I'm sure this question has been asked a billion times already.
I've got a few of these cheap Chinese amplifiers but this one buzzes especially loudly compared to the others.
Just wondered if anyone could cast an eye over what has been done and comment on possible solutions. It buzzed in two different rooms with different cabling, location and speakers. So pretty sure it's the AMP itself... well if you slot a different amp into the same location the buzzing stops... so 100% related to the design of this particular amplifier.
To be just about bearable in a room the volume knob on the front has to be at about 50%. Any more than that and it sounds like a bee hive.
I've got a few of these cheap Chinese amplifiers but this one buzzes especially loudly compared to the others.
Just wondered if anyone could cast an eye over what has been done and comment on possible solutions. It buzzed in two different rooms with different cabling, location and speakers. So pretty sure it's the AMP itself... well if you slot a different amp into the same location the buzzing stops... so 100% related to the design of this particular amplifier.
To be just about bearable in a room the volume knob on the front has to be at about 50%. Any more than that and it sounds like a bee hive.
They write about your amplifier here (and some read it)))
JLH 10 Watt class A amplifier
Was he originally like this? The reasons can be a variety of incorrect installation, incorrect adjustment, defective parts.
What skills in electronics do you have?
JLH 10 Watt class A amplifier
Was he originally like this? The reasons can be a variety of incorrect installation, incorrect adjustment, defective parts.
What skills in electronics do you have?
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skills wise I'm fine with the majority of soldering jobs. I get a bit phased when it comes to checking components and measuring resistances and that sort of thing. Mainly because I don't trust my equipment a great deal. Only got basic old multi-meters with failing batteries and dodgy leads.
I've had a little browse of that mega-thread but it's like looking for a needle in a haystack. I've tried a keyword search.
There is an image of another assembled copy of yours here:
https://www.audiosciencereview.com/forum/index.php?attachments/20180530_160419-jpg.12944/
Have a look and see how yours compares. I can see a couple of minor differences at first glance. For example there is a blue lead from the transformer case/chassis to where the alps pot is - (your wire is yellow) - connected to a different spot. I can't tell if it makes a difference from photos, but you should be able to see if it is connected the same electrically.
The way your transistors are mounted is different (nuts showing versus screw heads showing). Make sure they are correctly isolated from the heatsink.
Does the buzzing still happen with inputs shorted to ground?
https://www.audiosciencereview.com/forum/index.php?attachments/20180530_160419-jpg.12944/
Have a look and see how yours compares. I can see a couple of minor differences at first glance. For example there is a blue lead from the transformer case/chassis to where the alps pot is - (your wire is yellow) - connected to a different spot. I can't tell if it makes a difference from photos, but you should be able to see if it is connected the same electrically.
The way your transistors are mounted is different (nuts showing versus screw heads showing). Make sure they are correctly isolated from the heatsink.
Does the buzzing still happen with inputs shorted to ground?
It is very very easy to get a ground loop in an amplifier with two separate channels on either side of a common transformer. If you disconnect (I mean completely disconnect) one channel, does the other one quit making noise?
How would you short the inputs to ground? Sorry if that's a silly question but 'shorting' can be a bit troublesome if done incorrectly - hahah.
Thanks for the other photo. Talking about the 'blue' wire v.s. yellow wire... another difference seems to be that my power socket is also earthed to the transformer case when the one in your example doesn't seem to be. I can see they've also insulated the cables with grey outer sleeving which isn't present in mine.
No input cables connected = no buzz.
If either left or right cable connected = buzzing returns. Only from the side which is connected.
One line of logic would suggest the source or the cable is providing the noise but not sure about that as I've had the same amp plugged into an entirely different setup with different everything and the noise is still there. With another amp in the same setup there isn't any.
That makes me suspicious that there might be a ground loop issue that they have hidden (on the other amp) by removing the ground (Protective Earth) = bad.
Just to be clear, don't ever remove the protective earth connection from a chassis to solve grounding issues. You can end up with a live chassis if things go bad.
Shorting the input can be done with a croc clip from the +in to the GND at each input RCA connector. You can also get a DIY RCA plug and just solder the insides together to form a shorting plug.
I notice the input wires run right alongside the transformer also. It might be worth cutting the cable ties and try putting some distance between the transformer and the input wires as part of your testing.
And powering just one amplifier channel / board at a time is a great idea.
Just to be clear, don't ever remove the protective earth connection from a chassis to solve grounding issues. You can end up with a live chassis if things go bad.
Shorting the input can be done with a croc clip from the +in to the GND at each input RCA connector. You can also get a DIY RCA plug and just solder the insides together to form a shorting plug.
I notice the input wires run right alongside the transformer also. It might be worth cutting the cable ties and try putting some distance between the transformer and the input wires as part of your testing.
And powering just one amplifier channel / board at a time is a great idea.
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Another thing I noticed is that the input wires appear to have some shielding (maybe) but the shielding is not connected at the GND end of the input RCA. Normally you would ground one end of the cable shield.
From what you describe, it sounds like you have a ground loop in the amp.
From what you describe, it sounds like you have a ground loop in the amp.
It sounds to me like the ground loop is not internal to the amp, but completed through the RCA cable shields. This unfortunately happens all the time with “kit” PCBs that are designed to be completely self contained. If disconnecting the shield on ONE of them at one end does not work, then you may have to resort to more drastic measures.
If by internal v.s. external you're talking about cables. I did have this amp in an entirely different setup with all different cables, different everything. In a setup which doesn't buzz with it's normal amp starts buzzing when you put this one in.
There is something internal to the amp that facilitates the ground loop, but the grounds on the input cables are necessary to close it. Do the two channels each have a direct connection between their respective power supply grounds and the chassis safety ground?
Not really. The source is a desktop computer. The amp is connected directly to the sound card output. But like I said earlier... it does the same in another totally different setup. With the source being a PC I can't imagine there would be any connection between the computer power supply and the sound card itself. The computer is turned off at the moment but the system is still humming.
In theory, there are two separate transformer windings. Each is connected to its own board, which has its own rectifier, electrolytic capacitor and capacity multiplier. The power ground is different for each board. Signal ground is also different for each board. How and where the earths connect is anyone's guess. The owner needs to trace (check) the wiring and independently draw a diagram of the connection of blocks and connectors.
Is the computer battery powered? Check with him. A mains-powered computer can generate noise if the amplifier does not have a common ground.
Is the computer battery powered? Check with him. A mains-powered computer can generate noise if the amplifier does not have a common ground.
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My guess is there is a connection between the center tap of each winding and the chassis ground. The two are physically separated by distance, making a large loop completed through the RCA cable shields. If the two amps are run off a common supply, and co-located, with ONE connection to the chassis the ground loop doesn’t happen, unless the source also has a safety ground which can create an additional one through the wall sockets. Fix that separately - can’t even diagnose that till this one is gone.
I wonder if it might be worth taking the dome off the power supply to see what is underneath? Some designs I've seen have a rubber mounting pad under the power supply and there are probably better and worse materials for insulating the power supply, wouldn't know what they've done without taking a look underneath.