Ground Loop? buzz?

[jdbleed01]

Hi Everyone - Just getting back into messing around with stereo equipment after a decade or so away from it. This time, the idea is to try and get my three-year-old little girl into music. Had a nice little set up back in the day and think she'd get into it.

Pulled out the Cambridge A500 integrated amp I bought back in 2001 and haven't used much in several years. Got some cheapo speakers off Amazon, some similarly cheap wires, and plugged everything in and got a buzz from both speakers. Buzz doesn't change if I adjust the volume. Read a little bit online about ground loops and am not sure that's the problem - tried several different outlets in the house and don't have any other components plugged into the amp. Tho to be honest, a lot of the ground loop articles I've read are waaaay over my head.

Big question now is...is there something wrong with the A500? It operates just fine as far as I can tell, the only major difference being the annoying buzz and the pop that comes through the speakers when I shut it off - there was always a little pop, more like a puff. Now it sounds like a gunshot from two blocks over with a bit of static thrown in. \

Thanks in advance for any help. Very much appreciated.

 

[markw]

Does the amp still hum/buzz when no sources are connected to it? If it does, the amp has major problems.

 

[jdbleed01]

Yes - Right now, I only have two speakers connected. Plug it in, turn it on and there's the buzz. No other components connected at all.

 

[markw]

Your amp is scrooched. Repair or replace.

 

[jdbleed01]

Yeah, I was afraid of that. Thanks for the response - much appreciated. Back to square 1 I guess.

 

[tcarcio]

I agree with Mark but before you repair the amp try a cheater plug. All that is is a plug with only 2 prongs and no ground prong. If the hum goes away it might not be the amp. You don't want to run it all the time without the ground but it might point in another direction.

 

[jdbleed01]

Have done some more digging around on the subject and then opened the amp to check out the insides. Everything looks quite clean and nice - except four a line of 8 back cylinders about the size of "B" size batteries. I think these are the capacitors. Four appear to be bad - leaning out of place and with some kind of brown gunk leaking out of the top. My understanding is that bad caps can cause a buzzing noise?

The big question now is whether I have room in my life for a soldering iron.

 

[slipperybidness]

Have done some more digging around on the subject and then opened the amp to check out the insides. Everything looks quite clean and nice - except four a line of 8 back cylinders about the size of "B" size batteries. I think these are the capacitors. Four appear to be bad - leaning out of place and with some kind of brown gunk leaking out of the top. My understanding is that bad caps can cause a buzzing noise?

The big question now is whether I have room in my life for a soldering iron.

A pic is worth a thousand words.

If these are indeed bad filter caps, then that could certainly cause the buzz.

 

[jdbleed01]

How does one post photos to the forum? My apologies, I'm new.

photo 1.JPG

 

[jdbleed01]

I've posted a couple of photos of the issue on the next page (I have to inflate my post count first)

 

[jdbleed01]

Okay - heres a photo of what I think are bad caps....

 

[jdbleed01]

Lets try this again - I THINK these are the caps....bad ones are in front

 

[slipperybidness]

View attachment 14041

View attachment 14042

View attachment 14040

Lets try this again - I THINK these are the caps....bad ones are in front

Man, that is painful to look at

Yeah, to me that looks like bad cap(s). That stuff up top is kind or gooey? And the tops are bulged out? If the answer to both of those is yes, then I would say that you almost certainly have some bad caps

Now, it would kind of depend on how difficult it is to get to the bottom of the board. You would need a solder gun and solder-sucker or a desoldering station to get those caps off and replaced. I would most likely pull a suspect cap and put it on a cap meter to be 100% sure before I went farther.

If I'm going to that much trouble, I also might look at upgrading the caps while I was in there. You could put caps with higher uF rating, higher temp and higher voltage ratings, or exact same spec caps, but not lesser caps than what is in there. The problem with upgrading is that new ones might not fit.

Hey, while you're in there, replace all of those p/s caps. You don't want to replace "just the bad ones", then have more fail a month later.

If you don't feel up to the challenge, then I'm sure you can find a stereo or electronics shop that could do it. I can tell you that replacing bad filter caps is probably like 75% of their work, so it would be a snap for a pro to handle. It's just a matter of how much $ they would want. The nice thing is that you could have them give the entire component a once over while it's in there.

Here's a few pics I found a while back for a similar surgery on my 1206. It should give you an idea of the work involved. Honestly, the price this guy quotes seems about double what I would expect to pay for this work.
Parasound Repairs

 

[slipperybidness]

Another thread on my 1206. But this thread made a good point! It seems that my 1206 does not have bleed-off resistors on the p/s caps!

What that means is that the p/s caps can hold a charge for a long time after the power has been shut off. If you accidentally short the cap posts, it won't be pretty and could be quite dangerous!

So, the moral of the story is to be careful! The last thing you want to do is short out a large and charged cap! Hopefully, yours has bleed off resistors on it. If not, then if I were working on p/s that doesn't have them, then I would see about obtaining a large W rating resistor to manually bleed off each cap before working on it.

http://www.audiokarma.org/forums/showthread.php?t=432229

 

[jdbleed01]

Thanks for info and the advice. I was able to get the board into a place where I could try removing and replacing the caps. That said, the more I think and learn, the more I think i should at least feel out the local pros and how much they'll want to fix it. I'm not wedded to this amp and would actually rather go for a vintage 70s solid state if the cost of fixing this one is more than buying a rehabbed Harman Kardon or Marantz.