Things That Go Pop





Thread: Things That Go Pop


This topic spun off from the thread on RFI Problems with Mixers, and discusses a different
issue. One consultant believes that a problem with a particular mixer caused a surge through the
system that destroyed all of their loudspeakers. This thread started with a conversation about RFI
problems in mixers. For the rest of the discussion see the thread entitled "RFI Problems with Mixers".


From: Kevin Potts (Las Vegas, NV)
Subject: Re: Mixer ideas needed

I know of two churches in Las Vegas who have had problems with Mackie.

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From: Rob Parpatt (Chilliwack, BC, Canada)
Subject: Re: Mixer ideas needed

Perhaps you can elaborate a bit on what the problems might have been or
are? Also, what models of Mackie do they have?

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From: Robert Enlow (Norwalk, OH)
Subject: Re: Mixer ideas needed

Hey guys!

Rather than just throw rocks at Mackie, or anyone's product, how about
some specifics. Sometimes rumors of one instance grow into multiples
really quickly.

Can you tell us exactly what the problems were, when did it occur,
(because there might have been a design problem that has long since
been corrected)and what was done to correct them?

Thanks.
Bob Enlow
RESOUND Co.
Norwalk, Ohio

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From: Nehemiah Lacar (Chicago, IL)
Subject: Re: Mixer ideas needed

For those of you who have heard of problems with Mackies, What kind of
problems were they? I'm thinking of purchasing a 56-8 for my live
production company in a few months and would be interested in knowing
what's happened. I own an 8 buss and the only problem I've had was a
wire that had broken in the power connector.

Who wouldn't pick a PM4000 over a Mackie! If you sold me one near the
price of a Mackie, I'd buy one. But there's a massive cost difference.
I'm also specing the A&H GL3300 and GL4000. The Spirit Live 8 got kicked
off my list after a friends board blew 3 times and it's only 6 months
old.

Please share your Mackie SR 40/56-8 horror stories.

Nehemiah Lacar

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From: Nehemiah Lacar (Chicago, IL)
Subject: Re: Mixer ideas needed

Regarding the Live 8 board that blew:

The Aux Master section blew when he patched it to an outboard effects
processor (Lexicon PCM70, PCM42, or Yamaha SPX900) and patched it back
into the stereo line inputs. The person who repaired the board couldn't
figure out what the problem was and suggested that Will (board owner)
had the outboard gear checked out. Will was confused because he's had
no problems before with the outboard gear with his Soundcraft B300.
He had his processors checked out with no problems. Have had no further
updates from him since.

Nehemiah Lacar

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From: Nehemiah Lacar (One Source Live Productions; Chicago, IL)
Subject: Re: Mixer ideas needed

I'm sorry.... By blew I mean... a pop (not quite as loud as a
firecracker) and a whif of electrical smoke. No fires though...
just a dead aux master section.

Nehemiah

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From: Kevin Potts (Las Vega, NV)
Subject: Re: Mixer ideas needed

Church Number One was using a SR24.4, this mixer killed the entire sound
system, as determined by an independent electronics consultant.

Church Number Two [NOTE from Editor: This portion of the message can be
found in the parallel thread titled Mixer Problems.]

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From: Curt Taipale (Taipale Media Systems, Inc.)
Subject: Re: Re: Mixer ideas needed <"Church Number One was using a SR24.4, this mixer killed the entire sound system, as determined by an independent electronics consultant.">

Huh!?! What does this mean? Please explain more.

Curt
curt@churchsoundcheck.com

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From: Blake A. Engel (Chicago, IL)
Subject: Re: Mixer ideas needed

The experience I was told about (actually, two of them) involved the
board sitting, turned on, not being used, inputs muted, outputs at
unity....the amps and speakers were blown, needed to be replaced.

Blake A. Engel (A.K.A. "Sound Guy")

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From: Joe De Buglio (Toronto, ON, Canada)
Subject: Re: Mixer ideas needed

I've encountered Mackie Mixers and other single circuit board mixers such
as the older Alesis Monolith mixers which don't have a grounding buss bar.
It seems that such mixers do become unstable when a mic is left open and
unattended. The cause of this is simple. When long mic cable (Cables over
100 feet) come into proximity to an EMF greater that a 20 amp source (in
these cases theater dimmer packs.) and within 10 feet of mic cables, the
magnetic field creates a low level static charge. (These were the conditions
I had tested the system in 2 different churches. These problems could happen
at lower amp levels) The static charge builds up very quickly when there is
no one to touch the mixer to ground the chassis. The way you can tell if
your system is getting EMF leakage is whether you get any static zaps around
the mixer. When the static builds to an unknown level, the charge will arc
from the chassis to the PC board and depending on where it happens in the
board, anything can happen. If it happens on an input stage, you loose a
channel. If it happens on the output stage of the mixer, anything down the
line can and is often damaged. I have seen an amp rack of 5 amps go down.
(The EQ was out of the system at the time.) I have also seen a cluster of
9 speakers burn up.

Mackie does have a fix for this, but there seems to be a debate about it too.
They suggest placing a .47 or .100 cap in the barrel of a mic from pin 1 to
the barrel and pin 3 to the barrel. The main reason for this is to correct
for RF problems, but it seem to cure the other problem too.

