Yamaha ST15 Owner's Manual

Thank you for purchasing the Yamaha ST15 Speaker Transformer.
This device is a matching transformer that is used for the parallel
connection of low impedance speakers to a high impedance type
distribution power amplifier.
Please read this manual carefully to get the most out of the ST15 and use
in a safe manner.
■ Outline
This device has a capacity of 15 W, the line output of the power
amplifier connected to the primary pole is assumed to be 100 V
(using a 70 V line is also possible).
The blue, yellow, orange and brown secondary cords each
correspond to speakers whose nominal impedance is 8, 6, 4 and 2Ω,
while the input impedance of the connected power amplifier is 670Ω.
■ Connection
1.
Turn the power switch OFF on the power amplifier you are
going to connect the ST15 to.
2.
Use two 4 mm (1/8") tapping screws, securely attach the unit to
a speaker or some other convenient location.
3.
Connect the ST15's white primary cord to the power amplifier's
100 V or 70 V negative (–) pole, connect the black cord to the
power amplifier's 100 V or 70 V positive (+) pole.
4.
Connect the white secondary cord to the speaker's negative (–)
pole. From the blue (8Ω), yellow (6Ω), orange (4Ω) and brown
(2Ω) cords, choose a cord that matches the speaker's impedance
and connect the selected cord to speaker's positive (+) pole.
5.
Bundle together the unused secondary cords to prevent shot
circuits, etc.
■ Advanced Applications
Connecting Speakers of Different Impedance
An 8Ω speaker can be connected to the lower impenitence yellow
(6Ω), orange (4Ω) cords however, low impedance speakers
cannot be connected to higher impedance cords. The capacity will
be exceeded creating a hazard.
When connecting speakers of different impedance, refer to the
following chart. Please use caution when in such applications
since speaker input dB and the input impedance will change.
● 100 V Line Connections
8Ω Speaker Input
Impedance
Blue 15 W 670Ω
Yellow 11.3 W 890Ω
Orange 7.5 W 1330Ω
Brown 3.8 W 2670Ω
● 70 V Line Connections
8Ω Speaker Input
Impedance
Blue 7.5W 670Ω
Yellow 5.65W 890Ω
Orange 3.75W 1330Ω
Brown 1.9W 2670Ω
■ Limitations for Parallel Use
Depending upon the manner in which this device is used, the
connection of multiple speakers is possible however; the number
of speakers will be limited according to the power amplifier's

specifications.

1.
The total input for the speakers that are being used should not
exceed the power amplifier's maximum output.
When the line output transformer is used, its capacity should
not be exceeded.
SPEAKER
TRANSFORMER
6Ω Speaker Input 4Ω Speaker Input
Impedance Impedance
× ×
15 W 670Ω ×
10 W 1000Ω 15 W
5 W 2000Ω 7.5 W
6Ω Speaker Input 4Ω Speaker Input
Impedance Impedance
× ×
7.5W 670Ω ×
5W 1000Ω 7.5W
2.5W 2000Ω 3.75W
ST15
2.
The total input impedance for the speakers that are being used
should not be less than the minimum load impedance of the
power amplifier, including the line output transformer.
The ST15 can be used in this manner as long as both conditions
1 2
and are met.
■ Specifications
Capacity
Frequency Response
Total Harmonic Distortion
Insertion Loss
Dimensions (W × H × D)
Weight
Coil Ratio
*BLU
*YEL
*ORN
*BRW
The contents of this manual apply to the latest specifications as of the
printing date. Since Yamaha makes continuous improvements to the product,
this manual may not apply to the specifications of your particular product.
To obtain the latest manual, access the Yamaha website then download the
manual file. Since specifications, equipment or separately sold accessories
may not be the same in every locale, please check with your Yamaha dealer.
* Color Chart
BLU: Blue
BRW: Brown
■ Wiring Diagram
Power Amplifier
Primary
Power Amplifier's
[SPEAKERS]
+ terminal
100 V Line
or
70 V Line
Power Amplifier's
[SPEAKERS]
670Ω
– terminal
1330Ω
100 V Line
or
70 V Line
■ Dimensions
670Ω
1330Ω
48 mm (1-7/8")
OWNER'S MANUAL
15 W Continuous
50 Hz–20 kHz
≤ 1% (1 kHz, 15 W)
≤ 1.5 dB
80 × 48 × 46 mm
(3-1/8" × 1-7/8" × 1-13/16")
450 g (15.8 oz)
Primary: Secondary Secondary Voltage Ratio
1:0.110
1:0.095
1:0.077
1:0.055
YEL: Yellow ORN: Orange
WHT: White BLK: Black
Primary Secondary
ST15
Secondary
(100 V Line)
BLU
8Ω
BLK
YEL
6Ω
ORN
4Ω
BRW
2Ω
WHT
Speaker (Common)
WHT
BLK
WHT
2 - ø4.5×6.5 mm
(2 - ø3/16"×1/4")
46 mm (1-13/16")
EN
0 dB
–1.25 dB
–3.0 dB
–6.0 dB
Speaker
(70 V Line)
15 W 7.5 W
15 W 7.5 W
15 W 7.5 W
15 W 7.5 W
BLU
YEL
ORN
BRW
WHT