Phantom Power

[bassace]

If I take a XLR cable out of my amp DI and it goes to a PA desk that is sending phantom power out will there be a risk of damage. Any advice gratefully received.

[gillento]

[quote name='bassace' post='870915' date='Jun 18 2010, 05:47 PM']If I take a XLR cable out of my amp DI and it goes to a PA desk that is sending phantom power out will there be a risk of damage. Any advice gratefully received.[/quote]

It depends on your amp.

What does the manual say?

[Bilbo]

Most desks let you turn the phantom power off....... at least that's what I thought.

[Bill Fitzmaurice]

[quote name='Bilbo' post='871148' date='Jun 18 2010, 04:29 PM']Most desks let you turn the phantom power off....... at least that's what I thought.[/quote]
It's usually on or off globally for all channels, unless it's a high end desk.
A transformer or capacitive coupled DI isn't bothered by phantom power, but some DIs inexplicably aren't one or the other, inexplicably as the cost of isolation caps is a few pence. Check with the amp manufacturer.

Edited June 18, 2010 by Bill Fitzmaurice

[Stewart]

Most cheaper desks only allow global phantom on/off (for all mic channels) - and you need it on if you have any active DI boxes or condensor mics.
Higher-end desks usually allow individual selection.

Phantom power *shouldn't* adversely affect any recent/decent amp, but you're not going to find out unless it goes pop.
I've never had any problems (Gallien Krueger) though a couple of venues have complained about hum (which has probably been introduced through noisy phantom power) - it's quiet as a mouse through any of my kit.

Easiest to just use a DI box before your amp for the desk in most cases though - invariably what the sound guy will prefer.
You could always mic your cab...

Edit "Dohhh" Bill got in there first

Edited June 18, 2010 by Stewart

[Mr Fudge]

I am no expert but on our Dynacord desk there are 3 or 4 channels that can be selected for phantom power. I was told that if we miked a drum kit up that phantom power would be good for cymbals. this may have been bollox though and we have never used it.

[chrisba]

I asked Ashdown the same question regarding my Electric Blue combo. They replied that it could damage the amp, so don't do it. This is not true of their more expensive amps.

My sound man gave me a little box ( home-made, I think ) that kills phantom power ( he called it a Ghostbuster )

[Lifer]

[quote name='Mr Fudge' post='871294' date='Jun 18 2010, 10:56 PM']I am no expert but on our Dynacord desk there are 3 or 4 channels that can be selected for phantom power. I was told that if we miked a drum kit up that phantom power would be good for cymbals. this may have been bollox though and we have never used it.[/quote]

Phantom power is only used to power mics/di boxes, so would depend entirely on the mics used! Generally condensor mics (most of which require phantom power) are used as overheads so kind of right. AKG C1000 for example, good cheap overhead for drumkit and needs power, either from batteries or phantom from a desk.

[Tinman]

In the manual for my Trace it says it's fine. Have a look in the book first

[gafbass02]

I've wondered this myself and had conflicting reports. Anyone know the score with little mark 2?

[ahpook]

it's not a bad album, but i prefer radiator

[bassace]

Thanks for the replies, guys. I asked the question because the band I play with is doing a lot of jazz festivals at the moment and set up time is very short - line check if we're lucky but no sound check - we are following the last band on. We don't use our PA but whatever is at the gig, usually supplied by 'professionals'. So I'm usually in a 'plug and play' situation. One way and another there is a chance that phantom power might be sent back from the desk to my amp DI, and I'm sure this may have happened before, but I want to control the risk if I can. Thanks for the well-meaning advice but of the three amps I regularly use - EA, AI, GK - none of their manuals mentions much about the DI socket, less so about phantom power. I emailed Acoustic Image and they sent back advice to the effect that the DI on the Clarus is designed to accept phantom power but they've been having a few failures recently so better not to(?!)

So I'll either get an outboard DI on or put a mic onto the double bass.

[warwickhunt]

I had a Tech Soundsystems amp (one of their most expensive ones) and not having had problems in the past with previous amps and Phantom Power, I hooked it up to our desk which had the PP 'on' for the drummers mic's; it simply fried the DI... not a great feeling and necessitated the use of a line-out to the desk which worked OK! As BFM says for what it costs to ensure this doesn't happen it seems ridiculous that [u]all[/u] amps don't have the DI isolated.

