Eletrical damage to mixer and equipment. Suggestions?

Discussion in 'Consoles / Control Surfaces' started by AngloSaxophone, Jun 12, 2012.

  1. AngloSaxophone

    AngloSaxophone Active Member


    I had a disaster last week while recording and I'm curious if anyone has a suggestion on what went wrong.

    I was using the PreSonus Firestudio recording system. For inputs I had 1 bass amp, 2 guitar amps, three drum mics, and a small PA system. I was outputting from the Firestudio mixer to a PC with firewire. We had all this equiment distributed to a few different circuits in our house.

    So we had everything connected and then we plugged in the mixer. This is when disaster struck. There were highly visible blue sparks zapping the back of the mixer and the computer. We quickly unplugged everything. The Firewire express card on the PC was fried, and we replaced it. The mixer was also ruined, luckily we had insurance on this and got it replaced.

    Then disaster struck again. This time we played it extra cautious and distributed the equipent to different circuits in the house and also used surge protectors on everything. I had a moment where my foot was touching the 1/4" output line from the PA and when I touched the metal casing of the PreSonus mixer I could feel a little shock. I should've stopped there, but I thought my mind was playing games on me. We plugged everything in again, and when we turned on the mixer, there was visible smoke from not only the mixer but also the bass head and PA system. WTF?!?! The bass and PA were unusable and two of the inputs in the PreSonus were fried.

    Does anyone have ANY idea what could be causing this? I tested the voltages on all the outlets in the house successfully. I mentioned this to someone at a repair shop and they suggested it might be a ground loop (not sure what this means). I've just never experienced anything like this before when recording. Am I doing something wrong?
  2. dvdhawk

    dvdhawk Well-Known Member

    Sorry to hear that, that sucks!

    When you say, you "tested the voltages on all the outlets in the house", how exactly did you do that?

    If you're welding, I'd bet the farm either one of the other outlets in the house is wired incorrectly, or an extension cord if you used one or more. Something is wired wrong - either Hot to Neutral, or worse yet, Hot to Ground.

    If you tested the voltages by sticking the probes from a voltmeter into the hots and neutrals of the receptacle only observing the voltage reading that's only a partial test. You need to observe the voltage from hot to neutral, hot to ground, and neutral to ground to be thorough on each receptacle. [you may very well know this, but for anyone else who might stumble across this thread in the future] On a standard 15-amp grounded (3-prong) Edison receptacle, the smallest slot is the hot, the slightly larger slot is the neutral, and the ground is pretty obvious. If you don't have a receptacle tester, you should get one.

    And I'm sorry to say - for future reference, you could easily run almost any home recording gear and a small PA on a single 15 or 20 -amp circuit as you would find in most homes. - Two circuits at the most. Pulling everything from all over the house introduces the potential for things like this and more ground loops etc.

    Do some more testing and let us know what you find.
  3. AngloSaxophone

    AngloSaxophone Active Member

    Thanks for the quick reply!

    I tested the outlets both with a recepticle tester and by verifying 120V on each outlet and power strip. We weren't using any extension cords. Everything checked out. I did this before the second "burnout".
  4. dvdhawk

    dvdhawk Well-Known Member

    Is there a "polarity" switch on the bass amp or guitar amps, like you would find on an older amp that originally wouldn't have had a grounded plug?
  5. matthewfreedaudio

    matthewfreedaudio Active Member

    Los Angeles
    You asked "Am I doing something wrong?"

    Well, obviously you are. You have electrical wiring problems in your place. Call an electrician.

    Your recording gear may also be faulty. Have a qualified electrician check them out and have the questionable pieces inspected at a musical instrument repair shop.

    Production Sound Mixing for TV, Film, and Commercials.
  6. DrGonz

    DrGonz Active Member

    Phoenix, AZ
    Okay lets pretend that you have all your Hot Neutral Ground lines in your outlets of your house wired correctly... So you have a bass amp, 2 guitar amps, a PA system, a mixer, Presonus Firestudio and a computer all plugged into some/one outlets. Or maybe your all scattered around the house... I don't know... You say on your posting that your all on different circuits the first time it happened then to be safe the next time your all on different circuits again. So, I would guess the first time you all were plugged in the same room, but the next time you all took more precautions. 15 amp lines will either blow a fuse or trip a breaker depending on the year of the house and wiring yadi yadi yadi. So, maybe you have an un-fused line running through your house? That can cause fires and all sorts of stuff to happen. CALL AN ELECTRICIAN AND STOP KILLING YOUR GEAR AND PUTTING YOUR OWN LIVES AT RISK!!!

