Hi, first time poster 🙂
I recently have built a power amp based on Hypex NC122MP board. I bought a Ghent Audio connection kit, and it went quite smoothly. The only issue I have is a humming noise in both speakers, not very strong, barely perceptible from the listening position, which seems to be specifically related to the input connection.
For reference, in the NC122MP, the inputs are mapped to the following pins of the J4 H-Box connector:
- for channel 1:
--- pin J4.1 - inverting signal ("-")
--- pin J4.2 - non-inverting signal ("+")
--- pin J4.3 - ground
- for channel 2:
--- pin J4.16 - inverting signal ("-")
--- pin J4.15 - non-inverting signal ("+")
--- pin J4.14 - ground
I use the Ghent Audio h-box connector to attach shielded 3-wire input cables, connected to the RCA sockets. "+" goes to RCA pin. "-" and "ground are soldered together, attached to RCA sleeve, and are grounded tot he chassis.
Here is what happens:
Case 1: Amplifier powered on, connected to 2 speakers, all wires disconnected from the J4 H-box -- dead silent
Case 2: Amplifier powered on, connected to 2 speakers, input wires, connected to the RCA input sockets, with sleeve grounded, are connected to J4 H-box, nothing plugged into RCA input sockets -- humming noise
Case 3: Amplifier powered on, connected to 2 speakers, input wires, connected to the RCA input sockets, with sleeve grounded, are connected to J4 H-box, a source (network streamer with volume control) is plugged into RCA input sockets -- very slight humming noise, I really need to put my ear to the speaker
Case 4: Amplifier powered on, connected to 2 speakers, all wires disconnected from the J4 H-box; 1 single wire, 2-3 cm long, attached with a JST connector to J4.2 (channel 1, non-inverting signal, or "+") - same humming noise in channel 1 speaker as in case 2.
Basically, looks like
- powered on, connected to speakers, but with nothing attached to input pins, the amp is dead silent (except the usual slight pop when powering the amp on or off).
- attaching anything at all to "+" signal inputs provokes humming in the corresponding speaker.
- attaching an actual source on the other end of the connection cable does not stop, but attenuates the humming.
Any advice on possible causes, or troubleshooting hints would be much appreciated. Thanks.
I recently have built a power amp based on Hypex NC122MP board. I bought a Ghent Audio connection kit, and it went quite smoothly. The only issue I have is a humming noise in both speakers, not very strong, barely perceptible from the listening position, which seems to be specifically related to the input connection.
For reference, in the NC122MP, the inputs are mapped to the following pins of the J4 H-Box connector:
- for channel 1:
--- pin J4.1 - inverting signal ("-")
--- pin J4.2 - non-inverting signal ("+")
--- pin J4.3 - ground
- for channel 2:
--- pin J4.16 - inverting signal ("-")
--- pin J4.15 - non-inverting signal ("+")
--- pin J4.14 - ground
I use the Ghent Audio h-box connector to attach shielded 3-wire input cables, connected to the RCA sockets. "+" goes to RCA pin. "-" and "ground are soldered together, attached to RCA sleeve, and are grounded tot he chassis.
Here is what happens:
Case 1: Amplifier powered on, connected to 2 speakers, all wires disconnected from the J4 H-box -- dead silent
Case 2: Amplifier powered on, connected to 2 speakers, input wires, connected to the RCA input sockets, with sleeve grounded, are connected to J4 H-box, nothing plugged into RCA input sockets -- humming noise
Case 3: Amplifier powered on, connected to 2 speakers, input wires, connected to the RCA input sockets, with sleeve grounded, are connected to J4 H-box, a source (network streamer with volume control) is plugged into RCA input sockets -- very slight humming noise, I really need to put my ear to the speaker
Case 4: Amplifier powered on, connected to 2 speakers, all wires disconnected from the J4 H-box; 1 single wire, 2-3 cm long, attached with a JST connector to J4.2 (channel 1, non-inverting signal, or "+") - same humming noise in channel 1 speaker as in case 2.
Basically, looks like
- powered on, connected to speakers, but with nothing attached to input pins, the amp is dead silent (except the usual slight pop when powering the amp on or off).
- attaching anything at all to "+" signal inputs provokes humming in the corresponding speaker.
- attaching an actual source on the other end of the connection cable does not stop, but attenuates the humming.
Any advice on possible causes, or troubleshooting hints would be much appreciated. Thanks.
Attachments
Not certain what you doing with the volume pot wiring, can you please do a drawing of what you have done?
Sorry about the confusion.
I have already disconnected the pot from the amp, as the first troubleshooting step. As it happens, it changed nothing in the hum.
I attach the updated shot - this picture corresponds to the last situation, on which I have run the test steps described in the first post.
