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Class D Switching Power Amplifiers and Power D/A conversion

TI TPA3255EVM
TI TPA3255EVM
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Old 23rd February 2019, 12:41 PM   #851
ABSNimes is offline ABSNimes  Europe
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Thank you Think


I carefully read the manual, but haven't found an explicit answer.
From what I understand, the answer is in reading schematic Page 18.
Her you can see Balanced J10/12 inputs pins and connexions.


I need to be assured to avoid mistakes


Cheers
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Old 23rd February 2019, 02:22 PM   #852
Think is offline Think  Netherlands
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TI TPA3255EVM
The schematic is page 17 not 18.

The thing that confused me is that I think J10 should be named
INA/B DIFF INPUT instead of INC/D DIFF INPUT, (just like J12)

And they should never be jumpered (tables correctly always show 'out') but are included in the tables so people don't as J4 and J19 are used for selecting between SE and DIFF.

You can use J10 and J12 or use the rca (2 per channel) connectors as differential inputs. On page 17 you can see that they are the same.
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Old 23rd February 2019, 02:53 PM   #853
mboxler is offline mboxler  United States
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You could connect the balanced inputs to the audio interface board, pins 11, 13, 15, and 17. Connect ground to pin 21. I think a 20 awg solid wire can easily be pushed into each pin.

This would bypass the op amps, and leave only the 10uf coupling capacitor in the signal path.

The chip's input impedance is 20k.

Mike
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Old 23rd February 2019, 05:56 PM   #854
Think is offline Think  Netherlands
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TI TPA3255EVM
I recently found these for this purpose and many more.
10PC Female&Male 40pin 2.54mm Header Socket Single Row Strip PCB Connector CA | eBay $1
Click the image to open in full size.
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Old 24th February 2019, 11:34 AM   #855
ABSNimes is offline ABSNimes  Europe
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Quote:
Originally Posted by mboxler View Post
You could connect the balanced inputs to the audio interface board, pins 11, 13, 15, and 17. Connect ground to pin 21. I think a 20 awg solid wire can easily be pushed into each pin.

This would bypass the op amps, and leave only the 10uf coupling capacitor in the signal path.

The chip's input impedance is 20k.

Mike


Many thanks Mike
I'll go this way.
Best regards
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Old 24th February 2019, 11:59 AM   #856
ABSNimes is offline ABSNimes  Europe
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Default Reset Switch

I'd like to put the RESET switch on the front panel.


Could you confirm that Pin 10 of J28 need to be connected to one side of the switch and the other side to Pin 22 (Gnd) ?
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Old 24th February 2019, 12:39 PM   #857
mboxler is offline mboxler  United States
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Quote:
Originally Posted by ABSNimes View Post
I'd like to put the RESET switch on the front panel.


Could you confirm that Pin 10 of J28 need to be connected to one side of the switch and the other side to Pin 22 (Gnd) ?
According to the schematic, that should work. You could test this by using a jumper wire (starting to wonder if 22 awg is better), and connect pins 10 and 22.

Seems like others have inquired about this, but not sure if anyone has actually tried it.

Let us know it that works.

Mike
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Old 11th March 2019, 12:42 PM   #858
ABSNimes is offline ABSNimes  Europe
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Hi,
"You could connect the balanced inputs to the audio interface board, pins 11, 13, 15, and 17. Connect ground to pin 21. I think a 20 awg solid wire can easily be pushed into each pin."

Today, I connect as you say, but nothing at the output.
Some plops could be haerd in speakers, I quickly power off the amp.


Maybe am I wrong with jumpers settings...
I leave them in SE configuration (stereo mode using RCA inputs).

Some hints are welcome

Regards

Last edited by ABSNimes; 11th March 2019 at 12:46 PM.
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Old 14th March 2019, 01:25 AM   #859
linuxfan is offline linuxfan  Australia
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ABSNimes, regarding differential input to the 3255EVM board, in stereo BTL mode, there are two slightly different approaches;

i) connect to the J10 and J12 headers (or all 4x RCA connectors, which I consider confusing) -
your audio signals will still be buffered by the NE5532 opamps, but remain fully differential.

ii) connect to pins 11,13,15,17 & 21-GND of the J28 header (as member mboxler suggested)
your audio signals will then bypass the opamps, and go to the TPA3255 simply via a DC blocking cap.

Which approach sounds better will likely depend on whether your particular source device benefits from a buffer in the chain. I suggest you try i) first.
Check your configuration - you want the board in 2 x BTL mode, with differential inputs;

J5(M1), J6(M2) should be in the "0" or "L" position.
J21, J7, J8 should be open.
J4, J19 should be in the "DIFF" position.
J26 should be in the "C" position.
J27 should be in the "D" position.
S1 should be in the "NORMAL" position.

If this works OK, and you want to then try ii)
I understand that the opamps should be grounded, since they will then be unused, and might otherwise generate some noise (or heat).
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