    Okay lets say that's not what happening then... Neutral is a type of ground as it is the point that draws the current or voltage back from the hot line. When you disconnect something you remove your negative terminal first as to avoid a spark or discharge. So, lets think here... AC: amperage = wattage/voltage... So, a bass amp that has 400watts is equal to>>> I = W/V... So, look at the fuses in your appliances and think hmmmmmm.....??? I have guitar amps that I work on all the time Fenders, Roland, Marshall, Traynor, Carvin, Peavey... you get the idea. Most have fuses from 1 amp up to 5 amps. So, a 400 watt amp draws 3.3amps = 400w/120v. Then you add two 100 watt guitar amps and maybe a 25 watt mixer... Totaling another 1.86 amps. So now we have about 5.2 amps on this one circuit. Lets say the the PA system is about 300 watts (which is just a guess) then we now have a total of 7.7 amps running on this one circuit breaker that can reach as high as 15 amps. So, lets say the computer has a 500 watt power supply, so lets add another 4.2 amps to that... about 12 amps currently on a 15 amp circuit and we are still in the clear. So moving around the house to different outlets is not the problem in my opinion.

    So, looking at the specifications of a Presonus Firestudio device I read>>> "This mic to line boost is generally a preamplification of over 400 times the voltage of the original mic level signal." That is significant is it not? I mean really what the Hell does that even mean? I am not really an authority on this at all but reading that one statement it makes me wonder about ohms law. I also read this statement as some form of sales man ship of this device to the people that will buy it... That meaning who knows exactly what they are saying and if any of it is really true. Now, take all of your ideas and shake them at this one statement... "This mic to line boost is generally a preamplification of over 400 times the voltage of the original mic level signal."

    How are you sending each amplifier into this device? Give us WAY more information as to help you in this situation you find yourself in... And stop ignoring electrocution through your input/output cables connecting these devices together. My thought is that something more needs to be said about how you are connecting all devices together as to make more sense out of your situation.

    ADDED Edit: "I had a moment where my foot was touching the 1/4" output line from the PA and when I touched the metal casing of the PreSonus mixer I could feel a little shock. "

    Look at this obvious problem in your signal foremost. Get rid of the PA and see if that is the problem and examine what you are really doing on this stage of the output of this device. Line level voltage multiplied by 400 times seems to be a problem in my opinion or maybe I am just stoopid!!!
  7. djmukilteo

    djmukilteo Well-Known Member

    Rainy Roads WA USA
    WOW!...So just to clarify...inputs 1, 2 & 3 with 3 microphones in front of your 1 bass amp and 2 guitar amps?
    Then you had inputs 4, 5 & 6 which were 3 mics for the drum set....
    And were you running something like a line out from the PA system into the mixer??...or were you just using the PA for stage monitors?
    What kind/brand of PA system was it?

    So everything happened at the back of the Presonus mixer right?
    That sure sounds like you fed something pretty high voltage or high current into the mixer inputs.
    Or you got an open hot 120VAC wire somehow touching the mixer!

    Again what microphones did you have plugged into the two inputs that fried?
    And if you were micing the bass cabinet how was the bass head amp or the PA system tied into the mixer?....you didn't somehow connect those amp outputs directly to the mixer or something...??

    The only other thing would be a huge short inside the Presonus, because that seems to be the source of the flames and sparks....
  8. Kapt.Krunch

    Kapt.Krunch Well-Known Member

    Inputs? Direct or mic'ed? Mic'ed inputs would have no physical connection to another device, so anything mic'ed won't cause that. That leaves anything directly connected as possible culprits.

    A "few different circuits"? As already mentioned, circuits...or even individual receptacles...can be wired incorrectly. You could have a problem if something is directly connected with the hot and neutral wires crossed on one. Also, it is "possible" that different circuits are running slightly different voltages, creating a voltage difference between two connected devices. As mentioned, you need to properly analyze the circuits. You may even find some weirdness with voltage between ground and neutral.

