© 2006 Wohler Technologies Inc. ALL rights reserved
8
VMQ Series
User Manual P/N
821504
Rev-
D
Section 2: Operation
Mounting
The unit should be mounted where convenient for operating persons, ideally at approximately ear level for best
high frequency response. Its superior magnetic shielding eliminates concerns about locating it adjacent to most
types of CRT monitors, including even high-resolution color monitors.
Heat Dissipation
Heat dissipated by the speaker amps is conducted directly to the sides of the chassis; no special considerations
for cooling are necessary as long as the ambient temperature inside the rack area does not exceed approximately
40°C (104°F).
Sympathetic Vibration
Sympathetic vibration from other equipment (cables, etc.), in the rack may be serious enough to interfere with
the unit’s sound quality out in the listening area. The use of thin card stock and/or felt or foam weather-stripping
type materials between adjacent vibrating surfaces, or tying up loose cables, etc., may be required to stop
vibrations external to the unit.
Mechanical Bracing
The chassis is securely attached to the front panel at eight points along its surface, not just at the four corners of
the chassis ears. This feature will reduce or eliminate rear bracing requirements in many mobile/portable
applications. The weight of internal components is distributed fairly evenly around the unit.
Electrical Interference
As with any audio equipment, maximum immunity from electrical interference requires the use of shielded cable;
however, satisfactory results can sometimes be obtained without it. The internal circuitry common is connected
to the chassis. In the VMQ-4 (standard analog inputs), unbalanced sources may also be applied to the balanced
inputs. For analog input signals, the gain is 6 dB greater with a single-ended source connected across both “hot”
terminals than when connected between either input and common. Note that the unused input terminal of a
balanced input should be connected to common, rather than being left floating, to insure best immunity to noise.
AC Power
The unit's AC mains connection is via a standard IEC inlet, with safety ground connected directly to the unit's
chassis. The universal AC input (100-240VAC, 50/60Hz) switching power supply is a self-resetting sealed
type, with automatic over-voltage and over-current shutdown. There is no user-replaceable fuse in either the
primary or secondary circuit.
Magnetic Shielding
We have defined five levels of magnetic shielding. Level One represents the most minimal shielding of the steel
chassis compared to the stray field of the speakers without any ferro-magnetic enclosure. Level One typically
results in a field strength of two Gauss at a distance of two inches from the enclosure surface. (Because of the
inverse square law, such a field is eight Gauss at one inch from the surface!) Because of the purity of color of
the CRT display, it is extaordinarily sensitve to magnetic fields making Level One shielding inadequate, even if
the CRT is several rackspaces away. (CRT color purity may be distrubed by fields as low as 1/2 Gauss.)
Level Two shielding, specifed as two Gauss or less anywhere along the top and bottom surfaces and front panel,
was an interim level, and is sometimes the best available for highly customized units, but is satisfactory in many
applications.
Installation
