FEDEVEL
Platform forum

Sakib816 , 02-23-2026, 03:46 PM

Can i use this single ended signal as differential, by using potentiometer? Many pam8620 module use potentiometer at the input side to control volume

Sakib816 , 02-23-2026, 03:46 PM

The android board and this amplifier are powered by smps 12V power supply

Sakib816 , 02-23-2026, 03:47 PM

Sakib816 , 02-23-2026, 03:47 PM

This type of signal when there is no audio.

Sakib816 , 02-23-2026, 03:48 PM

Sakib816 , 02-23-2026, 03:48 PM

No audio, but noisy

Sakib816 , 02-23-2026, 03:48 PM

QDrives , 02-23-2026, 03:48 PM

If that is you power suppy, then I would say "no wonder you have a hissing sound".

Sakib816 , 02-23-2026, 03:49 PM

What should i do now?

Sakib816 , 02-23-2026, 03:50 PM

As the android board is powered by smps, i cannot change the power supply

QDrives , 02-23-2026, 03:51 PM

Where does the power from PVCCL and PVCCR come from?

Sakib816 , 02-23-2026, 03:51 PM

From smps 12V, all the power are delivered from this

QDrives , 02-23-2026, 03:55 PM

Place 1uF film cap parallel to C14.
Add LC filter from +15V in to AVCC.

QDrives , 02-23-2026, 03:56 PM

Or replace C14 with tanalum cap of 1uF.

Sakib816 , 02-23-2026, 03:57 PM

What will happen if i do this?

QDrives , 02-23-2026, 03:57 PM

Noise on the input (both audio and power) will cause noise on the output.
Piezoelectric capacitors also cause noise.

Sakib816 , 02-23-2026, 03:59 PM

Can you suggest me what type of LC value should used?

QDrives , 02-23-2026, 04:04 PM

It is a bit what you can get and have space for, but 1mH and 470uF gets you 230Hz.
https://www.omnicalculator.com/physics/lc-filter
And make sure you have aluminum or tantalum capacitors. You can add parallel some C0G/NP0 capacitors for higher frequency decoupling.

Sakib816 , 02-23-2026, 04:06 PM

Please tell me in this picture which capacitor should I change the value of?

Sakib816 , 02-23-2026, 04:06 PM

In this schematic where should i change, please tell me 😊C9,C10,C11,C12 and C14?

Sakib816 , 02-23-2026, 04:07 PM

I used mlcc capacitor only, so where i put which type of capacitor

QDrives , 02-23-2026, 04:13 PM

For the 'analog' signals, you do not want X7R (or X5R or Z5U).
Film, tantalum, aluminium or C0G (ceramic) are good. Each has their advantages and disadvantages. Just as a high(er) or low(er) ESR can be a (dis)advantage.

Sakib816 , 02-23-2026, 04:19 PM

....

Sakib816 , 02-23-2026, 04:19 PM

In this schematic where should i change, please tell me 😊C9,C10,C11,C12 and C14?

QDrives , 02-23-2026, 04:21 PM

C9...C12 to film, C14 **add** film or tantalum.
But **first** make sure you analog power is low noise by adding LC filtering.

Sakib816 , 02-23-2026, 04:39 PM

Ok, i will do some change and send you feedback

QDrives , 02-23-2026, 04:40 PM

Also make sure you measure correctly.
Do **not** use the crocodile clip, but the spring tip.

Sakib816 , 02-23-2026, 04:41 PM

ok

Sakib816 , 02-23-2026, 04:42 PM

Can you provide me with the schematic of this amplifier module? If possible. I know it’s difficult for you.

QDrives , 02-23-2026, 06:57 PM

No

Sakib816 , 02-24-2026, 03:50 AM

Is there any need of add extra filter in input side?

Sakib816 , 02-24-2026, 03:50 AM

Sakib816 , 02-24-2026, 03:50 AM

Like this one?

Sakib816 , 02-24-2026, 04:23 AM

Can i use this?

Sakib816 , 02-24-2026, 06:00 AM

Hello @QDrives

QDrives , 02-24-2026, 03:13 PM

For the initial test you want to 'short' the audio input.
Then make sure that the 'analog' section of you amplifier is quiet.

