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Recently purchased a Hafler 9500 Transnova. Works just fine, nice sounding amp. But one channel has an intermittent crackling noise, happens for just 10-20 seconds every few hours or sometimes not at all for several hours. The transistors were recently replaced before I bought it.
Any ideas as to where to start? Possible cold solder joint? Resistor?
Thomas
Follow Ups:
Opened up the Hafler this afternoon and cleaned the solder connections as best as I could. The board has seen better days, some connections were so close together I had to remove some excess solder and scrape the board where the connections may have been making intermittent contact. First attempt was a failure, screeching noise... Second attempt and all is good, no noise, dead quiet for the last few hours. But will leave it on for a few hours more and see how it goes. It looks like the amp was worked on too many times over the years and the board is not really in good condition, no loose tracers, though.
Thomas
They are a great amp when they work but the TransNova series which is a Rockford, is a real BITCH when it comes to tracking down noise issues..I had a hell of a time desoldering the parts in the unit and even the factory service doesn't have the answers on fixing these because this one was at the factory and sent it back to the guy.
I got lucky and the way I fixed it was with a hair dryer and a can of freeze spray..I heated up the right channel components on the driver board and once the noise reappeared,I sprayed each individual component until the noise went away..It turned out to be the inner stage drivers before the actual drivers and I replaced the pair and then for added insurance, I ended up making a heatsink out of a pair of alligator clips.I ran the unit for a day and half without shutting it off and the noise didn't return but I have no idea if it is still going because this was 5 years ago..The guy was local to me. This was the earlier series but it was a nightmare.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
Edits: 06/18/16
So the driver transistors were having the problem?
Maybe he could get the schematic and find the driver resistors and caps, replace them with a higher voltage rating part????
Yes.I ran it a day and a half and the guy did some work for me on my house so I fixed his amp.I should call him and ask how it's working.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
The previous owner had replaced all the caps, resistors and transistors on the driver board. So far so good, no bad noises for 6 hours of use. usually the crackling noise would show up after about 20 minutes of warm up. I'm confident I have found the area on the board that was causing the noise, if it comes back I can try and clean it up a little better. Need to get a good magnifier and a very small file.
Thomas
The problem would appear in 30 minutes or it could appear hours later.You say he replaced all the transistors and still had the issue? That board is very populated with parts and it is very hard to get the parts out..Had I had my pace soldering station at the time,I'm sure it would have gone smoother.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
I think the best thing for that amp is to leave it alone.
Like working on NAD boards. You get one shot and some times even that doesn't go well.
I agree
Intermittent problems can be horrible to find,especially in over engineered circuits like the Transnova.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
I use this and it works very well.
If it ain't broke then just leave it. Seems too many people have already had there hands on those boards. SO it looks like they will not take much more. Try not to mess around with the board coatings. That is what is supposed to keep the solder from "shorting" out trace leads.
If it's working then just leave it.
But great job finding the problem. Hope it never returns. If you really like the amp consider having it PROFESSIONALLY restored. I think Mike does only tubes. But you could ask him for a reference for a restorer. BTW Mike is the best in the business!!!!!!! As well as one of the worlds nicest guys. Also Jim McShane is another one to contact. Also a hell of a wonderful guy.
Could be anything from a loose connection (internal or external) to a failing component.
first switch all the cables, inputs and speakers to the other side and listen if the crackling stays on the same (amp) channel.
Then if you're up for it try the pencil test. Take a PENCIL or wooden stick and just poke. Poke the boards, wires, connections, everything. Listen if you an reproduce the sound.
If it continues and you don't find it have it restored. Sounds like something is trying to go. And it will take something else with it!!!
I will give it a shot, I am pretty sure it's a loose connection or crack on the board. Crackling doesn't increase with volume.
Thomas
Look for lifting of the circuit tracings, recent solder joints, that kind of stuff.I think in the end you will need it restored. A nice amp so it is worth it.
I did do a little search on that amp. And they do have a history of crappy filter caps. Just the way it goes with some things.
Consider replacing them at the least.
charles
Edits: 06/17/16
Sounds like a bad cap. If it still has all original caps, its time to go through and change them. Re-capping if reasonably cheap.
New caps.
Old Caps.
Your amp needs new electrolytic capacitors.
I just replaced the filter caps on my son's Adcom GFA-5400 power amp. While I was there I replaced the crappy binding posts as well.
Meat; It's the right thing to do. Romans 14:2
It needs recapping.
If a thing's worth doing, it's worth doing well
(Proverb)
Try cleaning all connections with contact cleaner?
Tried that a while back. No luck.
Thomas
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