Noise in electronic circuits Interview Questions 

Ok i have been looking for amps for an amp for a while for my 12" kicker L7 2ohm DVC 750RMS and narrowed it down to these to amps witch one is best

JBL-Efficient High-frequency switching Class D power supply
12dB per octave electronic crossover
RCA low-level inputs
Full-range preamp outputs
Variable bass boost circuit for optimized system response
787 watts RMS x 1 @ 4 ohms
1114 watts RMS x 1 @ 2 ohms 14.4V supply
Dynamic Power 1339 watts at 2 ohms
Damping Factor: 6.348 at 4 ohms
maximum Input Signal: 6.1V
Variable electronic crossover and bass-boost

VS

MTX-# Class D technology
2000 WATTS PEAK OUTPUT (1,000 TRUE RMS)
Speaker level inputs
12 dB bass boost @ 40 Hz
Subsonic filter
Built-in low pass crossovers
Large extruded heat sink
700wrms x 1 @ 4ohms
Anodized finish
1000w RMS x 1 @ 2 ohms
2 ohm stable
THD at 4-Ohm RMS Power: <1%
Built-In Crossovers
Bass Boost: 12dB @ 40Hz
Frequency Response: 20-200 Hz
Signal to Noise Ratio: >75 dB
Channel Separation
Subsonic Filter: 20Hz to 50Hz,12

1. In selecting the wire size for a line cord, you should remember that
A. No. 16 is larger than No. 12.
B. No. 14 carries more current than No. 18.
C. No. 8 is smaller than No. 10.
D. No. 4 carries less current than No. 6.

2. Which one of the following appliance parts gets the hardest service?
A. Switch
B. Thermostat
C. Heating element
D. Line cord

3. The color used for the hot side of house wiring is
A. green.
B. white.
C. gray.
D. black.

4. An AWG No. 16 line cord with type HPN insulation has an ampacity of
A. 12 amp.
B. 13 amp.
C. 15 amp.
D. 17 amp.

5. To heat a room quickly, some electric room heaters are provided with
A. a heavy metal case.
B. a motor-driven fan.
C. a push-button switch.
D. an automatic thermostat.

6. If the current flowing through an electric heater increases from 6 to 12 amp while the voltage remains the same, the heat produced by the heater will be
A. reduced one-half.
B. unchanged.
C. two times the original heat.
D. four times the original heat.

7. The wires used in a heating element are usually made of
A. copper.
B. steel.
C. aluminum.
D. Nichrome.

8. Why does a thermostat blade bend when heated or cooled?
A. It is made of two different materials.
B. There is a difference in temperature between the blade ends.
C. Different currents are applied to each end.
D. Mechanical pressure is caused by the high resistance.

9. When you are checking an electric heating appliance, the first test made should be for
A. excessive leakage.
B. the normal voltage supply.
C. an open circuit.
D. low resistance.

10. Why should you NOT repair heating elements by soldering?
A. Solder does not conduct electric current.
B. Solder joints are mechanically too weak.
C. Solder melts at the operating temperature of the heater.
D. Soldered joints have too high a resistance.

11. What type of selector switch can be used to control the heat output of three elements connected in parallel?
A. SPST switch
B. DPST switch
C. DPDT switch
D. Shorting-bar-type switch

12. Thermostats used in electric irons differ from those in small room heaters in that they are
A. smaller in size.
B. operative at higher temperatures.
C. connected directly to the appliance plug.
D. mechanically more fragile.

13. How can you clean out the scales in an electric iron without taking the iron apart?
A. By blowing out the holes with compressed air
B. By scraping the tank and tubes with a drill bit
C. By brushing the clogged tubes with a stiff wire brush
D. By rinsing the tank and holes with a water-diluted chemical

14. Bus bars are used in an electric iron as
A. thermostat supports.
B. heat-adjusting resistors.
C. connectors between the thermostat and the element.
D. electrical terminals.

15. The water in a spray iron is prevented from returning to the tank by the action of a
A. suction tube.
B. check valve.
C. water pump.
D. pressure spring.

