Packburn 325 Owner's Manual - page 4
noises first. In the case of recordings containing no transient
noise, such as analog master tapes and copies thereof, the
Continuous Noise Suppressor will be the only one needed.
The Continuous Noise Suppressor is a variable low-
pass filtering circuit that responds in accordance with the
nature of the program material. When the program material is
quiet and contains little in the way of high frequency energy,
the high frequencies that the listener is aware of are almost
entirely those in the noise. The cutoff frequency of the filter
closes down to its lowest value. In loud and/ or brilliant
passages when the signal is effectively making the noise, the
cutoff frequency assumes intermediate values. The operator
controls the extent to which the filter closes down and opens
up, so a substantial reduction of hiss can be achieved without
audible degradation of the program material and without the
swishes and pumping that have been the undesirable by-
product of similar devices.
Metering of the input: The two input channels are metered to
assure that the proper signal levels are provided to the Audio
Noise Suppressor. Metering takes place after the input level
control and before the channel balance control.
Channel balance control and audition of difference signal:
the balance control is needed for balancing of signals into the
Switcher when playing monophonic disk or cylinder recordings.
In reproducing vertical-cut recordings, the balance control also
serves as a canting control. Audition of the difference signal
as well as of the sum signal allows one to set the channel
balance or canting adjustment with accuracy.
Test Switch: This switch enables selection of either the
quieter or noisier groove wall by the Switcher. It is useful for
demonstration and diagnostic purposes. Also, in the case of a
full-width monophonic tape recording in which the oxide is
flaking off, one can play it with a two-track head and use the
Switcher to choose the momentarily louder channel and thus
avoid dropouts.
FACILITIES ADDITIONAL TO AND SUPPORTIVE OF THE
NOISE REDUCTION PROCESSORS
A number of necessities and conveniences are included in the
Audio Noise Suppressor to assist the user in achieving
optimum performance with disk and cylinder playback as well
as other signal sources, as follows:
Playback from either channel: There is the ability to play
from either channel separately of a monophonic disk or
cylinder with the lower frequencies of the two channels mixed
so as to eliminate rumble. This is a necessity in reproducing
those occasional recordings in which one side wall is
consistently noisier than the other. Such a condition can
indicate that the optimum stylus is not being used, but some
recordings persist in this behavior with any stylus that one may
try. For these recordings it is preferable to play from just the
quieter side wall of the groove and use just the Blanker for
transient noise suppression.
Transient Noise Suppressor can be switched out: The
Switcher plus the Blanker, which constitute the Transient
Noise Suppressor, can both be switched out by means of a
single toggle switch whenever one wishes to process a
recording only through the Continuous Noise Suppressor
.
Eight position bass equalization switch: This allows
selection of the commonly used bass equalization curves for
78s manufactured prior to the recording industry’s
standardization on the RIAA curve in 1953. Also includes the
RIAA curve.
Six position treble equalization switch: This allows
selection of the commonly used treble equalization curves for
78s as well as for those long playing records that were
manufactured prior to the recording industry’s standardization
on the RIAA curve in 1953. Also includes the RIAA curve.
Cutoff frequency meter: This meter displays the ever-
fluctuating value of the cutoff frequency when the Continuous
Noise Suppressor is operating.
Bypassing the Audio Noise Suppressor: The Audio Noise
Suppressor is provided with a bypass relay. This connects the
output terminals to the input terminals when the power is OFF
or when the ANS switch is in the “0” position. Thus, the Audio
Noise Suppressor is easily removed form the circuit when it is
not needed.
HALF THE
HEIGHT
(3.5 INCH)
ATTACHABLE 19
INCH RACK
MOUNT EARS
THREE NOISE
REDUCTION
STAGES
EQUALIZATION
SETTINGS FOR LP
AND EARLY
RECORDS
(8 TURNOVER,
6 ROLLOFF)
TABLE TOP
DESIGN
ERGONOMIC
CONTROL
LAYOUT