How to interrupt +48v DC phantom power

[Jay Menon]

I use a TC Electronic G Natural - the TRS outputs of which will be fried by phantom power.

However, if we switch off phantom power at the mixer, the closed loop hearing aid system will cease to function. Our old SoundCraft mixer has a phantom power on-off switch that applies to all channels simultaneously (you cannot switch it off for one or two channels)

So is there any way to interrupt phantom power please?

[Hugh Robjohns]

Stick a transformer in the way !

So connect the G Natural via a DI box (passive or active) plugged into the console mic inputs, or use a line isolation transformer like the ART Cleanbox2 or DTI boxes plugged into the console line inputs.

[Jay Menon]

Thanks Hugh

It would most convenient for me to plug into the microphone inputs in the mixer (there is an XLR ‘patch bay’ close to the stage), so I’m guessing your recommendation would be a twin passive DI box?

[MarkOne]

Second Hugh’s post about the ART cleanbox (everyone should have one in their gig bag )

But I’m amazed that TC electronics produce a gig centric FX pedal that can’t just deal with phantom power.

[Wonks]

The manual says no phantom, so no phantom it is.

[Jay Menon]

Can I use a line isolation transformer like the ART Cleanbox II (which I believe has TRS outs)

- but plug it into two mic inputs (with 48v phantom power switched on) please Hugh?

I ask because there is a box near the stage which will take 3 XLR inputs (most conveniently) and leads to the mixer at the back of the hall via a snake cable.

[Hugh Robjohns]

The Cleanbox2 (and DTI) use 1:1 transformers and thus the output level is the same as the input level — nominal line level from your G Natural, which may be too hot for the mic inputs of your desk.

In your situation I'd use a dual-channel passive DI. There are plenty to choose from, but if it helps I use a Radial ProD2. Line level in, mic level out. Plug into a stage box. Protect the G Natural from phantom..all boxes ticked.

[N i g e l]

But I’m amazed that TC electronics produce a gig centric FX pedal that can’t just deal with phantom power.

+1 for compatibility but a modern mixer might have a combi jack inputs [xlr/trs] where the phantom is only on the XLR part.

[Wonks]

The outputs are mic level according to the manual (it tells you to connect them to mic inputs on the mixer).

[Jay Menon]

The outputs are mic level according to the manual (it tells you to connect them to mic inputs on the mixer).

That's right Wonks
Balanced outputs on 1/4” TRS jack. These outputs may be connected directly to balanced mic inputs with 1/4”TRS to XLR adapters.

So what do I do?

[Hugh Robjohns]

The outputs are mic level according to the manual (it tells you to connect them to mic inputs on the mixer).

The manual also says you can connect them to guitar amp and interface inputs.

The Specs section gives max output levels as 20dBu/14dBu... I suspect it means +20dBu because the two numbers are for balanced/unbalanced connections, and you'd expect the latter to be 6dB lower.

There's also mention of an Output Range setting with four options of 20/14/8/2dBu, with the latter options being better suited to mic inputs.

I'd have a gander in the menu for output volume options... and set it to the +20dB mode to use with a DI box.

I'm confident it will be perfectly workable via a passive DI box...

[Jay Menon]

Would one of these work please? It's an awful lot cheaper than the radial device...

http://orchid-electronics.co.uk/dual_isolator.htm

[ajay_m]

I've got to be honest and say these devices work pretty well in most scenarios https://www.google.com/search?q=amazon+ ... e&ie=UTF-8

There are a number of vendors selling these on Amazon but I think the actual units are identical. They are stereo devices and I'm using one currently on a Yamaha seqtrak which otherwise introduces terrible ground loop noise into my mixer. Not quite the same scenario of course but the isolation requirements are the same. I put this device through my siglent oscilloscope and the audio performance is pretty good with the natural resonance of the transformer way above the audio range. As with all magnetic coupling devices distortion can start to rise below 50Hz or so. But... They are very cheap and work surprisingly well.

[Jay Menon]

Or this one

ART DTI Dual Transformer Isolator

https://www.soundonsound.com/reviews/art-dti

[Hugh Robjohns]

Yes. Both are transformer line isolators. You get the same output level as the input level.

I use ART DTI boxes a lot for problem solving and for stage isolation duties. The ART Cleanbox2 is the same inside, but only has TRS connections (like the Orchid offering). I prefer the DTI because of its greater versatility.

I've not used the Orchid box, but knowing the designer I have no doubts about it.

The Radial is more expensive, partly for the name, partly for the exceptionally heavy engineering that will last forever, and partly for the very good quality transformer which can take +18dBu at 20Hz without saturating.

The ART DTI is not quite that good — but its not far off.

All transformers are inherently sensitive to loading, so the input impedance of whatever it's feeding can affect the tonality — especially the extreme high-end.

And all transformers are prone to generating distortion artefacts, particularly from high levels below 100Hz or so. This may be welcome (added warmth!), or may not... The better (and more expensive) the transformer, the less the distortion artefacts.

[Jay Menon]

Thanks everyone for explaining things so clearly.

On balance using the TC Electronic G natural is a rather complex affair and for acoustic guitar and vocals it seems better to go with something simple like the Line 6 POD X3 Live or HD500.

I just need a nice vocal plate reverb - the additional bells and whistles on modern acoustic/vocal processes (harmonies, pitch correction etc) are of no interest to me.

I could not however ascertain from the user manual(s). Are the outputs on the line 6 devices 'protected' or will phantom power damage them?

[Sam Spoons]

Just my 2 pence worth but, for me the best thing you can do for a piezo equipped acoustic guitar* is plug it in to a device that has an IR loader built in. It is the only way I have found to effectively remove the dreaded 'piezo quack'. The Rolls Royce of acoustic IR processors is the Tone Dexter but I also have a TC Impulse IR which has a few acoustic guitar IRs onboard and can easily load custom IRs from 3rd party sources. The usual way to send these pedals to a PA is via a DI box of some kind and I use Orchid Micro DIs for this purpose.

[Hugh Robjohns]

I could not however ascertain from the user manual(s). Are the outputs on the line 6 devices 'protected' or will phantom power damage them?

I don't know, but I always assume line outputs are not protected. It's the only safe way...

Personally, I ALWAYS use a DI box (or line isolation box) in every live sound situation. It's not just to protect the device from phantom, but also to protect both the equipment and me from potential electrical faults in the PA equipment.

And for that you must use a DI /line iso box with a good transformer in it (not all active DIs use transformers — beware!).

[Wonks]

I could not however ascertain from the user manual(s). Are the outputs on the line 6 devices 'protected' or will phantom power damage them?

They are line/instrument level outputs, so you'd normally run them into a line input (so no phantom power) if going directly, or into a DI box if using mic inputs (and so negating any risk from phantom power).