Help trouble shooting DI

omie · #1 04-17-2013, 09:21 AM

Mesa M-Pulse 600

I recently started up with a new band. Band Leader has a nice PA and after several practices we started putting me into the PA via the DI to see how it sounded and for me to get use to getting most of my volume thru the PA.

DI worked through about 4 practices and at the end of a practice the DI cord was removed while the amp was still on and made a popping noise(not by me). I'm not sure if this was the last that the DI worked properly, but now all I get is a light persistent static noise and no other signal. I don't believe that the DI level knob has any effect on the volume of the static.

Any ideas on what I can do to trouble shoot this? I cannot determine that there is anything else wrong with the amp as it has been working fine through my 410 diesel cab. Volume, compressor, EQ and Solo all work fine through my footswitch. I've probably got about 40 hours of practice time on it in a month since the DI quit working properly.

I have no expectation that I'll need more volume for our first gig in 3 weeks, but I'm 2 1/2 hours from Phoenix in the middle of nowhere and don't have easy access to any repair shops.

Practice time has been a premium and we've not taken the time to sit down and have a hard look at this. I'm going to the practice space tonight to see if I can figure out if I'm doing something wrong.. or if my DI is burnt.

Can anyone offer advice or thoughts on what I can do to trouble shoot and try to ensure that I'm not looking at any more serious issues? Anybody in the Phoenix area know of any good repair shops that I could take this if I can't figure out that I'm doing something stupid?

This is my first gig with this amp.. I'd hate for my amp to go down in the middle of a 4 set gig.

georgestrings · #2 04-17-2013, 09:29 AM

I've been gigging an M-pulse 600 for a couple of years now - it's a great amp, with an outstanding DI... My *guess* is that phantom power was on your channel when the XLR cable was unplugged - and now your DI is toast... It doesn't sound like you're doing anything wrong, and under normal conditions, phantom power won't damage that DI - but you should never unplug an XLR cable with phantom power on...

If it were me, I'd buy a DI box to use, then eventually get my amp's DI fixed - since that amp has a great sounding DI, and it's quite handy to have...

I'm no expert on this, just making an educated guess based on past experiences, and your description - good luck...

-georgestrings

PS - I'd probably also send the amp to Mesa to be repaired, as soon as I could afford to be without it long enough... IME, they're great to their customers - call 'em, and see what they say...

BassmanPaul · #3 04-17-2013, 09:39 AM

i agree with George. Global phantom power can cause problems with an amp's DI if the voltage has not been taken into account by the amps's designer. The electronics need to be isolated either by capacitors or a transformer. I always prefer the latter.

jmclearnon · #4 04-17-2013, 09:48 AM

^^^ Yeah desk Phantom Power is usually pretty unreliable.

TBH i never use an on-board DI but that's me, but be very careful with the Phantom Power issue.

Good luck with getting your amp fixed!

georgestrings · #5 04-17-2013, 09:50 AM

Quote:

Originally Posted by BassmanPaul

i agree with George. Global phantom power can cause problems with an amp's DI if the voltage has not been taken into account by the amps's designer. The electronics need to be isolated either by capacitors or a transformer. I always prefer the latter.

Acording to Mesa, that DI is phantom power safe - but it's never good to unplug while phantom power is still on... I DI at pretty much every gig, which are always fully PA supported - generally, that means atleast one or two condensor mics on the drums - which in turn means phantom power present... Fortunately, nearly all the consoles I'll run into at those gigs won't have global phantom power - and typically have soundmen experienced enough to know better than to fry my DI that way... Agreed 100% about the isolation thing, too...

- georings

georgestrings · #6 04-17-2013, 09:54 AM

Quote:

Originally Posted by jmclearnon

^^^ Yeah desk Phantom Power is usually pretty unreliable.

On a decent console, running thru a good snake and cabling, AND operated by someone that knows what they're doing, phantom power is very reliable - but for anything other than that, it *can* cause issues...

I also gigged for awhile with a singer who used a Shure 87a exclusively - so, I have a little experience dealing with phantom power issues...

- georgestrings

BassmanPaul · #7 04-17-2013, 10:24 AM

Come on George, give me a break!

Yet again I agree with George. I have been using Condenser mics since the seventies, EV PL77, PL76 I converted to phantom power and AKG C something or other. I have yet to have a problem with unreliable phantom power. I do carry a power supply in the kit tote but have yet to use it.

craig.p · #8 04-17-2013, 10:59 AM

What I typically run into is miswired snakes that fail to get phantom up to the snake head. Seen it twice in the past year and a half. So I started out by carrying an ART phantom for my SM86, but lately I've just been packing an e835 as backup because I really can't tell the difference in the mix except for the fact that the Senn has less proximity effect, which is fine with me.

On the DI thing: Before whatever head or preamp goes into my truck, I jam up the XLR cavity with crumpled electrical tape, then tape over the connector with white tape and write NO on it. Because when I get there, who knows what someone's gonna do while my back is turned. All it takes is one wrong button press at the board. There's a sticky in this forum that says I can't comment further.

omie · #9 04-17-2013, 11:24 AM

Thanks for the replies.

I still think I should thoroughly go over my amp to ensure I'm not doing something stupid. That often seems to be the case.

I'm also going to a music store tonight to see if I can pick up a 1/4 to XLR adapter for my Rusty Box! pre/DI... I use it more as a OD than a true pre, so I'm interested to see how that will sound compared to my amps DI in the PA.

The only good from all of this is that its happening at practice instead of live. Again, my rig should have plenty of volume, but this is my first experience with an amp with so many bells and whistles so that's why I was trying out the DI. Also, I just want to make sure I have a back up solution in case my amp explodes.... Or whatever.

Gearhead17 · #10 04-17-2013, 11:36 AM

Are you using Mesa head's DI as Pre or Post EQ? If PRE, you are probably better off getting separate DI box and life will be good. You can decide to fix the Mesa head DI in the future.

omie · #11 04-17-2013, 04:07 PM

I tried both and never determined a preference. I run a pedalboard with dirt and modulations.... Do you have any advice?

Gearhead17 · #12 04-17-2013, 09:03 PM

Quote:

Originally Posted by omie

I tried both and never determined a preference. I run a pedalboard with dirt and modulations.... Do you have any advice?

If you run the pedals before the amp, the "Pre" setting is just the signal at the input. If you do post, you get the sound of the amp (depending on the circuitry), the tone controls and whatever you have plugged in leading to the amp.

Depends on what you want and the tone you are trying to get. Personally, I would run the effects on one DI line and a clean bass tone on the other DI line. The overdrive/distortion signal would need a steep roll off at 4khz and higher to work right, but doing two channels will make sure you lose nothing of your clean tone. This would allow you to use the amp on stage as purely a monitor.

trentagxw · #13 04-17-2013, 09:14 PM

I'd probably also send the amp to Mesa to be repaired, as soon as I could afford to be without it long enough