Hi,
I’ve had a problem with a fairly loud 50Hz hum coming from the speakers of my home audio system, whenever my GivEnergy inverter is switched on. (I have another stereo that emits a similar hum from its chassis when it’s on, but not the speakers.)
The amp went back to the distributors, who said after testing it that it was working as expected. While i might otherwise take that with a pinch of salt, the fact that it (and the chassis hum from the other machine) stops when the inverter is switched off seems to pretty clearly indicate that the problem is being caused by some sort of electromagnetic interference from the inverter.
Does anyone have any experience with this? Does it indicate that my inverter is faulty or might have been installed incorrectly? Can anyone recommend any filters or similar that might work? (I’ve tried a couple of things, including one that the amp supplier sent as a trial, to no avail. )
Many thanks in advance,
Gareth
How close are your inverters to the amps?
Are you running your home on the EPS circuits of your inverter?
Personally not heard of that issue before, sorry
Thanks, Geoffrey. The inverter is in the loft and the amps are on the ground floor (two-storey house).
Assuming EPS = Emergency Power Supply, we don’t have that. The inverter is full-time grid-synced only.
strange, those were the obvious sources of possible interference
you said that the noise comes when the inverter is on, is it when the inverter is charging/discharging, literally just turned on and the batteries idle, and any correlation to solar generation?
when the solar is generating or batteries are discharging the grid voltage in your home will get pushed up a little and I was wondering if that was what your amp was susceptible to? You could measure that with a volt meter
wonder about one of those electrical noise suppressor plugs or extension leads you used to get for computer equipment?
It’s the same whenever the inverter is switched on. No correlation with whether it’s charging/discharging/idle; no change in the pitch or volume of the noise depending on which of these states it’s in. The activity of the solar - nor indeed whether the solar inverter is switched on - also makes no difference.
I looked at the grid voltage. It was reading very high, particularly when sunny and cold, apparently because there are quite a few solar installations in the estate. I managed to persuade the DNO to come and fix it. No change to the amp issue.
Re filters, the supplier of the amp sent out an Audiolab DC Block 6 to see if that helped. (This was actually before I’d realised that the problem was associated with the Giv-AC, because in my testing to that point I’d stupidly only turned off the solar inverter at the consumer unit, thinking both inverters were on that circuit - i blame the installer for not labeling the breakers! 
) Again, no difference at all.
I’m starting to wonder whether a filter should be installed close to the inverter, on the line from it to the consumer unit.
“no variance with volume control” - so even with the PrePro disconnected you hear the hum. Bit of a pain, but is it possible to transport the PA and Speakers to another room (i.e. different mains circuit). Maybe even a neighbours house, too?! (cf your concern about the relatively high Vac in your area.)
“I don’t think I’d describe it as having a buzz” - should be pretty clear to hear if it’s got a “high”-frequency (100Hz / 150Hz, etc.) element to it. As long as it’s just a low ‘thrum’, then it’s just pure 50Hz (so no rectification occurring somewhere).
There’s no noise if no source is plugged into the amp. I suspect this is because it essentially has a ‘sleep’ mode if no input signal is detected, though.
To be clear, the high VAC issue has now been fixed by the DNO - grid voltage readings per both my solar and Giv inverters and a clamp multimeter are consistently within an acceptable range.
Re moving to a different room, I have tried running it through an extension lead from a socket on a different main. No change. I could try running a longer extension lead from a neighbour’s house, I suppose. Moving everything will be very tricky, to say the least. I’m not really sure the value of this, anyway, as the problem is so clearly associated with the Giv inverter? Will running it noise-free at another location tell me anything that switching the inverter off at the consumer unit hasn’t already?
Buzz: yeah, there’s no discernible high frequency component.
There is a bit more information about the power amp that I’ve not mentioned previously for simplicity and because I don’t think it changes the fact the problem stems from an interaction between the inverter and this particular amp: it’s modular, with some channels run by mono, single-channel modules and some by dual-channel stereo ones. Both types use A/B class amps. The ones on the mono modules are OK. It seems that there’s something about the stereo module design in particular that interacts with the noise being put out by the inverter. I’ve tried swapping some speakers around and the problem is still linked to the module type so it’s doesn’t look like it’s anything to do with the particular speakers or speaker cabling.
I’m pretty sure there’s something about the design of these that is part of the problem - my old AVR (D-class, driving the same speakers) didn’t have this problem and I’ve not noticed problems with other stuff in the house (other than the chassis noise from the other device).
I’m increasingly starting to think that the inverter is turning the wiring of the house into a transmitting aerial that’s emitting EMI that the amp modules are sensitive to. Apparently, hammies often face the same problem. This would explain why placing a filter on the amp’s power cable wouldn’t sort the problem and is why I’m increasingly thinking about whether some kind of filter needs to be installed near the inverter.
So, you’re descending into the murky (not to say black magic) world of RF/EMI. Sorry I couldn’t help, and I wish you the best of luck. Let us know how you get on…
One thing I will say, if the issue does turn-out to be caused by the Giv inverter, then that might have implications for their CE compliance rating.
Or the amp rating. EMI compliance works both ways…
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I’m not expert but could you try and wrap a cardboard box in tinfoil and place said amp in the box for testing purposes. In essence a DIY Faraday cage to confirm your EMi interference logic. Even if it just reduces it. Along with a surge protector or even a small computer ups which would should clear up the sign wave for power going into the device.
Just an idea.
Bob
one thing to try is add a ferrite to the Amp’s power input. See if it changes.
That way you know its coming in via the power supply