***
Re pot wiring, it's an Alps stereo 10k pot. There are 3 connectors per chanel. When looking from the face of the pot
- Left : ground
- Center: output
- Right: input
Red wire is RIGHT channel
Black wire is LEFT channel
For the right channel:
- red wire picks up signal at the central pin of the PCA input socket and connects to the right leg of the pot
- second red wire picks up pot output at the central leg of the pot and returns back to the back of the enclosure
- at the back of the enclosure, the red, is connected to the (+) wire of the shielded cable leading to the J4 h-box.
- at the pot, the left, ground, is connected by yellow cable to the chassis.
As I mentioned, being new to this, I was not sure about shielding of the wires going to the pot, I thought maybe they were catching EMI or what not, so I disconnected the pot completely, and basically did the reference connectivity layout advised by Ghent Audio, with RCA feeding directly the input H-box.
Unfortunately it had zero effect on hum (or fortunately, because looks like the pot did not cause the problem).
I have already disconnected the pot from the amp, as the first troubleshooting step. As it happens, it changed nothing in the hum.
I attach the updated shot - this picture corresponds to the last situation, on which I have run the test steps described in the first post.
***
Re pot wiring, it's an Alps stereo 10k pot. There are 3 connectors per chanel. When looking from the face of the pot
- Left : ground
- Center: output
- Right: input
Red wire is RIGHT channel
Black wire is LEFT channel
For the right channel:
- red wire picks up signal at the central pin of the PCA input socket and connects to the right leg of the pot
- second red wire picks up pot output at the central leg of the pot and returns back to the back of the enclosure
- at the back of the enclosure, the red, is connected to the (+) wire of the shielded cable leading to the J4 h-box.
- at the pot, the left, ground, is connected by yellow cable to the chassis.
As I mentioned, being new to this, I was not sure about shielding of the wires going to the pot, I thought maybe they were catching EMI or what not, so I disconnected the pot completely, and basically did the reference connectivity layout advised by Ghent Audio, with RCA feeding directly the input H-box.
Unfortunately it had zero effect on hum (or fortunately, because looks like the pot did not cause the problem).
Attachments
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I thought so, but literally length of wire plugged into (+) starts the hum - even a 50 mm of wire will do that. I am wondering if the problem is how I positioned the board - in my layout the input cables basically go over the switching power supply part, this may be causing interference.
Can improper grounding somewhere cause this?
I am puzzled: I simply connect a single wire or random length to the input pin on the board, with the other end of this wire floating, not connected to anything at all; why does it start the hum? What's the difference between the pin sticking in the air (4mm long) and the pin with wire hooked on it sticking in the air (40mm long)?
I am puzzled: I simply connect a single wire or random length to the input pin on the board, with the other end of this wire floating, not connected to anything at all; why does it start the hum? What's the difference between the pin sticking in the air (4mm long) and the pin with wire hooked on it sticking in the air (40mm long)?
I had a similar experience with RCA into a balanced input until I implemented an RC network (100nF, 100 ohms) as per the Hypex application note on page 5/5 of "Dealing with Legacy pin 1 problems"
And as other's have stated make sure the RCA sleeve is not connected to the case.
I'd bet money that if you connect the module to a balanced source, with XLR, bypassing your RCA's and pot you won't have any buzz
And as other's have stated make sure the RCA sleeve is not connected to the case.
I'd bet money that if you connect the module to a balanced source, with XLR, bypassing your RCA's and pot you won't have any buzz
In my very first configuration, I had the Rca sleeve isolated from the chassis.
The connection was:
- rca pin to "+" (non inverting signal)
- rca sleeve - not grounded to the chassis - to "-" (inverting signal) and "ground" soldered together at the RCA socket side.
With this configuration, I got very loud 50-60 herz noise, think what nespresso machine makes at half a meter distance. That's why i grounded the socket sleeve.
As a result, I got mere "hum" - something I can barely hear at 2-3 meters. This is what I am trying to solve.
The connection was:
- rca pin to "+" (non inverting signal)
- rca sleeve - not grounded to the chassis - to "-" (inverting signal) and "ground" soldered together at the RCA socket side.
With this configuration, I got very loud 50-60 herz noise, think what nespresso machine makes at half a meter distance. That's why i grounded the socket sleeve.
As a result, I got mere "hum" - something I can barely hear at 2-3 meters. This is what I am trying to solve.
I built a couple of class D amps. I had a lot of problems with the last one around hum but managed to eliminate it.
First to say, the case for my build was earthed (which is important to do for safely). But, it does now mean you have a circuit, which is your case, that can carry noise.
