Download In-Wall Volume Control Installation Instructions

In-Wall Volume Control
Installation Instructions
Stellar Labs™ In–Wall Volume Controls are designed for
connection between the speaker output of an amplifier,
speaker selector, or distribution box, and a speaker pair.
They adjust the volume of remote speakers by attenuating
the audio signal, after the amplifier. To assure maximum
power transfer and efficiency, and minimal heat, these
controls use autoformers instead of L-pads or resistor
networks. These controls are available in four different
colors, with models capable of handling 100W or 300W of
peak music power.
All Stellar Labs™ Volume Controls represented here are
impedance-matching type. While they are perfectly suitable
in applications utilizing only one pair of speakers, they also
enable a typical stereo amplifier to drive up to 16 pairs of
speakers, without impedance related problems.
Impedance Matching Volume Controls
White
Ivory
Almond
Black
Model
100 Watt
50-7820
50-7821
50-7822
50-7823
300 Watt
50-7840
50-7841
50-7842
50-7843
Stellar Labs
Division of MCM Electronics
650 Congress Park Drive
Centerville, Ohio 45459
www.mcmelectronics.com
© 2010 MCM, a Premier Farnell Company
SPEAKER and AMPLIFIER IMPEDANCE
Calculating Speaker Impedance
All speaker systems place a load on the amplifier driving them. That load, determined by the impedance of each speaker
system, is measured in ohms (designated by the Ω symbol). The actual impedance of a given speaker system will vary
depending upon the frequency at which that impedance is measured. To ease impedance calculations, speaker manufacturers
rate speakers at average (or nominal) impedance, across the rated frequency response of that speaker. For consistency, most
in-wall and ceiling speaker manufacturers follow an established standard of 8Ω. This ensures that multiple–speaker installations
have power distributed evenly across the entire system.
From this point forward, all calculations will be with regards to one amplifier channel. In stereo applications, the same
consideration must be given to both the left and right channels.
Since all speakers in a given system are typically be the same impedance, we will use a very simple method to calculate the
total impedance of multiple speakers connected to an amplifier. Simply divide the impedance of the speakers by the number of
speakers connected. If one pair of 8Ω speakers is connected to a stereo amplifier, the resulting load on each amplifier channel is
8Ω. If two pairs of 8Ω speakers are connected, the resulting impedance is 4Ω. If three pairs are connected, the resulting
impedance is 2.67Ω, four pairs result in 2Ω and so on.
The challenge encountered with distributed audio systems, is they normally involve many speaker pairs connected to a single
amplifier, and most amplifiers cannot handle speaker loads below 4Ω (although some models handle loads as low as 2Ω).
Because of this, systems utilizing more than two pairs of speakers on a 4Ω amplifier must have the speaker impedance
increased to ensure the load does not become too low.
Stellar Labs™ Volume Controls
This is where Impedance Matching Volume Controls come in. Each Stellar Labs™ In-Wall Volume Control includes an
Impedance Matching circuit, with selectable multiplier taps, enabling a single amplifier to drive a large number of speaker pairs.
Located on the rear of each control are jumper pins, with an attached shorting bar. By selecting the appropriate pins, the
impedance of the connected speaker is multiplied by x1, x2, x4 or x8. For example, an 8Ω speaker connected to a control set for
x4, now becomes a 32Ω speaker load. If the control is set for x8, the speaker load is now 64Ω. As you can see, this enables a
far greater number of speakers to be connected to a standard amplifier, and maintain a load above 4Ω. Additionally, if multiple
speaker pairs are used, that happen to have differing impedance, the multiplier can be used to even out the actual impedance
load of each speaker.
When connecting multiple speaker pairs to a stereo amplifier, a separate volume control should be used for each pair. Also,
depending upon the number of speaker pairs used, and the impedance of each speaker, it may not be possible to achieve a final
impedance of 4Ω per channel at the amplifier. Since most amplifiers operate most efficiently between 4Ω and 8Ω, it is perfectly
acceptable as long as the resulting impedance falls within that range. If that value is not possible, a resulting impedance above
8Ω is also fine, although the amplifier will not operate as efficiently. The critical issue is not to fall below 4Ω (unless the amplifier
happens to be 2Ω stable), because at that level many amplifiers will fall into protection mode and shut down, and possibly
sustain damage. If you are not certain of the minimum load of the connected amplifier, assume it is 8Ω.
