Hi. I'm having a problem with a loud hum in an integrated amplifier.
The hum is louder when the amplifier volume is increased, but it doesn't change with changes in the preamp volume. I do get the source audio out of the speaker, but it seems distorted. ? Hard to tell over the hum.
Almost sounds like a bad ground somewhere.
The amp is in quite good condition. I inspected for any signs of heat damage or component damage and could find none.
I then tested the bridge rectifier and the filter caps, and they all seem normal. I also tested a number of diodes around the PS portion of the board and didn't find anything off.
Not sure what to look at next.
Anyone interested in helping out?
The hum is louder when the amplifier volume is increased, but it doesn't change with changes in the preamp volume. I do get the source audio out of the speaker, but it seems distorted. ? Hard to tell over the hum.
Almost sounds like a bad ground somewhere.
The amp is in quite good condition. I inspected for any signs of heat damage or component damage and could find none.
I then tested the bridge rectifier and the filter caps, and they all seem normal. I also tested a number of diodes around the PS portion of the board and didn't find anything off.
Not sure what to look at next.
Anyone interested in helping out?
Have you looked at the filter cap ripple with an oscilloscope?
Have you looked at the output waveform with a scope?
The fault appears to be in the amp, but could also be injected on the signal common. Disconnect the preamp and report.
Have you looked at the output waveform with a scope?
The fault appears to be in the amp, but could also be injected on the signal common. Disconnect the preamp and report.
Unfortunately, I don't have access to an oscilloscope these days. I just checked the rectifier, caps and diodes with a multimeter.
I will check to see if I can find a way to disconnect the preamp section from the power amp section...
I will check to see if I can find a way to disconnect the preamp section from the power amp section...
The issues are poverty and transient housing.
Would one of the cheap hand-held digital scopes work well enough? I might be able to get my hands on one of those.
Would one of the cheap hand-held digital scopes work well enough? I might be able to get my hands on one of those.
I would love to see if I have DC coming from the PS, but not sure where to get my hands on a vintage scope.
I was about to suggest that very idea. Install an appropriate cap in series with the meter if there's any doubt about its ability to reject DC riding on the ripple.
I agree with Anatech that a scope is the best tool by far for your dilemma.
Good luck!
I agree with Anatech that a scope is the best tool by far for your dilemma.
Good luck!
You really need to see the shape of the ripple waveform. It tells you a great deal about the capacitor. Meters don't tell you much, and the AC reading depends a great deal on how they detect AC waveforms.
Try Ebay, or any Facebook or other market place. Hit up old shops, I have some equipment I"m selling but it doesn't make any sense for someone far away from me.
Try Ebay, or any Facebook or other market place. Hit up old shops, I have some equipment I"m selling but it doesn't make any sense for someone far away from me.
Is there an SG97 syndrome that has spread here?
The guy shows up here, provides absolutely nothing information, neither model, nor brand, nor diagram, asks a random question, shows that he has absolutely no idea of what he is doing and in three or four messages, you tell him advise the purchase of an oscilloscope although I am not sure that it makes the difference between an LED and an incandescent bulb...
Is there something I missed or something?
I have already been told to try to simply ignore this type of situation but I can't do it, and to the extent that they are increasing, I would like it not to become the norm.
The guy shows up here, provides absolutely nothing information, neither model, nor brand, nor diagram, asks a random question, shows that he has absolutely no idea of what he is doing and in three or four messages, you tell him advise the purchase of an oscilloscope although I am not sure that it makes the difference between an LED and an incandescent bulb...
Is there something I missed or something?
I have already been told to try to simply ignore this type of situation but I can't do it, and to the extent that they are increasing, I would like it not to become the norm.
What's wrong with trying to point someone in the right direction?
That is your wish, not necessarily everyone else's. Feel free to ignore this thread and similar threads, but please respect others who do decide to try and help.
That is your wish, not necessarily everyone else's. Feel free to ignore this thread and similar threads, but please respect others who do decide to try and help.
Could you give is some more info like make and model? Maybe some photos?
