Its almost 3 months since i built a lm3886 based gainclone .till now I had kept all the components on a wooden board and the GC was dead silent on when powered.I put all the components in a metal box including the transformer.Now the GC gives a hum it is quite audible.Have I done anything wrong over here??Please suggest some ideas to eliminate this problem.
Preplexed
Nuuk,
I have read your website may be "n+1" number of times
Infact it was a source of inspiration to start the work. I have taken all ground loop problems into account.The PCB is also designed properly.What I am not able to understand is there was no hum when everything was mounted on a wooden board but once everything is transfered into a metal chasis there is hum. Infact the bottom of the box is isolated properly. really strange!!
One more thing that I noticed was the bass response has come down!! I know its nothing to do with the box but I have added two speaker connecting terminals now ,I presume that is acting as a sort of HPF! Am I correct?
Nuuk,
I have read your website may be "n+1" number of times
Infact it was a source of inspiration to start the work. I have taken all ground loop problems into account.The PCB is also designed properly.What I am not able to understand is there was no hum when everything was mounted on a wooden board but once everything is transfered into a metal chasis there is hum. Infact the bottom of the box is isolated properly. really strange!!One more thing that I noticed was the bass response has come down!! I know its nothing to do with the box
but I have added two speaker connecting terminals now ,I presume that is acting as a sort of HPF! Am I correct?
Contents
I dont have a Digicam so I will put the list here.I dont know if this will help to solve the problem but still.
Contents of the metal box:
1.One monster 220VA EI transformer[it may weigh around 800 grams]
2.One 4A slow blow fuse with holder
3.One bridge rectifier nest to the transformer with 6800uf Cap per rail
4.2 3886 based pcb along with the heat sink towards the edge of the box
5.One stereo to RCA cable that goes as input signal to the amps
6.Two speaker connectors mounted at the back of the chasis.
Thats pretty much it.Its a simple 2 channel GC.Before putting these components into the box there was no hum and sound was very good. Now there is slight hum also bass response seems a bit low I need to increase the gain by controlling the vol control from the PC to get more bass.
I dont have a Digicam so I will put the list here.I dont know if this will help to solve the problem but still.
Contents of the metal box:
1.One monster 220VA EI transformer[it may weigh around 800 grams
]2.One 4A slow blow fuse with holder
3.One bridge rectifier nest to the transformer with 6800uf Cap per rail
4.2 3886 based pcb along with the heat sink towards the edge of the box
5.One stereo to RCA cable that goes as input signal to the amps
6.Two speaker connectors mounted at the back of the chasis.
Thats pretty much it.Its a simple 2 channel GC.Before putting these components into the box there was no hum and sound was very good. Now there is slight hum also bass response seems a bit low I need to increase the gain by controlling the vol control from the PC to get more bass.
I'm not totally convinced that this is all the truth. Can't you take picture?
Is it "soft" hum 50 Hz even with input shorted? Is it "hard" 100 Hz hum with lot's of harmonics.
50 Hz, problem with ground loops and the input.
100 Hz some trouble with your power supply and grounding technique.
Is it a stereo amp (yes), one transformer(yes) , same hum in both channels?
Is the transformer more near your Lm3886 now than before? (picking up magnetic field)
Is it "soft" hum 50 Hz even with input shorted? Is it "hard" 100 Hz hum with lot's of harmonics.
50 Hz, problem with ground loops and the input.
100 Hz some trouble with your power supply and grounding technique.
Is it a stereo amp (yes), one transformer(yes) , same hum in both channels?
Is the transformer more near your Lm3886 now than before? (picking up magnetic field)
..
>>I'm not totally convinced that this is all the truth. Can't you take picture?
I dont have a Digicam thats the problem.
>>Is it "soft" hum 50 Hz even with input shorted? Is it "hard" 100 Hz hum with lot's of harmonics.
Its a soft hum not very loud.But it is noticeable.
>>Is it a stereo amp (yes), one transformer(yes) , same hum in both channels?
yes,It is a stereo amp.Single transformer.Yes the hum is same in both the channels.
>>Is the transformer more near your Lm3886 now than before? (picking up magnetic field)
Yes,Now its is very near one of the lm3886 chips.before everything was spread out.So could it be magnetic field?
Can I connect the PCB grounds,mains earth to a single point on a chasis??
>>I'm not totally convinced that this is all the truth. Can't you take picture?
I dont have a Digicam thats the problem.
>>Is it "soft" hum 50 Hz even with input shorted? Is it "hard" 100 Hz hum with lot's of harmonics.
Its a soft hum not very loud.But it is noticeable.
>>Is it a stereo amp (yes), one transformer(yes) , same hum in both channels?
yes,It is a stereo amp.Single transformer.Yes the hum is same in both the channels.
>>Is the transformer more near your Lm3886 now than before? (picking up magnetic field)
Yes,Now its is very near one of the lm3886 chips.before everything was spread out.So could it be magnetic field?
Can I connect the PCB grounds,mains earth to a single point on a chasis??
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