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Friday, July 4, 2014

Fixing Up a Behringer 31 Band EQ

On Amazon, under the listing for the FBQ3102 31-Band Stereo Graphic Equalizer, you may find the following notes in the review section:

"This equalizer works fine and is easy to use. But I am uncomfortable with the high heat it generates. It gets VERY hot on the back panel around the sub output. It gets so hot in that area, it hurts to keep a finger there. This is very strange as the heat is generated even when the EQ it not wired to anything but the A/C power. It is not on top of warm equipment either. I have observed this high-heat behavior on two units. Two different calls to Behringer yielded two results. The first time it was suggested that I exchange the device, which I did. The second time I was told the heat was O.K. Weee, multiple choice from customer support."  (By Dr. James Williamson on July 15, 2010)"

In fact, one will find (on Musician's Friend, Amazon, and other sites) many mixed reviews with this and other similar products (low end home-studio, inexpensive semi-pro equipment).

These units (many brands and models) all seem to fail frequently in partial functions or even completely, after heavy use or leaving them on for extended periods.

This can almost always be traced to HEAT PROBLEMS as a result mainly of cutting corners and assuming that consumers will not run the units 24/7 or for more than an hour or so at a time.

The manufacturers typically use smaller heat-sinks (or no heat-sinks at all),
or they skip on fans, or provide poor ventilation to allow heat to escape at
an adequate heat-transfer rate for continuous use (i.e., extended on-times).

On the one hand, you will read great reviews praising the performance of the products, and on the other hand you will also read seemingly contradictory horror stories of how these products fail after only moderate extended use, often just outside the warranty time limits!.

This is precisely what is to be expected.

Luckily there are solutions.

If you're trying to save a few dollars with these inexpensive units,
and since the warranty will rarely work in your favour anyway,
you can take a bit of risk voiding the warranty and instead modify
the unit so that it at least has a chance of functioning normally
and without problems under extended or continuous use.

This usually means providing better ventilation and heat-transfer,
and even adding fan-cooling or larger heat-sinks or metal components.

Here's what we did to deal with the heat problem on our 31 Band EQ:

First, we opened up the unit to discover a lot of empty space in there,
and one seemingly adequate, but unfortunately sealed, heat-sink
in the input area at the top, which accounts for the high heat you can
feel on the top of the left side of the case when its powered on for any
length of time.

I was initially thinking I would add a heat-sink to the outside, so as
not to deface the unit, by gluing it on.    But inspecting the inside showed
me that this would not really work.  The chip doing the heating was not
screwed to the case as I anticipated, but had its own heat-sink already,
which was not touching the case at all!

This is doubly disturbing, since the case was incredibly hot in spite of
not being connected directly to the heat-sink.

Obviously the real problem was no ventilation, not no heat-sink.

Heat-sinks can't operate properly unless there is some air-flow that can
transfer heat continuously to the outside without build-up.

So I took a 'nibbler-tool' and cut a square hole right above the heat-sink,
and also one on the bottom of the unit about the same size,
so that air can flow naturally by convection up through the bottom,
over the heat-sink fins, and exit the unit at the top.


Also of concern if you are 'roading' the unit is to make sure things you do can't introduce more problems: I used some Locktite on the nuts holding the screen in place above, just to make sure that they didn't work loose and start bouncing around inside the case, shorting out electrical components. You can also just use a bit of paint or glue, to make sure screws don't come loose with jiggling over time.

To prevent injury, I also filed the sharp edges of the hole I cut with a file,
and then 'painted' the edges with a permanent magic-marker to remove
any unsightliness.


This seems to have solved the heat problem, but keep in mind that
these window-vents might get blocked still, if the unit is mounted tight against
other equipment in a rack.


There is also plenty of space on the back of the unit to cut a hole,
instead of the bottom, if that is better in your situation. (e.g., if the bottom hole will be blocked otherwise.)  I cut the bottom because it would be less visible,
and I had planned to tilt the unit in a special rack.

Another way to protect EQ units is to use them properly.

Here you can see I have left EQ centered and flat except for
subtractive notches to take out room-boom and feedback points.
No frequencies are boosted, because that is better done with wider Q
tone controls on the channels and mains, i.e., a parametric EQ.

The very ends of bass and treble can be rolled off too,
to protect bass speakers and remove harshness from horns.

EQ should be used in an insert on the mixer board so that what it
is doing to the sound can be monitored at the board with headphones,
for both Front of House (main FOH) or monitors (e.g., stage monitors with
a separate EQ channel).

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