Fixing Humming Noise for Subwoofers

6 December 2019

A Kentwood Subwoofer was found lying around after we retired the Sherwood Receiver.   It is a passive Subwoofer,  meaning it does not have a built-in amplifier.

 


















After buying a new TV for our sitting room,  we decided to add a sound bar. This sound bar made in China was called  “万音 JY A9S.  It claimed to have 8 speakers but 4 of them are  just “dummies”.  We also found that the Subwoofer output of the sound bar could not drive the passive woofer.

We have 3 options:

1.  To re-refurbish the existing Sherwood Receiver;

2.  To buy another Amplifier receiver;

3.  To upgrade the Kenwood Subwoofer

We choose to upgrade the Subwoofer because it is the cheapest.  We found this Subwoofer amplifier at TaoBao with many good reviews.  The amplifier cost  about CNY$230/= (SGD$44)  including shipping.  The delivery took around 2 weeks by sea.

The Installation

The installation took about 2 hours. Cutting the hole at the back board of the Subwoofer took sometime. The Subwoofer produced fantastic bass. It is worth the money spent.

 

The Problems

There was this loud humming sound coming from Subwoofer whenever the music stopped. Otherwise,  it delivered beautiful sound.  During the test, the sound bar was connected to the phone using Bluetooth.  

Trouble-Shooting

1. The humming would stop under these circumstance

   a)  The music resumes playing;

   b)  The input cable is unplugged;

   c)  The sound bar is switched off

2. The multi-meter showed some ohmic readings when it is connected to the coaxial cable. There was no readings when the music stopped playing. It was as if the sound bar had some sort of mechanical switch "isolating and cutting off" the cable;

3. The humming noise did not go away when the inputs are short-circuited to earth are the Subwoofer;

4. There was no humming sound when the Subwoofer was connected directly to the phone using a 3.5mm to RCA cable

Other Observations

1.  The power supply of the sound bar is a 24 volts switching power without any earthing terminal;

2. The sound bar delivers beautiful sound without humming when connected alone.

What could be wrong?

Floating ground or earthing. There will always be a small voltage between the switching power supply terminal and the earth of the Subwoofer amplifier as shown below. This small voltage will cause humming noise. The humming noise was suppressed when the sound bar was playing music.

The Solution

1.  Open up the sound bar and solder a 25 V 100 uf capacitor in series with a low resistor around 20 ohms as shown

Precautionary Safety Measures

Always made sure that the Subwoofer amplifer has proper earthing. Also make sure the earth is connected to  the  main power supply earth.  

   

Why There are so Many Protests in Hong Kong from another angle.

3 December 2019
# Hong Kong protest,  reasons

The 2019 Hong Kong protests started in Mid-March 2019,  it is now over 250 days and still on going very strong.  it started as a protest against Extradition Law Amendment Bill (Anti-ELAB) and extended to include the following 5 demands:

1  Full withdrawal of the extradition bill;
2. A commission of inquiry into alleged police brutality;
3.  Retracting the classification of protesters as “rioters;
4. Amnesty for arrested protesters;
5. Dual universal suffrage, meaning for both the Legislative Council and the Chief Executive.



So far,  only the first one i.e. the "withdrawal of the extradition bill"  has been fulfilled.

There were much speculations about why Hong Kong has so many street protests.  Tons of videos have been made and web articles have been written to argue about the reasons.  Many were just speculation;  for example,  "someone wants Hong Kong to be separated from China";  "Hong Kong people were losing the high degree of autonomy " etc. etc.  After reading these speculative articles  one could be more confused. 

This video clip found in YouTube made attempts to give the answer from a different prospective:

What are the differences between LED, qLED and OLED TVs?

5 November 2019

Many users must have heard about the 3 types of TV.  The 3 have been around for quite sometime now.   Some might have owned them;  others might have regretted buying.  This article intends to explore the differences to help new users make up their minds.

What are differences between them?

The main differences are in the construction of the TV panel.  The LED and qLED panels are actually LCD panels powered by LED backlights.   The qLED has a special nanopartical layer sandwiched in between the layers.    OLED with an "O" that stands for "Organic" is by itself a special  tiny LED dot developed to emit color lights without the needs of any LED backlight.  

