power amp hum

[dmorton]

I moved recently and finally got around to hooking up my ht. I started with my Rotel RB 993 3-channel power amp. As soon as I plugged it in, I heard this loud hum. If I turn up the volume, I can still hear the music in all 3 speakers. So I unplugged everything except for the center channel to test. Hum was still there and it's loud. So I plugged in my 2channel amp and no hum at all. I'm thinking it's the power amp itself as the 2channel amp worked fine with everything plugged in.

So my question is what is the solution? It affects all 3 channels so it must be a global issue. Something must have gone awry from the move. I opened the cover and saw nothing apparent that was loose and checked all the connections that I could see and made sure all screws were tightened. Any ideas would be of great help.

Thanks!

Dave

[wkhanna]

Hi Dave.

So sorry to hear of your tribulations.
It does not sound like there is much more you could do on your own.
I feel the amp is worth getting repaired.

I recommend a shop who has done fantastic work for me.
Give Tom a call & see what he says.
http://Vintage Hi-Fi of Pittsburgh/


412-369-8823
The shop usually opens around 4:00 PM.

BTW, I have fully refurbished RB-990, a solid, good sounding amp that has served me V well for many years.

[dmorton]

Thanks Bill,

I was afraid of that. Some local clown at a stereo shop said it was my house ac and i needed to go back to the breakers and all that. I know it's the amp. I know it sounds good when it works and its done a great job so far.

[wkhanna]

If you get the noise with the 3 ch amp, but not with the 2 ch amp, it seems likely the amp is the issue.
But not guaranteed.

The two amps may have different grounding topology, or a number of other factors may be at play in this instance.

Give Tom a call, he will have good advice for determining the cause & what other things you might try & options you may have.

[madmac]

My Rotel amp hums......and I believe it's somewhat normal. Hell, even my CD player hums. However, it is not bothersome for me and I can only hear it if the room is deafly quiet. It's when the hum comes out of your speakers that it is, in my opinion, an issue.

[Kevin D]

Just to make sure it's not a ground loop issue. If you have only the amp and speakers plugged in (no input cables) do you still get a hum?

Kevin D.

[PewterTA]

I agree with Kevin... I've got my system completely silent, but every once in a while when I disconnect things from my 5ch Rotel amp... when I plug in the Interconnects, I'll get a loud buzzing/hum from the speakers... once I turn on the pre-amp then connect the interconnects, it goes away completely and until the next time I unplug and it happens again. Almost like something happens if the pre-amp isn't on when I connect (I think) the center or surrounds to that amp. Funny is my 2ch amp doesn't have this issue at all for the L/R from what I remember.

[dmorton]

Just to make sure it's not a ground loop issue. If you have only the amp and speakers plugged in (no input cables) do you still get a hum?

Kevin D.

Yes I do. Talked with some Tech guy at Rotel and he thinks it's the DC Filter Cap.

[PewterTA]

If that's the case depending on where you live it might be over all cheaper to send it to Vintage HiFi. I know I saved about $400 on fixing mine this way (I was able to drop it off though)...

[dmorton]

There's a local place in chicagoland that a couple rotel dealers recommended so I'll probably go that route. Thanks for all the responses.