. So I guess there's definitely no way this will work.


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Read my green comment.  That is how you safely get mono through 1 channel on your amp.
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Offline Jwillis

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Re: Connecting right and left output on amplifier board
« Reply #11 on: March 06, 2018, 07:10:42 pm »
I'm sorry for leading you astray.I was thinking in terms of much older prehistoric equipment made from stone and mammoth bone.Much easy then when stereos could handle 2 ohms to as high as 16 ohms.
You still can sum the channels in a similar way with a resistor network similar to the attached image you need to select them so that the left and right channels stay at the same impedance.There are other ways as well.Here's a link that may be of help.http://retrotechnologist.blogspot.ca/2013/07/a-simple-audio-spliitingcombining-pad.html
He explains it much better than I could.
 

Offline paulca

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Re: Connecting right and left output on amplifier board
« Reply #12 on: March 06, 2018, 09:15:58 pm »
If you look at the board guys.  The source is on the board.  It only has outputs, (EDIT: it might have a 3.5mm jack input) it's got a trace antenna and (I assume) a  bluetooth chip. 

The only real option is to just use one output channel and leave the other unloaded.... or put a power resistor on it to match the speaker.
"What could possibly go wrong?"
Current Open Projects:  3 Channel Audio mixer with DAC, BT, pre-amps and h/phone amp, WS281x LED controller Version 2 5V/5A w/Atmega328, FY6600 Power supply, 5A DC Load (Still!)
 

Online BrianHG

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Re: Connecting right and left output on amplifier board
« Reply #13 on: March 06, 2018, 10:12:22 pm »
If you look at the board guys.  The source is on the board.  It only has outputs, (EDIT: it might have a 3.5mm jack input) it's got a trace antenna and (I assume) a  bluetooth chip. 

The only real option is to just use one output channel and leave the other unloaded.... or put a power resistor on it to match the speaker.
Didn't notice that.  Ok, get the data sheet on the amp chip and short the left and right inputs together if there is already a series resistor inline coming from the blue-tooth RX ic.
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Offline SL4P

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Re: Connecting right and left output on amplifier board
« Reply #14 on: March 07, 2018, 12:30:05 am »
If the speakers are small enough, buy a second speaker and use it normally,
-or-
Place the speakers face-to-face (with room for the difference in air pressure to escape*), and wire one of them out of phase - then the speakers will work together - in phase.

*Not having any baffle will let the speakers (in any configuration) flap in the breeze. so you may want to look at loading the speakers as well - *see baffle
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Offline dclevy1

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Re: Connecting right and left output on amplifier board
« Reply #15 on: March 13, 2018, 12:29:33 am »
Be aware that any phase difference between left and right will cause cancellation and reduced in volume.  Any in phase signals left and right will be increased in volume.  Simply adding L and R signals together never sounds as good as you hoped.  It's often better to just listen to left or right.  To achieve that you would connect the Left (or Right) input to both Left and right inputs.
Unfortunately, tying the left and right output together wont work like that.  In phase mono audio going into the amp will come out at normal volume.  Mute one channel going into the amp, and at the output, 1 output be trying to drive the no sound 0v, and the other channel trying to drive sound, creating a short circuit, to such an extent that you will burn up the amp chip, or draw too much current from your power supply as 1 channel with sound fights the other which is trying to stop the sound.  With out of phase stereo audio going into the amp, this effect gets even 4x worse.  And then the magic smoke might come out.

The easiest way is at the input of the amp, just use a series of two 1k resistors connected from your left and right audio source, with the center going to 1 input channel on the amp.  EG: use the left.  That channel will now have a mono sound.  Now, tie the left output to your speaker.  Just ignore the right channel.
Thanks for your input I was afraid of this. By the way I am using Bluetooth audio which comes this with this board as well. So I guess there's definitely no way this will work.


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Read my green comment.  That is how you safely get mono through 1 channel on your amp.
Green comment?


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Offline dclevy1

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Re: Connecting right and left output on amplifier board
« Reply #16 on: March 13, 2018, 12:33:35 am »
If the speakers are small enough, buy a second speaker and use it normally,
-or-
Place the speakers face-to-face (with room for the difference in air pressure to escape*), and wire one of them out of phase - then the speakers will work together - in phase.

