Connecting right and left output on amplifier board

[dclevy1]

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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[Jwillis]

-R and -L tie together  +R and +L tie together so you have one channel  + and -

[dclevy1]

-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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[paulca]

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.

[BrianHG]

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.

[tooki]

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.

[tooki]

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.

[dclevy1]

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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[MattHollands]

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


Sent from my iPhone using Tapatalk

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?

[Adhith]

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

[BrianHG]

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.

[Jwillis]

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.

[paulca]

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.

[BrianHG]

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.

[SL4P]

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

[dclevy1]

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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[dclevy1]

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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[dclevy1]

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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[dclevy1]

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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[BrianHG]

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.

[dclevy1]

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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[techricky]

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.

[IanMacdonald]

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. 

[dclevy1]

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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[Audioguru]

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.
 

[Audioguru]

Since you are using a small box then how will you cool the amplifier??

[chrsm]

Hi
I have figured out how to configure the amplifier board to have a mono output with an stereo input.
I have between the bluetooth controller and the TDA7492P amplifier inserted 3 resistors that combine the input from left and right to the right input of the amplifier.
Hope this can be helpful for others.

[CaptDon]

Since you now have a true 'mono' sum input it may be possible
to parallel the outputs + to + and - to -  which although will not
increase the output voltage it will increase the output current.
This allows the use of a speaker with half the impedance of a single
channel (use 4 ohm instead of 8 as an example) and that single
speaker will be driven with twice the power for a 3db increase
in volume. For testing if this is feasible you could place a 10 ohm
resistor on both outputs and use a scope to verify that the signal
on both outputs when measured + to + and - to - are 'in phase'
and equal amplitude. In other words there is no differential voltage
from + to + and - to -, if that is true you can parallel the outputs!!!
This is commonly done on very powerful mono-block amplifiers by
paralleling the stereo outputs and inputting a mono source. The only
advantage come when you half the speaker impedance also.
 

[tooki]

Since you now have a true 'mono' sum input it may be possible
to parallel the outputs + to + and - to -  which although will not
increase the output voltage it will increase the output current.
This allows the use of a speaker with half the impedance of a single
channel (use 4 ohm instead of 8 as an example) and that single
speaker will be driven with twice the power for a 3db increase
in volume. For testing if this is feasible you could place a 10 ohm
resistor on both outputs and use a scope to verify that the signal
on both outputs when measured + to + and - to - are 'in phase'
and equal amplitude. In other words there is no differential voltage
from + to + and - to -, if that is true you can parallel the outputs!!!
This is commonly done on very powerful mono-block amplifiers by
paralleling the stereo outputs and inputting a mono source. The only
advantage come when you half the speaker impedance also.

Hi! I’m writing this here because private messages don’t support attachments unfortunately.

FYI, please don’t enter manual line breaks. Not only is it not necessary, as text will wrap automatically, it often produces horrific results on smaller screens. I’ve attached a screenshot of what a recent post of yours looks like on an iPhone, as an example. It’s better to just type away and use line breaks only to separate paragraphs.

Thanks!

[tooki]

Hi
I have figured out how to configure the amplifier board to have a mono output with an stereo input.
I have between the bluetooth controller and the TDA7492P amplifier inserted 3 resistors that combine the input from left and right to the right input of the amplifier.
Hope this can be helpful for others.

That’s basic passive summing, the worst way to mix signals (short of bridging them without resistors).

See https://sound-au.com/articles/audio-mixing.htm

Since you now have a true 'mono' sum input it may be possible
to parallel the outputs + to + and - to -  which although will not
increase the output voltage it will increase the output current.
This allows the use of a speaker with half the impedance of a single
channel (use 4 ohm instead of 8 as an example) and that single
speaker will be driven with twice the power for a 3db increase
in volume. For testing if this is feasible you could place a 10 ohm
resistor on both outputs and use a scope to verify that the signal
on both outputs when measured + to + and - to - are 'in phase'
and equal amplitude. In other words there is no differential voltage
from + to + and - to -, if that is true you can parallel the outputs!!!
This is commonly done on very powerful mono-block amplifiers by
paralleling the stereo outputs and inputting a mono source. The only
advantage come when you half the speaker impedance also.
 

What you’re talking about is a BTL (bridge tied load) configuration. But if you look at the amp IC’s datasheet, you’ll see that that amp already uses a BTL configuration internally. So you absolutely cannot bridge its outputs!

Chrsm’s choice of grounding the unused input via a capacitor is pretty much the only option here.

