Solar Panel 15kHz noise issue

[James Perrett]

Do you have a good ground on the audio system. Many audio devices don't have any kind of ground at all which leaves them open to interference like this.

[Wonks]

I’d have a look and find out the make/model of the inverter the solar panels use, see if you can find the installation manual for it online, and depending on your electrical knowledge, you may be able to check whether it’s been cabled to those requirements.

For example, if the manufacturer says two core SWA (steel wired armoured) cable between the inverter and the feed-in meter, and they’ve used standard twin and earth, then that could be part of the problem.

But I’m used to frequency converters for electric motors which don’t produce pure sine-wave outputs like a feed-in inverter should do, so good shielding of output cables probably isn’t necessary. But if the inverter casing isn’t correctly earthed, there may still be some emissions issues from the electronics.

[SafeandSound Mastering]

Something worth a go....

15kHz wavelength at audio frequencies is = 2.3cms
At RF frequencies = 20kms

That is due to differences in the speed of propagation between sound through air and radio through the ether.

There is a suggestion (from the drop in level using a DI box) the unbalanced audio lead is your problem.

If that is acting as an antenna.. find a bit of wire.. 5m piece of wire to start (guitar cable would do) if you touch the 5m wire to the shield of the TS connector... and also try the the positive of the unbalanced connected wire and watch your spectral analysis as you do so. If the 15kHz goes up in level (and probably if it is effected at all) you may find this increases the efficiency of the 'antenna' if so it will likely be RF bourne.

You may only need to bring the 'wire' close to the unbalanced and connected cable for it to form a kind of RF director/reflector. Albeit grossly inefficient at the wavelengths involved 20kms vs 5m. Antennas typically start with 1/4 wavelength elements.

We cannot be sure that 15kHz is the fundamental yet, but that is what we have to go on.

You can even start with picking up and holding the unbalanced cable in 2 places, and seeing if your spurious signal changes as your hands will possibly introduce an effect on reactance.

It is worth a shot.

[Stuart79]

Update (for anyone that cares)
The issue is being caused by the solar panels. Switching off the solar PV at the mains board made the interference go away immediately. Switching it back on, the interference returned after a delay of about ten seconds (presumably whilst something booted up again).

My question:
- Are there any realistic steps I can take to minimise the noise getting into everything that gets recorded?

Please bear in mind:
1) I'm not an electrical engineer in the slightest, just a lowly hobbyist.
2) The property affected by this issue is not mine.
3) The issue affects all types of signal: balanced/unbalanced, line/mic.

Thanks again.

[SafeandSound Mastering]

You could try the shortest possible unbalanced cabling and make the longer ones balanced. Though it gives only some attenuation.

Otherwise you need to build a Faraday cage which is 100pct impossible of course unless you dwelling a fully fledged lab facility. Then you need wiring to come in which it could breach, cannot even choke 15kHz at cabling as it is in the audio pass band.

I will mull it over on a walk but cannot think of much right now.

Maybe give your mains earth pins a scrub with a wire brush/wire wool.

A very unpleasant find indeed.

Maybe you can ask landlord to get solar company back and see if they can apply more filtering at source ?

[Lostgallifreyan]

Update (for anyone that cares)
The issue is being caused by the solar panels. Switching off the solar PV at the mains board made the interference go away immediately. Switching it back on, the interference returned after a delay of about ten seconds (presumably whilst something booted up again).

My question:
- Are there any realistic steps I can take to minimise the noise getting into everything that gets recorded?

Is the noise constant for all times of day? If so it's not the panels, but the charge controller. Wonks mentioned the cabling between the 'inverter' and the meter that controls the tariff and timing of a grid tied inverter (my system is off-grid so I don't have this specific problem). Try waving a portable AM radio at either end of that cable to see if you get a signal strong enough to interfere with a French station (or maybe the Irish RTE station on longwave if you can hear it). That might give you some idea if the cabling was badly managed in some way.

Good grounding, balanced lines wherever possible, is all you (or most people) can ever do. If the connectors are small or fragile, give them an easy life! I have found that the 'Rean' micro XLR's are particularly poor when it comes to good ground continuity. Use full size XLR if you can.

In many cases you might get away with recording some silence, complete with that noise, immediately before and after the sound you want, then using something like Sonic Foundry's noise reduction to get a noiseprint from the silences, and then remove most of that noise from the signal you want. This NR method is very good at reducing a fixed frequency narrowband sound in the upper part of the audible spectrum, so that might help with some of your past recordings too. (I use it to remove the 19 KHz pilot tone from FM recordings).

