Amp DI out and phantom power

[thinman]

I'll be wanting to plug my head into our mixer soon via its DI out as we'll have enough PA oomph but we the phantom power on the desk is only globally switchable and we need the phantoms on for a couple of condensor mics.

Is it likely to be a problem for the heads or do they generally have caps or transformers on the output to isolate any DC?

[BOD2]

It's safest to ask the manufacturer.

In theory it shouldn't but this is one of these things that could vary, depending on how well the DI circuit has been designed.

[budget bassist]

I wouldn't try it mate, they're not designed to work with phantom power, buy a better desk or some dynamic mics.

EDIT: when you put the phantom power on, does it just send the 48v out of the XLR plugs? If that's the case you should be safe to plug it into one of the jack inputs in the desk i'd think. Just buy a new lead.

Edited October 4, 2008 by budget bassist

[warwickhunt]

I seem to recall reading something on TB about Phantom Power frying the DI on 'some' amps. I certainly had no problem up till I read that and wouldn't have even been aware of it if I'd not read that but were I to change my amp (I know this one works OK ) I'd consider buying a small DI box. Take the DI from the amp into the DI box and from there to the desk, that way if there is a problem your amp doesn't suffer. Alternatively as has been suggested use an unbalanced line out or effects send from your amp to the desk.

[obbm]

Make a very short XLR-M to XLR-F lead with the screen disconnected, i.e pins 1. This will isolate the phantom volts negative rail from your amp. The DI lead will get its screen from the mixer.

Be sure to mark the cable clearly and keep it short so it doesn't get used as a mic lead.

[Protium]

[quote name='warwickhunt' post='299733' date='Oct 5 2008, 08:12 AM']I seem to recall reading something on TB about Phantom Power frying the DI on 'some' amps. I certainly had no problem up till I read that and wouldn't have even been aware of it if I'd not read that but were I to change my amp (I know this one works OK ) I'd consider buying a small DI box. Take the DI from the amp into the DI box and from there to the desk, that way if there is a problem your amp doesn't suffer. Alternatively as has been suggested use an unbalanced line out or effects send from your amp to the desk.[/quote]

Or a DI box which runs on phantom power

[BassBod]

From memory, this is a potential problem for some older amps (like my SWR220) but much less likely to cause a problem on anything designed in the last ten years or so (since phantom power has become commonplace). I run a passive transformer DI from a jack output, and connect that to the PA, which blocks it completely. Also has the advantage of never overloading, which seems to happen with a lot of active DIs when you connect a line level amp output.

BB

[charic]

hmm, could have similar problem. Running a line6 di

[The Funk]

[quote name='Protium' post='299824' date='Oct 5 2008, 12:09 PM']Or a DI box which runs on phantom power [/quote]

My EBS MicroBass II does. Bloody love that thing.

[thinman]

[quote name='obbm' post='299771' date='Oct 5 2008, 10:12 AM']Make a very short XLR-M to XLR-F lead with the screen disconnected, i.e pins 1. This will isolate the phantom volts negative rail from your amp. The DI lead will get its screen from the mixer.

Be sure to mark the cable clearly and keep it short so it doesn't get used as a mic lead.[/quote]

Sounds like a cheap and practical way out.

[bassmansky]

as said before dont risk it.

[Tengu]

I run both a TE bass head and a Line 6 guitar amp into our mixer. Phantom power is on to supply the DI box for the other guitarist's amp.

Never had any trouble with either DI.

I did have a little trouble with one Marshall amp that would cause a loud pop whenever it was plugged in to the desk or the phantom power was turned on whilst it was connected. Making up a special lead, as above, fixed that problem.

The advice to check with the manufacturer is absolutely the best.

[pedroferreira]

Use a XLR -> Balanced Jack.
Phantom power only goes through XLR inputs. You get a balanced signal without phantom power.

Pedro

[BOD2]

[quote name='pedroferreira' post='300201' date='Oct 5 2008, 10:53 PM']Use a XLR -> Balanced Jack.
Phantom power only goes through XLR inputs. You get a balanced signal without phantom power.

Pedro[/quote]

That would work but provided you put the balanced jack at the MIXER end and not vice versa (assuming your mixer has a balanced jack input).

Just thought I'd better clarify that !

[pedroferreira]

[quote name='BOD2' post='300340' date='Oct 6 2008, 10:55 AM']That would work but provided you put the balanced jack at the MIXER end and not vice versa (assuming your mixer has a balanced jack input).

