Hello,
I've been playing with little PAM8403 amplifier and I have problem with a noise. I have to say I didn't analyze the spectrum in any software but by hearing it I would say it is something close to white noise. It doesn't change at all with turning the volume knob up or down or shorting the inputs. So I started looking on the internet for possible causes.
I found out that it could be the chip itself (PAM8403 doesn't have the best SNR value) but then I found some tests of different cheap boards with the same chip (not the PAM8403) and there were big differences between them in term of audible noise, similiar to what I'm hearing. And since then I wonder:
What causes this audible level of noise and can I get rid of it? It's a broad question, I know, sorry for that. I have two ideas on my mind - It's problem with filtering the power supply rails - or - The chip is causing this and those cheap chinese boards, whose tests I've seen, were using just bad clones of original chip.
I bet it's much more complicated than just this. So thank you very much for any useful informations or materials. I really appreciate it!
I've been playing with little PAM8403 amplifier and I have problem with a noise. I have to say I didn't analyze the spectrum in any software but by hearing it I would say it is something close to white noise. It doesn't change at all with turning the volume knob up or down or shorting the inputs. So I started looking on the internet for possible causes.
I found out that it could be the chip itself (PAM8403 doesn't have the best SNR value) but then I found some tests of different cheap boards with the same chip (not the PAM8403) and there were big differences between them in term of audible noise, similiar to what I'm hearing. And since then I wonder:
What causes this audible level of noise and can I get rid of it? It's a broad question, I know, sorry for that. I have two ideas on my mind - It's problem with filtering the power supply rails - or - The chip is causing this and those cheap chinese boards, whose tests I've seen, were using just bad clones of original chip.
I bet it's much more complicated than just this. So thank you very much for any useful informations or materials. I really appreciate it!
I believe the problem is high frequency Pulse Width Modulation (PWM) noise from PAM8403 due to inadequate filtering at the output of the amp.
PAM8406 is also ultra low budget but it is a slightly better performer.
I was not aware of chinese clones but one better uses original ICs.
Do you happen to use a cheap SMPS as power supply!?
I was not aware of chinese clones but one better uses original ICs.
Do you happen to use a cheap SMPS as power supply!?
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I had that idea too. But how can I filter that out at the ouput when the noise is already in audible frequencies?
Yes, I'm using an SMPS. I should have mentioned that. That's also why I'm talking about filtering power supply rails. Maybe a decent CLC pi filter will do the thing?
An LC filter may well do the job for you. Mark Johnson has a design for a SMPSU filter : https://www.diyaudio.com/community/...all-warts-preamps-hpa-korg-nutube-etc.354213/
A decent linear PSU for such an ultra light power amplifier is built in a breeze with usually better results than an SMPS with whatever filter. What is not created does not need to be filtered. It is surprising (no it is not) that I can predict beforehand in many cases that an SMPS is used when the complaint is noise. Should at least tell something about those wonders of technology 🙂 We are talking 5V 2A max. here and many would probably use 5V 1A 😀
BTW you state that the PAM8403/6 are not OK with SNR but they ar not so bad in that aspect really.
BTW you state that the PAM8403/6 are not OK with SNR but they ar not so bad in that aspect really.
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Thanks for your reply @jean-paul.
The main reasons I'm using SMPS is size and weight. I wanted to build it as small as possible. Can't imagine how could I fit any transformer there. Maybe SMPS + linear regulator would do the thing but I didn't have any suitable SMPS for this purpose.
With reference to SNR, I thought 80 dB is not much good since I've seen chips with very similiar specs and SNR well over 90 dB (PAM8008 for instance).
I'll try more ways to reduce that noise and see which will come up best 🙂
The main reasons I'm using SMPS is size and weight. I wanted to build it as small as possible. Can't imagine how could I fit any transformer there. Maybe SMPS + linear regulator would do the thing but I didn't have any suitable SMPS for this purpose.
With reference to SNR, I thought 80 dB is not much good since I've seen chips with very similiar specs and SNR well over 90 dB (PAM8008 for instance).
I'll try more ways to reduce that noise and see which will come up best 🙂