Stereo TPA3255 to Mono

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#4
The TI TPA3255EVM evaluation module "supports two BTL (stereo 2.0) output channels, one PBTL (mono 0.1) output channel, one BTL plus two SE (2.1) output channels, and four SE (4.0) output channels configurations." User's Guide I don't think the typical commercial TPA3255 amps are designed this way. The EVM has several jumpers that need to be changed for each mode of operation.
 
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#6
WASTd said:
So I have to buy a Mono tpa3255, correct?
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Yes.

The design of the TPA325x chips allows for three possible modes of operation:
4 mono channels
2 BTL channels
1 PBTL channel

There is no MFG or board (as far as I am aware) that uses the first mode. All the "stereo" boards are already in BTL (bridged) mode, so you cannot yet again bridge those channels. The PBTL mode just puts both BTL channels in parallel with each other in order to provide more current for low impedance loads (e.g. 480W @ 2R) but at 4R has no real advantage over the BTL mode.

So, if you want mono and you can use it on a 2 Ohm nominal load, then the mono PBTL board is what you want.
If you will be connecting to a 4 Ohm load, just get a stereo BTL board.
To get maximum power, choose a board that supports a 48-50Vdc supply and use a supply of that max possible voltage with sufficient current capability. That rules out most of the cheap Asian boards found on Ebay, AliExpress, Amazon, etc.
 
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#7
CharlieLaub said:
Yes.

The design of the TPA325x chips allows for three possible modes of operation:
4 mono channels
2 BTL channels
1 PBTL channel

There is no MFG or board (as far as I am aware) that uses the first mode. All the "stereo" boards are already in BTL (bridged) mode, so you cannot yet again bridge those channels. The PBTL mode just puts both BTL channels in parallel with each other in order to provide more current for low impedance loads (e.g. 480W @ 2R) but at 4R has no real advantage over the BTL mode.

So, if you want mono and you can use it on a 2 Ohm nominal load, then the mono PBTL board is what you want.
If you will be connecting to a 4 Ohm load, just get a stereo BTL board.
To get maximum power, choose a board that supports a 48-50Vdc supply and use a supply of that max possible voltage with sufficient current capability. That rules out most of the cheap Asian boards found on Ebay, AliExpress, Amazon, etc.
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Awesome idea on using the stereo BTL board, but how would I go about connecting the driver so that left and right channels work the same way?
 
#10
WASTd said:
Awesome idea on using the stereo BTL board, but how would I go about connecting the driver so that left and right channels work the same way?
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I meant that you should use 1 channel of a BTL amp for your speaker, and leave the other output discconnected and ground those inputs. This is because, for a 4 Ohm load, the BTL and PBTL modes will give you about the same amount of power. It is only with 2 Ohm loads that there is a difference - the BTL board is not rated for that impedance. Only the PBTL mode (mono board) can deliver more power into a 2 Ohm load. See attached image, from the TPA3255 datasheet.
 

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#11
CharlieLaub said:
I meant that you should use 1 channel of a BTL amp for your speaker, and leave the other output discconnected and ground those inputs. This is because, for a 4 Ohm load, the BTL and PBTL modes will give you about the same amount of power. It is only with 2 Ohm loads that there is a difference - the BTL board is not rated for that impedance. Only the PBTL mode (mono board) can deliver more power into a 2 Ohm load. See attached image, from the TPA3255 datasheet.
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Would it be fine to leave one output disconnected? Wont put any pressure on the chip since Class D amps always want a load connected?
 
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#12
WASTd said:
Would it be fine to leave one output disconnected? Wont put any pressure on the chip since Class D amps always want a load connected?
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If you ground the inputs (+ and - input connected to input GND) then that amp channel is not really doing anything. But if you are concerned about it you could connect a dummy load resistor to the unused output to prevent a high Q resonance around 20kHz. Not a bad idea I guess. You probably just need a 3W-5W 4 Ohm resistor for that since no power will be dissipated.
 
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#13
CharlieLaub said:
If you ground the inputs (+ and - input connected to input GND) then that amp channel is not really doing anything. But if you are concerned about it you could connect a dummy load resistor to the unused output to prevent a high Q resonance around 20kHz. Not a bad idea I guess. You probably just need a 3W-5W 4 Ohm resistor for that since no power will be dissipated.
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What do you exactly mean by grounding the inputs? So If for example I'm connecting only the left channel, I would connect the right channel's + and - to the left channel's -?
 
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#14
Each input is balanced, so there are three terminals available to you:
(+) = positive input
(-) = negative input
GND = local ground

Connect both + and - to GND using short wires to "ground" the inputs.

If you have a version of a TPA3255 amp that is single ended, you will only have + and GND. In that case just connect those two terminals via a short wire.
 
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#15
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