[Stuart79]

Update (for anyone that cares)
The issue is being caused by the solar panels. Switching off the solar PV at the mains board made the interference go away immediately. Switching it back on, the interference returned after a delay of about ten seconds (presumably whilst something booted up again).

My question:
- Are there any realistic steps I can take to minimise the noise getting into everything that gets recorded?

Is the noise constant for all times of day? If so it's not the panels, but the charge controller. Wonks mentioned the cabling between the 'inverter' and the meter that controls the tariff and timing of a grid tied inverter (my system is off-grid so I don't have this specific problem).

It's a consistent, steady noise regardless of the time of the day.

Noise reduction software is a good shout. I'd prefer to deal with it source of possible, but removing it after the fact might make things manageable.

[Hugh Robjohns]

Okay, so you know the general source of the interference.

It seems to be getting in to the system via RF interference.

Personally, I'd go back to the PV installer and get them to sort it out because some part of their system is clearly not EMC compatible... but if you didn't commission the installation I appreciate that might be difficult.

So, the next best option is to try and stop the interference getting in.

I can't remember what you're recording into, but the first step is to see if the recorder is clean. Set it up as usual, but don't plug any mics etc in. Press record for 30 secs, and then check the playback. Is the 15kHz interference there or not?

If not, great — the recorders not the problem. If it is, it may be due to unterminated inputs. Make up some xlr plugs with 150 Ohm resistors between pins 2/3 and try again (or plug in a capacitor mic but leave phantom power off).

If quiet, great... if still showing the interference signal you're going to need a better recorder.... or a new house...

If the recorder is quiet, you can move on to the cables. Plug in an XLR cable with the 150 ohm dummy plug or an unpowered capacitor mic. Interference back? Try a different cable....

Different cables have different screen arrangements, and some are better than others. Foil screen is very good, although the cable may not be as flexible.

Sometimes changing the XLRs to the Neutrik EMC type works wonders! These have a ring of capacitors built in between the shell and pin-1, and they are often very good at preventing RF interference.

Star-quad may help, because most have double reussen screens and greater capacitance. So worth a try...

If you can find a solution where the recorder and cable are noise-free, then you just have to worry about your mics. Again, some have much better shielding than others. There's little you can do about it, other than try to find mics that dont pickup RF...

And as has been said already, all of this assumes the recorder has an good, solid, low-impedance Earth connection. Without that keeping RF out will be trickier. Not impossible, but definitely trickier!

Alan experiment to help identify where the interference is getting in, it can be useful to create a makeshift Faraday Cage by wrapping the recorder / cables/ mics in aluminium foil!

[Stuart79]

Okay, so you know the general source of the interference.

It seems to be getting in to the system via RF interference.

Personally, I'd go back to the PV installer and get them to sort it out because some part of their system is clearly not EMC compatible... but if you didn't commission the installation I appreciate that might be difficult.

So, the next best option is to try and stop the interference getting in.

I can't remember what you're recording into, but the first step is to see if the recorder is clean. Set it up as usual, but don't plug any mics etc in. Press record for 30 secs, and then check the playback. Is the 15kHz interference there or not?

If not, great — the recorders not the problem. If it is, it may be due to unterminated inputs. Make up some xlr plugs with 150 Ohm resistors between pins 2/3 and try again (or plug in a capacitor mic but leave phantom power off).

If quiet, great... if still showing the interference signal you're going to need a better recorder.... or a new house...

If the recorder is quiet, you can move on to the cables. Plug in an XLR cable with the 150 ohm dummy plug or an unpowered capacitor mic. Interference back? Try a different cable....

Different cables have different screen arrangements, and some are better than others. Foil screen is very good, although the cable may not be as flexible.

Sometimes changing the XLRs to the Neutrik EMC type works wonders! These have a ring of capacitors built in between the shell and pin-1, and they are often very good at preventing RF interference.

Star-quad may help, because most have double reussen screens and greater capacitance. So worth a try...

If you can find a solution where the recorder and cable are noise-free, then you just have to worry about your mics. Again, some have much better shielding than others. There's little you can do about it, other than try to find mics that dont pickup RF...

And as has been said already, all of this assumes the recorder has an good, solid, low-impedance Earth connection. Without that keeping RF out will be trickier. Not impossible, but definitely trickier!

