Studio Technologies 41 2013 - Manual (Page 20)

Issue 3, November 2013 Model 41 User Guide
Page 20 Studio Technologies, Inc.
be noticed, especially since monitoring
is generally done using headsets, head-
phones, or earpieces.
Is it possible to reduce the crosstalk that
is created? Absolutely, as long as a non-
standard cable connection is made. This
becomes a trade-off between an improved
crosstalk figure and ease of installation
and use. Using two full pairs can sig-
nificantly reduce crosstalk. Several con-
nection schemes are possible; the exact
one selected will depend on the specific
installation and personal technical philoso-
phy. Two unshielded twisted pairs can be
effectively used. The first pair would carry
the DC and channel 1 audio signal and
common. The second pair would carry the
channel 2 audio signal, again along with
common. There will still be some capaci-
tance between the conductors carrying
the two audio channels but it should be
significantly less. Two shielded pairs can
also be used as was discussed in the
Installation section of this guide.
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
current limiter. While this is a simple and
inexpensive solution, it’s not without
significant limitations. The major problem
with this method is the type of voltage-cur-
rent “knee” that is created. As the load
current increases past about 50 percent
of the rated maximum the output voltage
begins to decrease. 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 significant in applications that use
long cable runs. As the IFB output volt-
age begins to drop problems with user
device performance can occur. Contrast
this situation with the performance pro-
vided by the Model 41. The DC voltage
supplied by its IFB outputs won’t “poop
out” when loaded over its 0 to 220 milliam-
peres range. This will allow IFB beltpack
and announcer’s console devices to func-
tion correctly in many more applications.
Figure 10 shows the IFB output voltage-
current curves for the RTS 4000-series and
the Model 41 Interface. The performance
differences are quite interesting.
It’s interesting to note the reason why
typical IFB output 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
simply 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.