What are your skills in measuring and repairing? Reading schematics, etc...
Describe the hum. Maybe you could even make a short recording and upload it with your response (zipped)?
Am I to understand by your remarks about the volume that the amp has a pre out?
More info is needed.
That doesn't stop me from saying what I think and that's exactly what I just did.
I have absolutely nothing against people who ask for help, quite the contrary, but there is a minimum of common sense to respect.
It's like this the OP came to tell us : "my car is having more and more difficulty going uphill, I looked at the tire pressure, I noticed that they were all circles, what can I do now ?."
Common sense is being lost more and more in our world.
A seasoned DIY-er will ask more precise questions and will provide more to the point info.
Let's wait, I'm sure we'll get all the questions answered, needed to pinpoint the problem.
This is not a professional environment, we're all just a bunch of fanatics. 😉
It might be as simple as a bad interconnect.
Hugo
Let's wait, I'm sure we'll get all the questions answered, needed to pinpoint the problem.
This is not a professional environment, we're all just a bunch of fanatics. 😉
It might be as simple as a bad interconnect.
Hugo
I understand your point of view, but if you're new at things, you don't know how to ask the right questions. That's where we can help.
I agree that there are also people who ask a question and expect an answer straight away that will help them solve their problem with minimal effort. They will soon be discovered and no doubt told to either put in more effort or move along. It's why I posted the questions to the OP after I responded to your post. Now I'll wait and see where things go.
Hi huggygood,
The OP, aftershock, indicated he was measuring things with a meter. He reached a point where he was about to begin the wild guess and try stuff approach to solving his problem. You and I both know that this is the road to causing damage and learning nothing, or am I wrong here? He is clearly intent on doing this himself.
Anyone experienced in troubleshooting knows what the next steps are, and they do not involved changing, disconnecting or replacing anything. The next step is to search for information. Correct? No one told him to buy a 'scope unless he didn't have access to one, in which case I advised him to get the most suitable scope, and one that would be less expensive than buying new. If he had no end of cash, my advice would have been the same.
This isn't a pink, warm fuzzy world. There are times you have to do some things, or spend some money to accomplish what you want to do. If you don't want to do that you need to face up to the fact that there are some things in the is world you are ill equipped to do, and that you need to stop. At that point, you either pay a person to do it, sell off what you can't fix (in this case) or wait until you are in a position to accomplish your goal. This is also education.
There are very good reasons why some test equipment is used by technicians. Mine isn't to impress people, it is a necessary tool. It is needed to do this job efficiently, and to do things with a directed reason - or to learn.
So if you have a problem with that- okay. In this case I think your objection is doing a disservice to those who want to learn. I told him he needs to use an oscilloscope because at this point in troubleshooting, he needs to use one. We need to learn what it tells us in order to suggest the next steps.
If I didn't have a scope, but it was on my bench with my experience I would have some good clues as to where I would look next. Iut I have to tell you, my scope probe would be i my hand very quickly. Knowing beats guessing every day of the week.
The OP, aftershock, indicated he was measuring things with a meter. He reached a point where he was about to begin the wild guess and try stuff approach to solving his problem. You and I both know that this is the road to causing damage and learning nothing, or am I wrong here? He is clearly intent on doing this himself.
Anyone experienced in troubleshooting knows what the next steps are, and they do not involved changing, disconnecting or replacing anything. The next step is to search for information. Correct? No one told him to buy a 'scope unless he didn't have access to one, in which case I advised him to get the most suitable scope, and one that would be less expensive than buying new. If he had no end of cash, my advice would have been the same.
This isn't a pink, warm fuzzy world. There are times you have to do some things, or spend some money to accomplish what you want to do. If you don't want to do that you need to face up to the fact that there are some things in the is world you are ill equipped to do, and that you need to stop. At that point, you either pay a person to do it, sell off what you can't fix (in this case) or wait until you are in a position to accomplish your goal. This is also education.
There are very good reasons why some test equipment is used by technicians. Mine isn't to impress people, it is a necessary tool. It is needed to do this job efficiently, and to do things with a directed reason - or to learn.