[CaptDon]

Guess you haven't messed around with BTL configurations very much. It is true that both the - and the + are active and not ground referenced exactly and the speaker is definitely not connected to ground but 'across' the class D switched mode outputs and inductors. If there is no differential between +L and +R and no differential between -L and -R than you can in fact tie the outputs together and get the same voltage but twice the current for a 3Db power gain. This would be paralleling the outputs and summing two equal amplitude in phase signals. In this case you could drive a 4 ohm speaker safely when each output was designed to drive 8 ohms independently. There is another way that big power amps can be bridged. Take the case of a stereo amplifier designed to be 500 watts at 4 ohms each side. There is a bridging mode where you input a mono signal, flip a rear panel switch and one channel will get an equal but inverted input signal. Then you connect a speaker of double the impedance (no longer 4 ohms on each side but a single 8 ohm) across the outputs from +L to +R and get 1000 watts at 8 ohms. Again, if the original poster sees no differential between +L and +R and no differential between -L and -R he can parallel the outputs and use a lower impedance speaker and take advantage of a 3db power gain. On the switching side of the inductors it makes no difference if the switching frequency is in phase or not, it only matters that the audio frequency after the inductors is equal and in phase and if that is true there is no reason the outputs can't be safely paralleled. The Carver PM2.0-T is bridged parallel for over 1000 watts at 4 ohms although it consists of two independent 'stereo' 500 watt channels at 8 ohms each. It uses a common ground which also happens to be tied to chassis as is the + and - power supply returns. The QSC units are different as both the - and + outputs move in opposite directions as measured to ground and the speaker is across these outputs and in bridge mono one of the channels gets an inverted input signal and the load gets connected +L to +R. The QSC amplifier output stages resemble the original posters amplifier but in his case he will be driving an in-phase audio signal and paralleling the outputs.
Apparently the majority of posters here don't use smartphones and also use hard coded line breaks. you are the first to mention it.

 

[CaptDon]

The original poster noted that he is only driving the right side with his mono sum from the resistors. He would need to bridge the mono sum to both inputs which would drive both amplifiers in phase and at the same amplitude making the outputs also appear as identical in phase and equal amplitude. With paralleled outputs there won't be an additional voltage gain but there will be additional current gain which 'could' drive a lower impedance speaker with 3db more power. Is it worth it for 3db? The fact that the outputs are class D switching is noted and that the + output and the - output are both active and the load is across an already bridged style of output. Again, if the left channel output signal is identical to the right side signal due to the fact that the input signals are identical and in phase then you can parallel the outputs regardless of what the spec sheet says. The spec sheet won't let you parallel the outputs if you have true independent stereo inputs that have 'differential' content as that difference on the paralleled outputs would resemble the outputs fighting each other in a manner similar to a short circuit. Believe what I say, I work on multi-kilowatt amplifiers with switched mode SMPS power supplies as well as class 'D' switched mode outputs. I stand by my reputation so much so that local musicians brought their Peavey Deca power amps to me for repair and modifications while they were still in warranty even though there was two authorized Peavey repair centers in the county and I wasn't one of them!! I am also the guy who wrote the 32 page repair manual for ONLY the power supply section of the Carver PM2.0-T a.k.a. the Carver/Clair Bros CBA-1000 in all three of its iterations. The amplifiers were bulletproof, the power supplies....not so much!!!
 

[tooki]

Guess you haven't messed around with BTL configurations very much.

No, not really, haven't needed to. But since I spent about half of last year working on the design of an active speaker project at work, I had to immerse myself in the topic. And I think you dismissed my comment without actually having carefully read what I wrote.

It is true that both the - and the + are active and not ground referenced exactly and the speaker is definitely not connected to ground but 'across' the class D switched mode outputs and inductors. If there is no differential between +L and +R and no differential between -L and -R than you can in fact tie the outputs together and get the same voltage but twice the current for a 3Db power gain. This would be paralleling the outputs and summing two equal amplitude in phase signals. In this case you could drive a 4 ohm speaker safely when each output was designed to drive 8 ohms independently.

[snip section below that goes into a different topic before you come back to this one]

Again, if the original poster sees no differential between +L and +R and no differential between -L and -R he can parallel the outputs and use a lower impedance speaker and take advantage of a 3db power gain. On the switching side of the inductors it makes no difference if the switching frequency is in phase or not, it only matters that the audio frequency after the inductors is equal and in phase and if that is true there is no reason the outputs can't be safely paralleled. The Carver PM2.0-T is bridged parallel for over 1000 watts at 4 ohms although it consists of two independent 'stereo' 500 watt channels at 8 ohms each. It uses a common ground which also happens to be tied to chassis as is the + and - power supply returns. The QSC units are different as both the - and + outputs move in opposite directions as measured to ground and the speaker is across these outputs and in bridge mono one of the channels gets an inverted input signal and the load gets connected +L to +R. The QSC amplifier output stages resemble the original posters amplifier but in his case he will be driving an in-phase audio signal and paralleling the outputs.

