One colleague got another Pre-amp from this person. He got the "grounding" problem.
You can check whether you got this problem as well.
1. Turn both Pre-amp and Power Amp ON. Volume can set to low level.
2. By using your finger, knock gently on the metal chasis / body.
3. Check to see if the "knock" will come out through the speakers.
TEST TWO
1. Turn on BOTH Pre and Power Amps
2. Don't connect any source yet.
3. Touch the volume. If the knob is plastic, remove the knob to show the metal part.
4. Touch the volume knob, you will probably hear "sss...sss" noise when you contact the metal knob.
1. The Ground has not connected to the Chasis. I checked it out for him.
Even after I connect the ground at the plug to the chasis, the problem
is still there. I tap on the chasis, the "dong" sound came out from the
speakers.
2. I can work on the Input wire and the e-caps for him. Will ask him
whether he would like to spend the money first. No need for really
expensive caps, right?
3. What is "HT"? You said one side of the HT should be connected to ground
Please advise.