Alan experiment to help identify where the interference is getting in, it can be useful to create a makeshift Faraday Cage by wrapping the recorder / cables/ mics in aluminium foil!

Thanks Hugh - that's very helpful and methodical.

The usual recording chain is Input source> Cranborne EC1 > Audient id44 > Scan 3XS Laptop.

[Lostgallifreyan]

And as has been said already, all of this assumes the recorder has an good, solid, low-impedance Earth connection. Without that keeping RF out will be trickier. Not impossible, but definitely trickier!

That is a good point, it reminded me of something that RF engineers sometimes mention. A solid ground CAN be important, but the real trick is knowing where the radio frequency circuit runs, because an RF counterpoise is needed, and that isn't always the actual ground.

The relevance in this case, is that there are ferrite beads that can be used around a cable, or better yet, pass a few turns of cable through a big bead or ring, so that turns count raises quality of result (goes up with a square law, so turns count matters more than most other details). This is something that might be doable for the single flexible mains cable that brings power to the audio gear. A simple pluggable mains filter may even help with this, but if trying a DIY method, the ferrite should have a high permeability (of 2000 or more, type 77 ferrite for example). This stuff will block noise on the outside of a coax, preventing it getting back to a sensitive listening antenna, so if you can thread several turns of a mains cable through a big ring of that, you might get some good results.

[Wonks]

I’d suggest that as it occurs all the time, not just when power is being produced and exported, it’s probably emanating from the inverter itself, probably not the cable as well.

So it may just be something as simple as a missing earth strap to a screening part of the enclosure. Though it could well be more complicated.

It would help to know the make and model of the inverter.

[Stuart79]

I’d suggest that as it occurs all the time, not just when power is being produced and exported, it’s probably emanating from the inverter itself, probably not the cable as well.

So it may just be something as simple as a missing earth strap to a screening part of the enclosure. Though it could well be more complicated.

It would help to know the make and model of the inverter.

It's a Sunsynk SG01/03LP1 3.6kw.

[Stuart79]

Okay, so you know the general source of the interference.

It seems to be getting in to the system via RF interference.

Personally, I'd go back to the PV installer and get them to sort it out because some part of their system is clearly not EMC compatible... but if you didn't commission the installation I appreciate that might be difficult.

So, the next best option is to try and stop the interference getting in.

I can't remember what you're recording into, but the first step is to see if the recorder is clean. Set it up as usual, but don't plug any mics etc in. Press record for 30 secs, and then check the playback. Is the 15kHz interference there or not?

If not, great — the recorders not the problem. If it is, it may be due to unterminated inputs. Make up some xlr plugs with 150 Ohm resistors between pins 2/3 and try again (or plug in a capacitor mic but leave phantom power off).

If quiet, great... if still showing the interference signal you're going to need a better recorder.... or a new house...

If the recorder is quiet, you can move on to the cables. Plug in an XLR cable with the 150 ohm dummy plug or an unpowered capacitor mic. Interference back? Try a different cable....

Different cables have different screen arrangements, and some are better than others. Foil screen is very good, although the cable may not be as flexible.

Sometimes changing the XLRs to the Neutrik EMC type works wonders! These have a ring of capacitors built in between the shell and pin-1, and they are often very good at preventing RF interference.

Star-quad may help, because most have double reussen screens and greater capacitance. So worth a try...

If you can find a solution where the recorder and cable are noise-free, then you just have to worry about your mics. Again, some have much better shielding than others. There's little you can do about it, other than try to find mics that dont pickup RF...

And as has been said already, all of this assumes the recorder has an good, solid, low-impedance Earth connection. Without that keeping RF out will be trickier. Not impossible, but definitely trickier!

Alan experiment to help identify where the interference is getting in, it can be useful to create a makeshift Faraday Cage by wrapping the recorder / cables/ mics in aluminium foil!

Working through your handy step-by-step method: the interface was okay, the cables were okay, but connecting mics brought the interference frequency back. Good to be aware of.

[Wonks]

I’d suggest that as it occurs all the time, not just when power is being produced and exported, it’s probably emanating from the inverter itself, probably not the cable as well.

So it may just be something as simple as a missing earth strap to a screening part of the enclosure. Though it could well be more complicated.

It would help to know the make and model of the inverter.

It's a Sunsynk SG01/03LP1 3.6kw.

https://www.sunsynk.org/3-6kw-hybrid-inverter

It looks like there's a required firmware upgrade which you may not have, so you might need to get that installed - it might help with the noise, it may not.

