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TPA3255 - all about DIY, Discussion, Design etc.
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Old 4th July 2019, 09:03 PM   #1311
Kay Pirinha is offline Kay Pirinha  Germany
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Wow! Without these input transformers there's one or two short glitches on the FAULT LED, then it stays off.
Why does the board behave this way? And what can I do if I need symmetrical inputs via XLR terminals, with the board being jumpered for symmetrical mode, and unbalanced, but floating (due to avoid ground loops) RCA inputs as well?
Best regards!
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Old 4th July 2019, 11:01 PM   #1312
doctormord is offline doctormord  Germany
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Does transformer has center tap on secondary side? Try with primary side shorted but connected transformers.
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Old 5th July 2019, 12:09 PM   #1313
Think is offline Think  Netherlands
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TPA3255 - all about DIY, Discussion, Design etc.
Default Earlier in this threat I read:

Quote:
Originally Posted by mboxler View Post
Thanks guys! I've been studying passive circuits, but with the purchase of this EVM I've started studying active circuits. Feedback is slowly sinking in!

Just to satisfy my own curiosity, I created a 400Hz signal at .64 volts and measured the speaker out voltage. It was 15.27 volts, which equates to a 27.5 dB gain. Since I'm running this amp BTL, the output voltage would double vs se, which would account for the extra 6 dB.

Mike
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Originally Posted by DPH View Post
Bingo -- right on the money, Mike. ......
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Old 5th July 2019, 06:40 PM   #1314
Kay Pirinha is offline Kay Pirinha  Germany
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Quote:
Originally Posted by doctormord View Post
Does transformer has center tap on secondary side? Try with primary side shorted but connected transformers.

No, the input transformers aren't CT. That's why I asked this question.


In the meantime it turned out fine, after I've rotated the board by 180 degrees .


The only issue that is left is the lack of input sensitivity. I'll try to source four of these super tiny (like a grain of sand!) resistors of 22 kohms.


Best regards!
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Old 20th July 2019, 08:44 PM   #1315
snickers is offline snickers
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I'm planing on building a 5 channel poweramp with the TPA3255 boards. Ideally the 3e one's.
Preamp will be an AVR witch cinch out's. Speakers will be 5x the Klipsch RP-280F on fullrange without Subwoofer. So I'm using a 5.0 system.

My speakers are from 3.31 Ohm up to 16.07 Ohm. They are specificated as 8 Ohm speakers.
So my question is: Which 3e board to use?
The TPA3255 stereo-board or the mono-channel one?
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Old Yesterday, 08:01 AM   #1316
kaytata is offline kaytata  India
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Quote:
Originally Posted by mboxler View Post
Also, if you are supplying a differential input, you can bypass the op amps altogether by connecting your inputs to the Audio Interface Board. That will give you 20K input impedance as well.

Mike
Hi Mike,


Cheers! I am new to this thread. I use the EVM with a differential input es9038q2m based modded dac.


My questions are:


1. Will there be sq benefit bypassing the opamps? I asked in the ti forum but did not get answers.
2. Can bypass be made with the 28pins Audio interface board socket? If so, which pins would correspond to the inputs?
3. In case bypass is a difficult job, do you think changing the ne5532 to a cleaner opamp like opa1612 result in better sq?


Regards,
Kay
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Old Yesterday, 10:40 AM   #1317
Turbowatch2 is offline Turbowatch2  Germany
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If you have a real NE5532 this is a "cleaner" OP amp. Just be sure not to have a faked one, which is very popular. A "real one" is usualy around 1$ per piece in single or low numbers. Cheap OP amps are 2 Cent.
An expensive OPA or the like will hardly give audible improvement, if not compared on a system of highest quality from source to speaker.
They may even sound worse than the original one, if the surounding partīs values donīt comfort it.
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Old Yesterday, 12:35 PM   #1318
mboxler is offline mboxler  United States
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Quote:
Originally Posted by kaytata View Post
Hi Mike,


Cheers! I am new to this thread. I use the EVM with a differential input es9038q2m based modded dac.


My questions are:


1. Will there be sq benefit bypassing the opamps? I asked in the ti forum but did not get answers.
2. Can bypass be made with the 28pins Audio interface board socket? If so, which pins would correspond to the inputs?
3. In case bypass is a difficult job, do you think changing the ne5532 to a cleaner opamp like opa1612 result in better sq?


Regards,
Kay
Hey Kay

I never tried using the Audio Interface Board inputs, as I don't have a source with diff outputs, but I know others have. @dubai200 ??? So I can't vouch for the sq benefit.

If you look at the EVM User's Guide (slou441), the schematic shows the AIB pins used.

Pins 11 and 13 for one diff input, pins 15 and 17 for the other diff input, and pins 21 and 22 for the grounds. I believe a solid 24 AWG wire can be pushed into the board for a good snug fit.

By doing so, you completely bypass the op amps. Only the 10uf coupling cap is between the source and the chip.

Hope this helps.

Mike
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Old Yesterday, 02:07 PM   #1319
kaytata is offline kaytata  India
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Quote:
Originally Posted by mboxler View Post
Hey Kay

I never tried using the Audio Interface Board inputs, as I don't have a source with diff outputs, but I know others have. @dubai200 ??? So I can't vouch for the sq benefit.

If you look at the EVM User's Guide (slou441), the schematic shows the AIB pins used.

Pins 11 and 13 for one diff input, pins 15 and 17 for the other diff input, and pins 21 and 22 for the grounds. I believe a solid 24 AWG wire can be pushed into the board for a good snug fit.

By doing so, you completely bypass the op amps. Only the 10uf coupling cap is between the source and the chip.

Hope this helps.

Mike

Thank you very much Mike,
Cheers,
Kay
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Old Yesterday, 02:11 PM   #1320
kaytata is offline kaytata  India
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Quote:
Originally Posted by Turbowatch2 View Post
If you have a real NE5532 this is a "cleaner" OP amp.

Thanks for the comments Turbowatch.



Yes, I have the ti evm so the opamp should be genuine. Since my dac is supposed to be -120db thd+n, I was thinking ne5532 can become the bottleneck in the chain.


Cheers,
Kay
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