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Old 27th February 2010, 09:17 AM   #21
Cristi is offline Cristi  Europe
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i will consider to add a crossover if there will be few more requests.
 
Old 3rd March 2010, 07:30 AM   #22
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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
 
Old 3rd March 2010, 10:48 AM   #23
Cristi is offline Cristi  Europe
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the heatsink is connected to the GND copper pour, through the screws which attach the module on the heatsink. the ic thermal pad is connected to VSSP, so it must be insulated from the heatsink. the 50Hz noise might be from a GND loop instead of heatsink connection. try to locate that first.
 
Old 3rd March 2010, 11:34 AM   #24
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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.
 
Old 3rd March 2010, 12:56 PM   #25
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Just a comment to my set-up. The source is a battery driven CD player, and the amplifier is the only device with power connection
 
Old 3rd March 2010, 05:59 PM   #26
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another thing I forgot to ask. Both amps have a high frequency noise (changing in pitch) the first seconds, then it dissapears. Is this normal?
 
Old 6th March 2010, 06:20 AM   #27
Cristi is offline Cristi  Europe
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this are transient phenomenons which are dependent on the supply voltage and power supply capacitors charge. they might be audible until the amplifier goes into normal operation mode, such as when you toggle between mute or idle and run. they normally last short time, less than few seconds.
 
Old 6th March 2010, 07:02 AM   #28
Cristi is offline Cristi  Europe
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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.
 
Old 22nd March 2010, 08:11 AM   #29
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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.
 
Old 23rd March 2010, 07:55 AM   #30
Cristi is offline Cristi  Europe
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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.
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