But there is also a 'low noise' mode more for acoustic noise, which alters the switching frequency from 15kHz to 20kHz. So whilst not ideal as you may still get interference, at least it moves it to a less noticeable frequency. I'd definitely try that, as it will also confirm the unit as the source of the noise.

There are ferrite beads inside the unit which various external cables are supposed to be wrapped around, but without knowing your exact set-up, these may not may not be used.

[Stuart79]

I’d suggest that as it occurs all the time, not just when power is being produced and exported, it’s probably emanating from the inverter itself, probably not the cable as well.

So it may just be something as simple as a missing earth strap to a screening part of the enclosure. Though it could well be more complicated.

It would help to know the make and model of the inverter.

It's a Sunsynk SG01/03LP1 3.6kw.

https://www.sunsynk.org/3-6kw-hybrid-inverter

It looks like there's a required firmware upgrade which you may not have, so you might need to get that installed - it might help with the noise, it may not.

But there is also a 'low noise' mode more for acoustic noise, which alters the switching frequency from 15kHz to 20kHz. So whilst not ideal as you may still get interference, at least it moves it to a less noticeable frequency. I'd definitely try that, as it will also confirm the unit as the source of the noise.

There are ferrite beads inside the unit which various external cables are supposed to be wrapped around, but without knowing your exact set-up, these may not may not be used.

Good spot!

[Wonks]

And if we can 100% track it down to the inverter unit itself (and not the outgoing cables), then there is the option of enclosing it in its own Faraday cage.

[Lostgallifreyan]

And if we can 100% track it down to the inverter unit itself (and not the outgoing cables), then there is the option of enclosing it in its own Faraday cage.

I doubt there's a need. The ferrite beads are the main thing, to stop the wiring becoming an antenna.

[Wonks]

But if there’s something in the inverter which is directly radiating the noise, then ferrite rings/beads won’t be much use.

One step at a time.

[ajay_m]

I rather doubt that the interference is being radiated given the long wavelength even if we assume harmonics at higher frequencies are being modulated.
Instead I think that the interference is being directly coupled back into the ring main.
As you can see from this link https://www.elexana.com/solar-power-inv ... -filtering
A pi filter is often used to suppress EMI and I suspect the current installation has inadequate filtering.

[Lostgallifreyan]

I rather doubt that the interference is being radiated given the long wavelength even if we assume harmonics at higher frequencies are being modulated.
Instead I think that the interference is being directly coupled back into the ring main.

I agree. My Mackie monitors radiate directly as direct magnetism, but it's very local. I'd have to play my bass holding it close to them to cause unrest. Coupling to wiring to cause emission by what amounts to a distributed antenna is the main way noise propagates from anything connected to the mains.

With a PV charge controller or switchmode PSU, or anything related, the main aim is efficiency. The byproduct of noise is caused by this, because the faster and harder a FET transistor can be forced on and off, the more efficient it is. (Same thing applies to computer IC's in an effort to reduce heat dissipation with higher clock speeds).

The pulse rate in the inverter described here seems to be either 15 KHz, or 20 KHz, depending on setting. The pulse EDGES will transmit as wideband noise (with quite a lot of energy, from power switching circuits), so any rectification in even one atom thickness of oxide film in a microphone connector, for example, might demodulate to allow the high pitched audio as a result. For this reason, you need to block the wideband RF at source, so it can't get into the long wiring, and this is what the ferrites are for. It's no accident that the makers of power switching devices provide for this.

[Stuart79]

FWIW and to wrap this thread up: this noise issue is now resolved.

The company that installed the solar panel system came back and replaced the inverter with one that apparently has better filtering. They also put some additional ferrite rings somewhere. Whether one or both of these things was responsible for correcting the issue, I don't know. I'm just grateful not to have unwanted noise on everything.

It took a lot of phone calls and a lot of having to repeat the same information to different call centre operatives who probably didn't care, but I'm glad I persisted.

I'm back to blissful self-noise alone now. Thanks to anyone who chipped in with advice on the matter.

[RichardT]

It's nice to hear you got a good result in the end!

[Martin Walker]

It's nice to hear you got a good result in the end!

And that you’ve identified and solved a problem that other musicians may suffer from in the future - thanks for following with the solution!

[Hugh Robjohns]

I've altered the title to make it more findable in searches.