Running PA speakers from battery AC inverter

[moley6knipe]

Hi - hoping to gain some thoughts from the hive mind on this PA thing I have.

Have need to run small a couple of active Yamaha MS speakers from a cheapo battery pack that gives AC out, in this case 80,000mAH / 300w. This thing: http://www.sbaoh.com/h-pd-20.html

 

When the speakers are powered via the AC outlet on the battery pack, at full charge (I assume it'll be the same as the battery drains), the amp in the speakers is buzzing. Here's a quick video on my OneDrive... https://1drv.ms/v/s!Arjk5eAqeURchJAPy1CG_CVBsVbMDg?e=fJcWBQ

 

When plugged into normal wall AC no such issue. It's obviously because the speakers aren't getting the sort of AC they like... but any thoughts on whether it'll cause damage for 2-3 hours of "not anywhere near full bore volume" running? The Yammys are in good health, the audio sounds fine - exactly the same whether powered from battery or mains - it's 100% an electrical circuit thing.

 

For completeness, the gear is: Battery AC out > short 4 gang extension, powering: Bluetooth to 3.5mm TRS socket adaptor (powered via your usual phone charger thing); Active DI box (9v DC power adaptor); 2 x Yammy speakers (2.5m IEC power leads).

 

Thanks!

[BigRedX]

The key words that you want to be looking for is "Pure Sine Wave".

 

If your inverter doesn't produce this, and most budget devices won't, then you will run into problems like the one you are experiencing.

 

Unfortunately unless you spend a lot of money on a device from a reputable supplier, ideally one who specialises in audio solutions, even devices which claim to be outputting pure sine wave AC won't be close enough to prevent problems.

 

Also exactly which model of Yamaha speakers are you hoping to use? I suspect that 300W of the inverter is insufficient to power a pair of them for any length of time.

[Phil Starr]

As above but with one extra hazard and that is that not all pure sine wave inverters are actually producing pure sine waves. The power supply in your amp may not be compatible with the sine wave they provide. There’s a long thread about this on Bass Chat somewhere.

[BigRedX]

There's also at least one thread on the Sound On Sound forums detailing these problems with input from people who know their electronics. Well worth having a look at that too

[moley6knipe]

Thanks everyone! I’ll have a read up some more. Much appreciated, and sorry for slow reply, been flat out busy this week…

[Chienmortbb]

The cheap inverters give out something approaching a square wave, as @Phil Starr says even those proportion be pure sine  wave produce a sort or castellated wave. A bit line a low bit rate A/D conversion. You may be better off with a generator. 

[Rosie C]

We use a Jackery brand battery pack which is pure sine and it works fine with modern amps. But they do work out at about £1/Watt.

[moley6knipe]

Thanks folks… a better quality box has been sourced which… is better but not perfect. We’ll go with that and if the speakers die I don’t need them in a gig until October 😀

Edited May 10 by moley6knipe