Help! noise problem.... PSC Cart Power + Inverter = bad noise

[johnpaul215]

This just happened to me today....

Lectro Venue, Fostex PD-6 and some other random things plugged into a PSC cart power distro box. Mackie Onyx 1220 board plugged into a pure sine wave inverter. There is a terrible noise coming through the board (main outs, headphone, everything). Also every channel on the board shows the -20 light lit. The noise is kind of pulsing as opposed to a steady hum. I have the noise if the inverter is plugged in to the Cart Power or tapped directly off the Optima battery. If i unplug the PD-6 and Lectro Venue from the Cart Power, it goes away. It seems to be some sort of ground loop situation, but it does not make the normal ground loop hum.

If I plug the Cart Power box and Mackie into a power strip and get AC, it sounds fine.

Has anyone had this happen, and is there a fix?

[studiomprd]

no, I have not had this exact experience...

but you could, of course, isolate if it is the Fostex (my guess!) or the Lectro.

in another topic we have discussed the RF spray from micro-processor devices, and this might be what is involved here; the spray is getting into the power.  Ferrite beads might help...

[Philip Perkins]

If you haven't already, try powering everything up without any of the audio connections made.  Monitor the gear individually, on the cart power but w/o being connected together.  You may have a ground problem in your audio wiring, esp if you are using the unbalanced aspects of the Onyx.  Can you look at the AC your invertor is making on a scope, and see if it is producing a nasty waveform?  Make sure the gear is isolated physically from the metal cart.

Philip Perkins

[RPSharman]

DO NOT PLUG THE ONYX INTO THE CART POWER.

The Cart Power is not equipped to handle that sort of draw.

Not sure about other issues, but I saw this and thought to advise you.

[johnpaul215]

DO NOT PLUG THE ONYX INTO THE CART POWER.

The Cart Power is not equipped to handle that sort of draw.

Not sure about other issues, but I saw this and thought to advise you.

Good to know.... I thought it might help because the Cart Power has isolated outlets.

@Senator Mike: I don't think it's RF spray because it does not happen when powered off AC power.

@Philip: Even if i pull all the audio cables, I still see the noise on the Mackie. It seems to be some sort of battery power related issue. I emailed PSC as well in case they have some insight.

[Glen Trew]

DO NOT PLUG THE ONYX INTO THE CART POWER.

The Cart Power is not equipped to handle that sort of draw.

The Cart Power, which is capable of 8 Amps, should not have any trouble powering the Mackie Onyx 1220. I did a current draw test, and with the Firewire board installed, the current draw of the mixer and inverter was just 3A @ 13.8VDC. The Venue and PD-6 together will probably pull another 3A or so, putting the total at around 6A.

Good to know.... I thought it might help because the Cart Power has isolated outlets.

The Cart Power outlets are not isolated. They have filters designed to reduce the possible audible interaction between the DC-DC converters of various equipment being powered together (rarely an issue) but the noise problem you are having is clearly not that kind of noise. In my experience, the Venue internal power supply is often a factor in this type of noise. As mentioned elsewhere in this thread, isolating the problem to a specific piece of equipment or a specific combination of equipment is the first step to fixing it.

Glen Trew

[RPSharman]

The Cart Power, which is capable of 8 Amps, should not have any trouble powering the Mackie Onyx 1220. I did a current draw test, and with the Firewire board installed, the current draw of the mixer and inverter was just 3A @ 13.8VDC. The Venue and PD-6 together will probably pull another 3A or so, putting the total at around 6A.

Glen Trew

While this is true, the individual outputs might trip the poly fuses if the draw is too high.  I experienced this on this unit and the Powerstation.  Ron modified my Powerstation with a beefy output for my inverter.  Now I use the Ultra, which was also modified for a high draw from my inverter on two of the outputs.

Robert

[cmgoodin]

Try Putting Ferrite Cores (Chokes) around the power cables about 2 inches from where they connect.  Many DC switching supplies emit a high frequency EMI signal around their DC leads. These can beat against other HF switching signals from the Inverter or other DC to DC power supplies and cause harmonic lower frequency  audible artifacts that travel over the DC power cables and into the audio board.

----Courtney

[johnpaul215]

So I have not solved this yet. I did unplu all audio cables. The inverter going straight to battery, the PD-6 and Venue in the Cart Power. Noise is still there. If i unplug the PD-6 or the Venue, the noise is there.

I connected all the audio cables and plugged the inverter into another (much smaller) battery and the noise goes away.

That makes me think it is not specific to the Venue or the PD-6, but the inverter fighting with the cart power in general.

[ChRiStIaN]

Hi,

you mean the inverter is connected on the same battery used also for the cart power?

What is your battery nominal capacity?

You probably need to put  a filter between the batt and the inverter (not just a ferrite core for EMI/RFI).

Or you can put an isolated dc/dc converter between batt and the cart power.

Something like TRACO TEN60 or equivalent.

Regards,

Ch

[johnpaul215]

Hi,

you mean the inverter is connected on the same battery used also for the cart power?

What is your battery nominal capacity?

You probably need to put  a filter between the batt and the inverter (not just a ferrite core for EMI/RFI).

Or you can put an isolated dc/dc converter between batt and the cart power.

Something like TRACO TEN60 or equivalent.

Regards,

Ch

Correct... all my cart hardware uses the same Optima blue top battery. It's pretty definitely a power issue. I can disconnect the audio cables, and the Mackie still has the "noise". if i unplug the Lectro and PD-6 from the Cart Power, but the cart power is still connected to the battery, everything is ok.

