FORUMS
Remove All Ads from XDA

[Mod] Weak microphone quality: Split up BT and Sys; Add external microphone(s)

103 posts
Thanks Meter: 61
 
By dnts, Senior Member on 1st October 2014, 07:13 AM
Post Reply Email Thread
Specific to KGL

I've had the KGL variant for a couple of weeks. Since I've had my share of Chinese Android devices of all sorts - I kind of knew what to expect in terms of software.. so I wasn't really disappointed BUT... the hands free in this unit was simply unusable... After getting my wife totally upset and my friends pissed at me for calling them using the unit I knew something had to be done.
So I took it apart.
Being that I'm skilled in electronics and pretty much hands-on, I figured out the problem pretty fast. Or should I say "problems" in plural?
Let me start by saying that if you have the KGL variant and suffer from extreme noise bleeding into the mic - there is no software workaround. You either need to send it back and get something else or open and modify it like I did.
Second - the hardware in this thing is of such low quality, and the design is so bad, it makes me cry. I estimate the production cost of this unit is under $50. Pretty pretty low... even for Chinese stuff.

So.. what's the story with the mic noise, you ask? very simple. The mic signal from the front panel is routed unshielded from a small PCB attached to the panel, via 3 PCBs and 2 ribbon cables, for over 15" until it arrives at the Bluetooth module MIC input. On the way, it picks up so much electrical noise and interference it's almost a miracle that you hear anything but static noise. When an external mic is plugged it, the front panel mic is NOT disconnected. Both are electrically connected in parallel which is unheard of (very bad practice). The Bluetooth module is thus responsible for MIC bias and preamp. The BT module is of unknown source and it's hard to tell what quality to expect there (not much, as we all know). Noise cancellation? echo cancellation? forget it!
Now - we know android needs an audio input - we can have some voice activation on the unit, right? so how is it done? simple! the signal from the BT mic input line is run back to the front panel and into a Wolfson CODEC. Just like that... so that the Android audio in would also suffer from the above issues.
This also explains the exact nature of the unit's BT implementation - the handsfree is not done by the Android - it's completely handled by the BT module. BT module has MIC in, AUDIO out (that goes to the BD37534 audio mixer chip) and RS232 control signals that communicate with the Android BT application for User Interface (probably via AT commands).
When you run an Android app that uses audio input - it comes from the Wolfson CODEC but it's essentialy the same lousy MIC signal that the BT also gets.

BUT!!!

I've made some modifications and lo and behold - I can make a good quality phone conversation now! and the google apps have somewhat better performance too... but it did require me to completely mess up the internal wiring and obviously void the priceless warranty
So after I've figured it out - I decided I needed to do the following:
- Give up the option to work with two mics at the same time and opt for the external mic only for voice calls
- Cut and bypass the original traces since they pick up so much noise
- Add a separate input jack for the external microphone since it was not feasible to cut the lines going into the original one
I started by installing the extra jack on the rear panel. Then I removed a jumper 0ohm resistor at the MIC input to the BT module, disconnecting the MIC input from the circuit. I ran a piece of shielded wire from the new jack to the MIC input signal pin ON the BT board. That completed the hands-free modification.
In order for the Android to have some audio input, I then moved to the front panel, and first installed a 0Ohm jumper that was missing by the WM8731 CODEC. This resistor connects the MIC BIAS pin to the MIC input - it is required when using an electret microphone. I then made a cut in the trace from the front panel microphone to the small PCB connector, and ran a piece of shielded wire from the mic terminals to the WM8731 MIC input.
Now the front mic is only for Android (voice commands etc) and the external mic serves hands free.. I could have probably added some smarter electronics but I don't think it would have added anything to the usage experience.
Let me know if anyone is interested in some pictures I've taken and I will upload.

Crappy piece of equipment but at least now it works.

All the best,
Nir
The Following 27 Users Say Thank You to dnts For This Useful Post: [ View ] Gift dnts Ad-Free
 
 
1st October 2014, 07:42 AM |#2  
OP Senior Member
Thanks Meter: 61
 
More
[Mod] Weak microphone quality: Split up BT and Sys; Add external microphone(s)
...

Moderation note form dark alex:
these are pictures which belong to dnts' tutorial and research
Attached Images
File Type: jpg connect back panel.jpg - [Click for QR Code] (120.8 KB, 10778 views)
File Type: jpg connect_wire_to_BT.jpg - [Click for QR Code] (87.0 KB, 9361 views)
File Type: jpg front mic.jpg - [Click for QR Code] (134.1 KB, 8927 views)
File Type: jpg remove_resistor.jpg - [Click for QR Code] (132.5 KB, 8163 views)
The Following 10 Users Say Thank You to dnts For This Useful Post: [ View ] Gift dnts Ad-Free
1st October 2014, 12:35 PM |#3  
OP Senior Member
Thanks Meter: 61
 
More
Quote:
Originally Posted by harlequin69

Great work and thank you for sharing. I can follow most of what you did there except for adding the jumper to the CODEC due to electret mic use, do you have any pics of this? also why did you choose to use both mics in the end? would it not be better to use the external mic for both BT and android?

