How easy is it to fry a pre?

[thedude400]

I just got a DMP3 and I used it once or twice already with my mxl v67g and an oktava mc012 and it worked fine. I'm still waiting on my interface in the mail so I just plugged in my Sennheiser phones into the DMP3 output. Today when I tried again it didn't work, neither channels are working, but the DI's work ok.

Here are the only things I've done with it. I took stereo Male XLR to TRS and plugged it into the back of my patchbay. That way I can just plug a Female stereo XLR to TRS from the Microphone into the front of the patchbay and don't ever have to fiddle with the back of my pre's. I've also plugged my phones into the DMP3's output and still no signal so I don't think its a broken patchbay signal (even though its a behringer patchbay ). I also ran the output through a Lexicon effects unti. I checked all the simple user-error possibilities like making sure the phantom switch is pushed in, checking the mics and cables.

I may be completely missing something but if I'm not, is it possible that I fried the pre's? It seemed to go wrong after I used the Mic>Female XLR-TRS>patchbay in>patchbay out TRS-Male XLR>DMP3, was this a mistake?

 

[mshilarious]

That should have been OK, but it sounds like you might be having a problem with phantom power. Do you have a dynamic mic that you can try instead?

Routing phantom through a patchbay should be OK as long as the patchbay is balanced. You should also try plugging the mic directly into the pre, just to remove the patchbay from the chain.

Finally don't forget to try a different mic cable!

 

[thedude400]

The DI's disable the Pre's. Thanks MS , though I probably coulda figured that out without posting . But if someone wants to post some No-No's with pre's that could potentially damage feel free (other than plugging in the toaster and coffee machine). Since that is the subject of the post.

 

[mshilarious]

A pre will normally have circuit protection on its inputs and limiting resistors on its outputs and phantom power to prevent damage. As long as you don't exceed the ratings of those components--probably in the 50 to 75V range on the inputs--nothing should blow up.

If a pre's output isn't designed to drive headphones, you might get really bad sound in the headphones, but again it shouldn't damage anything.

 

[dgatwood]

If a pre's outputs aren't designed to drive headphones, you probably won't hear anything at all, or else not very much. That said, headphones are very low impedance compared to what a pre is designed for. I suppose there's a small chance some idiot didn't put in short circuit protection on the output.

That said, it's easy to fry a pre. Just hook up a power amp's output to the instrument input.

 

[Big Kenny]

Easier to fry the phantom than the pre. Plugging and unplugging with phantom engaged will burn some pres

 

[andydeedpoll]

Easier to fry the phantom than the pre. Plugging and unplugging with phantom engaged will burn some pres

saying that, what about switching the pre on and off altogether? i've often wondered this with my mixer - whether it could damage the mics or the mixer to have the phantom on, switch off the mixer and then switch it back on.

it doesn't sound like something i'd risk doing anyway. but it'd be nice to know whether i was being this careful for no reason...

Andy

 

[mshilarious]

saying that, what about switching the pre on and off altogether? i've often wondered this with my mixer - whether it could damage the mics or the mixer to have the phantom on, switch off the mixer and then switch it back on.

it doesn't sound like something i'd risk doing anyway. but it'd be nice to know whether i was being this careful for no reason...

Andy

It shouldn't . . . but I always turn off phantom before plugging or unplugging microphones, it shouldn't hurt the mics or pre, but it can make a nasty spike in your mains. Better safe than sorry.

 

[MadAudio]

At my last job, a coworker killed an AKG mic by disconnecting it without turning off the phantom power. I'd be nervous about "hot swapping" through a patchbay, myself.

 

[soundchaser59]

At my last job, a coworker killed an AKG mic by disconnecting it without turning off the phantom power. I'd be nervous about "hot swapping" through a patchbay, myself.

You are better off to just not do it. Always turn the phantom power off first, before you change anything with the mixer or the mic connections. Phantom is 48v, and when you just pull the plug like that, there is an arc. Arcing is the worst thing that can happen to your gear. It wont withstand that forever......

 

[sound125]

I've seen a few of the walwart based pres damaged b/c someone has swapped out the transformer with one that has a completely different rating. The amperage rating being the most crucial factor, versus a slight variance of 1 or 2 volts, which usually won't hurt things.