    Something about all that doesn't make sense. If it were distributed to different circuits when it blew the first time, why would it seem a good idea to do that again? And...what possible scenario could cause your "foot to touch the 1/4" output line from the PA"...while you were touching the mixer? Just wondering. That sounds weird.

    Was the bass direct from a bass amp "preamp out"? Apparently, the "PA system" was? (Hopefully, they were "Pre-out" or "Line out"...and not "Speaker out"?)They had to be, or they wouldn't have been electrically connected so one could take out the other. ANYthing that was connected directly could have caused it. Maybe something in something went bad the first time, and every single piece of equipment that was to be directly-connected wasn't tested fully to be sure none was bad when you plugged them all back in?

    You should have only connected the new interface to the computer, and tested to be sure that was OK. Then, you should have plugged in another device to power it on...but NOT connect it until you checked the voltage potential across both devices with a voltmeter....AFTER you tested each individual unit for proper operation.

    After a catastrophic failure like you had, you should NEVER just plug everything back in together, and apply power.

    I suspect you had something wrong, it blew things up, you reconnected everything without checking EVERY possible cause...and a part that was still bad made it worse? Or, you are running bad voltage differentials/shorts/etc. from different circuits.

    Hmmm... just extra long 1/4" connection cords, or mic cables...and the amps, etc. in different rooms to be close to all those different circuits throughout the house? Not that it really matters...it just sounds odd that all this is connected to a bunch of different circuits without extension cords.

  9. djmukilteo

    djmukilteo Well-Known Member

    Rainy Roads WA USA
    I'm pretty sure the OP took amp outputs and plugged them directly into the mixer (both times).
    That would do it right there....only explanation I can think of....and a very common thing I've seen with people who don't know. That's why I asked about what was plugged into what!
    I don't think it's the AC power because everything was fine until the OP plugged the mixer in....then BAM! duh

    Everything went right through the mixer and overloaded the mixers PSU the wrong way, took out the FW card right back to the PC card. And then the second time it came back through the bass amp and PA.
    So you have to ask the question....how could that happen if they weren't connected directly to the mixer?!?!
    And what was on the two inputs on the mixer that "fried"....facepalm
  10. AngloSaxophone

    AngloSaxophone Active Member

    No the bass amp head, guitar amp, and PA were plugged directly into the mixer. There was a Beta 52 micing the Bass drum, a codenser mic overhead of the drums, a condenser for the snare, and a condenser for the other guitar amp. I cannot remember the model of these mics as they were borrowed from a friend.

    The inputs that were fried were the bass head and the PA system. They were plugged into the mixer via their line outs. After this whole ordeal, the PA, bass head, and the guitar amp that were plugged directly into the mixer were all fried as well.
  11. AngloSaxophone

    AngloSaxophone Active Member

    We were all excited about jamming, something we only do twice a year, and definitely didn't think things through as well as we should have. Hindsight is always 20/20. We had run the cables from the equipment to the mixer and I had them laying on the ground near the mixer while I was plugging them in. I had plugged in a couple inputs, (I can't remember which) when I felt the jolt.
  12. AngloSaxophone

    AngloSaxophone Active Member

    Please talk more about this. I'm a very amatuer producer, if you haven't been able to tell, and it sounds like this may be what went wrong.
  13. djmukilteo

    djmukilteo Well-Known Member

    Rainy Roads WA USA
    Well many amp "head" units have a "line out" that is actually for additional speaker cabinets to connect to and not really "line out".
    The line out you may have used was actually an amp out so your talking a lot of power there!
    Same with the guitar amp or the PA. Sparks are gonna fly doing that! And it sounds like that's exactly what happened.

    So first time through you fried the mixer inputs and power supply and it went through the FW of the mixer and took out the PC board with it. Then you only checked the 120VAC that all looked fine. Got the mixer fixed and didn't change anything and.....fried it again but this time it took out the mixer and the amps...ya never know which direction it will go when something blows...it will for sure take out as much as it can...duh
    I'm sorry you had to learn this the hard way!...it's no fun doing that with your nice new stuff...it's a hard lesson to learn! Are you able to get it all repaired or whats the status now?.....

