IDIOT ALERT: Accidentally sent phantom into EZ1290 [SOLVED]

The title says it all, really. Working with my ez1290 into my Apollo unit, had it on mic mode so I could control the preamp remotely from my tracking room. But alas! My patch bay was set up incorrectly and wasn't bypassing the ez1290! I realized it almost immediately and turned the phantom off right away. Still passes audio, but it's very fuzzy and crackly

The insides look spotless still, so my biggest fear is that a trafo is fried. I also have the jlm go between between my input jack and input trafo.

If it is a transformer issue, it's not too big of a deal, since I'm buying transformers for the next three channels soon anyway, I can always pick up some replacements, but I'd like to know for sure as they're expensive.

Another note, there was no smoke so far as I saw, and again, everything looks pristine inside still. Audio is passing, but very poor quality. Any help in diagnosing the problem would be very much appreciated!

*UPDATE*

The problem was actually not phantom power related, but due to some sort of faulty ground caused by a loose screw on the 2N3055G transistor. Unit is back up and running better than ever!

No idea what an EZ1290 is.  Leads to 10 pages of search hits, none with any info. 

Also unclear, you put phantom into the output of the 1290?  If the 1290 has an output transformer, that should isolate and it would be fine in most cases.  But it's not clear. 

The EZ1290 is a preamp, my apologies for not making that clear in the post.

The bigger issue is that I sent phantom to the INPUT of said preamp. It does have an input transformer and an output transformer.

Update on my issues.

With the help of a friend, I just was testing it out. It still passes signal, actually quite clearly when we initially fired it back up. I have a trim pot installed, so we were working our way through the gain stages. The rotary switch occasionally popped which seems normal for the unit, however at random spots we would hear a burst of static that lasted about a second before clean signal began passing again.

We kept testing it and tested the pad and polarity switches on the go between, which seemed to work just fine. In an effort to leave no stone unturned, we turned the pad on, lowered the trim, and turned gain to the max. Again, no problems, but when I began lowering the gain again, the static came back, this time persistently so we had to shut the unit off. The persistent static is what I had experienced before making the original post.

To be doubly clear, this unit is not very old, but has never give me any issues until I accidentally introduced its input to phantom power. Maybe the two are unrelated, but it seems unlikely. I'll search the forum in the meantime for similar experiences, but any help would still be appreciated.

Any problem you have should be unrelated to phantom power.  What you did is no different than using an external phantom supply, unless there's something really strange with the design. 

Okay, that's a good sign. Thanks for your replies.

But I think I may have confused myself a little bit, here was the signal chain:

Apollo 8 (Providing phantom power) ==> EZ1290 pre ==> Microphone

So I guess the phantom WAS fed into the output of the unit?
Sorry again, I got a little confused.

Still, I think you might be right. The phantom power may not have caused the issue.

It still seems strange that I would start having problems after that though. Any ideas what could be causing the problems?

I am still trying to follow what you did. How did you get phantom to the ez1290 input?  how is the ez1290 very old? it's a DIY build that is pretty new. Please explain.

As far as I know the EZ1290 pre, as a NEVE clone, should have an input and an output transformer.
It doesn't care about phantom power at the input, and it doesn't care about phantom power at the ouput.

I'm trying to understand the signal routing, and it makes no sense, or I'm missing a coffee...

You had a Mic, connected to the EZ1290 INPUT, and then the 1290 OUTPUT connected to a soundcard INPUT with Phantom power enabled. Right?

So the 48V was applied to the OUTPUT of your preamp, not the input (maybe you connected the input of the soundcard to the input of your preamp?, or do you have a soundcard which send 48V in the outputs? )

Whatever you did, there's no way P48 can fry a transformer.
Can you do the same test with a different preamp? And with a different input?
I understand you have connected the output of your preamp to the mic input of your soundcard. This may have fried the mic input, if the output of the preamp was hot.

Hi again everyone, thanks for all of your replies so far. I'll try my best to clear everything up in this post now. Sorry for the confusion, I realize that this setup is fairly confusing.

So, when I accidentally sent the phantom power, this was the setup. I had a condenser mic going into the EZ1290 preamp which then went into my Universal Audio Apollo 8. The Apollo is my interface, it also has 4 built in mic preamps capable of phantom power and the like. The way my setup is, if I want, I can bypass the EZ1290 and have the mic go straight to the Apollo preamp so I can control the preamp settings remotely from my control room. The default setting for my studio though has the EZ1290 between the mic and the interface, so I had forgotten to bypass it with a patch cord when I sent the phantom power signal.

From your replies so far, it seems like the phantom power shouldn't have done any harm at all to the preamp since it has transformers at both input and output. Still though, this problem that I described in my second post is a new one that didn't really reveal itself until very recently. It seems like it might be a problem with the switch? I checked the solder pads already, but I'll double check them again just in case.

Thanks again for your help everyone, I really appreciate it. If you have any idea though what the actual cause of these issues might be, don't be afraid to share your thoughts, because I'm not sure what the problem could be.

Also! I know that the input of the interface is not the issue, as I was using it with a different preamp later in the day and having no issues.

O.k. that makes more sense now.  As he others have said phantom power will not effect your unit due to he transformers.
You are fine and did not cause any issues. It is purely confidential that you now have an issue after this happened.

You said you bypass the EZ1290? How exactly? If it was a patch cable that you physically pull out, it could be that when you pulled the jack out, one signal contact momentarily had +48V and the other was grounded. That would put 7mA through the secondary of the OT. By itself that probably wouldn't do anything either but there might be an inductive kickback that could be a couple hundred volts.

Thanks for the replies, everyone. Glad to know that my transformers are fine.

squarewave said:

You said you bypass the EZ1290? How exactly? If it was a patch cable that you physically pull out, it could be that when you pulled the jack out, one signal contact momentarily had +48V and the other was grounded. That would put 7mA through the secondary of the OT. By itself that probably wouldn't do anything either but there might be an inductive kickback that could be a couple hundred volts.

Click to expand...

I do bypass it via patch bay, but in this instance I had no patch cables in it. Which now that you say that, I'm glad I didn't, because my first instinct probably would have been to pull the cable.

squarewave said:

there might be an inductive kickback that could be a couple hundred volts.

Click to expand...

Not likely. Unless the xfmr is disconnected from its source. That may be the case if the unit is turned off.

Hi everybody,

First off, thanks to everyone who replied and let me know that the phantom power was not the cause of my problems. Once I figured that out, I dug through the official EZ1290 thread again and found some people with similar issues. As it turns out, the bolts that couple the 2N3055G transistor and heat-sink to the PCB had been shaken loose by the vibrations from my monitors. I retightened them and put on some loctite so they wouldn't move around anymore. Also, for good measure, I added a bit more solder to all the switch pads just in case one was faulty.

tl;dr The problem was a loose screw, and now my preamp is working as it used to.

emrr said:

No idea what an EZ1290 is.  Leads to 10 pages of search hits, none with any info. 

Click to expand...

Doug, first page of hits has all the info:

https://groupdiy.com/index.php?topic=22828.0

The 1290 is the Mic Pre circuit in the Neve 1073 and 1084 console modules. Both the 1073 and 1084 have Mic Pre + Filters + EQ
It's the most famous Neve mic preamp circuit and the most praised.

The EZ1290 is a pcb and project made by Madrianse to make it easier to DIY the 1290 mic preamp, it's one of the most popular Neve type projects in this forum

It has a transformer input, 3 discrete amplification stages and  a transformer output.

Transformers for this project nowadays are made by Carnhill
The originals used Marinair transformers, and some had StIves input transformers.
Carnhill bought St Ives.