Hi all, I am installing some more powerful sub amps in my home set up and I have an interesting 'problem'
To cut a long story short when I earth the chassis I have a GND loop sound the signal GND is NOT connected to the chassis earth and I have double checked. So the chassis each is only a safety earth and not related to 0V signal in any way directly as far as I can measure. The chassis has no connection to the board. Apart from the heat sink and this houses the output transistors in the normal way, no short as far as I can see or any leakeage
Any ideas, it has a relay for soft start but this is only on the Signal out. The transformer has L, N only connections and I have rewired the unit for mains as I have added a 12V fan with power supply (thermally operated) so very clear on all of the mains connections. It works its just the 'GND loop' sound that I want to remove but still want to keep it safe and have the chassis earth
Any ideas ?
To cut a long story short when I earth the chassis I have a GND loop sound the signal GND is NOT connected to the chassis earth and I have double checked. So the chassis each is only a safety earth and not related to 0V signal in any way directly as far as I can measure. The chassis has no connection to the board. Apart from the heat sink and this houses the output transistors in the normal way, no short as far as I can see or any leakeage
Any ideas, it has a relay for soft start but this is only on the Signal out. The transformer has L, N only connections and I have rewired the unit for mains as I have added a 12V fan with power supply (thermally operated) so very clear on all of the mains connections. It works its just the 'GND loop' sound that I want to remove but still want to keep it safe and have the chassis earth
Any ideas ?
What amplifier is this? It is unusual for there to be no ohmic connection from the circuit to the chassis.
It's a plate power amp a kit based amp. I can't measure any connection between the chassis and circuit. I have two of them, they have 12 MOSFET outputs each
I added a 10k pot and connected up RCA connections and Powercon mains in and Speakon out connections. Not a lot of room, but I tried with RCA direct to the board to see if I needed more shielding and it was the same. Remove the chassis Earth and it's quiet
I added a 10k pot and connected up RCA connections and Powercon mains in and Speakon out connections. Not a lot of room, but I tried with RCA direct to the board to see if I needed more shielding and it was the same. Remove the chassis Earth and it's quiet
And if you connect both the chassis to earth and the signal ground to the chassis at the same time?
If it helps I have a very low impedance Signal GND layout- all back to the Blu-ray player which is attached to earth and signal GND is very where else is low impedance daisy chained
A good question I haven't tried that to see. So essentially leave the earth pin disconnect and join the signal GND to the case ?
I will try tomorrow and let you know.
I will try tomorrow and let you know.
Do not connect anything to the input jack, but short the signal pin to ground at the input jack. Yes, and also connect your audio circuit ground to the chassis earth.
At what point of the audio ground did you connect to the chassis earth? The best point would be the point of the cleanest ground of the audio circuit. A good place for that is the ground point at the last power supply filter capacitor.
At what point of the audio ground did you connect to the chassis earth? The best point would be the point of the cleanest ground of the audio circuit. A good place for that is the ground point at the last power supply filter capacitor.
Okay a test today. I desoldered the volume pot back (passive) so signal to pot to board and signal GND to board
1. Quietest nearly okay but still a little background noise (too much for me) no connection between case and GND, no connection between earth and case
2. Next quietest possibly exactly the same (unable to discern if less or more noise as amp not next to speaker) connected GND to case and earth Not connected
3.Just earth the Case- Very noisy and sounds like GND loop, signal not connected to earth for case. Noisier than the fist two by a LOT
4. Connect all three so case earthed and signal connected to case and earth. Noisier than 1,2 but only by a small amount
In terms of relative noise if 1 is background noise (slight 'hiss' or hum up close) and 10 is 70db of hum. 1 is 2-3, 2 is 2-3, 3 is 8, 4 is 3
I need to unsolder and desolder to confirm that removing the pot (again) is actually quieter than with the pot in place
I might also build the other amplifier board into this case and confirm it behaves the same.
At the moment 1 is too noisy, my 500W BK panel amp is very quiet and you need to put your ear next to the cone to hear anything
1. Quietest nearly okay but still a little background noise (too much for me) no connection between case and GND, no connection between earth and case
2. Next quietest possibly exactly the same (unable to discern if less or more noise as amp not next to speaker) connected GND to case and earth Not connected
3.Just earth the Case- Very noisy and sounds like GND loop, signal not connected to earth for case. Noisier than the fist two by a LOT
4. Connect all three so case earthed and signal connected to case and earth. Noisier than 1,2 but only by a small amount
In terms of relative noise if 1 is background noise (slight 'hiss' or hum up close) and 10 is 70db of hum. 1 is 2-3, 2 is 2-3, 3 is 8, 4 is 3
I need to unsolder and desolder to confirm that removing the pot (again) is actually quieter than with the pot in place
I might also build the other amplifier board into this case and confirm it behaves the same.