So if you have a problem with that- okay. In this case I think your objection is doing a disservice to those who want to learn. I told him he needs to use an oscilloscope because at this point in troubleshooting, he needs to use one. We need to learn what it tells us in order to suggest the next steps.
If I didn't have a scope, but it was on my bench with my experience I would have some good clues as to where I would look next. Iut I have to tell you, my scope probe would be i my hand very quickly. Knowing beats guessing every day of the week.
Forum members, thank you for keeping helping everyone. Even those who are not equipped or do not plan to make a career or develop their skills into a major hobby.
Now as a newbie, I understand that buying a scope might not be the first solution. There is space consideration (especially with the old analog ones) and safety (learning how to properly ground your setup), etc...
My advise, to aftershock is to look for any loose wire connection (at the solder join) and for noisy transistors if your amp is old. I just went through a similar problem. And if you ever decide to change some transistors, don't do them all at the time like I stupidly did. Try one first to see if you correctly installed it. Then, one section, then the entire channel, etc..
Look for this thread on AK: https://audiokarma.org/forums/index...ilure-prone-whatever-and-replacements.731653/
Now as a newbie, I understand that buying a scope might not be the first solution. There is space consideration (especially with the old analog ones) and safety (learning how to properly ground your setup), etc...
My advise, to aftershock is to look for any loose wire connection (at the solder join) and for noisy transistors if your amp is old. I just went through a similar problem. And if you ever decide to change some transistors, don't do them all at the time like I stupidly did. Try one first to see if you correctly installed it. Then, one section, then the entire channel, etc..
Look for this thread on AK: https://audiokarma.org/forums/index...ilure-prone-whatever-and-replacements.731653/
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Hi jrbastien,
I read that thread. Please don't encourage others with this. Much is untrue as a matter of fact.
Sometimes to do something, you absolutely do require certain pieces of equipment. It doesn't matter if this will not be a career or how you plan to do things later. If you need something, you simply need it. Suggesting anything else is a complete cop-out.
To work on an amplifier, you really do need a good meter, an oscilloscope and also an THD meter. You need these things for very good reasons, sorry. That is why they designed and sold these instruments. You can buy them used, I had to buy new at the time so you have it easy.
Can you replace parts like a robot? Maybe not. You may damage PCBs, choose the wrong part types, fail to match parts that require matching and even damage new parts by installing them incorrectly (I'm not talking about polarity). Most meters people use are not good enough to even set bias current and most people don't even understand why. Then the topic of sounds good and distortion. You simply do not have any clue. I get stuff in measuring well over 1 % (and higher) THD when people say they sound great now. After fixing the faults, they say they can't believe they thought it sounded good.
So, to do a job you have to know how to do it correctly, you absolutely at least need access to the correct instruments that work properly, and you have to verify your work. Most of all, your mind has to be free from the silliness I saw in that thread. Just stupid.
-Chris
I read that thread. Please don't encourage others with this. Much is untrue as a matter of fact.
Sometimes to do something, you absolutely do require certain pieces of equipment. It doesn't matter if this will not be a career or how you plan to do things later. If you need something, you simply need it. Suggesting anything else is a complete cop-out.
To work on an amplifier, you really do need a good meter, an oscilloscope and also an THD meter. You need these things for very good reasons, sorry. That is why they designed and sold these instruments. You can buy them used, I had to buy new at the time so you have it easy.
Can you replace parts like a robot? Maybe not. You may damage PCBs, choose the wrong part types, fail to match parts that require matching and even damage new parts by installing them incorrectly (I'm not talking about polarity). Most meters people use are not good enough to even set bias current and most people don't even understand why. Then the topic of sounds good and distortion. You simply do not have any clue. I get stuff in measuring well over 1 % (and higher) THD when people say they sound great now. After fixing the faults, they say they can't believe they thought it sounded good.
So, to do a job you have to know how to do it correctly, you absolutely at least need access to the correct instruments that work properly, and you have to verify your work. Most of all, your mind has to be free from the silliness I saw in that thread. Just stupid.
-Chris