    I don't think you mentioned what model PA amp, Bass amp and guitar amp were you using or what the label was on the units you hooked up directly to the mixer?
    If you list the models and what you connected to....then I can look up the specs and see what you did wrong.
    Bottom line is you plugged an amp out from one or more of those amps into the mixer inputs that is designed for Mic or line in which are signal levels in the millivolts...instant toast!
  14. Kapt.Krunch

    Kapt.Krunch Well-Known Member

    OK. So, you had unattached cables lying on the floor, and your bare foot apparently touched (probably) the tip of a live unattached cable, while you were touching the mixer?

    Unless, you actually do have voltage differentials in the outlets (between the grounds). See...if they were both properly grounded to the same ground potential (no ground voltage differential) and the unit with the unattached cable that you stepped on was turned off, you shouldn't have been shocked. There SHOULD have been nothing coming through the (+), or tip, or the cable. If you had the unit turned on? Don't do that. Don't connect things with power on to anything, if you can help it. (You CAN plug something into a mixer that is turned on...but should be careful that all the volume and trims are completely down, and the amp (or amp section) is down or off...and the connected unit is off...then turn on. But, you really shouldn't even do that. You should connect everything with all units off. Then, double-check your connections.)

    If you are getting shocked between things plugged in, but everything is turned off, then there may be a voltage differential between the two devices that is carried through the ground of one or the other. You may have an ungrounded device that seeks ground as soon as you connect it to a grounded device (or use yourself as a conductor between the two...DON'T do that!)

    When you get ready to plug everything back in, take everything ONE AT A TIME. Plug two devices into a live power outlet. DO NOT connect audio cables, or Firewire/USB, etc., yet. With power off on both units, take a voltmeter and measure for any voltage between the cases (or metal screws in the case, or the ground rings of input/outputs, etc.) If there is no voltage present, turn one of the units on, and do the same thing. If still no voltage, turn on the other unit. If that looks good, it's likely OK to TURN OFF POWER ON BOTH UNITS to connect any cables.

    Now, turn on whichever device, first, that is going INTO another device. (Turning on the input device first prevents a live receiving device from receiving a transient surge, pop, thump...whatever...that blows speakers and circuits.) If still no smoke, turn on the other device. If it's something that you can test by feeding something through it, test it, if it hasn't malfunctioned.

    Do this for every piece that you have used, and are going to use. ONE at a time. Keep connected what you have already connected, but turn off EVERYTHING, and run the voltage tests between every new device you add, and the connected system. With such a catastrophic, widespread mess that you had, you don't know WHAT might still be bad.

    And, double- and triple-check that you aren't running speaker level outs into line inputs. Don't plug things in live, unless you are SURE of what you are doing. Don't plug everything in all at once, unless you are reasonably SURE everything is working properly.

    It's up to YOU to find out if your circuits are correct. It's up to YOU to make sure you are plugging in proper levels. It's up to you to have patience, find out what caused all this, and remedy it so it won't happen again. It's up to you to test all your equipment ONE PIECE AT A TIME, and to be sure any new pieces of gear are working properly, and can be connected safely in the future. It's up to you to learn how to do all that, or find someone who can teach you. This is fairly basic stuff that you WANT to know.

    Unless, of course..you just like tossing money down the toilet?

    Good luck,

  15. hueseph

    hueseph Well-Known Member

    This is a testimony to the merits of reading the manual.
  16. dvdhawk

    dvdhawk Well-Known Member

    All very true, and that was why I was initially betting on a mis-wired receptacle or power cable.

    But as I catch up on more info that has been revealed I see condenser mics being used which require phantom power. I've seen mis-wired snakes at church installs I was cleaning up that threw little sparks due the phantom power and improper grounding elsewhere. No big blue arc, but I could feel the tingle of electricity when I touched the stagebox. When you introduce 48vDC into the ground of other AC powered equipment in the chain and it creates possibilities for all kinds of electrical mayhem. Under the right/wrong circumstances it can be lethal.

    One (or more) pieces of your equipment is polluting the rest when they're interconnected. And it seems like a significant voltage, please seek out someone close to you with the technical skills to test everything TWICE.

    If you could tell us in much more detail every piece of equipment used, and how it was interconnected - we might be able to give you a few more things to test yourself, but I'd recommend finding a professional.

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