Apart from that differences,  OLED has better color rendering but qLED has better brightness level.   Also,  OLED has a very fast refresh rate,  making it better for gaming   Price wise,  OLED is not only more expensive but also has shorter life. 

The main differences are summarized as follows

	LED	qLED	OLED	Remarks
What it stands for	Ordinary LED	Quantum LED	Organic LED
In Layman's Term		A regular LED TV with a nanoparticles layer called “Quatum Dot” with purpose to improve the color and brightness	A special tiny LED with conductive and emissive coatings of  Hydrogen and carbon modules  to produce colour lights
Materials used of the screen		cadmium selenide (CdSe) nanocrystals	organic module of Hydrogen and carbon
Year Debut	1969	2017	2013
Size	19" to 100"	43” to 85”	55”to 77”
Resolution	4k and 8K	4K and 8K	4K and 8K
Price	Low	Medium	High
Brightness level	Medium	Medium to high	High	The higher the brightness,  the higher the electricity consumption.
Refresh Rates	2 to 8 mSeconds	2 to 8 mSeconds	0.1 mSeconds	Due to other restrictions, most TVs run around 120 Hz
Power Consumption (55”)	Low	Higher	Low to high,  varying widely with brightness level
Color  Contrast	Normal	Good	Excellence
Brightness (cd/m2)	200	500	450
Back Light Required	yes	yes	No
Type	edge-lit, direct-lit, and full array.	backlights enhanced with "quantum dots
Thickness	>=2.5mm	<=1.5mm	<=1.5 mm
Viewing Angle	54	54	84
Life	More than 10 years	More than 10 years	Less than 10 years	OLED has lesser life;   some said less than 5 years

Who Sells What in the Market ?

Almost every TV makers are selling LED TVs;  however,  the makers are divided when it comes to selling qLED and OLED TVs.    Samsung appears to sell mainly the qLEDs and  LG and Sony are the sellers for OLED TVs. 

The following compares the 55" specification with the important details highlighted

Doubleclick to Enlarge

Which Type is more popular and Which to buy?

LED and other  TVs are still having the lion share of the TV market in 2018 according to IHS Markit,  a leading source of information for businesses.  This is followed by qLED and OLED at 1.2% and 1.1% respectively as shown

Judging from the sale statistic,  it would not be hard to come up with a conclusion that most users will  choose to buy an LED TV,  not only because LED TV is much economical  but also there isn’t much cheaper and free 4K movies and medias  available to justify paying the additional cost.  

Moreover,  running the TVs at higher brightness level with brilliant colors will not only shorten the life but also requires more electricity.  At the moment,  the high end TV  is just not  just a "piece of cake"  for the common users.    

Why TV’s HDMI ARC Not Working?

4 November 2019

google:  https://tinyurl.com/w5p53tj
# ARC # MiTV4 # sound system

1) Why ARC Not Working?
2) How to Set up the ARC?
3) Why There is still no Sound?
4) Why the Audio Receiver’s Sound is Always Muted?
5) Why no 5.1 Sound Surroud? 
6) About Audio Connection options
7) More about Audio Connection
5) How to Tell Cable can work in ARC?

 

Many MiTV and other TV users found their Audio Receivers connected to their TV’s HDMI ARC not working.  This article attempts to explain why and how to fix this connection problem

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Why?

To know why,  one must understand how ARC (Audio Return Channel) works.  ARC was a new HDMI feature in 2009 when HDMI came out with version 1.4.  What ARC does is to convert the TV’s input HDMI ports into an output HDMI port so that the TV can send signals in reverse to the output of the connected devices such as Audio Receivers.

 

For this to happen,  the TV and the connected devices must be set so that the TV can “command” the connected devices to convert their output port ready to receive the signal from the TV.   This commanding action is done through HDMI’s CEC control (pin 13 of the HDMI cable).   Many users often neglect to turn on this CEC control and therefore, the ARC will never work.

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How to Set up the ARC?

