dbx 128 - DETAILED OPERATING INSTRUCTIONS; General Setup and Handling

10
DETAILED OPERATING INSTRUCTIONS
GENERAL NOTES
Mounting
The 128 is supplied in a handsome cabinet that can be
placed almost anywhere. Avoid mounting the 128 above any
source of heat or strong electro-magnetic fields, such as those
generated by power amplifiers or vacuum tube equipment.
Level and Impedance
The input levels, output levels and impedances of the 128
are designed for most hi-fi and semi-pro equipment. The128’s
input impedance (for both the noise reduction and compres-
sion/expansion sections) is 50k-ofims, which means it can be
driven from high or low impedance sources. The 128 input
will accept a wide range of voltages. The output will drive
up to 7 volts into 5000-ohms or greater. This means that
you can confidently connect the 128 to almost any type of
equipment found in a normal hi-fi or semi-pro system. See
the specifications section on Page 39 for greater detail.
Grounding
The 128 is not grounded to the power mains through its
power cord. !t obtains a ground via the shields of the inter-
connecting audio cables from the preamplifier (or receiver)
and/or from the tape machine. No special ground wires need
be connected between the 128 chassis and any other equip-
ment. If you hear hum, try reversing the AC plug, and if that
does not help, check to make sure all audio cables are prop-
erly installed, and that there are no broken conductors in
any cable. Also try cleaning the connectors on your cables
since hum and radio station pickup are sometimes caused
by microscopic dirt particles between the mating surfaces of
the connectors.
Cable Length
Some installations will tolerate longer cables, but when-
ever possible it is a good idea to keep signal cable runs under
10 feet. This will minimize hum and noise pickup, and also
help prevent high frequency losses naturally caused by cable
Capacitance.
dbx and Dolby®* Together
The dbx II tape noise reduction system provides at least
20 dB more reduction of noise than Dolby “B” tape noise
reduction systems, and 15 dB more than Dolby “A”, so there
is no need to use Dolby processing. If your tape machine has
internal Dolby processing, leave it off, and use only the dbx II
encoding and decoding. Dolby processed tapes are not com-
patible with dbx I] decoding (and vice-versa); if a tape was
recorded with Dolby encoding, it must be Dolby decoded.
A Dolby decoded tape may then be expanded.
NOTE: It is possible to combine both dbx 11 and Dolby
processing, though we do not recommend it. Any imperfec-
tions in the Dolby encode/decode processing will be magni-
fied by dbx I! treatment. Since dbx II processing alone re-
duces noise to inaudibility, there is really no need to use
dbx !1 with another system.
*“Dolby” is a trademark of Dolby® Laboratories Inc.