Right, that's classic paralleling. The thing is, that's all fine and true in theory, but modern class-D amp ICs use all sorts of clever sorcery to eke more power out of less, in particular, weird proprietary modulation schemes. So while you definitely can parallel the smoothed output of two completely independent amplifiers, you definitely cannot make that assumption about two amplifier blocks within the same IC. Some class-D amplifier ICs today have explicit PBTL support which you must enable in order to use them in that configuration (for example, the TI TPA3156D2).

There is another way that big power amps can be bridged. Take the case of a stereo amplifier designed to be 500 watts at 4 ohms each side. There is a bridging mode where you input a mono signal, flip a rear panel switch and one channel will get an equal but inverted input signal. Then you connect a speaker of double the impedance (no longer 4 ohms on each side but a single 8 ohm) across the outputs from +L to +R and get 1000 watts at 8 ohms.

So… bridge tying the load. Which as I explained, in the TDA7492P (like the TPA3156D2) the outputs are already configured as a BTL. As I understand it, you can't bridge the bridged outputs again, because you're already at the limits of the power supply voltage x2 (p-p).

Apparently the majority of posters here don't use smartphones

No idea what the stats are, but I'm definitely far from the only person to access the forum by phone. I, of course, use the forum on all my devices (computer, tablet, phone), just depends on the situation. How the forum gets rendered on a given device will vary; I think I remember others saying it's also really annoying on the mobile forum skin and on tapatalk.

Apparently the majority of posters here […] also use hard coded line breaks.

Absolutely not. There's a tiny handful (like… 2 or 3?) of intransigent die-hards who refuse to stop putting in line breaks even after the problem has been explained to them, but the overwhelming majority of forum members do not use hard line breaks every line. They use line breaks the way they're intended to be used on the web and in word processors: for semantic grouping, i.e. separating paragraphs.

Thank you for being receptive to the feedback, it's much appreciated!!

you are the first to mention it.

I may be the first to mention it to you. But I know the topic has come up a few times elsewhere on the forum (not regarding you specifically, but others who've done the same).

[JohnnyMalaria]

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.

All commercial music is mixed so that it will sound acceptable in mono. If you experience significant cancellation, something else is wrong.

[CaptDon]

I love your use of the operative word 'acceptable' and I would say that's true. Any english word which carries a higher value than acceptable would start to stretch the truth a bit. I worked as a broadcast engineer for 13 years back in the 1980's through the 90's and we would sometimes gather in one of the production studios and play around with audio mixing and tweaking and phasing and so forth just for fun. It was nice to have an X/Y oscilloscope to display phase differences in the stereo mixdowns and to see what signals would either 'go away' or become accentuated in a mono mixdown. One of the funny things about commercially released productions is that if you invert the phase of one channel the vocals tend to go away but the reverb of the vocals remains. Also the bass and kick drum tend to disappear. I was at a live gig years ago and if you stood stage center in front of the F.O.H. system the low end completely disappeared. The sound man had his two bass cabinets hooked up to a stereo type amplifier in a normal fashion but he had the amplifier in the bridge mono mode so one channel was inverted and if you stood at the correct sweet spot there was no low end even though I could see the grass moving in front of his 18" loaded E.V. scoops!!!

[JohnnyMalaria]

Indeed.

Cancellation of the vocal by inverting the phase of one channel is how some karaoke machines work. Anything panned dead center in the mix will disappear (which usually includes bass and a lot of drums - depending how the kit was mixed).

I love my old Tektronix 465 'scope because of how glorious things look on XY. Can't say the same about my modern DSO.

[CaptDon]

I have found the DSO type scopes to be 100% useless for displaying an A.M. modulated (music) R.F. carrier!! At any reasonable sweep speed the R.F. tends to alias and the display simply looks horrible. Your 465 would be the much better choice!!! My favorite for years was the older 453 'Silver Anniversary' portable scope. The 465 and 465M are also timeless and very affordable these days!!! My DSO is a TDS644B and the little lunchbox TDS2024C. My analogs are the SC502 (15meg) SC504 (80meg) and the little guy SC501 (5meg?). I recently grabbed a fully functional analog storage scope of the 51XX series from the company dumpster. There were several vertical modules and a couple of delayed timebase horizontal modules in the dumpster with it. I think the mainframe is 60mhz?

[JohnnyMalaria]

My bad - it's a 475 (manufactured in 1974).

Here's a clip comparing XY mode with my DSO:



To be fair, seeing both reveals information about the signal that using just one of the 'scopes would miss.