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Old 23rd March 2010, 08:06 AM   #31
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Quote:
Originally Posted by Cristi View Post
as you said, for BTL mode must provide the same phase input signal for both left and right input. the left input is already inverted with 180* so, the left output will be the negative speaker output and the right output will be the positive speaker output. GND is not used for speaker connection, just for input and power supply.
GND for speaker was incorrect use of terms - sorry.

What i ment, was that the application note mention, that the left speaker output should be reversed, so minus on the board is plus on the speaker. In BTL mode should I then connect both plus speaker out from the circuitboard? That is what I would normally do.
 
Old 23rd March 2010, 09:25 AM   #32
Cristi is offline Cristi  Europe
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the left speaker should be reversed in single ended mode, stereo application since the input is also reversed. in BTL mode, the left output will be the negative speaker connection and the right output will be the positive speaker connection.
the reason why i the left channel is inverted, is because in this way the voltage pumping will be much lower than when both channels are in phase, IF the input signal has the same amplitude and similar program content. if one channel plays lower volume than other then the pumping will not be attenuated. another reason is because with this connection, using the amplifier in BTL mode doesn't require any modification, or an external signal inverting stage.
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Old 23rd March 2010, 09:56 AM   #33
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Default Mute TDA8950th for 5-10 seconds

As I have mentioned before, I have noise when powering up the amps. The noise are there for approx. 5 seconds. How can I add a simple 5 sec delay to the mute pin?

The amps do sound good, and almost class A like in the bass region. I have some noise when playen at low listening level. The noise is there as well, when playin louder but the level is not increasing with the music. It's not directly the amps, but at combination of the amps and my Behringer DCX2496, that gives this noise. The noise are modulated by the music, and always have the same level, regardless og volumesetting form my source.

I have ordered the MiniDSP crossover and digital in/ut, so I can go optical from source to DSP. I hope this will help.
 
Old 23rd March 2010, 10:32 AM   #34
Cristi is offline Cristi  Europe
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The power-on noise can be supressed by adding a capacitor between the Mute pin and GND. the delay depends from it's value. a 100-220uF capacitor should provide few seconds delay. a speaker protection circuit can also be used.
the noise can have multiple causes, most probable is a GND loop, the class D amps are sensitive at this. another cause is an oscillation, and this can be discovered easy, by monitoring the zobel resistors temperature. when there is an oscillation, this resistors become very hot. you can try the amp without the input connected. just simply remove the input connector and power the amp to see if the noise is still there.
another cause can be the higher noise floor of the signal source.
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Old 23rd March 2010, 10:53 AM   #35
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Quote:
Originally Posted by Cristi View Post
The power-on noise can be supressed by adding a capacitor between the Mute pin and GND. the delay depends from it's value. a 100-220uF capacitor should provide few seconds delay. a speaker protection circuit can also be used.
the noise can have multiple causes, most probable is a GND loop, the class D amps are sensitive at this. another cause is an oscillation, and this can be discovered easy, by monitoring the zobel resistors temperature. when there is an oscillation, this resistors become very hot. you can try the amp without the input connected. just simply remove the input connector and power the amp to see if the noise is still there.
another cause can be the higher noise floor of the signal source.
The capacitor trick is simple to implement, thanks for that one.
The heat sink, does get really hot, and it's quite large! I can touch the heatsink, but I guess it's at least 45 degrees Celsius. Whith no signal (no cables), the amps a almost dead quiet. Even with cables/source but no music, there is no noise. Only when the music plays, the noise is audible.

What do I do, if I have oscillation? And where do I find the zobel resistor?
 
Old 26th March 2010, 07:50 AM   #36
Cristi is offline Cristi  Europe
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the zobel resistors are Through hole type, close to the output inductors, and they have the role of dissipating the reactive energy in case of oscillation, or to damp the oscillation. to prevent oscillation, the input cables must avoid forming a GND loop and do not wire them close to the output section. also, placing a low-pass filter on the input, can help. a siple R-C network, one 2.2-4.7K resistor in series and one 470pF-1nF cap to signal GND. this will not have negative effect on the high frequencies if the resistor has no bigger value than 4.7K or the cap is not bigger than 1nF.
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Old 26th March 2010, 08:12 AM   #37
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Then I have been dead wrong in my design. I have placed input and output just next to each other (1 cm apart/ inch apart), and both left/right input/output are 2x5 cm square (1x2 inches).
 
Old 26th March 2010, 10:27 AM   #38
Cristi is offline Cristi  Europe
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the module can be placed in the box with the input on one side, and output on the other side, for example input on the right and routed with short shielded wires to the connectors on the backside of the board at the right corner, then the output route to the middle-back and the transformer place on the left side of the box. in this way, there will be at least 5cm between input and output connections.
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Old 6th April 2010, 10:30 PM   #39
alkasar is offline alkasar  France
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Hello Cristi
I am not shure of the layout of the connectors of the TDA 8920 v1.0 board.
Could you confirm I got it right ?
Click the image to open in full size.

Last edited by alkasar; 6th April 2010 at 10:33 PM.
 
Old 7th April 2010, 04:40 AM   #40
Cristi is offline Cristi  Europe
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The connections as you drawn are correct. keep in mind that the left channel output must be connected inverted, the loudspeaker will be connected with + at left GND and - at Left Out. this because the left channel input signal is applied to the inverted input of the ic, and the right channel signal is applied to the noninverted input. there are advantages of this type of connection such as the bus-pumping cancellation and easy BTL connection.

congratulations for the nice drawing, btw
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