16. The heating element in an electric iron is in good working order if the resistance across the terminals of the element reads approximately
A. 0 ohms.
B. 15 ohms.
C. 120 ohms.
D. 1000 ohms.

17. Why does the heat of the heating element stop when the desired temperature in an electric iron is reached?
A. The thermostat blade opens electrical contacts.
B. The circuit through the element is closed.
C. The switch bypasses the thermostat.
D. The contacts on the blade touch.

18. Jumpering out the resistors in a resistance-controlled three-speed fan will cause the motor to
A. run at highest speed.
B. run at medium speed.
C. run at lowest speed.
D. stop immediately.

19. A fan equipped with a gearbox is capable of
A. running at three speeds.
B. being tilted downward.
C. oscillating from side to side.
D. reversing the direction of the motor.

20. If the fan blades rattle while the fan is turning, you can stop the noise by
A. oiling the blades.
B. adjusting the blade angles and the blade tip position.
C. tightening the motor end bells and motor mounts.
D. cleaning the blade surfaces.

21. The recommended way to hold a loose hub on a fan is by
A. riveting.
B. soldering.
C. welding.
D. cementing.

22. Quiet operation of a fan depends mostly upon the
A. weight of the blades.
B. material of the blades.
C. motor balance.
D. balance of the blades.

23. The blades of small fans are made of
A. aluminum.
B. steel.
C. tin.
D. copper.

24. A modern variable-speed fan does NOT use
A. a tapped inductor.
B. a multiple-winding motor.
C. an electronic speed control.
D. a dropping resistor.

25. An attic fan, or power ventilator, may have its power inadvertently tapped from
A. an upstairs bathroom.
B. an attic lighting circuit.
C. a basement service.
D. an air conditioning circuit.

Hifonics BXi606 1-Channel Car Audio Amplifier
Monoblock Class A/B Amplifier with Bass Level Control
RMS Power Ratings:
1 ohm: 600 watts x 1 channel
2 ohms: 300 watts x 1 channel
4 ohms: 150 watts x 1 channel
Hifonics New Illuminated Heat-Sink Design With Blue LED Light Pumps
Hifonics Blue Illuminated Logo
Maxxsonics Illuminated "M" End Panel Logo
Heavy-Duty Ultra-Fi" MOSFETS
Highly Efficient Super D-Class Amplifier Circuitry With Oversized MOSFET Output
Fully Adjustable Accu-Cross" Crossovers
±18dB Variable Bass Equalization @ 45Hz
180° Variable Phase Control (15 to 35Hz)
Dash-Mountable Bass Remote Control Included
Variable 24dB Subsonic Filter
Brutus Pulse Wave Modulated MOSFET EXVP (Exponential Vari-Power Supply)
Twin-Turbo Torroid Coil Design
HSMD Hifonics Surface Mount Design
Balance Line Inputs for our 18-Volt Line Drivers
RCA Line Output for Amplifier Daisy Chaining
Gold 4-Gauge Power Connectors
Dimensions: 9.84"L x 10.39"W x 2.63"H
1-year Techronics.com warranty
MTX Audio TA2301 Thunder 2301
300W RMS, Class D Monoblock Amplifier Thunder2301 Product DescriptionThunder TA Series Class D Monoblock Car Amplifier
RMS Power Rating:
4 ohms: 150 watts x 1 chan.
2 ohms: 300 watts x 1 chan.
Max power output: 300 watts x 1 chan.
MOSFET power supply
Wired remote bass level control included
Thermal and short LED indicators
Tuned Bass EQ (0-12 dB bass boost at 40 Hz)
Adaptive Class D Technology: With MTX innovative approach, the amplifier’s switching energy is constantly changing and is moved away from FM radio frequency ranges as the amplifier’s load and output increases.
Thermal and short protection
StreetWires Connectors
Xtant Technologies Cooling (XTC) thermal-regulated, turbo-charged intercooler
Variable low-pass filter (at 80 or 120 Hz, 24 dB/octave)
CEA-2006 compliant amplifier
Dimensions: 12-11/16"L x 9-5/8"W x 2-1/2"H
4 or 8-gauge power and ground leads recommended. Contact us for information regarding a discount on a select amplifier kit when purchased together.
1-year Sonic Electronix warranty
Amplifier Specifications:

Amplifier Class D
Number of Channels 1 - Mono
RMS Power (4 ohms) 150 watts x 1 channel
RMS Power (2 ohms) 300 watts x 1 channel
RMS Power (1 ohm) Not Stable
Bridged RMS Power N/A
Peak Power Output N/A
Minimum Impedance Unbridged 2 ohms
Minimum Impedance Bridged Not Bridgeable ohms
THD at Rated RMS Power .5%
Speaker Level Inputs No
Preamp Outputs Yes - 1 pair
Built-in Crossover Low-pass (LP)
High-Pass Crossover Frequency N/A
Low-Pass Crossover Frequency 80
Subsonic Filter N/A
Signal-to-Noise Ratio 73 dB
Channel Separation N/A
Bass Boost 0 - 12 dB
Bass/Gain Remote Yes
Fan Cooled Yes
Fuse Rating 20A x 2
2000W Pyle Dryver PLAD413 4 Ch High Power MOSFET AmpBrand New Pyle Dryver PLAD413 2000 Watt 4 Channel High Power MOSFET Amplifier
4x 200W RMS at 4 Ohms
4x 500W MAX at 4 Ohms
2x 800W MAX at 4 Ohms Bridged
4x 350W RMS at 2 Ohms
Electronic Crossover Network
Bass Boost Circuit
Bridgeable at 4 Ohms
2 Ohm Stereo Stable
Tri-Mode Capable
Gold Plated RCA Inputs
Line Outs for 1 and 2 Channel
Low Pass Filter Control
High Pass Filter Control
Remote Bass Level Control
Power and Protection LED Indicators
Red Lighting Illumination
Side Leg Mounting
THD: <0.04%.
S/N Ratio: >90dB
Input Sensitivity : 100mV ~4V
Channel Separation : >65dB
Freq. Response : 10Hz ~ 30KHz
Patent Pending
Soft Turn-on/Turn-off
Dimensions : 8.6''(W) x 2.74''(H) x 12.6''(L)
Item Manual: PLAD413 Click Here

I know telephone lines are a complete loop between the phone company and an individual's home phone, hence the current changes result in changing magnetic fields, which push on a speaker to make noise. As a current is the actual electronic messenger, it makes sense that a closed loop between the two phone talkers is neccessary.

Then I was watching tv and was wondering if the television is part of a closed circuit with the cable company. Is the electronic signal transmitted by cable a closed path or not? If it isn't a closed circuit, then the message could not be transmitted by current right? It must be an EMR wave?

When you turn it off, you hear a electronic pop in my stereo system and TV surround system. Both are on different circuits from the fan (and different from each other). I have 3 other fans in my house and none do this. I've replaced the switch mechanism in the fan. Oh, and it is not the wall switch, same pop happens when the fan is turned off with the pull cord. It also pops when you use the pull cord to reduce the speed. Doesn't do it when you turn it on with either the wall switch or built in switch. Just off or reduced speed with both the wall or internal switch. Happens both forward and reverse. No noise with fan running.

Fan is on a 20 amp circuit with plenty of headroom. Wire to the box is 12/2.

I'm thinking it is the fan itself but would welcome any other ideas.

Please no "call an electrician". I built and wired this house myself, 30 years ago.

Thanks.

Microwave slowly stopped working while heating a bowl of soup. It did not make any noises, show any other signs of problems, just slowed down and died (like batteries running down in an electronic device). No display, no power.

Plugged it into another outlet and still nothing. Circuit breaker at box is still on (other items plugged into original outlet work fine).

Panasonic Model NN-S763BF 1350 Watt
Genius Sensor Inverter
Purchased from Costco 1.5 years ago (out of warranty)

What are the 2 main source of noise? and how could each be handled?