Yamaha P-2200 - Manual (Page 25)

has a stereo phone jack input, but if the input source is
monaural, the transformer lead to the ring of the T.R.S.
input jack may be moved to the jack's tip so that a
standard T.S. phone plug input will feed both transfor-
mers. Alternately, the box may be built with separate
T.S. phone jack inputs, or with XLR inputs. Two
standard (2-wire) phone jacks outputs are provided for
connection to the "left" and "right" inputs of the
P-2200. Construct two cables from dual conductor,
shielded cable and T.S. phone plugs to connect the
transformer box output to the P-2200's input. Locate
the step up transformer box at least 5 feet from the
P-2200 to avoid hum pickup from the amplifier's power
transformer. However, the cables from the transformer
box to the amplifier should be no longer than 1 0 feet,
since this is a high impedance circuit. Use low
capacitance, coaxial, hi-fi type cable between the box
and the amplifier. Since the inputs of the P-2200 are
unbalanced, connecting two cables to its input forms
a short ground loop as shown in Figure 60 (see dis-
cussion of grounding on Page SIX 13). To keep hum
pickup at a minimum, run the two cables close
together; this minimizes the area (and therefore the
hum) enclosed by the loop.
The two diagrams show circuits using a Triad A-65J
transformer, and a UTC A-24 transformer. Similar 600
ohm to 15K-ohm transformers are acceptable. The 1/4
watt, 10%, 15K-ohm resistors are used to terminate the
transformers, for lower distortion, and improved
frequency response.
Bridging Transformer Box
When a single, low impedance, balanced source which
must remain balanced feeds several P-2200 inputs, the
TRANSFORMER AVAILABILITY
The matching and step-up transformers mentioned
in the preceding subsections are available from many
electronic parts dealers. Yamaha does not endorse
specific products by citing them herein; rather, these
transformers are mentioned for convenience only. If
you are unable to locate the transformers from your
local electronic parts dealer, contact the manufacturer
at the address shown below.
Sescom, Inc.
P. 0. Box 590, Gardena, CA 90247
Phone (800) 421- 1828 (213) 770-3510
Shure Brothers, Inc.
222 Hartrey Ave., Evanston, Illinois 60204
Phone 1 3 1 2 ) 323-9000 Cable: SHUREMICRO
Triad
305 N. Briant St., Huntington, Indiana 46750
Phone ( 2 1 9 ) 356-6500 TWX: 816-333-1532
UTC
150 Varick St., New York. NY 1 0 0 1 3
Phone ( 2 1 2 ) 255-3500 TWX: 710-581-2722
A line of very high quality transformers, suitable for the
most critical applications, is available directly from:
Jensen Transformer Company
10735 Burbank Blvd., North Hollywood, CA91601
Phone (213) 876-0059
Fig. 41 - Step-Up Transformer Box