Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

MIC has big noise? Audio circuits not matching?

Status
Not open for further replies.

tony_lth

Advanced Member level 5
Joined
Jul 28, 2010
Messages
2,086
Helped
377
Reputation
756
Reaction score
368
Trophy points
1,363
Location
Beijing
Activity points
12,621
Hi,
I am not familiar with audio design.
My designed module has a classic circuit for MIC +- input, as the attachment Our1.jpg.
The other side is another vendor, which has a classic mic circuits as Other1.jpg.
The problem is when Other1.jpg P and N linked to Our1.jpg MICP and MICN,
the user can hear big noise and the voice is not clear.
What's the issue?
Is it the matching issue? If I link a 1.2K resistor between MICP and MICN, can this issue be solved?
Many thanks.
Best,
Tony LIU
 

Attachments

  • Our1.JPG
    Our1.JPG
    102.8 KB · Views: 108
  • Othe1.JPG
    Othe1.JPG
    68.4 KB · Views: 108

Hi,

The first picture is useless. It doesn´t show what´s the input nor the output, nor where they are connected to...

Second picutre:
* General rule: Don´t leave any (unused) inputs floating. This is true for digital inputs as well as analog inputs.

Why there are so many differences to the datasheet?
* Whats the use lf L1 and L2
* Gain setting only possible with "A" suffix devices
* Where is the power supply bulk capacitor?
* Where is the PCB layout?

Is it the matching issue? If I link a 1.2K resistor between MICP and MICN, can this issue be solved?
Why not simply test it on your own?

Klaus
 
It's an audio power amplifier rather than microphone preamplifier, you may be watching just the expectable noise level. SNR is specified with -104 dB at 1.4 W output, in other words around -40 dB at 1 mV level. But there may be additional problems, e.g. oscillations of the unconnected channel.

Circuit biasing looks O.K., surely there's no impedance matching problem.
 
HI, Dear KlausST,
Thanks first.
The first picture output is the red noted P and N, which links to the female connector. But its input, by the vendor, who said the 560R is the terminal, before the 560R, there is a MIC with PTT used by user.
The second picture is no problem, because which has been used for many years, and my module has no audio issue with the 3rd and 4th partners. I just omitted unused circuit.
L1 and L2 are used for EMC, because the audio circuit is inserted in the same box with RF circuits.
I will check the BOM tomorrow , if we used with A suffix.
The power supply bulk capacitor is in another sheet which is the output of a LDO.
PCB layout is no problem, verified in many years.
I can't simply test because the vendor of 1st picture is 1000KM away, and I can only test in his lab, but in my lab, I can't verify.
So I want to clarify the root cause, and find all the possible cause, so that the test can be once done in the future.
So, it should not be matching issue? Any comments.
Many thanks.
Tony Liu

- - - Updated - - -

Hi, Dear FvM,
Yes, it's a power amplifier.
The other channel of MAX9719 is for earpiece, which has clear voice quality, so I omitted the other channel circuits.
So, what's the possible cause of the big noise?
Many thanks.
Tony Liu
 

We do not know what is your problem because you did not describe "the big noise".
Is it all the time or only when a person speaks in the mic?
Is the noise high frequency hiss or low frequency hum? Both?
Is the noise severe loud distortion because the gain is too high?
Is the noise acoustical feedback howling because the mic can hear the speaker and a sound goes around and around?
Is the noise a frequency response problem with rumbling or squeaking speech?
Is the sound fluttering due to low frequency oscillation (motorboating)?
 
Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top