Four areas of noise:
1. Ground loop interference. (google this it is likely the issue you are having).
how-to-get-rid-of-hum-and-eliminate-other-noises-from-your-audio-and-video-systems
2. For my build, noise was introduced via the dc power for internal Bluetooth circuit. Putting in a DC isolator solved this.
3. The Bluetooth would also pick up noise when it switched out to the aux input then there was no Bluetooth signal being transmitted. Since there was no aux connection, I closed this aux circuit (connecting it to itself).
4. The case itself, because it is earthed, is now a EMI inductor taking any interference to earth. So it can induce noise and in turn induce this into the audio cables. Even if they are insulated when going into the case, noise can be inducted cables and components like the volume control potentiometer. I moved the potentiometer so it was 2 cm inside the case and used a plastic connector the knob.
All of the above resolved it so there is no hum.
Without the case being earthed, there would be no hum (except for 2). But earthing a DYI case is absolutely essential should to ensure safety.
The system above was build using two 50ASX2BTL (2x 85w 8ohm)
First to say, the case for my build was earthed (which is important to do for safely). But, it does now mean you have a circuit, which is your case, that can carry noise.
Four areas of noise:
1. Ground loop interference. (google this it is likely the issue you are having).
how-to-get-rid-of-hum-and-eliminate-other-noises-from-your-audio-and-video-systems
2. For my build, noise was introduced via the dc power for internal Bluetooth circuit. Putting in a DC isolator solved this.
3. The Bluetooth would also pick up noise when it switched out to the aux input then there was no Bluetooth signal being transmitted. Since there was no aux connection, I closed this aux circuit (connecting it to itself).
4. The case itself, because it is earthed, is now a EMI inductor taking any interference to earth. So it can induce noise and in turn induce this into the audio cables. Even if they are insulated when going into the case, noise can be inducted cables and components like the volume control potentiometer. I moved the potentiometer so it was 2 cm inside the case and used a plastic connector the knob.
All of the above resolved it so there is no hum.
Without the case being earthed, there would be no hum (except for 2). But earthing a DYI case is absolutely essential should to ensure safety.
The system above was build using two 50ASX2BTL (2x 85w 8ohm)
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I built a couple of class D amps. I had a lot of problems with the last one around hum but managed to eliminate it.
First to say, the case for my build was earthed (which is important to do for safely). But, it does now mean you have a circuit, which is your case, that can carry noise.
Four areas of noise:
1. Ground loop interference. (google this it is likely the issue you are having).
how-to-get-rid-of-hum-and-eliminate-other-noises-from-your-audio-and-video-systems
2. For my build, noise was introduced via the dc power for internal Bluetooth circuit. Putting in a DC isolator solved this.
3. The Bluetooth would also pick up noise when it switched out to the aux input then there was no Bluetooth signal being transmitted. Since there was no aux connection, I closed this aux circuit (connecting it to itself).
4. The case itself, because it is earthed, is now a EMI inductor taking any interference to earth. So it can induce noise and carry this to earth. In turn, the current it is carrying can be induced into audio components. Even if they are insulated when going into the case, noise can be inducted into components like the volume control potentiometer. I moved the potentiometer so it was 2 cm inside the case and used a plastic connector the knob. My other cables are all internal since it is Bluetooth with external aerial and using a sleeved cables.
All of the above resolved it so there is no hum.
Without the case being earthed, there would be no hum (except for 2). But earthing a DYI case is absolutely essential should to ensure safety.
The system above was build using two 50ASX2BTL (2x 85w 8ohm)
First to say, the case for my build was earthed (which is important to do for safely). But, it does now mean you have a circuit, which is your case, that can carry noise.
Four areas of noise:
1. Ground loop interference. (google this it is likely the issue you are having).
how-to-get-rid-of-hum-and-eliminate-other-noises-from-your-audio-and-video-systems
2. For my build, noise was introduced via the dc power for internal Bluetooth circuit. Putting in a DC isolator solved this.
3. The Bluetooth would also pick up noise when it switched out to the aux input then there was no Bluetooth signal being transmitted. Since there was no aux connection, I closed this aux circuit (connecting it to itself).
4. The case itself, because it is earthed, is now a EMI inductor taking any interference to earth. So it can induce noise and carry this to earth. In turn, the current it is carrying can be induced into audio components. Even if they are insulated when going into the case, noise can be inducted into components like the volume control potentiometer. I moved the potentiometer so it was 2 cm inside the case and used a plastic connector the knob. My other cables are all internal since it is Bluetooth with external aerial and using a sleeved cables.
All of the above resolved it so there is no hum.
Without the case being earthed, there would be no hum (except for 2). But earthing a DYI case is absolutely essential should to ensure safety.
The system above was build using two 50ASX2BTL (2x 85w 8ohm)