Studio Technologies 41 2004 - Manual (Page 18)

Model 41 User Guide Issue 1, October 2004
Studio Technologies, Inc. Page 19
Superior Power Delivery and
Audio Quality
As previously discussed, one of the Model
41’s strengths is its ability to very effec-
tively deliver energy to the connected IFB
user devices. This allows more devices
to be supported over longer cable runs.
How does the Model 41 accomplish this?
Simply by having circuitry that is superior
to that used in most of the “industry-
standard” equipment. In most IFB in-
terface devices, an adjustable voltage
regulator integrated circuit is used as a
combination of audio modulator and cur-
rent limiter. While this is a simple and inex-
pensive solution, it’s not without significant
limitations. The major problem with this
method is the type of voltage-current
“knee” that is created. As the load cur-
rent increases past about 50% of the rated
maximum the output voltage begins to de-
crease. This means that the usable power
delivered to the connected device(s) will
start to drop well before the rated output
is reached. This limitation will become sig-
nificant in applications that use long cable
runs. As the IFB circuit voltage begins to
drop problems with user device perfor-
mance can occur. Contrast this situation
with the performance provided by the
Model 41. The DC voltage supplied by its
IFB circuits won’t “poop out” when loaded
over its 0 to 200 milliamperes range. This
will allow IFB belt pack and announcer’s
console devices to work correctly in many
more applications. Figure 9 shows the
IFB circuit voltage-current curves for the
RTS 4000-series and the Model 41 Inter-
face. The performance differences are
quite interesting.
It’s interesting to note the reason why
typical IFB circuit audio quality is less
than pristine. It’s not hard to notice the
background “hiss” that is always present
on pin 2 (DC with channel 1 audio) of the
interface connector. Technically, it’s white
noise that comes from the adjustable
voltage regulator being used as an “AM”
modulator and current limiter. The noise is
an artifact of the design topology and sim-
ply can’t be overcome. How does Studio
Technologies know this? Because our first
“breadboard” designs used this method
and achieved the same poor results! Only
after the problem came to light did work
on an improved circuit begin. The results
were worth the effort.