2 years ago I bought a NAD 3020a amplifier on ebay.
During the first few months it worked very well, until one of the speakers started going weaker and weaker. I did a whole bunch of tests (switching speakers - the problem switched to the other speaker, listening with the headphones - great sound, etc.) and I concluded the problem came from the amplifier.
I had a friend bring the amp to a friend of his who knows eletronics well, and he fixed this problem by changing the set of 4 capacitors (35v, 2200 microF) that seemed to have swollen a bit. This totally fixed that problem, as the sound is now equal on both sides.
However, the sound is now extremely dull, kind of muffled, as if I didn't have any mediums and trebles anymore, which wasn't the case before.
Does any one know if the capacitor change could be the cause? The replaced ones were of course of exactly the same voltage and capacitance. Could it be that he broke something while changing them? A resistance?
Any tests I should try to figure it out?
Since I don't really know the guy and he was really nice to help me out the first time for free, I don't want to bother him too much, so I'm seeking some potential help here before doing so.
There's always the possibility a service job could have resulted in other problems. Having no idea just how well your friend's friend knows electronics and is capable of doing repairs, there's no way to tell whether he actually did something which is now causing problems.
One possibility is that one problem resulted in the other before you handed the amp over for repairs. Caps and resistors are in a circuit and when one component goes bad, it often results in more damaged components in that same or subsequent circuits. It might also be the two issues are merely coincidental to each other and in an older amplifier parts have simply begun to wear out. Or, your friend's friend might not have checked or properly set the bias to the outputs after replacing parts . That normally wouldn't be part of replacing caps but most techs will simply go through an amp to check for overall correctness of aging parts when any part of a circuit has been repaired. There's no way to tell over a forum what was done and what was left undone - if anything at all.
I would say ask the guy. He did the work and he knows what he did. Once again, depending on just how qualified he is at doing repairs, he might have an idea what is causing the problem. Or, he might not. That's the chance you take when you try to save a few bucks and have a friend of a friend do repairs. I once spent an entire blazing hot Dallas summer weekend trying to help a neighbor change the struts on his Lexus because he wanted to save a few dollars. In two days time we got one strut replaced and then he thought it was worth the money to have a tech do the rest. In the end he spent far more than what it would have cost him at the shop for both struts and now he has strut changing tools he'll never use again.
You'll have to decide whether you want him to work on the amp now or whether you think it's best to get a qualified tech in on the job. I wouldn't blame the guy even if the tech says he might have caused the damage unless you begin to get the impression he's really flying by the seat of his pants. If he has no test equipment beyond a hand held meter, that's a good sign he isn't the person who should be "repairing" anything. And, even then, remember that you agreed to let him put his hands in the amp.
You didn't say whether the sound was poor in only the one channel he worked on or in both channels. If the problem exists in both channels, then it's unlikely the amp has a similar problem in both channels and you might experiment with your speakers. It's not at all uncommon for an amp to do damage which takes out a tweeter. You can consider it unlikely the guy did work on both channels if only one had a problem, but you can't be sure of that. Check the speakers for proper operation and go from there. I suspect you'll eventually want a shop to look at the amp.
Yeah the "muffled sound" problem is now on both channels, where as the "weakness" problem was only on one. I used to use the amp with a great sound only on one channel 'till I tried to get that fixed.
What you're saying about the speakers is that, when I got my amp back and tried it again, it could have damaged my tweeters? The speakers were fine untill then, and they're brand new (Eltax Monitor III).
I went for the solution of a friend's friend mostly because, where I live, the only 2 professionals that work on these things are, from what I heard, not very nice and very expensive. Since i bought the NAD for 150 euros, I didn't feel like paying much to get it repaired. Also, the guy works in electronics (but like on an industrial level) so I felt quite confident.
But yeah I will try to contact him again to see if he can do something, and maybe pay him if he fixes it so he might take some time to do it well.
One last question/need for advice: Could I get a new amp around 100-300$ (amount I have that I could spend on a new amp today) that sounds as good as the NAD 3020? Or would it be worth it to actually pay to try to get it repaired? (That might be subject to opinion but I'd really like to have other people's).
Opinions vary and my opinion isn't going to matter to what you hear. What you'll need to do is, no matter who works on the amp, ask them for an estimate of repair costs before you do anything else. In the meantime, look at what's available for the amount you want to spend. After considering a repaired amp you claim to have liked vs another amp you don't really know, make your decision as to which is the better course of action. Certainly, a working NAD is worth something on the trade in market while a NAD paperweight isn't anything most people are looking for.
Contact NAD and discuss other options for getting the amp repaired.
Alright, many thanks for your take on this! I'll look around a bit to see if I can get it repaired, if not I'll look into buying a new one, maybe sticking to some newer NAD amps...