Just thought I'd better clarify that ![/quote]

Of course. It could be difficult to put the jack inserted in the Xlr output of the amp

[Thunderhead]

[quote name='BassBod' post='299832' date='Oct 5 2008, 12:23 PM']From memory, this is a potential problem for some older amps (like my SWR220) but much less likely to cause a problem on anything designed in the last ten years or so (since phantom power has become commonplace). I run a passive transformer DI from a jack output, and connect that to the PA, which blocks it completely. Also has the advantage of never overloading, which seems to happen with a lot of active DIs when you connect a line level amp output.

BB[/quote]+1

Those passive "cheap", "old fashioned", transformer DI boxes also sound very nice for instrument amp DIs too - much nicer than any modern active DI, to me. Transformers (even high-grade audio ones) have some limitations which actually make them sound very nice for slightly distorted signals, which the output of an amp often is even if it's not actually clipping. This is one of the reasons valve amps sound so good for both bass and especially guitar, since they all have output transformers whereas solid-state ones generally don't.

I generally dislike active DI boxes entirely except for things like acoustic instruments where they do sound much better, partly because they are capable of reproducing everything cleanly but mainly because they don't load the instrument down like a passive one does (which doesn't matter when the signal is coming from an amp).

Edited October 13, 2008 by Thunderhead

[Ray]

It says in the manual for my Aguilar head that phantom power will not affect the unit and is safe to use.

As has been said above, check with the manufacturer.

[woolleydick]

SWR's are famous for not being protected against Phantom Power - they will fry if attached to it.

[pedroferreira]

[quote name='Ray' post='305426' date='Oct 13 2008, 12:58 PM']It says in the manual for my Aguilar head that phantom power will not affect the unit and is safe to use.

As has been said above, check with the manufacturer.[/quote]

My AG500 is not phantom Power safe. Is is from late 2006.

Since August 2007 they changed that. This was told to be by Mr. Dave Boonshoft:

Hi Pedro,

I sorry, I can see I wasn't clear. We changed the circuit so that the DI is protected in August 2007.
Apparently, between the on-line manual and the paper one, the manual information is not consistent-but the DI is!

What I was trying to say was that we changed the DI so that there is no chance of phantom power damage; but that prior to doing this we have not heard about any phantom power damage on this amp.

I hope this is more clear now. If you think others may have found my answer confusing, feel free to post my reply.

Best Regards,

Dave
__________________
Dave Boonshoft
aguilaramp.com
myspace.com/aguilaramp

[dave_bass5]

I use my MB SA450 connected to our Yamaha desk with the global phantom power switched.

Ive not had any issues but reading this thread makes me think i need to stop using the XLR on the desk.

[Thunderhead]

[quote name='dave_bass5' post='307110' date='Oct 15 2008, 02:21 PM']Ive not had any issues but reading this thread makes me think i need to stop using the XLR on the desk.[/quote]Don't worry, you'd know by now if there was a problem. The damage will most likely occur within a few seconds of the first time you use it, if it's going to.

Why anyone would design an XLR output on an amp that cannot be connected to a system where phantom power is likely to be present, without damaging it, is beyond me - it's just basic bad design. But they do...

Even when phantom power was not 'commonplace', it has always been a feature of some balanced systems and so it could never have been expected that an amp would NEVER be exposed to it if DI'd.

Edited October 15, 2008 by Thunderhead

[dave_bass5]

[quote name='Thunderhead' post='307218' date='Oct 15 2008, 04:40 PM']Don't worry, you'd know by now if there was a problem. The damage will most likely occur within a few seconds of the first time you use it, if it's going to.[/quote]

Cool, thanks.
We only have it on because our drummer uses a condenser mic on his snare.

[charic]

[quote name='dave_bass5' post='307237' date='Oct 15 2008, 04:57 PM']Cool, thanks.
We only have it on because our drummer uses a condenser mic on his snare.[/quote]

that mic must be wrecked by now then

[alexclaber]

[quote name='charic' post='308770' date='Oct 17 2008, 05:17 PM'] that mic must be wrecked by now then[/quote]

The C1000 makes a pretty good (and robust) live snare mic, as do other small diaphragm condensers designed for similar use. I wouldn't want to put any studio type condensers near a drummer's sticks!

Alex

[clauster]

We usually two C1000s as kit overheads but last weekend had one a floor tom - sounded really good