Hello!
I have bought a 2.1 Chinese system which i was planning to modify originally. So, i knew what i was buying. It sound good for me, but there is a problem with humming and hissing.
Humming and hissing is present constantly and is not dependent on volume level. Humming from sub was 150Hz
So, i replaced the cheap transformer (which was "singing") with toroidal transformer, added 4700 caps and it helped a lot. Now sub is humming only 50 Hz and very very liitle. Good enough for me.
However, side speakers are still hissing and humming at too high level for me.
I checked the circuit further.
It uses TDA2030A and dual supply with central point from transformer. There is no real ground anywhere (only L+N from socket). I have read the datasheet and it said that metal plate of TDA2030A is connected to V- and must be isolated from heat sink when using dual voltage supply. I checked and there is not isolation between metal plate of TDA2030A and the heat sink.
Then i figured that when i touch the heat sink with my finger the 50HZ humming because a lot less.
Is my following understanding correct:
1) The heat sink works like antenna and all the noise it collected goes to V- creating extra 50HZ humming
2) Heat sink must be isolated and grounded
3) I need to bring ground from socket and connected it to central point from transformer (common wire)
If so, then how do i mount tda2030A isolated from heat sink? I need to use a screw, and screw thread will touch the metal inside TDA hole and the hole inside the heat sink. Need some kind of plastic screw?
On the attached picture:
1) blue dots - input from transformer (- and +)
2) greeen dot - central point from transformer
3) red does - output from rectifier bridge
I have bought a 2.1 Chinese system which i was planning to modify originally. So, i knew what i was buying. It sound good for me, but there is a problem with humming and hissing.
Humming and hissing is present constantly and is not dependent on volume level. Humming from sub was 150Hz
So, i replaced the cheap transformer (which was "singing") with toroidal transformer, added 4700 caps and it helped a lot. Now sub is humming only 50 Hz and very very liitle. Good enough for me.
However, side speakers are still hissing and humming at too high level for me.
I checked the circuit further.
It uses TDA2030A and dual supply with central point from transformer. There is no real ground anywhere (only L+N from socket). I have read the datasheet and it said that metal plate of TDA2030A is connected to V- and must be isolated from heat sink when using dual voltage supply. I checked and there is not isolation between metal plate of TDA2030A and the heat sink.
Then i figured that when i touch the heat sink with my finger the 50HZ humming because a lot less.
Is my following understanding correct:
1) The heat sink works like antenna and all the noise it collected goes to V- creating extra 50HZ humming
2) Heat sink must be isolated and grounded
3) I need to bring ground from socket and connected it to central point from transformer (common wire)
If so, then how do i mount tda2030A isolated from heat sink? I need to use a screw, and screw thread will touch the metal inside TDA hole and the hole inside the heat sink. Need some kind of plastic screw?
On the attached picture:
1) blue dots - input from transformer (- and +)
2) greeen dot - central point from transformer
3) red does - output from rectifier bridge
Attachments
You need a mounting kit like the link below. Can't believe that they would sell this amp without the transistors being isolated. The mounting screw uses the black washer as isolation, however the screws used in the amp may not be the right size for the washer.
https://www.ebay.co.uk/itm/322543932436?epid=941570253&hash=item4b191dd414:g:q4cAAOSwk9dZoisz&amdata=enc:AQAIAAAA0Beo850jtPLLR7vdGJrZDj4UiLmDBJxZZAVeaFlqQKRrpzGdq+MiVPXVQ4+A9tIyN2pBeg5IF64TnJT/jLbHNchtoFWTLnlvTs9HXZ4B2LFW9S5P4K9+sSV+Jjw/f/wTc2raLKk7gLCY6nmFTkE5204QpKDpnB6zdgkxudCLGr4T+7F+BwJh1jyrTabYWHrJ4BPVIi6P9iLrXCX5RO8t58RMRqP8pscVGY0JNArJDNGgxX1DUpYuBH9pVElTtVm1399+4T3cJAG5etYZ/UGKqEg=|tkp:Bk9SR6z-zKqBYw
https://www.ebay.co.uk/itm/322543932436?epid=941570253&hash=item4b191dd414:g:q4cAAOSwk9dZoisz&amdata=enc:AQAIAAAA0Beo850jtPLLR7vdGJrZDj4UiLmDBJxZZAVeaFlqQKRrpzGdq+MiVPXVQ4+A9tIyN2pBeg5IF64TnJT/jLbHNchtoFWTLnlvTs9HXZ4B2LFW9S5P4K9+sSV+Jjw/f/wTc2raLKk7gLCY6nmFTkE5204QpKDpnB6zdgkxudCLGr4T+7F+BwJh1jyrTabYWHrJ4BPVIi6P9iLrXCX5RO8t58RMRqP8pscVGY0JNArJDNGgxX1DUpYuBH9pVElTtVm1399+4T3cJAG5etYZ/UGKqEg=|tkp:Bk9SR6z-zKqBYw
Thank you! I will look for such kit locally.
