I cannot measure the hum, my DMM reads 0 at the speaker outputs when set to AC.
I need to mention that the buzz is 60 hz ( measured it today ).
input open - almost no buzz
inputs shorted - same as open
input with stereo source with vol pot set to 0 - quite a bit louder buzz than the above
The buzz sounds like the buzzing of an electric guitar that has a ground loop.
I also noticed while poking at it that the transformer also buzzez at 60 hz ( but not quite as loud as the amp does when connected to a source )
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There are a few mistakes that you have made in the layout that are causing the hum.
The 0V(GND) leads between the amps and PSU are too long. See the layout used in the link in post#1.
The speaker returns should connect to the Speaker protection board and then to the amp boards.
A possible problem with the speaker protection board with its additional ground connection.
Can't see if the 0V(GND) is connected to PE, this will also cause hum.
The 0V(GND) leads between the amps and PSU are too long. See the layout used in the link in post#1.
The speaker returns should connect to the Speaker protection board and then to the amp boards.
A possible problem with the speaker protection board with its additional ground connection.
Can't see if the 0V(GND) is connected to PE, this will also cause hum.
Ok, so i rewired the entire amp, the noise is still there, but I found out something new, and found the ground loop.
So currently it is wired as such:
Input:
Ground from each rca to their posts on the amp board ( rin-rin on board rgnd-rgnd on board and so on )
Output:
Power and ground from board to speaker protection, from speaker protection to speakers.
Each amp has + - and Gnd, they route back to the filtering board.
On this board Rgnd, Lgnd, transformer connon and capacitor common meet. It is a "star" point of sorts.
Thing is, if I have only one channel connected to a source ( eg, just one rca connected ) there is NO noise, on either speaker. But if i hook both channels, it starts humming. So I figured I have a ground loop on the input.
Sadly I don't know how to fix this.
Another mention is I added this http://sound.whsites.net/earth-f4.gif to the ground line. The hum is still there.
So currently it is wired as such:
Input:
Ground from each rca to their posts on the amp board ( rin-rin on board rgnd-rgnd on board and so on )
Output:
Power and ground from board to speaker protection, from speaker protection to speakers.
Each amp has + - and Gnd, they route back to the filtering board.
On this board Rgnd, Lgnd, transformer connon and capacitor common meet. It is a "star" point of sorts.
Thing is, if I have only one channel connected to a source ( eg, just one rca connected ) there is NO noise, on either speaker. But if i hook both channels, it starts humming. So I figured I have a ground loop on the input.
Sadly I don't know how to fix this.
Another mention is I added this http://sound.whsites.net/earth-f4.gif to the ground line. The hum is still there.
Start with this:
Remove everything but the transformer, PSU and amp boards. Connect as illustrated. Speakers and inputs connected to the amp boards. Even better if you can rotate the amp boards to reduce the lead length between the two boards.
Measure DC at the speaker terminals before testing with speakers and use a dim bulb tester thingy.
Remove everything but the transformer, PSU and amp boards. Connect as illustrated. Speakers and inputs connected to the amp boards. Even better if you can rotate the amp boards to reduce the lead length between the two boards.
Measure DC at the speaker terminals before testing with speakers and use a dim bulb tester thingy.
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^ I am currently rearranging the boards, rotating to make the leads shorter, and wiring them as you mentioned.
On question, Right now, I am using a wooden chassis, so no need to earth that, but i am running a wire from the mains earth connection to the power supply " star " point, that means that everything is connected to the house's earth, and the transformer common also. Is it a cause for the hum by any chance ?
On question, Right now, I am using a wooden chassis, so no need to earth that, but i am running a wire from the mains earth connection to the power supply " star " point, that means that everything is connected to the house's earth, and the transformer common also. Is it a cause for the hum by any chance ?
What are you using as a source for the amp? If the source also has a PE connection, the ground loop may cause hum. Try with and without PE connected.
Think in terms of power ground (0V), input+feedback ground and speaker ground. It is impossible to connect all these to a single point as these connections have already been made on the amp boards.
It is my opinion that the length of the leads connecting the PSU to the amps is the main cause of the hum. I don't expect to fix the hum problem in one go.
