I've got a sold state guitar amp with a bad mains ground hum. It was working fine when I tested it before I bought it and even when I got it home for a bit. Then I cranked it up and bam, got a very loud 60hz hum louder than the input signal. I have concluded it's not a thermal issue. The main power supply caps 'look' OK. The hum level does change with the master volume knob, but at the half way point it starts to go back down again, so it's quieter at 0, louder at 5, then quieter (same as 0) at 10.
Any advice on this?
Any advice on this?
Pictures don;t tell us much. WHy not let us in on what the amp is? Marshall, Hartke, Fender, Peavey, GK, etc? Make and model.
Since the volume control affects the hum, does the amp make the hum with NOTHING plugged into the input jack?
The master volume affects the hum, but do any of the other gain controls affect it? And do the tone controls affect the tone of the hum? If the amp has channels and channel switching, do all the chanels hum or just one?
Since the volume control affects the hum, does the amp make the hum with NOTHING plugged into the input jack?
The master volume affects the hum, but do any of the other gain controls affect it? And do the tone controls affect the tone of the hum? If the amp has channels and channel switching, do all the chanels hum or just one?
It's a Randall RH200 2x12 Combo amp.
Yes, the amp hums with nothing plugged into the input jack.
The preamp is not a part of the problem, meaning it does not change based on the preamp settings of either of the channels. With both of the preamp volumes all the way down doesn't make a difference. It's definitely in the power amp section of the amplifier.
Thanks for asking and for any advice or things to try.
Did it. When the input from the preamp is unplugged from the power amp, the hum is quieter but still there. I unhooked it while it was also on to compare the difference. The master volume knob is before this input, which makes sense now, but for some reason I thought it would be more part of the power amp.
I'm not sure if this makes the preamp guilty or not. I had all the volume levels on the preamp channels turned all the way down and it still hummed more with the preamp plugged in. Does that make it the source of the ground problem?
I'm not sure if this makes the preamp guilty or not. I had all the volume levels on the preamp channels turned all the way down and it still hummed more with the preamp plugged in. Does that make it the source of the ground problem?
Do you mean the main input jack on the front panel of the amp or the input plug on the power amp board?
With respect to chassis ground, there will be two main power rails in the power amp. The easy place to check that would be the center leg of the power ttransistors. The two on the left is one supply and the two on the right the other.
Also look at each power transistor, and see a litttle bit of metal exposed in the mounting tab area. That is electrically the same as the center leg. Just make sure your meter probe does not short that to something nearby in the process.
Also look at each power transistor, and see a litttle bit of metal exposed in the mounting tab area. That is electrically the same as the center leg. Just make sure your meter probe does not short that to something nearby in the process.
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