*Not having any baffle will let the speakers (in any configuration) flap in the breeze. so you may want to look at loading the speakers as well - *see baffle
This won't work because I'm using a small box in the project was supposed to be a budget Bluetooth speaker materials laying around as well as materials bought but another speaker not in the question


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Offline dclevy1

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Connecting right and left output on amplifier board
« Reply #17 on: March 13, 2018, 12:35:19 am »
If you look at the board guys.  The source is on the board.  It only has outputs, (EDIT: it might have a 3.5mm jack input) it's got a trace antenna and (I assume) a  bluetooth chip. 

The only real option is to just use one output channel and leave the other unloaded.... or put a power resistor on it to match the speaker.
I'm sorry for leading you astray.I was thinking in terms of much older prehistoric equipment made from stone and mammoth bone.Much easy then when stereos could handle 2 ohms to as high as 16 ohms.
You still can sum the channels in a similar way with a resistor network similar to the attached image you need to select them so that the left and right channels stay at the same impedance.There are other ways as well.Here's a link that may be of help.http://retrotechnologist.blogspot.ca/2013/07/a-simple-audio-spliitingcombining-pad.html
He explains it much better than I could.
If you look at the board guys.  The source is on the board.  It only has outputs, (EDIT: it might have a 3.5mm jack input) it's got a trace antenna and (I assume) a  bluetooth chip. 

The only real option is to just use one output channel and leave the other unloaded.... or put a power resistor on it to match the speaker.
Didn't notice that.  Ok, get the data sheet on the amp chip and short the left and right inputs together if there is already a series resistor inline coming from the blue-tooth RX ic.
Possible to combine two outputs on the chip itself using the schematic to find the right and left output


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Offline dclevy1

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Connecting right and left output on amplifier board
« Reply #18 on: March 13, 2018, 12:38:18 am »
I also have a question involving the voltage input and current consumption. This board is rated for 10 through 25 volts. if I give it More Voltage will it consume less current?


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Online BrianHG

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Re: Connecting right and left output on amplifier board
« Reply #19 on: March 13, 2018, 01:31:19 am »
If you look at the board guys.  The source is on the board.  It only has outputs, (EDIT: it might have a 3.5mm jack input) it's got a trace antenna and (I assume) a  bluetooth chip. 

The only real option is to just use one output channel and leave the other unloaded.... or put a power resistor on it to match the speaker.
I'm sorry for leading you astray.I was thinking in terms of much older prehistoric equipment made from stone and mammoth bone.Much easy then when stereos could handle 2 ohms to as high as 16 ohms.
You still can sum the channels in a similar way with a resistor network similar to the attached image you need to select them so that the left and right channels stay at the same impedance.There are other ways as well.Here's a link that may be of help.http://retrotechnologist.blogspot.ca/2013/07/a-simple-audio-spliitingcombining-pad.html
He explains it much better than I could.
If you look at the board guys.  The source is on the board.  It only has outputs, (EDIT: it might have a 3.5mm jack input) it's got a trace antenna and (I assume) a  bluetooth chip. 

The only real option is to just use one output channel and leave the other unloaded.... or put a power resistor on it to match the speaker.
Didn't notice that.  Ok, get the data sheet on the amp chip and short the left and right inputs together if there is already a series resistor inline coming from the blue-tooth RX ic.
Possible to combine two outputs on the chip itself using the schematic to find the right and left output


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Nope, it's a switching, balanced (a mirror drive for each wire, +&-, of the speaker) output which requires the parallel low pass filters.  (Those 4 big power inductors marked with the '330')  Since it is a switching class D amp, each output is either switched/shorted to V+, then GND at the IC before the filters, as all 4 outputs oscillate back and forth at different duty cycles at 768Khz (this figure may differ from IC to IC...) synthesizing an analog voltage after the low pass filters.  Shorting the left and right outputs will short the IC as soon as one output on one channel goes to V+ and on the other channel goes to GND, and the IC will either go into over current protection and shut down, or, the magic smoke will come out.
« Last Edit: March 13, 2018, 01:36:06 am by BrianHG »
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Offline dclevy1

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Re: Connecting right and left output on amplifier board
« Reply #20 on: March 14, 2018, 12:50:35 am »
If you look at the board guys.  The source is on the board.  It only has outputs, (EDIT: it might have a 3.5mm jack input) it's got a trace antenna and (I assume) a  bluetooth chip. 

