[suicidal_orange]

This has probably been discussed before but I don't know what it's called to search so I'll ask again.

Recently I have started listening to classical music and it is recorded/mastered quieter (as everything should be, but thats another rant!) so I've had to turn my amp up.

There is a noticable constant buzz during quiet parts - maybe 60Hz mains hum? If I join either RCA ground to the case using my finger and thumb the noise stops almost instantly, but using a wire does nothing. Is there an electronic component that acts like a human conductor I can attach to solve the problem?

This is with noting connected to the inputs, so it's definitely an amp problem. I'm in the uk so it's on 3 pin mains power including ground which is connected to the PCB. Components are all default for 4.1x gain except it has a 10k stepped attenuator for volume. Probably too much info but rather too much than too little

Feel free to link to a thread with answers, I'm sure this is a common problem (that or my first DIY build is rubbish, despite sounding great for 6 months of near daily use!)

 

[amb]

First, checking for noise/hum with nothing connected to the input and the volume turned up is not a valid test. An "open" input is like an antenna and will pick up noise and interference.

Second, if you hear hum while a source is connected, does it vary with the volume control?

Is the power transformer in the same case as the amp board? How far is the power transformer from the amp board? Are the input and volume pot wiring routed well away from the transformer wiring?

You said that the AC ground is connected to the amp's ground. I presume it is via the metal casing? What source are you using and does it have a three-prong AC power cord? Is its AC ground also connected to its signal ground? If so then you have a ground loop problem and need to use a ground loop breaker (see the "wiring & ground" section of the CK²III website).

 

[suicidal_orange]

Thanks for the quick reply, not sure whats going on but having unwired just about everything (had soundcard in and out and a turntable on a cheap switchbox with this amp and a hi-fi - a mess!) to try various combinations I now have a ground loop - it's a different hum and not volume controllable as the original noise was. Nothing I can do will bring back the original noise which was actually less anoying than this one as even at very low volumes it's audible. I'm guessing one of the connections was "open" causing the noise, maybe wired up wrongly (the switchbox has video sockets too)

Incase there is something I should know:

I'm using the standard hammond case with the standard transformer in it, due to the length of the attenuator the transformer is virtually touching the PCB next to the right power connector. The signal wires run down the left side of the case as far away as I could get them from the power, inputs are vertiacally spaced on the left side volume is also on the left.

The case itself isn't connected to anything as I'm using the plastic end panels it seemed easier to just wire the mains ground to the PCB with some mains wire. Other than that my wiring looks very similar to the wiring page all round, trying to avoid going over the PCB as much as possible. Should I get a bigger case?


EDIT:
Sorry, just read the last line - will make a loop breaker ASAP!