Bridging TPA3123D2 Amp - diyAudio
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Old 4th March 2015, 12:18 AM   #1
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Join Date: Mar 2015
Location: CA, USA
Default Bridging TPA3123D2 Amp

Hello DIYers,

I'm a long time lurker first time poster. Please excuse the Cheap-o parts I'm using in this build. I'm really just trying to learn and have fun.

I built a small sub for my car. I've been driving a 5.25" 50W 4 Ohm sub, with a Muse Audio 2 x 50 W Class D and a Pololu 12v to 24v Step up. Below are the links to my parts:

Sub from this 5.1: Detailed specifications on HTS3541/F7
Amp: 2X50W Stereo Class D Audio Power Amplifier Circuit Board TI TPA3123 | eBay
Stepup: https://www.pololu.com/product/2569

Here it is in all it's DIY glory:

Click the image to open in full size.

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It worked well but I was getting clipping when I ran the amp any where above 1/2 power. I think it has to do with the fact that the sub is 50W MAX. So I want to get a bigger sub. I want to get a 6.5" 100 W sub. But I'm not sure how to get that output from my amp, and what bridging will do to the ohms.

Now, I did some research and found Elliot's Sound products, specifically project 20 : Simplest Ever Bridging Adapter for Amplifiers

What I'm wondering:

1) Is this the right way to bridge the 2 channels? I know I need to invert one of the 2 channels. Would this, do that?
2) If were to bridge the 2 channels on my 2x50w, 4 ohm amp, would the output be 100w 8ohm?
3)What kind of resistor do I need?
3)How exactly do I bridge the 2 outputs? Where would I solder the leads?

From these questions, I think it's obvious I know very little about real electronics.

Here are some pictures of the board. Click to zoom in. Please ignore the super glue on the R+ and R- outputs.

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.

Here's what I've found out so far from my high-school level of electronics knowledge:

I think that the board runs the stereo input to the back of the board near the yellow LED and red On/OFF, and everything from the Op-Amps back seem to be grounded to the audio input signal. Then the TPA3132D2 chips and everything around them are grounded to the Vin power supply, on the output side of the board. Some of this is probably wrong but I'm trying.

Can someone throw me a line here?

Thanks in advance for any help!

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Old 4th March 2015, 01:53 AM   #2
kp93300 is offline kp93300  Malaysia
diyAudio Member
 
Join Date: Mar 2007
Hi
I like this board also.
The TPA3123 is being used in the bridge mode in the board. the signal input is split into 2 phases by the op amp on board.
Is the clipping due to signal input overload. The board as designed has a 36db gain that clips easily with standard 2 V rms .
cheers
kp93300
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Old 4th March 2015, 02:59 AM   #3
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Join Date: Mar 2015
Location: CA, USA
Hey KP93300.

Quote:
Originally Posted by kp93300 View Post
The TPA3123 is being used in the bridge mode in the board. the signal input is split into 2 phases by the op amp on board
So you are saying the output is already bridged? Can I run a single 100w 4 ohm speaker by connecting R+ and L-?

Quote:
Originally Posted by kp93300 View Post
Is the clipping due to signal input overload. The board as designed has a 36db gain that clips easily with standard 2 V rms.
I see. Should I change the feed back resistor on the 2 op-amps to a higher resistance to drop the gain? or Is it as simple as just leaving it a 1/2 volume? I'd like to get the maximum wattage out of the amp before it clips, what do you think?

Thanks!
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Old 4th March 2015, 03:19 AM   #4
kp93300 is offline kp93300  Malaysia
diyAudio Member
 
Join Date: Mar 2007
hello,
I am not an expert in electronic .

So you are saying the output is already bridged? Can I run a single 100w 4 ohm speaker by connecting R+ and L-?

Ans This is not possible in this board

I see. Should I change the feed back resistor on the 2 op-amps to a higher resistance to drop the gain? or Is it as simple as just leaving it a 1/2 volume? I'd like to get the maximum wattage out of the amp before it clips, what do you think? Ans. You cannot change gain by changing the op amp resistor. You have to change it via the gain setting pins of the TPA3123 chip
Thanks![/QUOTE]
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Old 5th March 2015, 07:06 AM   #5
diyAudio Member
 
Join Date: Mar 2015
Location: CA, USA
Quote:
Originally Posted by kp93300 View Post
hello,
I am not an expert in electronic .

So you are saying the output is already bridged? Can I run a single 100w 4 ohm speaker by connecting R+ and L-?

Ans This is not possible in this board

I see. Should I change the feed back resistor on the 2 op-amps to a higher resistance to drop the gain? or Is it as simple as just leaving it a 1/2 volume? I'd like to get the maximum wattage out of the amp before it clips, what do you think? Ans. You cannot change gain by changing the op amp resistor. You have to change it via the gain setting pins of the TPA3123 chip
Thanks!
I see! Thank you for that info.

Okay, after doing some more research it seems I was trying to sum/combine speaker level signals, which I've read is not recommended/not the right way to approach this problem.

I also now realize what the op-amp is doing and why summing them at the Op-amp or the TPA3132D2 won't work. I would need to add the summing circuit to the middle of the board between the Op-amp's and the TPA3132D2's and run the signal through one channel, But it would be better just find/build an amp board that doesn't split the single stereo channel input into 2 channels, and then amplify that one channel to my desired wattage.

Can some one confirm this theory, for my sake?

What I've opted to do instead, is buy a DVC Sub with 4ohms on both coils and run the left and right channels of this amp board to the separate coils. Since the amp input comes from my head-unit's sub output, I should be fine to do so. The amp out puts 4 ohms to the Left and Right Stereo channels so I should be fine in doing so.

Again, can someone confirm?

I was worried a first that doing so would damage the sub, but after reading this ( http://www.adireaudio.com/Files/Dual...oilDrivers.pdf ) I'm not worried.

I'm gonna test it on a cheap $40 sub and see what I get.

I realize that ideally I would just buy a matching sub and amp with the correct wattage output (rms) and the correct impedance but then I wouldn't have learned this much.

Thanks for your time. I will post my results for any future readers.
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