Hi!
I have two old NAD amplifiers, a NAD 319 and a NAD 3100, each with their own problems..
NAD 319
This amp has had issues for a while. When in use, a humming sound starts building up and eventually becomes louder than the music playing. The noise' volume is independent of the volume of the music. I have more or less ignored this issue (deadly sin..?). The noise disappears if I slide an RCA cable across the inputs (so basically connecting their grounds together?), and recently I grounded the chassis to wall ground, which also seems to resolve the issue.. But I am sure this is not a very good solution..
Recently, another issue has appeared. If playing at low volumes, one or both speakers will either cut out completely, or at least start crackling at a very low volume.
NAD 3100
This amp never had problems before, so I figured I would use it as a replacement for the 319 until I potentially could fix it. However, this one also has developed some problems. When switching on, either none of the speakers work, both speakers work, one or both speakers might play at a very low volume, or a combination of these. It seems completely random which speaker works or not. By pressing the speakers A/B button in and out a bunch of times, I can eventually get to a state where both speakers play normally, but I would rather not have to spend 5 minutes repeatedly pressing a button..
Does anyone have an idea what might be the cause of these issues and what might be done to fix them? I also do not currently have an oscilloscope or a signal generator, only a multimeter and a soldering iron, so I am limited on what I can do. I am sure there are more details I should give, so just ask away. Thanks in advance for any help, and I hope my temporary fixes doesn't hurt you too much 🙂
I have two old NAD amplifiers, a NAD 319 and a NAD 3100, each with their own problems..
NAD 319
This amp has had issues for a while. When in use, a humming sound starts building up and eventually becomes louder than the music playing. The noise' volume is independent of the volume of the music. I have more or less ignored this issue (deadly sin..?). The noise disappears if I slide an RCA cable across the inputs (so basically connecting their grounds together?), and recently I grounded the chassis to wall ground, which also seems to resolve the issue.. But I am sure this is not a very good solution..
Recently, another issue has appeared. If playing at low volumes, one or both speakers will either cut out completely, or at least start crackling at a very low volume.
NAD 3100
This amp never had problems before, so I figured I would use it as a replacement for the 319 until I potentially could fix it. However, this one also has developed some problems. When switching on, either none of the speakers work, both speakers work, one or both speakers might play at a very low volume, or a combination of these. It seems completely random which speaker works or not. By pressing the speakers A/B button in and out a bunch of times, I can eventually get to a state where both speakers play normally, but I would rather not have to spend 5 minutes repeatedly pressing a button..
Does anyone have an idea what might be the cause of these issues and what might be done to fix them? I also do not currently have an oscilloscope or a signal generator, only a multimeter and a soldering iron, so I am limited on what I can do. I am sure there are more details I should give, so just ask away. Thanks in advance for any help, and I hope my temporary fixes doesn't hurt you too much 🙂
Welcome to diyAudio 🙂
That at face value suggests possible problems with the switches. They may respond to cleaning. All these faults really should be tested using an oscilloscope, it just makes it so much easier and more definite. If you have no audio at the speaker sockets then you simple look and see if audio is present at the amplifier output itself. If audio is present then you know you have a connectivity issue between amp and socket.
The NAD319 could be more difficult. If you suspect ground issues and linking input grounds seems to improve things then have a look for cracked or damaged solder around where the inputs sockets may connect to the PCB. The crackling at low volume if it effects both channels suggests a common cause but nothing obvious comes to mind. I don't think this model uses a speaker relay which can give that sort of fault.
It could be anything, poor joints, power supply issue. Again a scope is your friend for faults like these.
That at face value suggests possible problems with the switches. They may respond to cleaning. All these faults really should be tested using an oscilloscope, it just makes it so much easier and more definite. If you have no audio at the speaker sockets then you simple look and see if audio is present at the amplifier output itself. If audio is present then you know you have a connectivity issue between amp and socket.
The NAD319 could be more difficult. If you suspect ground issues and linking input grounds seems to improve things then have a look for cracked or damaged solder around where the inputs sockets may connect to the PCB. The crackling at low volume if it effects both channels suggests a common cause but nothing obvious comes to mind. I don't think this model uses a speaker relay which can give that sort of fault.
It could be anything, poor joints, power supply issue. Again a scope is your friend for faults like these.
Thank you 🙂
As I feared I guess. I will have to look around for a reasonably priced oscilloscope. Nice to have in any case for many things.
As I feared I guess. I will have to look around for a reasonably priced oscilloscope. Nice to have in any case for many things.
I picked up a second hand analogue scope for £45 on ebay.
Must have had it 10 years now.
An alternative is a cheap USB PC scope.
I went ahead and bought a cheap USB scope - a Picoscope 2204A 🙂
When testing the NAD 319 now, it seems like it is only the right channel that drops out/starts crackling. It also seems to cut out at very random times, sometimes working perfectly and other times just constant crackling. I checked resistance across the input terminals, and they all measured to about .1 Ohms, so doesn't seem to be any problems there.. The left speaker seems to be outputting a much louder 'hissing' noise than the right speaker, but is only audible from about half a metre away.
The B speaker output on the 3100 seems to work better than A, and I can get it to work every time. The left channel never works at first, but works perfectly after turning the volume knob to an unpleasant volume for an instant. Guessing this should be pretty easy to troubleshoot, identifying where the signal stops in the amp.
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That is a classic symptom of a poor (oxidised) contact in a switch or relay. The higher voltage and current as you turn up the volume 'punches' through the thin oxide layer. The scope should prove/disprove that theory by showing audio at all times on the bad channels main output directly at the amplifier itself (before any switches).
The 319 might be more difficult. First thing would be to see if the crackling responds at all to gentle tapping, prodding and poking the PCB which if it does would indicate a possible bad joint or joints somewhere.
Audible hissing if its bad could be a noisy input transistor but its not a particularly common sort of issue. Freezer spray applied sparingly can help on suspect parts can help in diagnosis.
The scope showed that the audio signal was present up to the relays for speakers A and B. Applied some CRC electronic cleaner, and now everything works perfectly 🙂
Next up 319, I will try your suggestions and see if I can spot anything.