Edited June 25, 2010 by warwickhunt

[thinman]

I was worried about phantom power with my amp too.

OBBM, who posts on here, suggested the following that works well and is about as cheap as you can get:

On a XLR pins 2 and 3 are both at +48v, i.e. common, relative to pin 1 ground. If you simply disconnect pin 1 there's no circuit for the phantom voltage any more (and it also cures any earth loop issues).

The signal out is carried by pins 2 and 3.

I made a short tail lead with pin 1 disconnected and it does the trick nicely.

[bassace]

[quote name='thinman' post='878792' date='Jun 27 2010, 01:22 PM']I was worried about phantom power with my amp too.

OBBM, who posts on here, suggested the following that works well and is about as cheap as you can get:

On a XLR pins 2 and 3 are both at +48v, i.e. common, relative to pin 1 ground. If you simply disconnect pin 1 there's no circuit for the phantom voltage any more (and it also cures any earth loop issues).

The signal out is carried by pins 2 and 3.

I made a short tail lead with pin 1 disconnected and it does the trick nicely.[/quote]

Thanks thinman, that's excellent advice. I've been on to OBBM and he has explained the science and is making me up a 1m tail, suitably modified.

[guybrush threepwood]

[quote name='gafbass02' post='877468' date='Jun 25 2010, 03:31 PM']I've wondered this myself and had conflicting reports. Anyone know the score with little mark 2?[/quote]
I asked Mark bass and they said it will be fine- it blocks phantom power

[flyfisher]

[quote name='chrisba' post='877352' date='Jun 25 2010, 01:20 PM']I asked Ashdown the same question regarding my Electric Blue combo. They replied that it could damage the amp, so don't do it. This is not true of their more expensive amps.[/quote]
I've got an Ashdown Mag Evo II with a DI output, so I checked the manual but it said nothing about phantom powering.

I emailed Ashdown asking them if connection to a phantom powered input could damage the amp and received the following reply:

[i]The DI output is indeed protected against phantom powering… It incorporated blocking capacitors in each line.[/i]

Frankly, I'd have been surprised if the DI output wasn't protected against phantom powering; (a) it's trivially simple and cheap, ('b) it's good design practice to protect any input/output against reasonable abuse and external faults.

Pity they didn't spell it out in the manual though.

Edited June 29, 2010 by flyfisher

[Bill Fitzmaurice]

[quote name='thinman' post='878792' date='Jun 27 2010, 08:22 AM']I was worried about phantom power with my amp too.

OBBM, who posts on here, suggested the following that works well and is about as cheap as you can get:

On a XLR pins 2 and 3 are both at +48v, i.e. common, relative to pin 1 ground. If you simply disconnect pin 1 there's no circuit for the phantom voltage any more (and it also cures any earth loop issues).

The signal out is carried by pins 2 and 3.

I made a short tail lead with pin 1 disconnected and it does the trick nicely.[/quote]
That might lead to grounding issues with some boards. The better option is to wire 1uF 50v tantalum capacitors in series with the pin 2&3 leads, and they're so small that they'll fit inside an XLR shell.

[BassBod]

I've always been concerned about this - my old SWR220 gets used most for festivals (as a preamp) and its of an age to be vulnerable to phantom power - although it may be proteced, I've never looked to see if there are any capacitors in there.

It seems the only way to be sure is to run a passive DI from a preamp output - I've never had any problems when dong this (noise, distortion) but I have had a few issues with using the DI outputs on modern amps (EA,GK Eden) either hums and buzzes (ground lifted or not) or level mismatches with desks.

For upright I use an active muting DI from Orchid Electronics (about £65?) which runs from phantom power...sort of turns a potential problem into a blessing! And having a footswitch to mute your double bass is a good thing when the engineer starts blaming you for all the feedack he's got.......

[gafbass02]

[quote name='guybrush threepwood' post='881128' date='Jun 29 2010, 04:46 PM']I asked Mark bass and they said it will be fine- it blocks phantom power[/quote]

Ace, thanks bud, good to know