I have almost finished my two stereo amps based on 8950th chip. One is almost silent, the other have, as I hear it, some 50 hz noise (I haven't measured it).
I would like to eliminate this noise. In the application note from NXD homepage, this i written "Connect the heatsink to the groundplane or to VSSPn using a 100 nF capacitor". Why? and would that have an impact on the noise? Note: I have not connected any capacitor too groundplane
I would like to eliminate this noise. In the application note from NXD homepage, this i written "Connect the heatsink to the groundplane or to VSSPn using a 100 nF capacitor". Why? and would that have an impact on the noise? Note: I have not connected any capacitor too groundplane
Tanks for the answer. I will try to shift the powerplug 180 dg., to see if that helps. Maybe the noise comes from the mains transformer. The two amplifier at 100% identical, so if a groundloop problem exist on one, shouldn't it be on the other as well?
How do I locate groundloop? I have only a cheap 10$ volt/ohm/ampere meter.
How do I locate groundloop? I have only a cheap 10$ volt/ohm/ampere meter.
since i was asked few times about a very compact version of the TDA8920 amplifier with on-board SMPS, i decided to make-it. here is it: Connexelectronic
it has on-board SMPS and is very compact, just 100x50x40mm including heatsink. can be powered from 110/230V mains and delivers 2x70W at 4 Ohms.
it has on-board SMPS and is very compact, just 100x50x40mm including heatsink. can be powered from 110/230V mains and delivers 2x70W at 4 Ohms.
In order to try BTL mode, do I just need one Y-split signal cable to provide both inputs with the same mono signal (either right or left)? I'm also a bit unsecure about the speaker terminals. On the left I have switch the phase 180 degrees. I BTL mode I should not use ground. Normally that means that you would use the two red terminals, but in this case I guess I have to use red teminal on rigth output, and black terminal on left output, since the left black terminal is actually not ground.
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.
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.
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.
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/óut, so I can go optical from source to DSP. I hope this will help.
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/óut, so I can go optical from source to DSP. I hope this will help.
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 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?
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.
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.
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
congratulations for the nice drawing, btw