Problem gear from US and Europe not happy together

I run into a problem trying to hook up a Mac*kie 24/8 (master) on 240 volts from European origine together with an extension 24 channels fed by a 240 to 110 volts PS.
There's a kind of low frequentie hum going on as soon as the 2 are both switched on. Leaving the extension switched of takes away the hum.
Checked for groundloops that's not the problem.
Masterfader down kills the noise but besides this everything muted except for the masterfader gives hum.
Since we like this setup to do some live-recordings the coming weekend a solution would be very welcome... Parts of these recordings will be the basis for an album, at least the drums as the drummer is leaving after this weekend to Japan for 9 months.

Worse case scenario will be renting of a European extension I'm afraid, but it' unlikely to find one in the coming 24 hours....

Cheers,

Tony

I'm not clear on what you mean by "240 to 110 volt PS." Do you mean that you're running a 110V PS with a stepdown transformer in front of it? If so, is this a real isolation-stepdown transformer, or a single-winding autotransformer? Is the master unit also running off this transformer? Perhaps you should open up Paint or some similar program and draw us a little diagram so there's no ambiguity due to language.

Btw. Europe is 230V area.

Michael,
Hellgium is 240V, we're always a bit hotter than the rest. At my place I measure always 238V more exactly, making it a less hot then the rest of Hellgium

Dave,
Yep, there's a stepdown transformer in front of it.

btw, just swapped the output going to the consoles of both PSU (+5, +12, +18/-18 and +48) and the hum disappeared for more then 50%?!

The 48 of the 110V PSU doesn't supply 48 anymore.
I'm trying to find out if it could be that these PSU's are happy with whatever they get fed from 110 up to 240, as there's no warning about connecting more then 110? If this is the case, then I could maybe get my 48 back. If I had a servicemanual I could start measuring things in the PSU.

The usual problem with US and European equipment not getting along is due to US Foreign policy.

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Okay, really... My guess is that you need to look at loop area and grounding philosophy. Having an exposed step-down or step-up TX in the middle of a loop is a prime cause candidate of dodgy humming.

Start with two pieces only and see if the hum goes away, or at what point the hum is introduced. Make sure that if there's a multiple ground path between two pieces of gear (i.e. a signal ground connection and a poweer ground connection) that you lift the SIGNAL ground, for electrical safety reasons.

Keith

I start up the main console with EU PSU, no problem.
I start up the extension with US PSU, voila hum.

Not much variables in this setting innit?
All channels are muted, all B returns as well. From as soon as the conditions are met and the L-R bus in engaged in the monitorsection, the hum is present. Masterfader needs to be up too.

?

I'm trying to locate the 48V problem, could be the caps or voltagestabilizers, or just about anything else in there. But I suspect caps to die sooner then resistors. The PSU's seem well constructed and the other one (EU version) is in use since 1998 without any problems so far. Other then not liking to work with his US collegue for some reason.

when I swap the PSU's and first turn on the US-PSU on the main console there's no hum, as soon as the other is switched on, the same as above happens.

I think this takes the stepdowntransformer out if the equation as well?

What is Hellgium?

[quote author="tony dB"]I think this takes the stepdowntransformer out if the equation as well?[/quote]
I'm really not understanding your logic here...

Keith

We found the problem.
When we remove the earth from one of the PSU PCB, leaving the power transformer connected to ground, the problem goes away.
Only thing to be fixed is the 48V supply in the US PSU as this is damaged.

Thanks for helping me out Keith, your post set me in the right direction.

Now we'll try to catch up on the lost time :? for the session

Tony

Sounds like you had a good ol' fashioned ground loop. But if you disabled the safety ground on one PSU to make it go away, that's not a good long-term solution. And I'm a bit worried when you say the power transformer is "connected to ground." That could mean many things, not all of them good. And are you talking about the stepdown transformer or the transformer inside the PSU?

Although your English is pretty good, I don't think we're quite grasping the specifics of how your system is connected. That's why I suggested drawing a diagram.

...also there's the question of what you're listening through to hear the hum... is it the onboard headphone amp, or do you have an amplifier connected to the console outs.

It is ABSOLUTELY, fundamentally critical to have a grounding strategy when installing any setup, if you want freedom from noise, electrical safety and reasonable immunity to interference. The plan should include safety electrical grounding (which you appear to be possibly bypassing according to your description, leading to NYDave's concerns) and preferably single-point audio ground for each path.

I recommend that everyone take a minute with each piece of gear to measure continuity from the electrical ground to the audio ground, and from audio ground to the chassis, BEFORE you screw it in the rack, connect it to the power or connect it to any other piece of audio gear. The best, quietest and safest installations all have reliable connections from any exposed metal surfaces to electrical ground, which do not rely on the rack screws to connect them through other rack gear... (or else they'd become unsafe as son as they were removed!) but NO connection to audio ground other than at a single central point in the installation.

Keith

Hi Dave and Keith,

I have a tested and completely balanced setup, also the amps connected are full balanced. The hum was heard tru HP amp AND main and studiomonitoring. I understand about getting a system well earthed etc...
and what cables to freefloat the ground, and wichones not too, in case unbalanced components come into play.

This was a mobile setup for a few days of rehearsalrecordings only, although with the experiences gained recent, this seems like a perfect preproduction setup too. Supertool as warmup for band and assistant :wink: a few days before starting in the studios.

To come back on the ground loop thing, even with all of the cables removed from the linked consoles (exept the link and 1 set of monitors of course) we got hum on the balanced mainsspeakers, it only disappeared when we removed the earth from one of both the PSU PCB, that is: not where the 110 comes in but in the middle of the PCB where the 5, 12, 18 and 48v are made.

Anyway, I'm a happy Tony once again, thanks for helping out.

I will learn about drawing stuff to post here too, making a lot of my endeavours more easy to explain :green:

Tony

PS1 Michael, Hellgium is this part of Belgium with loads of:
{cynic :evil: mode on}
corrupt politicians,
strange working justice departments,
incompetent staff at crucial places at work (go to this person to find out that, and overthere they know jack sh*t about their own department,
overtaxing of the population & especially independant employed people (always have been easy bate) by the government,
too much meat industry,
fast growing racist inspired population (and stupid media in their best effort making this even look bigger) and ....
stupid weather, when it's cold it feels even colder, when it's hot, it feels hotter (too much humidity in the air - today we had 34°C, the day before yesterday hardly 17°C, this happens all the time and I hate it),
ozon pollution, industrial pollution, farmers have been thrown too much dump on their fields for years, soil is acid as is all underground and surfacewater, what they didn't kill, industry soon will finish, aaaarghh.
The day before yesterday we saw a report on the TV-news about tests done on the blood from the umbellical chord of youngborn kids showing Belgian kids get born with extreme high levels of heavy metal (cadmium, ...) dioxines and other crap!

well don't get me started huh :twisted: :evil: :evil:

I would love to live outside this country for 1000's of reason's...
(Dave, if you need an assitant in North Italy, we need to talk :green: )
Maybe one day, when I feel p**sed enough I'll start a thread in the Brewery about this. {cynic :twisted: mode off}

PS 2 I want a better analog setup in my first studio as with this experiment it became once again very clear that analog rules bigstyle over a lot (if not ALL) of digital mixers...
Anyone feel like pointing me to a good midclass console for tracking and everynow and then mixing? A*M*E*C 2500 or something like it?
In the 2nd room the long talked about SSL will be installed, pictures in few weeks, to drool on :green:

PS 3 :roll: was I hyperventilating a while ago???