Think in terms of power ground (0V), input+feedback ground and speaker ground. It is impossible to connect all these to a single point as these connections have already been made on the amp boards.
It is my opinion that the length of the leads connecting the PSU to the amps is the main cause of the hum. I don't expect to fix the hum problem in one go.
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I have separated the "supply" part of the ensable from the amp boards. Basicly i have cut the large wooden board into 3 pieces, each amp has it's own wooden board and the toroid, filtering and soft start are all on one board.
I will be stacking the amp boards one on top of the other to shorten the leads as much as possible without making the layout a nightmare.i will be testing the unit without the speaker protection just to make sure that is not a possible source of the hum.
Is there a problem if i stack the amps as described? I have done this in the past with some lm1875 and had no problem, so i am guessing it should be fine.
I will be stacking the amp boards one on top of the other to shorten the leads as much as possible without making the layout a nightmare.i will be testing the unit without the speaker protection just to make sure that is not a possible source of the hum.
Is there a problem if i stack the amps as described? I have done this in the past with some lm1875 and had no problem, so i am guessing it should be fine.
After alot of rewiring, i managed to get NO BUZZ! The amp sounds evem better than before, and seems to somehow stay cooler.
But i have another problem, the layout is going to be a nightmare.
I found the source of the buzzing, when the dc cables are too close to the trafo, the buzzing starts. I think i am going to rearrange the "supply" board also so the traf is further away from the other components.
Thank you guys, especially AndrewT for the advice.
But i have another problem, the layout is going to be a nightmare.
I found the source of the buzzing, when the dc cables are too close to the trafo, the buzzing starts. I think i am going to rearrange the "supply" board also so the traf is further away from the other components.
Thank you guys, especially AndrewT for the advice.
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Hello Friend.
I was watching your post, tell me how your amplifier was after adjustments?
I am mounting an amplifier with two LM3886 150W Sterio boards.
I would like to know that you did the medication and DC offset adjustment for R4, R12, R17.
Yesterday I started the settings on my amplifier.
In R4 and R12, I managed to reach zero, but in R17, I can not, it is around 13mv.
Tell me, do you remember the numbers of the individual displacement that you have reached?
I was watching your post, tell me how your amplifier was after adjustments?
I am mounting an amplifier with two LM3886 150W Sterio boards.
I would like to know that you did the medication and DC offset adjustment for R4, R12, R17.
Yesterday I started the settings on my amplifier.
In R4 and R12, I managed to reach zero, but in R17, I can not, it is around 13mv.
Tell me, do you remember the numbers of the individual displacement that you have reached?
Hello Friend.
See photos of my LM3886 150w.
I'm feeding, with only a 250VA transformer. (25V+0+25V) 10 amper.
2 rectified source, with 40,000UF, each source, one for each amplifier.
1 - Speaker protector
All resistors and capacitors with tolerance of 0.1%, I bought on ebay (seller petelex - England).
The problem:
I measured the individual DC displacement, apparently set it to 13mv each.
I solved the resets 5W 0.2ohms.
I called everything.
Everything working and no buzzing, not yet in the office.
However, one hob is getting very hot, the other is not heating up.
What can this be ?
I think:
DC offset adjustment, which was not correct.
Some output lm3886, is in trouble.
Considering that I have already assembled all the components, will I have to remove again R7, R9 and R14, to test the DC offset again?
Any suggestion !!!
See photos of my LM3886 150w.
I'm feeding, with only a 250VA transformer. (25V+0+25V) 10 amper.
2 rectified source, with 40,000UF, each source, one for each amplifier.
1 - Speaker protector
All resistors and capacitors with tolerance of 0.1%, I bought on ebay (seller petelex - England).
The problem:
I measured the individual DC displacement, apparently set it to 13mv each.
I solved the resets 5W 0.2ohms.
I called everything.
Everything working and no buzzing, not yet in the office.
However, one hob is getting very hot, the other is not heating up.
What can this be ?
I think:
DC offset adjustment, which was not correct.
Some output lm3886, is in trouble.
Considering that I have already assembled all the components, will I have to remove again R7, R9 and R14, to test the DC offset again?
Any suggestion !!!
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