Hey everyone!
I just built Peter Daniel's LM3875 kit in a stereo amp. I used one toroid and one rectifier bridge. Then I used a copper bridge between the OG on the amp boards and connected the PGs to the bridge from the rectifier board then used a wire to connect to the chasis ground which is connected to the mains earth. I also used insulated RCA connectors, but did not use a volume pot. (I tried to mimic Peter Daniel's build in the "Commercial Gainclone" build thread.
My problem is that I have a hum when a source is connected. When there is no source the amp is dead quiet, but when I connect a source there is a slight hum. As music plays for a while, the hum gets louder. If I connect the amp to my ipod and pause the music, I can make the hum go louder and smaller as i change the volume (as the volume is louder the hum gets louder). Then when I unpause the music, the hum disappears and gradually builds again.
I thought my grounding scheme was adequate but I guess it's not? Can anyone help me diagnose the problem?
I can post pics in a little bit.
I just built Peter Daniel's LM3875 kit in a stereo amp. I used one toroid and one rectifier bridge. Then I used a copper bridge between the OG on the amp boards and connected the PGs to the bridge from the rectifier board then used a wire to connect to the chasis ground which is connected to the mains earth. I also used insulated RCA connectors, but did not use a volume pot. (I tried to mimic Peter Daniel's build in the "Commercial Gainclone" build thread.
My problem is that I have a hum when a source is connected. When there is no source the amp is dead quiet, but when I connect a source there is a slight hum. As music plays for a while, the hum gets louder. If I connect the amp to my ipod and pause the music, I can make the hum go louder and smaller as i change the volume (as the volume is louder the hum gets louder). Then when I unpause the music, the hum disappears and gradually builds again.
I thought my grounding scheme was adequate but I guess it's not? Can anyone help me diagnose the problem?
I can post pics in a little bit.
Hey everyone,
Here are the pics of my amp. Sorry the casing is pretty ghetto. =P
Here are the pics of my amp. Sorry the casing is pretty ghetto. =P
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Well first You made a big antenna there to pick a lot noise, you did not fallow Peter wiring. and how come you are not using any caps on the ps board
when I had mine I had them with 20000uf and sounded really good.
PS: How come you are using double wires in almost all the connections?
when I had mine I had them with 20000uf and sounded really good.PS: How come you are using double wires in almost all the connections?
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Well first You made a big antenna there to pick a lot noise, you did not fallow Peter wiring. and how come you are not using any caps on the ps board
PS: How come you are using double wires in almost all the connections?
I'm sure he'll say it's what he had on hand but I'm sure someone can come up with some theory on distributed inductance and capacitance and why this is REALLY the way it SHOULD be done. Or not.
G²
Yea it's all I had on hand unfortunately.
What do you mean by big antenna? If you look at this post: http://www.diyaudio.com/forums/audi...-kit-building-instructions-2.html#post1518369
It should be similar (other than the cooper bridge is a lot thicker....)
What do you mean by big antenna? If you look at this post: http://www.diyaudio.com/forums/audi...-kit-building-instructions-2.html#post1518369
It should be similar (other than the cooper bridge is a lot thicker....)
Did you see the heat sink?...I did not see any!
Maybe it is on the bottom?
The heatsinks are on the other side... they are mounted through the big holes through the case.
I would eliminate that thick wire and start using just one wire from PS board to IC boards and from IC boards to ground. these IC's are very sensitive to ground noise and RF too. just fallow direction from Audiosector.com.
I hooked up a different source to my amp directly and found that there was no hum at all!
I'm wondering if this is related to mainly my source and some ground loop between my source and the amp. Is there any way for me to get rid of the hum when I use sources that may or may nto be grounded properly?
I'm wondering if this is related to mainly my source and some ground loop between my source and the amp. Is there any way for me to get rid of the hum when I use sources that may or may nto be grounded properly?
I had that problem too with mine with my cable box.and I got a Monster power filter and it got away.Now I do not have it anymore. I build something else!.
please check that power supply line conection particulary the nuteral and the ground are correct.if these are reversed it could still work but cause a ground loop.causing hum being fed in the ground side of the circuit. not sure since i can't see the power plug.you stated "When there is no source the amp is dead quiet, but when I connect a source there is a slight hum".you may very well need bigger filter caps,but please recheck the line side aswell.there was another person with a similar problem he had a lose ground and also he put a 220pf cap across the + and - inputs and the hum went away.if your ipod is running on its battery power and there is hum the i'd say there is 60 cycles coming in from the ground side
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I'm pretty sure that the power supply wiring is right but I will double check when I get home. Good point about the ipod, it was running on battery.
Where exactly would the caps go? I'm not sure I understand where they are suppose to go...
Also could someone with more experience than me look over the pics to make sure that it's safely grounded? I really don't want to kill anyone... I noticed that some people use a 10R power resistor to connect the ground from the PSU / amps to the mains earth. Would that help my hum problem?
One more question: As evident in the pictures I didn't use a volume pot. Did I need to do something if I'm not using a volume pot? I saw something on Nuuk's digital dungeon about dangerous oscillations and mentions using a 56K resistor but I wouldn't know where to put it.
One more question: As evident in the pictures I didn't use a volume pot. Did I need to do something if I'm not using a volume pot? I saw something on Nuuk's digital dungeon about dangerous oscillations and mentions using a 56K resistor but I wouldn't know where to put it.
Hey!
Yes I did read through that when I was first starting but it's been a while
. I guess what I need is a Zobel network to prevent the oscillations.I figured out what was causing the hum I think. The isolated RCA jacks that I bought are not so isolated causing a signal ground loop.
Do people have any recommendations? Also I was still curious about that resistor between mains earth and the star ground and a safety check on the pics. (Sorry this is turning into a wishlist.)
Hey!
Yes I did read through that when I was first starting but it's been a while
I figured out what was causing the hum I think. The isolated RCA jacks that I bought are not so isolated causing a signal ground loop.
Do people have any recommendations? Also I was still curious about that resistor between mains earth and the star ground and a safety check on the pics. (Sorry this is turning into a wishlist.)
Well, when I build mine I did not build a zobel. and for the RCA input wires I use this from parts express,Parts-Express.com
ayton MSC-100 Microphone/Signal Cable 100 ft. | mic cable microphone cable bulk microphone cable bulk mic cable mic wire mic cable instrument cable it is microphone wire it is double isolated to prevent any interference and it worked perfectly.even now I used it for my new amp. you do not need to use a resistor on the start ground.
Hey!
Yes I did read through that when I was first starting but it's been a while
I figured out what was causing the hum I think. The isolated RCA jacks that I bought are not so isolated causing a signal ground loop.
Do people have any recommendations? Also I was still curious about that resistor between mains earth and the star ground and a safety check on the pics. (Sorry this is turning into a wishlist.)
OK, Here are some old pictures of my LM3875 from Peter Daniel.
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