One of my amplifiers (crown 810) is distorting the sound alot. It sounds like the kind of distortion you might get when setting a compressor very high. Also, some days after it has been left on for about 5 hours it will make a loud pop, and this pop will increase in frequency to about one every 3 minutes. Does anybody know what would cause these symptoms? I'm going to open it and inspect the circuits tomorrow. I think it might be a capacitor.
Amp problem, please help
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themuzicman
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DO NOT open up the amp and start poking at capacitors unless you know how to work with them. Do you have a capacitor discharge tool? Getting a capacitor to discharge in your arm would really ruin your day.
That being said, before you pop it open take out all the variables.
Get a known working speaker (clean audio across all frequencies with a known working amp) and attach it to the amp in question. Next plug in your iPod or tone generator or something directly into the amp and play audio. See if playing audio without anything else causes the amp to work correctly.
That being said, before you pop it open take out all the variables.
Get a known working speaker (clean audio across all frequencies with a known working amp) and attach it to the amp in question. Next plug in your iPod or tone generator or something directly into the amp and play audio. See if playing audio without anything else causes the amp to work correctly.
If you know it is the amp, like 100% certain, then I'd take it in to someplace that will service a Crown amp, or at least call them, and see what it would cost. If it is a high schools equipment, the school may be able to pay to have it fixed. And, I highly doubt they would approve of you taking apart their equipment.
I do have permission to open it as they trust me and trust that I won't attempt anything that I don't know how to do. I would not risk doing anything to the amp that I'm not 100% sure I could do. I am opening it just to see if I can find anything wrong, and if it isn't an easy fix, I would take it to a pro. My teacher is trying to avoid pricey repairs and lengthy time of having a pro deal with it at a different location. I'm just asking to see if anyone has had the same problem, and knows what exactly is wrong.
Tex
Active Member
I had the same symptoms last year plus an ugly hum even with no input. It was a bad cap and I sent it for repair. To try and repair it with the tools available to me would have been very frustrating and time consuming, and I solder pretty well.
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I would bet its a capaciator problem, but DO NOT open the amp to find out. There are many reasons why, besides the obvious fact that there is high voltage stored inside even if the amp has been powered down and disconnected. Attempting to discharge this high voltage in the wrong way could damage the amp further and easily damage YOU to! And if you get hurt messing with the schools equipment, there will be liability clauses and other legal nastiness headed your way. If money is a problem, and you don't mind voiding the warranty if its still in effect, Id have it sent to a local electronics shop, they can probably do a simple cap replacement for less money than crown would charge. Modern high power amplifiers are very tricky to work on, much more involved than say a guitar amplifier, or even an older pa amplifier. They are not something that a novice can mess with safely.
I had tested the caps after opening it and they were discharged. As for making sure they still had all of their capacity; my volt meter couldn't count that high. Also I have an other amp, that I was about to use to replace the broken one, that maKes a 6o Hz buzz out of one of the output channels.
60hz buzz would mean a failing filter capaciator. Those can be expensive to replace. Going back to the original amp mentioned, Im suprised it didn't go into thermal protect mode with a cooling fan out. The heat could have damaged an output transistor or capacitors or anything really. I doubt it's something you could troubleshoot with a multimeter but I could be wrong. I mostly work on older equipment so my knowledge of amp design post 1985 is a little weak.
When I opened the amp I saw two huge caps going to a transformer. Are those the filter caps. As for the transistors, they were lined up on a heatsink and looked fine. I would never have guessed that the fan seized up if I had not have noticed some liquid on a circuit board under the fan blades. The fan got me off track from finding out what the liquid was, but it could have been from one of the capacitors.
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Yes, those large caps are the filters. Just because the transistors look fine, does not mean they are fine. There are ways to test transistors, but you need serious test gear. The liquid probably was from a capacitor. I bet it didn't have much to do with the fan freezing, sometimes fans just seize up from wear or dust or a combination of the two. The heat from the amp running hot could have cooked a capacitor or transistor or something. Check all the electrolytic caps in the area for signs of bursting or heat stress. If a failing cap caused the voltages in the amp to be off, the outputs would distort in the way you described. Also, if you have a schematic of the amp, you can check for proper bias and b+ voltage. This would help in troubleshooting; if for example the bias voltage was way off you would know that something failed in the bias supply. Actually, if the problem is the same in both channels, you can be sure that the issue is in the power supply someplace. A power supply fault would effect both channels in the same way, while a problem in one channel such as a blown driver transistor would only effect that channel. So you can at least narrow your search a bit. Sorry for the rambling post, hope this helps.
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The liquid is likely from a blown electrolytic. Given the heat stress the poor beast went through, I would replace as many of the electrolytics as possible. Those that haven't failed will soon. The exception might be the large "can" type capacitors, because they often to have to be purchased from the equipment manufacturer to get proper mechanical fit. You can fudge lead spacing on the little ones with wire leads, but not the big ones. And the big ones have to fit the mounting or that has to be retrofitted.
Use good quality components and be sure to carefully note the polarity of the capacitors when removing and replacing them. A reverse polarized electrolytic will fail or explode in just a few minutes.
I will make a minor correction to what Aman121 said. Most modern power amp have independant supplies except for low current stuff, like for input stages.
Use good quality components and be sure to carefully note the polarity of the capacitors when removing and replacing them. A reverse polarized electrolytic will fail or explode in just a few minutes.
I will make a minor correction to what Aman121 said. Most modern power amp have independant supplies except for low current stuff, like for input stages.
Whoops, like I said I'm used to working on older amps where they do share a power supply. Thanks for the correction.
bobcatarts
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