Sakib816 , 02-24-2026, 03:57 PM

Please tell me elaborately, what will happen if i do it! 😊

QDrives , 02-24-2026, 11:03 PM

"**it**" as in shorting the input?
You eliminate noise on the input.
But if you short the output of android board... perhaps smoke?
However, you want to eliminate noise sources where possible in order to change and verify those parts that need improvement.

gee , 02-25-2026, 03:10 AM

With the android board and amplifier running off the same PSU, and another ground connection happening across the audio leads, you've probably got yourself a ground loop.

gee , 02-25-2026, 03:11 AM

got a cellphone or portable game console or something else battery powered with a headphone jack you can use as an audio source?

Sakib816 , 02-25-2026, 05:17 AM

Is this circuit is ok or not? is there any need of modification? I want to do like this : i want to add extra filter circuit before 1uf capacitor.

@QDrives @gee

Imad_RF , 02-25-2026, 09:19 PM

Hello, first of all I would try to powerup the amplifier from a different power supply, in order to eliminate the probability that the conducted ripple of your android SMPS is affecting the output directly.

bring another "clean" power supply, try... and share the results with us please!

Imad_RF , 02-25-2026, 09:20 PM

also, can you share with us a screenshot from your PCB layout editor?

Imad_RF , 02-25-2026, 09:23 PM

with all the respect to QDrives, I doubt the problem has to do with the use of X7R or whatever MLCC type in the audio path, although it is true that they introduce distortion, but not that much!

QDrives , 02-26-2026, 12:18 AM

I am not stating the capacitors **are** the cause. They **could** be contributing to it.

QDrives , 02-26-2026, 12:20 AM

Hence the reason to short the input to gnd and see if the noise is gone.

gee , 02-26-2026, 01:18 AM

X7Rs can be piezoelectric/microphonic, but they're not bad enough that they'll cause an amplifier like this to just sit there and hiss. There's countless X5R/X7R's out there in audio equipment, doing things like DC blocking and filtering with low corner frequencies, that aren't creating this problem.

I'm still guessing a ground loop. Class D amplifiers have discontinuous current draw and put a lot of current ripple on their power supplies, and if the di/dt isn't entirely absorbed by the bulk capacitance on the amplifier card, then it'll pull the remaining di/dt from the source power supply with the return current going through the ground. Causing the local ground voltage to bounce around relative to the power supply ground.

And embedded linux machines can create their own noise on their power supplies in my experience. If you've got a system timer running at 1KHz waking the processor up from a sleep mode, same thing, that can induce its own di/dt on the power supply and cause audible noise.

Join both of those things together with an unbalanced audio connection + ground and you've got a recipe for all kinds of fun.

But yeah, run the card with the inputs disconnected.

QDrives , 02-26-2026, 02:03 AM

"*X7Rs can be piezoelectric/microphonic*" -- not "can", but "**are**".
"*...doing things like DC blocking and filtering with low corner frequencies, that aren't creating this problem.*" -- They do not have to create this kind of problem in these situations. You need physical noise for them to create a voltage. I have no idea how noisy his lab is.
"*...and if the di/dt isn't entirely absorbed by the bulk capacitance on the amplifier card, then it'll pull the remaining di/dt from the source power supply...*" -- the source power supply has impedance, so do your bulk capacitors. With dI/dt , the voltage will drop. The bulk capacitors follow the simple rule Q = C * dV. So the bigger the dV the more current they supply. Depending on the capability for the power supply to provide the dI/dt, the voltage drop will vary.
"*...with the return current going through the ground. Causing the local ground voltage to bounce around relative to the power supply ground.*" -- That is **always** the case, regardless of where the power comes from. However, "ground loops" are not the issue then. Ground loops are an EMC issue and more myth than an actual problem (considering input filtering). That said, if the input negative (LINN and RINN) come from a place that has a different ground potentential than the Gnd used for the positive inputs (RINP and LINP) then you get problems with "ground bounce". Again a reason to first short the audio inputs to the local Gnd.
"*And embedded linux machines can create their own noise on their power supplies in my experience.*" -- Absolutely agree! That is why the analog power section (e.g. AVDD) need to be filtered additionally and heavily to keep out (most) noise.
"...*run the card with the inputs disconnected.*" -- No, connect to Gnd. You do not want 'floating' inputs.

Imad_RF , 02-26-2026, 09:01 AM

great discussion! and great knowledge as always @QDrives !

Imad_RF , 02-26-2026, 09:05 AM

@Sakib816 why do you want to use this specific IC from diodes? if you're looking for a cheap, reliable class-d amplifier chip go with TI, they provide "good" evaluation boards for their ICs, schematics, layout tips, which will make your life a bit easier by copying the recommended design.