One more idea.
The electronics module has BT receiver, the output from BT goes to the amp board.
See attached image.
I disconnected it and immediately 50Hz noise went to negligible level.
I reconnect it and move the wire close and further to/from the transfomer - 50HZ hum increased/decreased.
Each channel has its one ground/common coming from BT output. It seems like there is a common wire loops working as antenna.
Should i cut the common wires from BT, connected them tother and connect them to the transformer center point ?
One more idea.
The electronics module has BT receiver, the output from BT goes to the amp board.
See attached image.
I disconnected it and immediately 50Hz noise went to negligible level.
I reconnect it and move the wire close and further to/from the transfomer - 50HZ hum increased/decreased.
Each channel has its one ground/common coming from BT output. It seems like there is a common wire loops working as antenna.
Should i cut the common wires from BT, connected them tother and connect them to the transformer center point ?
Attachments
If you do not intend to use the BT facility then isolating it would seem to cure your problem. I have not messed with anything B Tooth so others would need to say yes or no to your suggestions.
I made a 2030 based amp some years ago using bare boards and it is a very nice sounding amp.
I made a 2030 based amp some years ago using bare boards and it is a very nice sounding amp.
I tried to understand how it works and how common wire goes.
So, there are two board: 1) control board with buttons and Bluetooth 2) amp board with power supply and TDA2030A
AMP BOARD is inside subwoofer and also has 2 outputs for side speaker. It also has 2 inputs for external source.
OUTPUT from control board goes to AMP board internal input using UL2547 28AWG shielded cable with 4 wires (GND as a shield and 3 signal cables).
Why are there 3 signal cables? It seems like subwoofer signal is separate. The control board has 3 regulators VOLUME, TREBLE and BASS.
VOLUME and TREBLE are stereo pots but BASS is mono and its output goes to separate output wire.
EXTERNAL INPUT from AMP board goes to contrrol board, passes through regulators and goes back to output.
So, how common wire (lets call it GND) goes for bt output:
+13V and GND from power supply go to power the control board. Then GND goes back to amp board via shielded cable with audio signals this creating a GND loop.
How GND goes from EXTERNAL INPUT
External imput connects to AMP BOARD GND at the socket point. Then it goes to control board with a 3 wire shielded wire (LEFT, RIGHT and GND), then this GND and power supply GND go back to amp board on audio signal shielded wire. So, we have 2 GND loops here. Also, even when nothing is connected to External Input sockets GND is still connected from it to conrol board.
So, as i understand there are at lesat 2 GND loops here working as antennas.
So i get it right that i need to cut the GND loops and make it STAR topology ?
So, there are two board: 1) control board with buttons and Bluetooth 2) amp board with power supply and TDA2030A
AMP BOARD is inside subwoofer and also has 2 outputs for side speaker. It also has 2 inputs for external source.
OUTPUT from control board goes to AMP board internal input using UL2547 28AWG shielded cable with 4 wires (GND as a shield and 3 signal cables).
Why are there 3 signal cables? It seems like subwoofer signal is separate. The control board has 3 regulators VOLUME, TREBLE and BASS.
VOLUME and TREBLE are stereo pots but BASS is mono and its output goes to separate output wire.
EXTERNAL INPUT from AMP board goes to contrrol board, passes through regulators and goes back to output.
So, how common wire (lets call it GND) goes for bt output:
+13V and GND from power supply go to power the control board. Then GND goes back to amp board via shielded cable with audio signals this creating a GND loop.
How GND goes from EXTERNAL INPUT
External imput connects to AMP BOARD GND at the socket point. Then it goes to control board with a 3 wire shielded wire (LEFT, RIGHT and GND), then this GND and power supply GND go back to amp board on audio signal shielded wire. So, we have 2 GND loops here. Also, even when nothing is connected to External Input sockets GND is still connected from it to conrol board.
So, as i understand there are at lesat 2 GND loops here working as antennas.
So i get it right that i need to cut the GND loops and make it STAR topology ?
Attachments
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