I have just finished building an SSE.
The amp sounds great, but i have some issue with static noise.
If no RCA is connected to the amp, it is quiet, no noise.
If I connect a mini jack to RCA cable, from my Macbook Pro to the amplifier, I can hear a fairly loud static noise.
The Macbook Pro has also an external screen plugged into it
I used to have the same issue with static with my Bottlehead Crack amplifier. If the amplifier was connected via RCA to the iPhone, it was quiet. If it was connected to the Macbook Pro (with external screen), I would hear static noise.
I tried different RCA cables, from the cheapo to homemade Canare shielded wire, they all produce noise when connected to the Macbook Pro.
I have tried plugging the SSE via a cheater plug. The static noise disappear.
What is causing this noise?
I am using as power transformer a Baldwin removed from an organ.
It has high voltage center tap, but it does not have 5v filament nor 6.3v filament center tap.
The AC prog has the green ground wire connected to one bolt of the power transformer. All other ground wires from the speaker jacks and RCA jacks (just one of the two) are also connected to the same lug screwed onto one bolt of the power transformer.
I would also add the amp makes a popping noise into the speakers when i turned off. Not sure if it is related somehow.
Thank you. Apart from this the amps sounds great!
The amp sounds great, but i have some issue with static noise.
If no RCA is connected to the amp, it is quiet, no noise.
If I connect a mini jack to RCA cable, from my Macbook Pro to the amplifier, I can hear a fairly loud static noise.
The Macbook Pro has also an external screen plugged into it
I used to have the same issue with static with my Bottlehead Crack amplifier. If the amplifier was connected via RCA to the iPhone, it was quiet. If it was connected to the Macbook Pro (with external screen), I would hear static noise.
I tried different RCA cables, from the cheapo to homemade Canare shielded wire, they all produce noise when connected to the Macbook Pro.
I have tried plugging the SSE via a cheater plug. The static noise disappear.
What is causing this noise?
I am using as power transformer a Baldwin removed from an organ.
It has high voltage center tap, but it does not have 5v filament nor 6.3v filament center tap.
The AC prog has the green ground wire connected to one bolt of the power transformer. All other ground wires from the speaker jacks and RCA jacks (just one of the two) are also connected to the same lug screwed onto one bolt of the power transformer.
I would also add the amp makes a popping noise into the speakers when i turned off. Not sure if it is related somehow.
Thank you. Apart from this the amps sounds great!
I would also add I am using a different Macbook Pro and external screen then the one I was using with the Bottlehead Crack, in a different location (office vs home). The static noise although sounded the same. Maybe something with the Macbook Pro and external screen in general producing some sort of static noise...?
It does sound like a ground loop.
An easy way to check this is to get a device that is basically a couple of 1:1 transformers in an enclosure with RCA pigtails, and put it in series with the inputs to the SSE, and, if the problem goes away, it's because the isolation transformers have broken the ground loop.
Radio Shack used to sell such a device and car stereo shops will probably have one. They'll have a name like ground loop breaker or similar. Ground loops are a common problem and can drive you nuts trying to solve them.
An easy way to check this is to get a device that is basically a couple of 1:1 transformers in an enclosure with RCA pigtails, and put it in series with the inputs to the SSE, and, if the problem goes away, it's because the isolation transformers have broken the ground loop.
Radio Shack used to sell such a device and car stereo shops will probably have one. They'll have a name like ground loop breaker or similar. Ground loops are a common problem and can drive you nuts trying to solve them.
The MacBook Pro charger has only two prong here in the states, but in my case the Macbook Pro gets its charge from the external monitor, an LG UltraFine 5K Display. The LG has a three prong plug. I have added yesterday a cheater plug to the LG wire, and this seems to resolve the issue as well...
The noise appears because when the signal cables are connected between the grounded monitor and the grounded amplifier, there is a second ground path for return current from the MacBook's supply current through the signal cable screens. This is the 'earth loop'. How much of the supply return current flows through the interconnect cable ground will depend on the balance of resistances of the two paths that the return current can flow through.