INSTALLING IN–WALL VOLUME CONTROLS
Mounting
All Stellar Labs™ in-wall volume controls are designed for installation in a standard single–gang electrical box. Take note that
depending upon model, these controls will require at least 3" mounting depth. Because volume controls are considered a low–
voltage device, they may suitably be mounted in open-backed boxes, brackets or mud rings. This type of mounting is often
considered desirable as it allows for more space behind the control for routing cables. Multiple gang brackets and electrical
boxes are available for installing multiple units in one location. These types of mounting devices are readily available from most
home building centers, and various models from Carlon, Caddy and Arlington are readily available directly from MCM
Electronics.
Caution: Low voltage devices, such as volume controls may not share an electrical box with standard AC wiring devices such
as wall switches, AC receptacles or dimmers.
Connections
When routing cable through walls to speakers and volume controls, care should be taken to avoid close proximity to AC power
lines. This is important for safety reasons, as well as reducing the possibility of noise being introduced on the line. When
selecting in–wall speaker wire, be sure to use cable designed for that purpose. Two or four conductor, 16AWG or 14AWG wire is
recommended, and most local electrical codes require cable to carry a CL2 or CL3 rating. Be sure to verify compliance with
local codes prior to installation.
Caution: Speaker cabling and AC power lines should never pass through the same opening drilled in interior wall studs.
FINAL SETUP AND USE
Testing
Once all controls and speakers are installed, it is recommended that the system be tested prior to connection to the amplifier.
This will ensure that the desired speaker load is present at the amplifier output, thus preventing possible amplifier shutdown or
damage. The most effective way to accomplish this is to measure the impedance at the amplifier (without the amp connected).
An impedance measuring device such as the Tenma Model 72-6947 is required to accurately accomplish this. This meter
measures the impedance of a speaker system, at an audio frequency of 1KHz. This step can serve as a reliable method of
preventing unreliable and potentially damaging operation later.
Note: Using a standard DMM, ohmmeter or multimeter is not effective for this purpose, as these devices measure impedance at
DC, not at an audio frequency. Since a speakers and volume control devices impedance varies with frequency, a standard ohm
meter will not provide accurate readings.
Setup
• Once the amplifier is connected to the system, prior to turning on the power, make sure that the amplifier gain
(volume) is set to the MINIMUM setting
• Be certain that all of the In–Wall volume controls are set to the MAXIMUM setting
• Turn the amplifier on and select a desired music source
• Slowly increase the volume of the amplifier until sound is heard from the speakers
• Walk through all areas in which speakers are installed, and make certain that sound is present at all speakers
o If sound is not present at any speaker, turn off the amplifier power and check speaker connections
• Adjust the volume or balance control fully to one channel (either left or right)
• Again, walk through all areas, noting that sound is present at only one speaker
• Change the volume or balance control to shift fully to the opposite channel (either left or right)
• Walk through all areas, noting that sound is present at the opposite speaker than in the prior walkthrough
o If incorrect results occur, turn off the amplifier power and check speaker connections
• Adjust the volume or balance control so that the left and right channels are now equal
• Now adjust the volume of the amplifier to just above the level that will be considered the maximum listening level
from the system
• Move through each area, adjusting the in–wall volume controls to a comfortable listening level
Note:
If at any time, the amplifier temporarily disengages, or shuts down, the system should be powered down and checked for proper
connections. If it is determined that all speakers, volume controls or other devices are connected properly, and the system
continues to shut down, there is possibly a speaker impedance problem.
In this case, power down the system, remove the volume controls from the wall, and select the next higher impedance multiplier
setting.
For additional information regarding distributed audio system installation, please consult documentation included with other
components. For additional questions, please contact the MCM Technical Support Department at 1-800-824-8324, or send an
email to [email protected].
Specifications
White
Ivory
Almond
Black
Power Capacity (RMS)
Power Capacity (Peak)
Frequency Response
Impedance Multipliers
Rotary Switch Positions
Attenuation step
Position 1~7
Position 8~11
Position 12
50-7820
50-7840
50-7821
50-7841
50-7822
50-7842
50-7823
50-7843
25W
100W
100W
300W
35Hz~20KHz
x1, x2, x4, x8
12
3dB per step
6dB per step
Off (fully counter clockwise)
Dimensions
25W RMS / 100W peak models
100W RMS / 300W peak models
MCM Custom Audio and Stellar Labs™ products are warranted, by MCM Electronics, against manufacturer
defects for a period of one year from the original date of purchase. This warranty is limited to manufacturer
defects, in either materials or workmanship. MCM Electronics, or any other worldwide divisions of Premier Farnell
PLC, are not responsible for any consequential or inconsequential damage to any other component, structure or
the cost of installation or removal of said items.
For questions or specific information regarding warranty replacement or repair, contact:
MCM Electronics
650 Congress Park Drive
Centerville, Ohio 45459
1-800-543-4330
www.mcmelectronics.com