Regarding external mic for both BT and Android - here is the catch - you need to add a buffer (amplifier circuit) to the mic signal before sending it to two destinations (BT and CODEC) otherwise you will get that awful noise back. The microphones have a high output impedance which makes them prone to electrical noise. Even if you run them using shielded wire to two locations - you will be picking up noise via the ground signal due to the high impedance.
So to keep things simple (for now) I opted for separate mics, with the higher quality one for calls.

As for the required jumper, I attached a pic. The red circle around the empty pads shows where you need to put a short. The green line shows where you would connect the internal mic. Either pad works (they are shorted on the PCB).
Nir
Attached Images
File Type: jpg CODEC connections.jpg - [Click for QR Code] (146.2 KB, 7756 views)
The Following 5 Users Say Thank You to dnts For This Useful Post: [ View ] Gift dnts Ad-Free
1st October 2014, 03:42 PM |#4  
OP Senior Member
Thanks Meter: 61
 
More
[Mod] Weak microphone quality: Split up BT and Sys; Add external microphone(s)
Specific for KGL

From the top of my head.. sorry for that.. Please use pics in my previous posts.
1. Remove unit. Remove screws holding front panel to the chassis (this varies from one car model to another - mine is KIA Sportage).
2. Carefully lay down front panel. Take notice of the two ribbon cables and don't pull them
3. Remove chassis top cover (2 side screws and one screw on the back).
4. Remove optical drive - 4 screws hold it in place. Carefully disconnect ribbon cable.
5. Install 3.5mm mono jack on the rear panel - 2 holes are available for that (those reserved for DTV antenna). Wire a piece of shielded conductor to the jack, shield going to the part touching the chassis (sleeve) and internal conductor going to the "tip" contact.
6. Locate BT module. It will be at the right side of the chassis (eyeing from front), close to the front end of the PCB.
7. Near the BT module, on the main PCB, locate the component marked "C32". It should be marked "0". Remove it. This is a jumper connecting the BT MIC input to the microphones.
8. Connect the other end of the shielded conductor to the BT module to the pin labeled "MIC+". Do if from the back size of the module. Secure the shielded wire in several places so it doesn't loose up over time.

At this point, the external mic will be the only source for BT audio in. It should (obviously) connected to the new jack we installed.

9. Locate the PCB holding the microphone to the front panel. Locate the PCB trace from the lower microphone terminal (the other terminal is connected to the ground plane of the PCB). make a cut to that trace.
10. Prepare another shielded conductor. connect shied to the mic terminal that is grounded (top one) and the internal conductor to the terminal connected to the trace we just cut. (please see picture titled "front mic").
11. Locate WM8731 CODEC chip. Identify missing "R45" pads (only vacant pads near the WM8731 chip). Make a jumper using some solder and a piece of wire. This calls for delicate soldering.
12. Connect other end of mic conductor to the pad of R42 and R45 further away from WM8731 (please see picture titled "CODEC connection")

13. Put everything back together - start with ribbon for the optical drive, 4 screws for the drive, top cover of chassis and front panel. Make sure, before securing the front panel, that the two ribbon cables are well connected and have not moved or shifted inside their connectors.
14. Cross fingers and connect back to power.

You're done.

Nir
The Following 12 Users Say Thank You to dnts For This Useful Post: [ View ] Gift dnts Ad-Free
13th October 2014, 01:15 AM |#5  
dsa8310's Avatar
Senior Member
Thanks Meter: 1,019
 
More
Relax, don't do it!
--
The Following 3 Users Say Thank You to dsa8310 For This Useful Post: [ View ] Gift dsa8310 Ad-Free
15th October 2014, 01:07 AM |#6  
dsa8310's Avatar
Senior Member
Thanks Meter: 1,019
 
More
--
The Following User Says Thank You to dsa8310 For This Useful Post: [ View ] Gift dsa8310 Ad-Free
16th October 2014, 10:57 PM |#7  
dsa8310's Avatar
Senior Member
Thanks Meter: 1,019
 
More
---
The Following User Says Thank You to dsa8310 For This Useful Post: [ View ] Gift dsa8310 Ad-Free
5th November 2014, 09:21 PM |#8  
dsa8310's Avatar
Senior Member
Thanks Meter: 1,019
 
More
---
The Following 3 Users Say Thank You to dsa8310 For This Useful Post: [ View ] Gift dsa8310 Ad-Free
6th January 2015, 08:08 AM |#9  
Junior Member
Thanks Meter: 7
 
More
[Mod] Weak microphone quality: Split up BT and Sys; Add external microphone(s)
Specific for JY

Quote:
Originally Posted by tomc99

I did find a capacitor linking the BT module on my JY unit, but removing it didn't give me the results I needed, so that's when I moved to cutting the leg on the BT module.