Of course current can not flow without voltage drop, so this connection causes a small, noisy voltage drop on the screens of the interconnects between the MacBook and the amplifier, which doesn't know the noise is not signal and thus amplifies the noise along with the signal. What you are hearing is the noise of the supply for the MacBook.
The cheater plug prevents any of the supply current for the MacBook being able to flow in the interconnects' screen by breaking the common path through the electrical safety earth, but it also removes the monitor's electrical safety earth which is there to protect your life in the event of equipment failure. (Equipment without an earth connection is required to be 'double insulated' so that it is inherently safe without a safety earth.)
The proper way to resolve the ground loop noise is to correct the design fault in the amplifier that is making it susceptible to ground noise.
To do this remove all signal and speaker wires from the electrical chassis ground lug. The speaker ground wires should go directly the the common terminal between the two power supply capacitors, as should the centre tap wire from the transformer. The RCA socket grounds should only be connected to amplifier 0 volts at one place; depending on the layout of the amplifier circuits that my be directly back to the circuit board; then there should be a single wire from the capacitor center tap to the circuit board ground.
Wired like this the amplifier may hum with no input connected because it no longer has a ground reference. To provide a ground reference for the amplifier connect a 47Ω resistor in parallel with a 100nF film capacitor between the capacitor center tap 0V and the chassis electrical ground lug where the power cord earth wire connects. The 47Ω resistor is a large enough value to stop troublesome ground currents flowing in the signal cable screens and the capacitor ensures that radio frequency interference is shunted directly to the electrical earth.
Of course current can not flow without voltage drop, so this connection causes a small, noisy voltage drop on the screens of the interconnects between the MacBook and the amplifier, which doesn't know the noise is not signal and thus amplifies the noise along with the signal. What you are hearing is the noise of the supply for the MacBook.
The cheater plug prevents any of the supply current for the MacBook being able to flow in the interconnects' screen by breaking the common path through the electrical safety earth, but it also removes the monitor's electrical safety earth which is there to protect your life in the event of equipment failure. (Equipment without an earth connection is required to be 'double insulated' so that it is inherently safe without a safety earth.)
The proper way to resolve the ground loop noise is to correct the design fault in the amplifier that is making it susceptible to ground noise.
To do this remove all signal and speaker wires from the electrical chassis ground lug. The speaker ground wires should go directly the the common terminal between the two power supply capacitors, as should the centre tap wire from the transformer. The RCA socket grounds should only be connected to amplifier 0 volts at one place; depending on the layout of the amplifier circuits that my be directly back to the circuit board; then there should be a single wire from the capacitor center tap to the circuit board ground.
Wired like this the amplifier may hum with no input connected because it no longer has a ground reference. To provide a ground reference for the amplifier connect a 47Ω resistor in parallel with a 100nF film capacitor between the capacitor center tap 0V and the chassis electrical ground lug where the power cord earth wire connects. The 47Ω resistor is a large enough value to stop troublesome ground currents flowing in the signal cable screens and the capacitor ensures that radio frequency interference is shunted directly to the electrical earth.
I have applied your suggestion, remove the cheater plug from both the amp and the external monitor and it seems to be quiet. If I remove the laptop from the charger (using the Apple MacBook brick charger) and I let it instead get its voltage from the external monitor, the noise is back. Definitely this LG monitor is a serious offender!
Made an account just to chime in and say that I'm also having this issue with the LG UltraFine 5K Display, which I resolved by using a cheater plug. I don't have a DIY amp, though, but fairly pricy commercial amps that I'd expect would be more robust to this sort of thing using the resistor/ ground reference that @johnmath describes: Stax SRM-D50 and Woo Audio WA7 Fireflies v3.
The LG monitor (LG UltraFine 5k). Not complete silence afterwards, but pretty damned close. However, I started getting paranoid about starting fire from the lack of real ground on the monitor, so I purchased one of these (Ebtech Hum X Ground Line Voltage Filter). Just installed it today (which reminded me of this thread). Seems to match or better the lack of static I found with the cheater plug, happily.
As an aside, one of the more interesting aspects of my interference was that it was audibly worsened in proportion to the speed of the image change on the monitor (e.g., it was very poor when entering or existing Mission Control, as that changed quite a bit of the pixels).