Hum problems...

[dasein]

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.

[geraldfryjr]

please post some pics.it wuold be easier to diagnose if any could see it.jer

[dasein]

Hey everyone,

Here are the pics of my amp. Sorry the casing is pretty ghetto. =P

[lanchile]

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?

[stratus46]

Originally Posted by lanchile

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?

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

[lanchile]

Originally Posted by stratus46

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

Did you see the heat sink?...I did not see any!
Maybe it is on the bottom?

[dasein]

Yea it's all I had on hand unfortunately.

What do you mean by big antenna? If you look at this post: Commercial Gainclone kit- building instructions

It should be similar (other than the cooper bridge is a lot thicker....)

[dasein]

Originally Posted by lanchile

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.

[lanchile]

Originally Posted by dasein

Yea it's all I had on hand unfortunately.

What do you mean by big antenna? If you look at this post: Commercial Gainclone kit- building instructions

It should be similar (other than the cooper bridge is a lot thicker....)

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.

[dasein]

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?