The only real option is to just use one output channel and leave the other unloaded.... or put a power resistor on it to match the speaker.
I'm sorry for leading you astray.I was thinking in terms of much older prehistoric equipment made from stone and mammoth bone.Much easy then when stereos could handle 2 ohms to as high as 16 ohms.
You still can sum the channels in a similar way with a resistor network similar to the attached image you need to select them so that the left and right channels stay at the same impedance.There are other ways as well.Here's a link that may be of help.http://retrotechnologist.blogspot.ca/2013/07/a-simple-audio-spliitingcombining-pad.html
He explains it much better than I could.
If you look at the board guys.  The source is on the board.  It only has outputs, (EDIT: it might have a 3.5mm jack input) it's got a trace antenna and (I assume) a  bluetooth chip. 

The only real option is to just use one output channel and leave the other unloaded.... or put a power resistor on it to match the speaker.
Didn't notice that.  Ok, get the data sheet on the amp chip and short the left and right inputs together if there is already a series resistor inline coming from the blue-tooth RX ic.
Possible to combine two outputs on the chip itself using the schematic to find the right and left output


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Nope, it's a switching, balanced (a mirror drive for each wire, +&-, of the speaker) output which requires the parallel low pass filters.  (Those 4 big power inductors marked with the '330')  Since it is a switching class D amp, each output is either switched/shorted to V+, then GND at the IC before the filters, as all 4 outputs oscillate back and forth at different duty cycles at 768Khz (this figure may differ from IC to IC...) synthesizing an analog voltage after the low pass filters.  Shorting the left and right outputs will short the IC as soon as one output on one channel goes to V+ and on the other channel goes to GND, and the IC will either go into over current protection and shut down, or, the magic smoke will come out.
Okay I understand and as far as the voltage question I asked does the current go down as the voltage goes up since it's rated for 10 to 25 volts? As far as just powering it


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Offline techricky

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Re: Connecting right and left output on amplifier board
« Reply #21 on: March 15, 2018, 05:49:56 am »
Because it is a differential output for each channel, you could try connecting your speaker between the - output of one channel and the + of the other..

This will give a mono sum of Left and Right, but no guarantees the module will like it if say the signals are very different in left and right, or if it will like one leg of each output being unloaded.

Ideally it will be fine and not too different from having no speakers connected or a very reactive load, possibly some instability or distortion but shouldn't damage it if you try.
 

Offline IanMacdonald

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Re: Connecting right and left output on amplifier board
« Reply #22 on: March 15, 2018, 07:26:15 am »
You MUST NOT short the L and R speaker outputs of any stereo amplifier together.

You also MUST NOT ground or short to chassis any speaker output terminal.

Not applicable here, but you also MUST NOT connect the speaker outputs of two amplifiers to the same speaker.

In the consumer trade this used to be a constant bone of contention with customer installing their own car audio and blowing the stuff up through doing these kinds of things. 
 

Offline dclevy1

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Re: Connecting right and left output on amplifier board
« Reply #23 on: March 22, 2018, 09:53:50 am »
Thank you guys I'm just going to connect the one speaker to the left output. It sounds pretty decent and I don't notice any missing tones or information by connecting that one to the left speaker


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Offline Audioguru

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Re: Connecting right and left output on amplifier board
« Reply #24 on: March 22, 2018, 03:28:46 pm »
Instead of blowing up the chip, why not look at the datasheet of the chip, made by ST Micro, not lied about by a Chinese Ali salesman?
1) Its spec's per channel are 50W into 6 ohms with a 25V supply when its clipping distortion is horrible. With an 8 ohm load its output power is less. With a 4 ohm load its heating is more and it will melt unless its supply is 22V or less. With reasonable distortion its output is less.
2) some IV stereo amplifier ICs have outputs that can be paralleled if their inputs are exactly the same, but not this one.
3) Of course you will be missing a lot of tones and information when you play only one channel of stereo. The bass is mono on both channels so your bass level will be half. Some information on the missing channel will be missing.
 
 

Offline Audioguru

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Re: Connecting right and left output on amplifier board
« Reply #25 on: March 22, 2018, 03:31:48 pm »
Since you are using a small box then how will you cool the amplifier??
 


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