Step by Step	Action	Remarks
1.   HDMI cable	Check version of cable	Must be HDMI version 1.4 and above
2.  Cable Connection	Check and remember which HDMI port has ARC connectivity;  Connect one end of the cable to TV’s HDMI (ARC) port and the other end to the HDMI output (ARC) port as shown	Double click to enlarge Double click to enlarge
3. TV Settings (For MiTV4 with Patch Wall OS)	1.  Turn on CEC control for the HDMI ARC port a)  Select the HDMI ARC port from [Signal Source] in the main menu b) Click the  [Menu] button (with 3 horizontal lines) on the right hand of the remote to show the menu as shown in the left.  c) Select [Playback setting] to show the picture on right;  then turn on the [CEC Remote Control] d)  Repeat the same for other HDMI but this time,   turn the [CEC Remote Control] off.	Double click to enlarge Double click to enlarge
	2.  GoTo the Apps Store,  select [Setting] and then [Sound] to set the [Speaker] to [HDMI ARC]  as shown	Double click to enlarge
3(a)  TV Settings for MiTV4 with Android TV OS)	1.  GoTo the [Setting] and select the connected  HDMI ARC input 2.  Turn the CEC’s HDMI Control on as shown on the right 3.  GoTo  [Sound] in the setting menu and change the speaker output to [HDMI ARC] 4.  Repeat same for other HDMI inputs but this time,  turn off the HDMI Control	Double click to enlarge Double click to enlarge
4.  Audio Receiver Setting	Read up the manufacturer’s manual to set the HDMI ARC port to receive signal from the TV
5.  Testing	Reboot the TV and Audio Receiver and check if there are sound output;

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Why There is still no Sound?

There may be a need to remove all the other HDMI devices connected to the TV.  This is because one or more devices might have “hijacked” the CEC control as they do not comply with the HDMI CEC specification.  

To isolate these devices,  remove all other  HDMI devices connected to the TV and reboot with only the Audio Receiver connected.   If there is sound,  switch off the TV and reconnected the other devices one by one;  repeat the above process for each reconnection until the “culprit” is found.

There are several ways to disable the CEC control of the “culprit”.  One way is to connect the HDMI cable of the “culprit” through a “CEC less adapter” as shown

The other way is to blank out and  isolate  pin 13 of the HDMI cable as illustrated in this picture

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Why the Audio Receiver’s Sound is Always Muted? 

When the TV’s CEC control is turned-on,  The TV’s remote controller will take over the following 3 functions from the Audio Receiver’s remote controller

1.  Sound mute
2.  Volume control

3.  Power on and off

Therefore,  it might be necessary to unmute the sound or turn up the volume using the TV’s remote controller  when there is no sound.

Some stereo system's muted light will show up when the TV is not sending any sound. Turn up the TV's volume using the TV's remote controller just to check..

If there is still no sound and the muted light on the Audio Receiver is still on,  try turning off the  TV's CEC control.  If the Audio Receiver's muted light won't go away,  try to unplug the HDMI cable and if necessary,  do a reset on the Audio Receiver;  after that reconnect the cable and reestablish the ARC connection.

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Why no 5.1 Sound Surroud?

1.  Make sure the TV and the Audio Receiver can support compressed audio signal such as DTS or Dolby Digital;  if not,  set the Digital Output to [PCM] for normal stereo sound system

2.  Otherwise,  set the Digital Output to [Digital Auto] or [RAW]

3.  For MiTV4 PatchWall OS,  there is a need to set the [Dolby Effect] to support [Virtual Sound Surrond] as follows

a)  GoTo the Setting/Sound/Sound Effect,  side step to new Dolby setting and enter the desired sound effect

                       

                                                                  (Double Click to Enlarge)

b) GoTo the HDMI ARC input screen, click the [Menu] button on the remote to bring up the Menu Screen, then select Sound and side step to select Setting 1 as shown below

    

                                      (Double Click to Enlarge)  

What is the difference between PCM,  RAW  and Dolby Digital 

PCM – stands for Pulse Code Modulation.  It is a standard form of digital audio.  It will deliver stereo sound whether or not the program is in stereo or 5.1 channel.

Dolby Digital – is a audio format developed for surround sound.  It enables surround sound to be delivered in 5.1 channels.

RAW – is a audio format that is in its natural form,  uncompressed.  It will deliver stereo sound for stereo track and 5.1 surround sound for 5.1 channels. 

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How to Tell Cable can work in ARC?

The HDMI cable must be version 1.4 and above for the ARC to work.  This is because those earlier version  will either have pin 13 or pin 14 or pin 19 of the cable either shorted to ground or not connected.  One could do the following to check with a multimeter.