how to reduce electret microphone sensitivity

[panneerrajan]

Hi Audioguru,

Please find the image of Post-17 for your reference, I 'm not using computer.
Using SOM based mixed signal processor module and Its provide Audio & Mic signal through Berg connector.

i'm using 4W mono amplifier IC with differential input, instead of using volume control (Trimpot) i plan to provide fixed resistor divider netwok for fixing audio volume.

MCU audio channel out signals = Headphone L, Headphone R & Headphone GND; Mic + and mic -
As per my post17, can i use resistor divider reference gnd as Headphone GND or common gnd
Please suggest

Thank you
Rajan

 

[Audioguru]

Since you are using the headphones output then use the headphones output ground.
If you use fixed volume with the resistor divider then how can you adjust the volume? Does the signal processor have a volume control for the headphones outputs?
Will the audio amplifier work properly with one of its differential inputs at ground?

 

[c_mitra]

Instead of resistor divider network for audio volume control, could you please share Amplifier level control concept/circuit.

Reducing the input signal to control the output is commonly considered a bad idea; it is far better to use the gain control. If you reduce the input signal, you introduce more noise. I do not know what IC you are using but the gain should be reduced to reduce the output signal.

 

[panneerrajan]

Hi,

Please find block diagram and audio fixed volume resistor network GND





My application not require to adjust volume, that's why i want to provide fix. volume.

Yes, Processor have volume control for headphone output

differential inputs - Processor have provision for differential output and my amplifier IC input also have differential inputs. pls find my image
(Audio output terminal have Headphone L, Headphone R & Headphone GND signal )

Which GND can i use for divider resistor ground reference? Headphoen GND OR common GND
Pls. suggest

Thank you

- - - Updated - - -

Hi Mitra,

But mostly all audio amplifier volume control used by timpot (reduce signal), then they connect to Amplifier IC input pin.
That's why i tried to use divider resistor instead of Trimpot.

otherwise i try to reduce from Micro processor and bypass hardware divider network

Thank you,

 

[Audioguru]

Your attachments do not work.

A differential output has a + wire and a - wire. Your headphones output is not differential, it is simply a single-ended left channel, a single-ended right channel and a ground.
We do not know the input sensitivity of your power amplifier, the headphones output levels might be fine feeding it without voltage divider resistors. Then adjust the volume with the processor volume control.

 

[BradtheRad]

I replaced the images in the two expired attachments. (By happenstance they were still available in my browser.) The cause of the broken attachments is not known.

 

[panneerrajan]

Hi,

Please find block diagram and audio fixed volume resistor network GND





My application not require to adjust volume, that's why i want to provide fix. volume.

Yes, Processor have volume control for headphone output

differential inputs - Processor have provision for differential output and my amplifier IC input also have differential inputs. pls find my image
(Audio output terminal have Headphone L, Headphone R & Headphone GND signal )

Which GND can i use for divider resistor ground reference? Headphoen GND OR common GND
Pls. suggest

Thank you

- - - Updated - - -

Hi Mitra,

But mostly all audio amplifier volume control used by timpot (reduce signal), then they connect to Amplifier IC input pin.
That's why i tried to use divider resistor instead of Trimpot.

otherwise i try to reduce from Micro processor and bypass hardware divider network

Thank you,

Hi,
I used PAM8303D Amplifier chip for your reference

Thank you

 

[c_mitra]

I used PAM8303D Amplifier chip for your reference u

Please read the datasheet: the gain is set by the input resistor Ri and the operating chopper frequency can be set externally.

 

[Audioguru]

The two 10k resistors add the two stereo channels together into mono. Their parallel value is the input resistor for the amplifier. The datasheet for the amplifier says that the input resistor should be 150k for a differential gain of 2, then each resistor is 300k, not 10k. Your input is single-ended, not differential so with two 300k input resistors then you do not need the 10k resistors and do not need your R1, R2 and R7.
The 300k resistors produce a single-ended mono gain of 1. If they are each 600k then the gain is 0.5 times. If they are each 1M then the gain is 0.3 times but you and I do not know how much gain you want.
The datasheet shows that the amplifier input resistors need coupling capacitors and the unused input pin5 has a series resistor half the value of the input resistors and capacitor to ground.

 

[panneerrajan]

Hi Audioguru,
Thank you for your clarification,
As per the attachment in post# 27, my Audio channel source provide Headphone GND separately and Analog audio GND separately. Can I consider it as a differential signal?
As per your input, I have modified the circuit with differential input. Please find the same attached with this post.




Can I put the Capacitor before resistor (as per datasheet)? Your recommended circuit (Post #29) has capacitor placed after resistor. What is the difference?

What frequency range should I consider to calculate input series capacitor (C=1/2*3.14*Fci)

Please suggest

Thank you
Rajan

 

[Audioguru]

As per the attachment in post# 27, my Audio channel source provide Headphone GND separately and Analog audio GND separately. Can I consider it as a differential signal?

Your headphones output is a stereo single-ended output, not differential. Since you are using the headphones output then you should also use the headphones ground.

Can I put the Capacitor before resistor (as per datasheet)? Your recommended circuit (Post #29) has capacitor placed after resistor. What is the difference?

My circuit uses only two input coupling capacitors, your circuit needs three capacitors.

What frequency range should I consider to calculate input series capacitor (C=1/2*3.14*Fci)

The calculation is c= 1/ 2 x pi x R x f where R is 300k or 150k and f is the lowest frequency you want which might be 20Hz.

Please suggest

Thank you
Rajan