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Humming sound from DC-AC inverter

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Humming sound from DC-AC inverter

Postby Guest » Thu Aug 01, 2019 5:02 am

From my CB days I remember that they had a special AC-DC inverter for them because they produced a lot of interference. Well I am getting the same thing when using my DC-AC inverter when I am recording sound and wondered if anyone had any suggestions on what to do?
Thanks
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Re: Humming sound from DC-AC inverter

Postby Mike Stranks » Thu Aug 01, 2019 9:13 am

First question.... why are you using an inverter? Is there an issue with your mains supply that means you can't connect direct?

The electronics experts will be along shortly, but my understanding is that the cheaper inverters don't generate a true AC sine-wave... which is probably the issue you're facing.

I'll stop there as speculating on solutions will probably only lead to subsequent embarrassment on my part! :)
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Re: Humming sound from DC-AC inverter

Postby ef37a » Thu Aug 01, 2019 11:11 am

Hi Mike, no expert on inverters either but I am not really sold on a non-sinusoidal waveform being such a bad thing?

Anything with a rectifier/big caps in it draws a far from sinusoidal current, basically gobbles juice in spiky lumps.

However, cash where gob is! I have a cheapo Maplin 500VA inverter and I have used it to run a 32" FSTV will no visible or audible issues. Will dig it out and test it on various things. I am suspecting a top range, Sony S cassettte recorder would be fussier than most audio devices? It is also pretty old technology but any suggestions from the 'sperts as to the definitive test kit gratefully recieved.

Oh yes, I have no idea what the OP is up to either!

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Re: Humming sound from DC-AC inverter

Postby Eddy Deegan » Thu Aug 01, 2019 7:45 pm

ef37a wrote:gobbles juice in spiky lumps

I absolutely love that phrase :D :clap:
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Re: Humming sound from DC-AC inverter

Postby Guest » Sat Aug 03, 2019 12:40 pm

Mike Stranks wrote:First question.... why are you using an inverter? Is there an issue with your mains supply that means you can't connect direct?
Recording from the car

Mike Stranks wrote:but my understanding is that the cheaper inverters don't generate a true AC sine-wave... which is probably the issue you're facing.
It's one out of Halfords. But hear is what it sound like anyway
https://www.dropbox.com/s/uvakqv2q4f2vq ... 4.m4a?dl=0

I remember recording last year in the caravan using the same inverter and not having this issue
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Re: Humming sound from DC-AC inverter

Postby Mike Stranks » Sat Aug 03, 2019 1:19 pm

Please give us a rundown of what kit you're using...
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Re: Humming sound from DC-AC inverter

Postby Trevor Johnson » Sat Aug 03, 2019 7:31 pm

The main reason for buying a 'pure sine wave' converter is to run power tools, e.g. a variable speed power drill, etc., which definitely don't like 'modified sine wave' converters.

I investigated this a few years ago when I needed an inverter to drive an electronic cathedral organ from a battery, (a big one), after someone had severed the three phase AC to the chapel.

No noise or other issues from the modified sine wave inverter, and there were other issues than cost, as a good modified sine wave inverter is not 'cheaper' than the pure sine wave, just have different usages.
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Re: Humming sound from DC-AC inverter

Postby Folderol » Sat Aug 03, 2019 8:05 pm

A word of caution. If you are running underpowered wall warts (the heavy ones with a transformer), a modified sine (Stepped actually) will make it work extremely hard, and get much hotter than usual.
If it's all switchmode stuff then the best of the lot is a a square wave inverter. The rectifiers and smoothing caps will sigh with relief :bouncy:
They will be seeing a steady voltage with just 100Hz tiny blips.

If it's all kit with a separate PSU, then the most efficient solution would be low voltage DC-DC converter - not necessarily the cheapest but definitely the quietest and kindest to both battery and kit.
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Re: Humming sound from DC-AC inverter

Postby Guest » Sun Aug 04, 2019 12:07 am

Hear is what I have as the inverter
https://www.screwfix.com/p/ring-power-s ... lsrc=aw.ds

Its only 150W; so with powering a laptop and a mixer though it, its near enough running at full capacity, so I had the engine running at the time it was all in use
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Re: Humming sound from DC-AC inverter

Postby Folderol » Sun Aug 04, 2019 7:58 am

The spec on that site doesn't say what type it is - unfortunate.
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Re: Humming sound from DC-AC inverter

Postby ef37a » Sun Aug 04, 2019 8:07 am

" I had the engine running at the time it was all in use"

Ignition spikes? Didn't have the bonnet open perchance?

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Re: Humming sound from DC-AC inverter

Postby Mike Stranks » Sun Aug 04, 2019 8:19 am

Possible/probable issues:

*The inverter isn't up to the job; insufficient current available;
*The inverter is poor quality and introducing hum into the system;
* Something(s) in your set-up needs an earth/ground and isn't getting it;
* You had the engine running.

Solutions:

* Use battery-powered kit;
* Get a better inverter with a separate earth/ground stud - and use it;
* Switch off the engine;
* Use a leisure battery rather than connecting to the car. Also means you're not 'tied' to the car.
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Re: Humming sound from DC-AC inverter

Postby Guest » Sun Aug 04, 2019 2:06 pm

Did anyone check my recording out in my second post, at the very start of it you can hear the humming sound problem
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Re: Humming sound from DC-AC inverter

Postby Tim Gillett » Sun Aug 04, 2019 2:21 pm

Yes. I couldnt hear any obvious hum.
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Re: Humming sound from DC-AC inverter

Postby Mike Stranks » Sun Aug 04, 2019 3:59 pm

Tim Gillett wrote:Yes. I couldn't hear any obvious hum.

Ditto

But if you're not happy with the sound then my suggestions above may help.

There is some slight 'system noise' at the start of the recording, but that sounded no different to noise I've heard many times from the electronics of the various components in a total system. I hear nothing that I'd immediately relate to AC 230v issues.
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Re: Humming sound from DC-AC inverter

Postby Guest » Sun Aug 04, 2019 4:47 pm

Mike Stranks wrote:
Tim Gillett wrote:Yes. I couldn't hear any obvious hum.

Ditto

But if you're not happy with the sound then my suggestions above may help.

There is some slight 'system noise' at the start of the recording, but that sounded no different to noise I've heard many times from the electronics of the various components in a total system. I hear nothing that I'd immediately relate to AC 230v issues.
Those noises what you heard at the start of the recording is what I was referring to. I did not notice that noise when I was using mains electric so I presumed it was coming from the inverter. Where do you think the noise is coming from?
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Re: Humming sound from DC-AC inverter

Postby Tim Gillett » Mon Aug 05, 2019 1:27 am

I now hear noise VERY briefly at the start but then the music comes in and covers it up. Please give us a file of mostly the noise with just a few seconds of the music for context , not the other way around.
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Re: Humming sound from DC-AC inverter

Postby Mike Stranks » Mon Aug 05, 2019 10:01 am

I may have thought of an explanation...

From another thread it appeared that the concept of an audio-interface was a new one to you.

That suggests that you may be connecting your mixer direct to the audio input (3.5mm) of your laptop.

You've not said what mixer you're using, but it may not be blessed with the quietest of preamplifiers... hence noise. Also the audio inputs of laptops can be notoriously unreliable and noisy.

Get an audio interface (not necessarily the first one of which I found a picture shown in the other thread) which can be powered from a USB interface on your laptop. Choose one with appropriate facilities to meet your needs and you should hear an improvement in the system noise-floor.

The other thread in which you asked a question about mixers/interfaces contains useful info about options, but you'll find a huge range of facilities - and prices! - here: https://www.thomann.de/gb/usb_audio_interfaces.html
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Re: Humming sound from DC-AC inverter

Postby ef37a » Mon Aug 05, 2019 11:14 am

Touche' Mike, touche'!!

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