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Model 233 User Guide Issue 1, September 2007
Studio Technologies, Inc. Page 13
The selected microphone is intercon-
nected by way of a 3-pin female XLR-type
connector which is located on the Model
233’s back panel. The mating connector
(male) should be wired so that pin 2 is
signal high (+ or hot), pin 3 is signal low
(– or cold), and pin 1 is shield. It’s possible
that an unbalanced microphone will also
work correctly but is not recommended.
However, if this is necessary the mating
connector (male) should be wired so that
pin 2 is signal high (+ or hot), and signal
common/shield is connected to both pins
1 and 3.
The Model 233 is not compatible with un-
balanced “electret”-type microphones that
require a source of low-voltage DC for op-
eration. These microphones, sometimes
found in low-cost headsets, are not gener-
ally suitable for on-air or other demanding
applications.
As of the writing date of this user guide,
the Sennheiser HMD25 headset remains
popular for on-air broadcast use. A fine
product, it works very well with the Model
233. Note that adding the suffix “-XQ” to
the headset’s part number (HMD25-XQ)
specifies a 3-pin male XLR-type connector
for the dynamic microphone and a ¼-inch
3-conductor plug for the stereo head-
phones. This configuration is very useful,
allowing the headset to work directly “out
of the box” with the Model 233.
If the writer may digress for a moment to
recount a story… an audio dealer once
shared a secret with me concerning head-
sets. He loved selling the “lower-end” (less
expensive) headset models, which he did
by the veritable “boatload.” Why? Because
these usually broke soon after going into
service! He knew that on a regular basis
he’d receive orders for more of them.
Had these users, from the beginning,
purchased only premium-quality headsets,
their total cost of ownership would have
been much less. Enough said…
Headphone Output
The Model 233’s headphone output is
compatible with stereo or mono head-
phones, headsets, or earpieces. Connect-
ing devices with a nominal impedance
of 100 ohms or greater is preferred. This
shouldn’t be an issue as essentially all
contemporary devices already meet this
condition.
Devices are connected to the headphone
output by way of a ¼-inch 3-conductor
phone jack located on the Model 233’s
back panel. As is standard for stereo
headphones, the left channel is connected
to the “tip” lead of the ¼-inch headphone
jack. The right channel is connected to
the “ring” lead of the jack. Common
for both channels is connected to the
“sleeve” lead.
Devices with ¼-inch 2-conductor “mono”
plugs can also be used with the Model
233’s headphone output. In this arrange-
ment only the tip lead (left channel) will
be active. The 2-conductor plug will
physically connect (“short”) the ring lead
(right channel) to the sleeve lead (com-
mon). Technically this won’t damage the
circuitry associated with the right-channel
headphone output. (51 ohm protection
resistors are electrically in series with the
headphone output circuits.) However,
energy will be wasted if an audio signal
coming out of the right channel goes into
a “dead” short. There is a simple means
of eliminating this issue; when configuring
the headphone sources simply do not
assign any to the right channel head-
phone output. Refer to the Configuration
section of this user guide for details.