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could my Boss GT6 blow up a Behringer PMP5000?
could my Boss GT6 blow up a Behringer PMP5000?
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Old 11th April 2009, 09:30 AM   #1
billywhizz is offline billywhizz  United Kingdom
diyAudio Member
Join Date: Apr 2009
Default could my Boss GT6 blow up a Behringer PMP5000?

hey all...new here and in a predicament...

I play guitar and I was around my friendes last night having a rehearsal when all manner of strange things happened...

He's got lots of electronic PA equipment, some of which was his dads, and we're getting things together for a gig we have coming up in July. We were both going through Boss GT6's into his Behringer PMP5000. I'm playing an Ibanez S470DXRM with a MoJoe bridge humbucker. He was using his Gibson Explorer. There were only the guitars and 2 Mic's going into the PMP and then into a Peavey speaker.

The set up was no different to any other week and I'd been using my gear earlier in the day with no problems.

My guitar wasn't quite loud enough so I changed the setting from combo amp to PA/Phones and the PA shut down. There was no power so we checked the fuse which was blown and tried another fuse... and smoke came out of the PMP with that horrible smell of burning electronics.........

We plugged into his old Peavey PA and carried on but after a couple of minutes that cut out as well. It's not known to be the most reliable PA though so we left it and it came back on later. Then we plugged into his dads PA which is very old but totally reliable and again, after a few minutes it tripped out.

I unplugged all my gear and he carried on for a good 15 minutes with no problems.

So...could it be my gear that is causing the problems and if so what kind of output should I be getting from it in terms of amps, volts etc? And is there a simple way of checking it? Is there any way a Boss GT6 could blow up a 1200w mixer??? And will it be safe to plug into my Marshall??

sorry for not being up on the technology front.. I'm fairly new to all this equipment and leave it to my mate who's been involved with it all his life. I just plug in where he tells me to.

Many thanks guys

Billy W
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Old 25th April 2009, 01:03 AM   #2
hardwareguy is offline hardwareguy  United States
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Join Date: Apr 2009
Hmm.... this is most puzzling.

1: Check your input levels. Are you playing so loud that the amps are overloaded?

2: Check the speaker impedance! Is your speaker arrangement such that the impedance in ohms less than what the amp can take?

For example, two 8 ohm speakers in parallel gives a 4 ohm load while the same speakers in series give a 16 ohm load. The amp will state on the back what it can safely drive. Some can do 2 ohms, some 4 and a few can't do less than 8. Of course, the amp will deliver less power into a 16 ohm load than a 4 ohm load.

To see this you need to know Ohm's law and its relative, Watt's Law:
Power in Watts = amps * volts (P=I*V)
Amps = volts / ohms (I=V/R)
Volts = amps * ohms (V=I*R)

Yes, it's maths but bare with me.

Let's say you have an amp putting out a 10V signal. With an 8 ohm speaker you get a current of 1.25A and since that current is motivated by 10V, the power is 12.5 watts. (10V * 1.25A)

Now lets do the same voltage with a 2 ohm speaker: Current into the 2 ohm speaker is equal to 10V / 2 ohms.....5 amps. 5 amps * 10 volts = 50 watts!

Now you see how an amp can easily overextend itself if given a hard load.

3: Perhaps you have a faulty speaker and the voice coil has a short? Try different speakers if possible.

4: Are the heatsinks inside the amps clean? Do the fans run?

5: This is not too likely but check for DC voltages on the output of your effects processor. The amp should block these on the input but you never know what the designers are thinking these days. Amplifying DC will result in a lot of excess current in the speaker....which the amp must supply.

It could be a number of issues that have been causing your amplifier woes.

If the PMP isn't under warranty, you can help me diagnose the issue by opening the case and taking pictures of what burned and the surrounding circuitry. Take care to avoid touching the big capacitors as they may still hold a charge even though the mixer is disconnected from the mains. (the caps in question are cylindrical objects)

Look for any obviously burned parts and post pics of what you find.
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Old 8th February 2010, 05:06 AM   #3
fredy2 is offline fredy2  United States
diyAudio Member
Join Date: Feb 2010
Location: Renton WA
Default PMP5000 information

The PMP5000 has a design defect involving insulation and clearances on the power amplifier. Major damage is done if it smoked. I have repaired one and am working on another. If the display work for the effects, the small power supply is working. If one side of the power amp works, then a single power amp is fried. If both are dead, then it is likely the large power supply is also fried. On one that I have repaired the failed power amp wiped several transistors, diodes, resistors and a switching regulator chip on the big power supply as well as the damage in the amp portion..

HINT: For all you that are resurecting power amps. Put a 100 watt lamp in series with your power cord to the unit. This saves a lot of transistors when you didn't quite get all the bad ones replaced before firing up.

There usually is insulation failure in vicinity ot eh collectors of the power switching MOSFETS in the power amp section. The clearance of drain to source of the three transistor switches breaks down and arcs. This often takes out the big power supply as well. The arcing occurs between an internal layer of the multilayer board and the heatsink and the source lead on the bottom of the power amp board.

Beyond the three switching transistors, in current unit I am working on, one zener and a 30 milliohm metering resistor fried (mass smoke evidence) The circuit board is slightly conductive from carbonizing and the drain lead of the two smaller (paralleled) switchers will have to be drilled out and isolated and hardwired.

There is just inadequate insulation when unit has a bit of humidity for example.
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Old 16th February 2010, 03:57 AM   #4
gain wire is offline gain wire  Canada
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Join Date: Nov 2004
Location: NCR
quite Frankly I'd go check your speaker that was connected to the Behringer and the Peavey. There is a possibility it might be defective, too low impedance, or have another weird defect. Like my old REGA speakers that presented an occasional SHORT-CIRCUIT when the voice-coil rubbed against the magnet walls, because the coil wire had its coating melted off at some places... That's what too much heat does to a speaker coil, among other things.
And as Hardwareguy pointed out the speaker impedance, or combined speaker impedance can make all the difference between a happy amp and a nearly-on-fire amp. Do not connect a speaker with lower impedance than the amplifier recommends. and if you're plugging in more than one speaker into an amplifier PA whatever, you need to know Ohm's law!
(I'm not shouting I'm just trying to get your attention)

good work! (luck)
Trans-directional-servo-logamp non-zerocrossing autogain compressing thingamajig

Last edited by gain wire; 16th February 2010 at 04:01 AM. Reason: added info like always I forgot to mention something.
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