At the moment 1 is too noisy, my 500W BK panel amp is very quiet and you need to put your ear next to the cone to hear anything
Signal in red, black spare signal GND, 10k pot at top, connection. to amp at bottom. the only cable 'unscreened is the small signal from red RCA to the pot and I did wrap some copper tape around and no difference
I feel for you as it's very frustrating to try and solve a problem like this. Is this the OMP base modules made by BK electronics? Their MXF range also had problems with hum and buzz.
I had issues with other "factory made" amplifiers that buzzed and hummed at low levels no matter what I tried. On two different models of amps in my collection I tried rotating the toroidal transformer just a little bit which actually reduced the buzzing. But couldn't totally solve the issue. I believe in my case it's down to emf radiation from the transformer.
I had issues with other "factory made" amplifiers that buzzed and hummed at low levels no matter what I tried. On two different models of amps in my collection I tried rotating the toroidal transformer just a little bit which actually reduced the buzzing. But couldn't totally solve the issue. I believe in my case it's down to emf radiation from the transformer.
Yes these are the BK MF1000's I do have 5 of the BPSP 500's and think they are great, very quiet and very happy with them. My plan was/is to swap the 500's driving my 18" and move the 500's on to 15" as my long term plan is to have 2x18, 2x15 and 3x12
I think the base amp is the same hence my interest. I have ordered some basic pre-amps to drive them as well.
The 500's inside
I think the base amp is the same hence my interest. I have ordered some basic pre-amps to drive them as well.
The 500's inside
Elliot Sound has a good article on connection to earth: https://sound-au.com/earthing.htm
He suggests connecting to earth at the clean end of the power supply and using a ground loop breaker. I have found that it works for me on my amp builds.
Hifisonix also has good info on grounding. This is one of the articles: https://hifisonix.com/wp-content/up...B-Design-Guidlines-for-Minimizing-Hum-1-1.pdf
There are other articles on the Hifisonics site.
He suggests connecting to earth at the clean end of the power supply and using a ground loop breaker. I have found that it works for me on my amp builds.
Hifisonix also has good info on grounding. This is one of the articles: https://hifisonix.com/wp-content/up...B-Design-Guidlines-for-Minimizing-Hum-1-1.pdf
There are other articles on the Hifisonics site.
I was looking for this article, and I just found it: https://hifisonix.com/wp-content/uploads/2019/02/Ground-Loops.pdf
This is a good reference.
This is a good reference.
So no connection of Audio GND to PE but chassis connected to PE? So floating Audio GND? Also when connected to another device?
Please try a 100 Ohm 2W resistor between common PSU point (Audio GND/ 0) and PE to see if it will be silent. Floating GND rarely works OK due to leakage of various sorts.
Also check the device that drives these amplifiers how things are arranged there. Just to know for sure. I think it is a combination of the driving devices ground scheme and coupling GND via cabling to the power amplifiers.
Never connect Audio GND directly to PE if you want stuff to be silent. Always have PE connected directly to metal casings for safety.
Please try a 100 Ohm 2W resistor between common PSU point (Audio GND/ 0) and PE to see if it will be silent. Floating GND rarely works OK due to leakage of various sorts.
Also check the device that drives these amplifiers how things are arranged there. Just to know for sure. I think it is a combination of the driving devices ground scheme and coupling GND via cabling to the power amplifiers.
Never connect Audio GND directly to PE if you want stuff to be silent. Always have PE connected directly to metal casings for safety.
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I have had a read and may try one of the proposed solutions I have been trying too see if its the amp output or input and removed the pot and wired in direct so full gain. It's quieter still so the pot is having some impact. But alas it's still too noisy and just audible from the seat (so unacceptable to me) I did wonder if I am okay to try a shorted plug on the input RCA or bride the input live the 0V input on the amp board too see if it is totally silent, no RCA connected vs connected is no different.
The amp input measures 97k and is specced at 100k and the output impedance of the DSP is 563 Ohms and specced at 560
The amp input measures 97k and is specced at 100k and the output impedance of the DSP is 563 Ohms and specced at 560