Oh, and the mixers in question were an SR32 and a SR40-8 1996 model

Joe De Buglio

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From: Ray A. Rayburn (Boulder, CO)
Subject: Re: Mixer ideas needed

Joe -

Sorry, but magnetic fields can't generate static charges.

I agree however that it is not good to leave the gain up on unterminated
mic lines since they can pick up undesired noise and RF. If the design is
poor I would guess that instability of some sort is possible.

Static zaps to or near the mixer could be just due to low humidity during
the heating season or other non-equipment related causes. You are of
course properly grounding the mixer :>)!

See also my message to Calvin on the "pin 1 problem". Mackie ties their
connectors to chassis but it can take a couple of inches to get there.
This is not ideal, and may have something to do with their known high end
of the AM band RF problems.

Ray Rayburn

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From: Curt Taipale (Taipale Media Systems, Inc.)
Subject: Re: Mixer ideas needed <"The experience I was told about (actually, two of them) involved the board sitting, turned on, not being used, inputs muted, outputs at unity....the amps and speakers were blown, needed to be replaced.">

Pardon me - why were the outputs set for unity if the console was not being
used? Was this perhaps just before a worship set? Or during rehearsal? I
want to believe the best, but I don't quite understand someone walking away
from the house desk with the house faders still up. There may indeed have
been something happen within the console to send some burst of energy out,
but I'd never walk away from the console without first muting the outputs
or pulling down the master faders. Leaving the main faders up is asking
for trouble.

Curt
curt@churchsoundcheck.com

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From: Bob Puff (Buffalo, NY)
Subject: Re: Mixer ideas needed <"I'd be curious to hear more as well. I've been very successful with Mackie consoles. I've placed them in several churches, and not a one has expressed any problem with them at all.">

Hi Curt,

I've also had some bad experiences with Mackie mixers. One church was
picking up at least three radio stations on a channel!

I've got a friend who has a SR24-4 who does a lot of live sound gigs.
He's fried some stuff due to ultrasonic oscillations that pass right
through the Mackie. Sometimes that wide bandwidth is too wide!

Bob

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From: Ray A. Rayburn (Boulder, CO)
Subject: Re: Mixer ideas needed

Blake -

Anytime a system fails that was left on unattended, I would be very
careful in trying to assign the blame to any particular item. Based on
your description, before blaiming the mixer, I would suspect power
problems or even some unauthorized person messing with the system.

Ray Rayburn

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From: Calvin Wilson (Garland, TX)
Subject: Re: Mixer ideas needed

If the static charge builds up on the chassis, why can't you fix this
problem by just grounding it to your main sound system ground point?
I think I'm missing something.

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From: Joe De Buglio (Toronto, ON, Canada)
Subject: Re: Mackie and other PC board mixers <"Sorry, but magnetic fields can't generate static charges.">

Then how else do you explain static when:
the only thing connected to the mixer is mic lines over 100 feet,
nothing on any outputs, no effects units, the mixer is plugged in
to a grounded AC plug and the only time you read current between
pin 2 and chassis is when the house lights are on - which is on
a separate AC panel with it's own transformer.

Electricity does always follow the rules. A few years back, a church
was hit by lightning. The current followed up the ground of a new
church that was only opened 6 weeks. Toaster, Computer, Alarm System,
Sound System and everything that had a 3 pin AC plug was destroyed.
The only items that were not damages were AC products with only 2 pin
plugs.

The NRC of Canada was called in by the insurance company. Their
conclusion, it was listened as an "Act of God." When I tell people
this story, people doubted it too, until people started to report it.
We think static and electricity always follow certain rules, but every
now and then there are new things to discover. Perhaps this is one of
those problems in which in certain instances the only solution is a
mixer that uses an older design method. Not everything that is new is
better.

Joe De Buglio R. E.

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From: Ray A. Rayburn (Boulder, CO)
Subject: Problem running cable

Calvin -

First I would suggest that you contact the AES (www.aes.org) and buy a
copy of the June 1995 issue of the Journal of the Audio Engineering Society.
In this special issue on shielding and grounding of audio wiring Neil Muncy
and others showed how most of the problems we face with interference being
picked up by audio cables is not due to our wiring practices, but instead
to a very common way audio equipment is wired internally. They showed the
existence of the "pin 1 problem" which occurs when the shield connection of
a cable is not connected DIRECTLY to the chassis of the equipment right at
the connector. Even a couple of inches of wire inside the box between the
cable shield connection and the chassis of the box can cause this problem.
When the "pin 1 problem" is fixed, then many things we have been told are
no no's become non to minor problems. This includes problems such as power
wiring being too close to audio, ground loops, high RF fields, and many
others. The only additional caution is that for best results you want to
use nothing but balanced inputs. Single ended outputs can be resistively
balanced such as Mackie does on many of their "balanced/unbalanced"
outputs.

As it happens Neil just sent a couple of somewhat relevant messages to the
Syn-Aud-Con ListServ... (Note from Editor: look for Neil's comments at the
SynAudCon website: <http://www.synaudcon.com>.)

There are few people in the world more qualified to solve your problems
than Neil Muncy. If you have the budget I would hire him. If not, then
read his paper and fix the equipment "pin 1 problems" yourself. After that
your wiring issues should not be a problem.

Ray Rayburn

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