Battery power on Stagepas 600BT

[MickeyDripping]

Our ukulele band use a Stagepas 600bt for live performances. Because we play for charity we go to some strange locations where AC mains is not always available. So we decided to power our rig (stagepas, twin HH powered monitors, two Shure dynamics and two Rode condensers) from one of these power station battery packs 280WHr which gives about three and a half hours use. Everything works fine except the condensers, running on the stagepas 30v phantom power, which buzz from the word go. On AC mains everything, including the condensers work spot on. So it must be the battery power. We checked the output of the phantom on mains and battery and it is a steady 30v on both. We broke the rig down removing one element at a time and were left with the amp, speakers, battery and condensers - still buzzing. Any ideas?

[Hugh Robjohns]

Lack of a solid ground reference? Or not a true sine-wave inverter output?

I'm assuming your powerstation provides an AC feed at 110 or 230V (are you in the US or Europe?)

Some inverters generate a stepped waveform rather than a true sine-wave. This stepped version is full of harmonics and can result in a noisy, buzzy audio system. The same problem applies to cheap UPS systems.

If the powerstation is a sine-wave type the lack of a solid ground may be the problem.

A normal AC mains connection will provide a solid ground reference via the safety ground. A battery-fed power supply isn't (normally) grounded.

Consequently, parts of the equipment that the designers expected to be grounded are left 'floating and, in poor designs, any inference picked up can get introduced into the signal path instead of being whisked away quietly into the ground.

Also, note that some (most?) stage equipment is 'class-1' with a three-pin mains connection and must be grounded for safety. Please check your equipment to see if any of your devices must have grounded power sources.

I dont know what the powering system you're using offers, but that may provide an external grounding facility. Most don't, and that's because adding a ground can introduce new safety issues... so I would strongly advise consulting a qualified electrician over grounding options in your application.

[MickeyDripping]

Thank you for your swift reply.
We are in the UK, so 230vAC. I read every review etc before purchase and someone had this on an oscilloscope and yes, it produces pure sine wave. There is no facility for fitting any sort of earth, so no go there. I did buy two Xvive 48v phantom rechargeable in-line power supplies to keep the power independent of the amp and battery, but to no avail. Needless to say all our cables are XLR balanced and carry ferrite rings. As a rank amateur this just about gets to the limit of my knowledge, but I have been in touch with the manufacturers who list Hi-Fi as one of the battery uses, and they have asked me to send a video.

I am now looking at the all in one column array portable PA's, but the battery powered ones don't have enough inputs (4 mics and at least I instrument).

Thanks for your help and if we get a resolution, I will let you know.

.

[Wonks]

If it's just the condensers, then is there any chance of swapping them for dynamics when you are using battery power? I know it all depends on the application as to what can viably be exchanged for a dynamic, but better that the sound isn't quite so clear than a lot of buzzing!

[MickeyDripping]

Hi Wonks
I agree! Using 4 dynamics was my plan for last Sunday's gig at a local village fete. However, MR Covid has come knockin' and left me in isolation. Next gig I will give it a go and see what happens.

[Wonks]

Also, how loud is the PA going? Does it still buzz if the output is turned right down? The power pack (if it's the Jackery one I found on Amazon) can supply 200W maximum and the Stagepass will peak at 800W input usage when providing the full 600W output. The Yamaha '100W' at 1/8 power is a typical average power consumption for a dynamic band situation but peak usage could be well over this, which may cause a non-sinusoidal output when on load.

As Hugh said, it's probably the lack of a ground that's causing the buzz, but there may be other contributory factors.

[Aled Hughes]

What are the condensers?
The Rode M3 are cheap, good sounding and can run on 9v battery, so wouldn’t need phantom power.

[Wonks]

It's not the phantom that seems to be the issue as the battery 48v supply should have fixed that when tried. Maybe something to do with the mic design and the amount of gain the mic's internal preamp provides allows it to pick up a lot of hum due to lack of a proper ground for the casing and grille.

A different capacitor mic may work better, or it may do just the same. With dynamics, all the preamp work is done within the Stagepas unit, which seems to be less prone to hum pickup

[Aled Hughes]

It's not the phantom that seems to be the issue as the battery 48v supply should have fixed that when tried. Maybe something to do with the mic design and the amount of gain the mic's internal preamp provides allows it to pick up a lot of hum due to lack of a proper ground for the casing and grille.

A different capacitor mic may work better, or it may do just the same. With dynamics, all the preamp work is done within the Stagepas unit, which seems to be less prone to hum pickup

Ah, thanks, missed the part about the battery phantom supplies.

Beyer M201s it is then