The 48V Phantom Power menace fried my preamp

[ialma]

Hello everyone,
happy owner of a boutique pedal, DI/Preamp whose brand I won't mention for the reasons you can imagine.
I hooked it to a XLR cable and the lovely soundguy had phantom power on, so he managed to fry a chip on the board of the preamp.
Just wondering if anyone skilled here has schematics for a small circuit I would add inside the shell of the preamp to avoid further problems.
No, I don't want to use anything like this:
Invalid Link Removed
or the Triton Phantom Blocker.
Any idea anyone?
@agedhorse maybe?
Best!

 

[agedhorse]

You are better off using the isolation transformer... or replace the preamp-DI with something that has phantom power protection built in. I can't imagine in this day and age, any product intended to be used on a mic line that is not phantom protected.

Have the original builder correct or update his product.

 

[Hoochie Coochie Man]

Some boards don't have the capability to turn the phantom power on and off individually. One switch turns it on or off for all channels.

 

[silky smoove]

I understand your reluctance to name the pedal in question, but it would be much easier to offer meaningful suggestions if we knew what was being used. It might also point to other solutions if it’s a known issue with a particular piece of gear.

 

[logdrum]

Unless you owe this builder a big one like saving you from getting shot, it's fair to mention the brand. This will prevent others from future mishap and let this boutique maker improve their product. State the facts even if you are overwhelmed emotionally. It can only lead to greater good.

My Demeter is vintage probably early 80's is already phantom power proof,. Can't imagine anything modern that isn't.

 

[bigdaddybass12]

I can’t answer your repair question, but I like to use a direct box to keep soundboards out of my equipment

 

[Chris Chong]

Pls let us know which preamp DI is that, so the rest of us would be cautious.

 

[Wasnex]

My guess is Avalon U5. Perhaps no so well known, but the U5 is not considered safe with phantom. I would use an add on phantom blocker rather than modding a U5.

 

[darwin-bass]

I always use a direct box even if the pre has already out. This is one reason why. Ground lift and pad are other reasons.

Radial for the win.

 

[Geri O]

You have a consensus on how you should proceed, but if anyone is wondering, the phantom power is not the menace here.
(And I’m not sure how you meant the post title to be taken, so I made an ASSumption….)

There’s no excuse for a boutique preamp or anything else to not have phantom power protection.

I was sure to check both the REDDI Tube DI and the Khan VTDI tube DI for such protection.

 

[newfuture]

Agree with all the above. For a few decades now, there's no excuse for not having phantom protection on an XLR output intended to connect to a mic preamp.

Isolation transformer, a DI, or find another preamp to use. If you really want to use the existing pre, and there's room, and you know what you're doing, you could add a transformer to the XLR output internally

 

[WI Short Scaler]

Some boards don't have the capability to turn the phantom power on and off individually. One switch turns it on or off for all channels.

That is how my Mackie ProFx16 is set up. Only my mic needs phantom power.

When I bought it I asked if I could plug my Rumble bass amp straight in from the DI out, was told yes and have done it that way as long as I've owned the board. Never had an issue and never really gave it a 2nd thought. I bought my Mackie speakers and mixer from the same store.

 

[S-Bigbottom]

Big design flaw. Phantom will be introduced to you again, guaranteed. It is very common on the line.
Likely Phantom has been sent to you all this time, you just did not know until the new pedal took a hit.

Did the Maker say it was not Phantom protected?
Could have been something else that caused the blow.

 

[ialma]

Agree with all the above. For a few decades now, there's no excuse for not having phantom protection on an XLR output intended to connect to a mic preamp.

Isolation transformer, a DI, or find another preamp to use. If you really want to use the existing pre, and there's room, and you know what you're doing, you could add a transformer to the XLR output internally

Yes, there is space and I would love to add a circuit inside to block the 48v. Found few schematics online but not sure which one would fit best.

 

[Podgorny]

Phantom power does not provide a ton of current (10mA max iirc). Not typically sufficient to destroy things if they are built correctly (and IMO anything with an XLR-M connector should be built with the EXPECTATION that it will see 48v). That said, my preference would be for a transformer-balanced output on any device that you will be connecting to gear of unknown provenance/functionality.

 

[newfuture]

Yes, there is space and I would love to add a circuit inside to block the 48v. Found few schematics online but not sure which one would fit best.

It could be as simple as some coupling caps or a transformer (which I would do). You could go as minimal as a neutrik 1:1 transformer as intended for XLR barrel adapters, or as expensive as you wanted to with Jensen, Lundahl, cinemag etc, or find a vintage UTC (did this in a couple homebrew DI's and tube preamps).

 

[eniac]

I would definitely go with an isolation transformer that offers full isolation. My favorite is the Radial IC-1.

In previous builds I've used coupling caps with resistors, and even zeners along with them for clamping the initial voltage spike at connection time. But the suitability of different implementations depends a lot on the circuit that needs to be protected -- its specs, what "mischief" it's designed to withstand at its output, and so on. With my stuff, everything was/is known. But with 3rd party equipment, it's often not knowable. So, that's another benefit of the transformer solution.

 

[ialma]

Unless you owe this builder a big one like saving you from getting shot, it's fair to mention the brand. This will prevent others from future mishap and let this boutique maker improve their product. State the facts even if you are overwhelmed emotionally. It can only lead to greater good.

My Demeter is vintage probably early 80's is already phantom power proof,. Can't imagine anything modern that isn't.

Missed your post sorry.
The fried preamp is a 3LEAF Enabler, Spencer told it has no protection against 48V.
He provided repair instruction, I asked him to add a protection circuit if I sent him the pedal.
Never got an answer.
Don't think I'll ever consider the brand again, nobody likes to be left in the cold by customer service.

 

[Geri O]

Missed your post sorry.
The fried preamp is a 3LEAF Enabler, Spencer told it has no protection against 48V.
He provided repair instruction, I asked him to add a protection circuit if I sent him the pedal.
Never got an answer.
Don't think I'll ever consider the brand again, nobody likes to be left in the cold by customer service.

Hate to pile on, but I had similar experiences with a bass preamp installation.

Not doing that again.

And to not be bothered with adding 48v protection sounds typical.

 

[ialma]

Just a small update. The Enabler is still fried in its box, I'm more than p**ed off and I'd like Spencer to answer and provide a decent solution for a problem that could have been avoided if considered beforehand. Asked him to repair the pedal (and to check it out to see if the spike caused further damage).
No answers.