Knoll Systems MA850 Important Safety Instructions, Hum and noise, Suggestion #1, Suggestion #2

Important Safety Instructions:

1)Read these instructions.

2)Keep these instructions.

3)Read all warnings.

4)Follow all instructions.

5)Do not use this apparatus near water.

6)Clean only with dry cloth.

7)Do not block any ventilation openings. Install in accordance with the manufacturer’s instructions.

8)Do not install near any heat sources such as radiators, heat registers, stoves, or other apparatus (including amplifiers) that produce heat.

9)Do not defeat the safety purpose of the polarized or grounding-type plug. A polarized plug has two blades with one wider than the other. A grounding type plug has two blades and a third grounding prong. The wide blade or the third prongs are provided for your safety. If the provided plug does not fit into your outlet, consult an electrician for replacement of the obsolete outlet.

10)Protect the power cord from being walked on or pinched particularly at plugs, convenience receptacles, and the point where they exit from the apparatus.

11)Only use attachments/accessories specified by the manufacturer.

12)Use only with the cart, stand, tripod, bracket, or table specified by the manufacturer, or sold with the apparatus. When a cart is used, use caution when moving the cart/apparatus combination to avoid injury from tip-over.

13)Unplug this apparatus during lightning storms or when unused for long periods of time.

14)Refer all servicing to qualified service personnel. Servicing is required when the apparatus has been damaged in any way, such as power-supply cord or plug is damaged, liquid has been spilled or objects have fallen into the apparatus, the apparatus has been exposed to rain or moisture, does not operate normally, or has been dropped.

15).Under no circumstances should the output terminals of the amplifier be short- circuited.

16).Be sure that the loudspeakers connected can handle the output power of the amplifier at the loudspeakers rated impedance. The warranty on the amplifier does not cover damage to loudspeakers that have inadequate power handling capabilities.

17)Where an all-pole MAINS SWITCH is used as the disconnect device, the location on the apparatus and the function of the switch shall be described, and the switch shall remain readily operable;

18)A push button is used to turn the power off and on.

19)A LED is used to show when the apparatus is powered on.

CAUTION: These servicing instructions are for use by qualified service personnel only. To reduce the risk of electric shock do not perform any servicing other than that contained in the operating instructions unless you are qualified to do so.

WARNING: This product contains chemicals, including lead, known to the State of California to cause birth defects or other reproductive harm. Wash hands after handling.

Hum and noise

In most cases, one of the following suggestions should help you solve a hum noise in your system. Please try these steps in the order shown, proceeding from one step to the next if the prior suggestion does not eliminate the problem.

Suggestion #1

To determine if a cable TV connection is responsible for the hum, first turn off all the components. Disconnect the cable TV feed to your system at the first place where it connects to your components. Alternatively, disconnect the cable TV wire where it is connected at the wall outlet. Turn your system back on, and listen if the hum has disappeared. If removing the cable TV feed has eliminated the hum, you will need to insert a Ground Loop Isolator (Knoll model GB634) before reconnecting the cable TV feed, or contact your cable TV operator to see if they can better isolate your cable feed.

Suggestion #2

Turn off all components in your system and then disconnect the input cables at the amplifier. Turn the amplifier back on to see if the hum is still present. If the hum disappears, the fault may be in the input cables used. Try replacing them with cables that have better shielding, and make certain that the input cables are not running on top of any AC power cords. Change the cables one at a time to determine if one or all cables are responsive. If the hum disappears when the input cables are disconnected but returns after the cables are changed and the system reconnected, your source device may be causing the problem.

Suggestion #3

Poor grounding of the electrical system in your home may also cause ground loop problems, particularly when there are multiple components with three prong, grounded, power cords. Unplug these components one at a time, and see if one or all of them is causing the problem. The ultimate solution to this type of problem is to rewire your house with an isolated, star type-grounding configuration. Knoll understands that this may be impractical and expensive. In some instances, the use of an approved AC Power Isolation Transformer (Knoll model PLB200) of sufficient capacity may solve this problem.

Warning: If you suspect that the grounding system in your home’s electrical wiring is causing the hum problem, it is important that you do not make any changes to the wiring. Only a licensed electrician should make any changes to household wiring and they must be made in full compliance with all local building, safety and electrical codes.