I seem to get some bias at the microphone socket - maybe a little low, from memory around 1.7 volts, but no audio whatsoever.

A little bit of a mystery to me is that after cutting the leg on the module the internal mic is now virtually clear of all buzzing that was evident beforehand.

I may spend a few hours this weekend and set it up on my bench power supply and have a better play with it.

Tom.


Sent from my GT-N5100 using XDA Free mobile app

I have a G2110 model( which is a Joyous JY) that suffered with bad buzzing and echoing when using hands free. In stock form testing internal MIC with sound recorder there was no issue. Recording was clear. When I made hand-free call buzzing and reverb sound occurred. I read over and over about the external mic modification and decided to try it. Opened up HU and located C32 which was actually located toward the front center of the unit. I removed it and tested and same issues occurred. I then reconnect C32 as it was apparent that this was not the correct one on this board. I then took advise of previous posts that the cap should be located somewhere near the Bluetooth module so did continuity checks from the + of internal MIC to the caps near the Bluetooth module. I found C102(located seemed to connect to internal MIC on one side and the Bluetooth Mic + on the other. I decided to remove that and test. After removal internal MIC still functioned but hands-free was dead. I am assuming that this was the correct cap that needed to be removed. I did not do anything to the legs of the actual module. I did add an external jack to the backside of the module per the previous posts on how to add external MIC. After I completed the task I tested and the two appear to be separated and the hand-free external seems to function. I still get a little reverb noise but nothing like it was. I am not an electrical guru so I'm not sure if what I did is correct but it seems to have helped somewhat. I took some pics.
Attached Thumbnails
Click image for larger version

Name:	image1.jpg
Views:	10564
Size:	184.9 KB
ID:	3100697   Click image for larger version

Name:	image2.jpg
Views:	10446
Size:	189.0 KB
ID:	3100698   Click image for larger version

Name:	image3.jpg
Views:	10302
Size:	186.5 KB
ID:	3100699   Click image for larger version

Name:	image4.jpg
Views:	9996
Size:	183.1 KB
ID:	3100700   Click image for larger version

Name:	image8.jpg
Views:	9902
Size:	196.7 KB
ID:	3100702   Click image for larger version

Name:	image9.jpg
Views:	9778
Size:	193.1 KB
ID:	3100703   Click image for larger version

Name:	image10.jpg
Views:	9826
Size:	194.5 KB
ID:	3100704  
The Following 6 Users Say Thank You to tdopko For This Useful Post: [ View ] Gift tdopko Ad-Free
13th November 2015, 10:17 AM |#10  
Senior Member
Flag Mermaid Beach QLD
Thanks Meter: 319
 
More
Ok...I need to do this as got that horrible Mike thing going with Bluetooth..

I still need to get my head around the best way to do it..

Best way is going to have to print this thread and work out a plan of attack..

At the moment I have not plugged in the mike at back but been using the front Mike for Bluetooth calls..and of course no one can hear me..

As for Bluetooth coming out to speaks..that all works fine..

Sent from my SM-G900F using Tapatalk
17th November 2015, 01:21 AM |#11  
Senior Member
Thanks Meter: 63
 
More
[Mod] Weak microphone quality: Split up BT and Sys; Add external microphone(s)
Quote:
Originally Posted by dgcruzing

Ok...I need to do this as got that horrible Mike thing going with Bluetooth..

I still need to get my head around the best way to do it..

Best way is going to have to print this thread and work out a plan of attack..

At the moment I have not plugged in the mike at back but been using the front Mike for Bluetooth calls..and of course no one can hear me..

As for Bluetooth coming out to speaks..that all works fine..

Sent from my SM-G900F using Tapatalk


I'm with you pal. This is pretty confusing, especially when you take into account the different models of the head units. I want to improve my mic, but I don't want to mess up and make it worse.

If anyone with a joying unit wants to put together an idiots guide to this mod, I would send a huge thank you your way.


Sent from my iPhone using Tapatalk
Post Reply Subscribe to Thread

Guest Quick Reply (no urls or BBcode)
Message:
Previous Thread Next Thread
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes