Monoprice 38171 User manual

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75-Watt Impedance Matching Rotary Speaker Volume Control
P/N 38171
Quick Install Guide
INTRODUCTION
This Impedance Matching Volume Control allows you to connect multiple speaker pairs to
a single power amplifier or receiver. It increases (or decreases) the impedance of the
connected speaker pair to ensure that the overall impedance level presented to the
amplifier is high enough to prevent damage to the amplifier. It can support amplifiers with
up to 75 watts of output power and fits into standard single-gang low-voltage junction
boxes or mounting brackets.
INSTALLATION
Perform the following steps to install one or more volume controls to your stereo system.
These instructions assume that you have already installed all speaker pairs and low-voltage
mounting brackets at the desired locations.
1. Refer to your amplifier's manual to determine the minimum impedance level that
can be safely connected. In most cases, the minimum impedance is 4, 6, or 8 ohms,
though some amplifiers are stable down to 2 ohms.
2. Determine how many speaker pairs are to be connected and the nominal
impedance of each pair. Note that only a single pair of speakers should be
connected to each volume control.
3. Refer to the following tables to determine the switch settings for each
volume control, depending on the minimum impedance load of your
amplifier, then set the switches on all volume controls to the indicated value.

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8-Ohm Capable Amplifier
Number of 8-Ohm
Speaker Pairs
Switch Position
1-4 pairs
4x
5-8 pairs
8x
More than 8 pairs
Not
Recommended
6-Ohm Capable Amplifier
Number of 8-Ohm
Speaker Pairs
Switch Position
1-5 pairs
4x
6-10 pairs
8x
More than 10 pairs
Not
Recommended
4-Ohm Capable Amplifier
Number of 8-Ohm
Speaker Pairs
Switch Position
1 pair
1/2x
2-8 pairs
4x
9-16 pairs
8x
More than 16 pairs
Not
Recommended
8-Ohm Capable Amplifier
Number of 4-Ohm
Speaker Pairs
Switch Position
1-4 pairs
8x
More than 4 pairs
Not
Recommended
6-Ohm Capable Amplifier
Number of 4-Ohm
Speaker Pairs
Switch Position
1-2 pairs
4x
3-5 pairs
8x
More than 5 pairs
Not
Recommended
4-Ohm Capable Amplifier
Number of 4-Ohm
Speaker Pairs
Switch Position
1-4 pairs
4x
5-8 pairs
8x
More than 8 pairs
Not
Recommended

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4. Run an in-wall rated speaker wire from the left-channel speaker to the low-voltage
mounting bracket intended for use with this speaker pair.
5. Connect the wire to the left channel speaker, taking note of the wire colors or
markings used for the positive (+) and negative (-) connections.
For best results, always use the same wire colors or markings for the positive and negative
connections.
6. Connect the other end of the left-channel speaker wire to the L+ and L- Output
terminals on the volume control, taking care to match the polarity.
7. Run an in-wall rated speaker wire from the right-channel speaker to the low-voltage
mounting bracket intended for use with this speaker pair.
8. Connect the wire to the right channel speaker, taking note of the wire colors or
markings used for the positive (+) and negative (-) connections.
9. Connect the other end of the right-channel speaker wire to the R+ and R- Output
terminals on the volume control, taking care to match the polarity.
10. Run an in-wall rated speaker wire from the low-voltage mounting bracket intended
for use with this speaker pair to the amplifier. Mark the wire as the left-channel wire
at the amplifier end.
11. Connect the left-channel amplifier wire to the L+ and L- Input terminals on the
volume control, taking note of the wire colors or markings used for the positive (+)
and negative (-) connections.
12. Run a second in-wall rated speaker wire from the low-voltage mounting bracket
intended for use with this speaker pair to the amplifier. Mark the wire as the right-
channel wire at the amplifier end.
13. Connect the right-channel amplifier wire to the R+ and R- Input terminals on the
volume control, taking note of the wire colors or markings used for the positive (+)
and negative (-) connections.

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14. Install the volume control into the low-
voltage mounting bracket, taking care
to ensure that the wires do not come
loose from their connections or become
pinched or shorted.
15. Repeat steps 4-14 for each additional
speaker pair, low-voltage mounting bracket, and volume control.
16. Ensure that the amplifier is powered off and unplugged from the power source.
17. At the amplifier, use a terminal block or wire nut to connect all the left-channel
negative (-) wires and a short length of speaker wire together.
18. Connect the negative lead on the short length of speaker wire to the left-channel
negative (-) terminal on the amplifier.
19. Repeat steps 17-18 for the left-channel positive (+) lead.
20. Repeat steps 17-19 for the right-channel negative (-) and positive (+) leads. The
image below illustrates a proper connection for two volume controls.

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21. Determine which room or speaker pair you want to be the loudest, then turn the
volume control fully clockwise to the maximum position. If all zones are to be the
same volume level, set all volume controls to the maximum level.
22. Set the volume control on the amplifier to the minimum level.
23. Plug in and power on the amplifier.
24. Start audio playback, then slowly increase the volume control on the amplifier until
the volume level in the selected room(s) are at the maximum level you will want
with no distortion. If distortion can be heard, reduce the volume level until
distortion can no longer be heard.
25. Leave the volume control on the amplifier at the set position, then use the
individual zone volume controls to set the volume in each zone to a comfortable
listening level.
ONLINE SUPPORT
Monoprice is pleased to provide free online support. For order related issues, contact the
Customer Service department through the Live Chat link on our website
www.monoprice.com or via email at [email protected]
For technical issues, contact the Technical Support department through the online chat
button on our website www.monoprice.com or via email to [email protected]
Check the website for support times and links.