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Class D Switching Power Amplifiers and Power D/A conversion

TPA3255 - all about DIY, Discussion, Design etc.
TPA3255 - all about DIY, Discussion, Design etc.
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Old 21st May 2019, 02:37 AM   #1231
KCN is offline KCN
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Join Date: Feb 2016
My amp now starts well, plays good for few minutes and then the sound slowly drops till you can hardly hear. some times it increases again and falls or some times remain ultra low voulme.
switching on and restart immediately has no effect. but switch off for 5 minutes and restart sound at normal volume and then again it slowly fades.
what may be the reason for this?? tried on multiple input source both bluetooth and dac/preamp.
running on 32v dc powersupply checked it and has steady output

Last edited by KCN; 21st May 2019 at 02:39 AM.
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Old 21st May 2019, 08:09 AM   #1232
Turbowatch2 is offline Turbowatch2  Germany
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I often read about D-amps having problems with Bi-amping loudspeakers.
This is a logical result on many designs!
The midd/ high part of a bi-amped speaker is a "no-load" situation for the lower frequency.
So if the amp does not like beeing driven with open output, it may fail or produce all kinds of problems, like overheating or sudden shut down, some even burn the chips internals.

So, first check the amps capabilities, then connect!

The "right way" of bi-amping is a two way active configuration, that eliminates the passive x-over. Often these two completely different topics get thrown into one bowl.
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Old 21st May 2019, 08:13 AM   #1233
Turbowatch2 is offline Turbowatch2  Germany
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@KCN
check the mute pin of your amp, it might charge up and enable itself after some time. Read the data sheet and compare your specific implementation. Maybe some safety feature engages?
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Old 21st May 2019, 10:19 AM   #1234
AnatoliyHill is offline AnatoliyHill
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Hi, Mate. What do you mean check the mute pin? What status/ voltage it should be and how to reset it?
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Old 22nd May 2019, 07:35 AM   #1235
chermann is offline chermann  Austria
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Hi anatoliy


i guess turbowatch is mentioned a circuit to avoid a faster power up of the TPA chip. i mean : if you switch on the amp board the rail voltage starts to rise and the tpa chip wants to "switch on" and therefore you will here this pop on sound.
to avoid this there is a circuit at the mute pin to "hold" the tpa chip "mute" = quiet.
at the YJ tpa3255 board there is a voltage superviser chip on board to do that.
-->TPS3802...please read some posts...its not so easy

What is wrong with TPA3255?
doctor created this circuit....


this mute circuit can be done with some RC divider too..pic 2


chris
Attached Images
File Type: jpg no pop noise.jpg (71.4 KB, 151 views)
File Type: jpg anti pop circuit.JPG (14.4 KB, 143 views)

Last edited by chermann; 22nd May 2019 at 07:39 AM.
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Old 22nd May 2019, 07:47 AM   #1236
chermann is offline chermann  Austria
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Quote:
Originally Posted by Turbowatch2 View Post
......
The midd/ high part of a bi-amped speaker is a "no-load" situation for the lower frequency.
.

hi turbowatch2


can you explain this:
The midd/ high part of a bi-amped speaker is a "no-load" situation for the lower frequency.


chris
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Old 22nd May 2019, 09:21 AM   #1237
doctormord is offline doctormord  Germany
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Quote:
Originally Posted by chermann View Post
this mute circuit can be done with some RC divider too..pic 2

The second circuit doesnt make sense here and will fry the TPA inputs due to overvoltage.
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Old 22nd May 2019, 09:50 AM   #1238
chermann is offline chermann  Austria
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Quote:
Originally Posted by doctormord View Post
The second circuit doesnt make sense here and will fry the TPA inputs due to overvoltage.

yes you are right...its bad to show the principle of the circuit with wrong values....


sorry
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Old 22nd May 2019, 12:17 PM   #1239
doctormord is offline doctormord  Germany
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It is not showing the principle of the circuit, it behaves completely different. (As it is totaly different)
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Old 22nd May 2019, 03:35 PM   #1240
KCN is offline KCN
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Join Date: Feb 2016
My speakers are not bi-amped. No mute pin in schematics.
i have changed the caps that i had put in earlier, even put lower value caps but same result.
the music plays normally and then reduces in volume. it is not complete mute. some times the voulme ebbs and dies but the sound is there at very low volume.
The large input cap near the dc jack? will and problem in that cause such result, as if the amp input current is fluctuating?
any input/help welcome.
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