I'm thinking a filter between the battery and the inverter is the next step. any suggestions on what kind to try? would i need something like the Traco for that?

thanks!

[Philip Perkins]

You should look at the AC output of your invertor on a scope and see if there is any hash there or if the output is looking

more like a square wave. 

Philip Perkins

[Scott D Smith]

FYI-

Every inverter I have ever used reflects hash back into the 12 VDC source, no matter how clean the AC output looks. Some are better than others, but they all do it. I would definitely not run any audio gear from the same power source as the inverter without inserting a serious choke and capacitor network between the inverter and the battery.

My .02

--Scott

[Glen Trew]

Is the inverter a square wave type or modified square wave type? I have had Mackie noise issues with the former but not the latter.

Glen Trew

[johnpaul215]

@Scott any suggestion on the capacitor setup? I've done that when building small op amps (to power little monitors in a radio station etc), but not something with this kind of power draw.

@Glen I'm using a: Wagan EL9863 300-Watt Pure Sine Wave Inverter

http://www.wagan.com/htmls/detail-9863.html (though the site is not properly loading any graphics right now).

It's odd because these inverters are intended to run AV gear in a motorhome (or something) as an upgrade to a cheaper inverter..... but the device plugged into the inverter is the one showing the noise. In most normal applications, the inverter would share the vehicle battery with gobs of electrical hardware that has no concern for line noise.

[Glen Trew]

For whatever reason, the Venue receiver rack (like the one I use) is often a factor in this noise caused by using a shared power supply system. I'm less familiar with the PD-6 power issues, but if it shares some of the same electronically balanced output design as the PD-4, then the way it's audio connecting cables are wired can be a factor. I suggest trouble shooting a little further by keeping the Venue and the PD-6 attached to your power supply, then one-by-one remove the audio cables until, hopefully, the noise changes or goes away. Then invesitigate how the cables are wired and alter the grounding scheme of the audio cables. If that fails, another possible solution is the Remote Audio Juicer cable that isolates the power supply from the device it is powering. Trew Audio is currently out of the Juicers, but other dealers may have them in stock. I know of several cases that using the Juicer to feed the Venue system has solved similar noise problems.

I forgot to mention another suggestion: Set your Venue receivers to line level output, and turn off phantom power on the mixer inputs that the Venue plugs in to, which can both significantly reduce power noise.

Glen Trew

[johnpaul215]

Venue is set to do line level outputs, and phantom power is off for the Mackie. I was doing wireless boom so everything came through the Venue.

It's weirder than that.... I can unplug ALL audio cables and still have the noise.

Mackie -> inverter -> battery <- Cart Power <- anything makes noise on the Mackie channels (even with sliders down).

If the PD-6 or Venue are connected to cart power I get noise, if neither is connected to cart power, the Mackie is happy.

I emailed PSC and their educated guess pretty much came down to it being the inverter doing something unusual and bad that they were not used to seeing in other setups.

I tried running the inverter off the Optima battery and the cart power off a much much smaller Bescor battery. Connected all the audio cables between the Mackie, Venue and PD-6 and everything was perfect.

I think the suggestions about isolating/filtering the lines going between the battery and the inverter are probably the solution.

I can't believe I am going through this much effort to use a Mackie board. I think it's a testament to buying something made for location sound and designed to run off 12 volt DC power. The nice thing about the Mackie is that it has the firewire card and I could, in theory, run Boom Recorder on my laptop as a backup multi-track recorder.

[Scott D Smith]

John Paul,

I am out of town at the moment, and will have to look up a couple of the schematics when I get back to my shop. I seem to recall using something like 200 mh chokes with a small value resistor across them, on BOTH the hot and ground, with 4000 Mfd. caps ahead and behind them in parallel. Basically a single order low-pass filter.

You might also check on some of the filters which are sold for hi-end car audio systems, designed to go between the audio electronics and battery system. Although intended more for dealing with ignition hash, they should help in removing the back-fed garbage from inverters as well. I haven't tried these out yet myself, but go for something with some big-ass caps and heavy-duty chokes. Here's one that Crutchfield sells, although it's only rated for 15 amps. http://www.crutchfield.com/p_003S15A/American-International-S-15A-S-25A-15-amp-250-watt.html?tp=2653

The Mackies are known to have very poor power supply filtering, as well as problems with RF pickup. What you are experiencing could be radiated hash getting into the mix buss, as opposed to being induced strictly through the power supply. Try moving the board further from the inverter to see if that improves things at all.

If the noise is being induced from the OUTPUT side inverter, then that's going to need some more serious suppression and some kind of shaping filter. If this is the case, I would start looking for a different inverter, as you are talking about some serious bucks for filtering.

--Scott

@Scott any suggestion on the capacitor setup? I've done that when building small op amps (to power little monitors in a radio station etc), but not something with this kind of power draw.

@Glen I'm using a: Wagan EL9863 300-Watt Pure Sine Wave Inverter

http://www.wagan.com/htmls/detail-9863.html (though the site is not properly loading any graphics right now).

It's odd because these inverters are intended to run AV gear in a motorhome (or something) as an upgrade to a cheaper inverter..... but the device plugged into the inverter is the one showing the noise. In most normal applications, the inverter would share the vehicle battery with gobs of electrical hardware that has no concern for line noise.