60 Hz hum

[Adam M.]

Soo many questions putting this thing together. I got an amp that makes music, but I also have a 60hz hum (measured with a DMM) that occurs with or without source connected.

The circuit layout is P2P on the chip, 50K pot as an input, connected to the input RCA and signal ground (which is the tab on the ground binding post)

I have 10,000uF soldered directly to the bridge(per rail), and 1000uF more on the pins of the chip. Power star ground on the chip is the 0V legs of the caps, which is connected by a wire to the signal ground. the chip signal ground then goes by a wire to the 0V pins on the 10,000uF chips, which goes to the ground tab of the plug.

Power wires from the bridge are twisted to help shield everything.

There is one power/signal wire cross, and it is at 90deg and not directly on top of each other.

The chip is a non-isolated version, but the heatsink is painted, so all the voltage is contained inside the paint (verified by checking the case that the heatsink is attached to against a 5 pound heatsink as the electron sink and the ground prong of a plug with the ground to the case disconnected)

Any ideas?

[Nuuk]

You don't need to connect your signal ground star to your power ground star more than once!

Your power ground star is between the two decoupling caps on the pins of the chip. That is connected to the signal ground star by a single wire.

So remove the wire from signal ground star to the 10,000 uF caps (which you shouldn't need either IMHO).

[Adam M.]

Thanks Nuuk, 60hz hum is gone, and replaced with a new problem. I now have a 120hz hum, but only when there is a wire connected to the input. No wire on the input, and I can turn the volume up to max, all clean. as soon as connect a wire to the input (doesn't matter if something is connected to the other end, happens either way) but I get a 120hz buzz that varies with the volume control. My circuit description is the same as above, with Nuuk's modification implemented. Thoughts?
THanks.

[Nuuk]

The circuit layout is P2P on the chip, 50K pot as an input, connected to the input RCA and signal ground (which is the tab on the ground binding post)

Re-reading the above, I detect another problem!

The speaker return is to the power ground star, not the signal ground star.

Taka a look at other people's circuits and try to get it clear in your head, the difference between the signal grounds and the power grounds.

[Adam M.]

Found the problems, hums are gone. One was the speaker ground going to signal ground, not power ground, whihc got rid of the 120hz hum. The thing was still picking up stray interference with a wire connected to the output, and I found I had the RCA backwards, neg on the inside and pos on the outside. Shielded the heck out of that return wire at the expense of the signal.

Anyways, I think I'm on my way to building a great sounding amp. I can't believe how low the noise on these things are, I literally can't hear anything from the tweeter when the volume is at max.

[Nuuk]

Good work Adam. I hope that your success will encourage anybody else who starts with the odd problem or two! Most things can be sorted out in the end.

[rs1026]

After going through the discussions I am still not clear with difference between signal ground and power ground.

Does power ground mean the connection that goes from centre tap of the tranformer to the bridge rectifier??

Nuuk or others can you please point out the difference wrt to this pcb??

Also what if we connect a active filter,amp ? what should be the method followed for grounding??