ampli & Teensy on same power rail

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emmanuel63

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Hello,

For a little portable synth, I try to power a T3.6 & a small amp (TDA 1822) with the same battery. It is working but I can't get completely rid off noise. I think I don't have any ground loop because I use 1 gnd point for my circuit. I try adding caps, using Analog ground but the best results I have so far is when everything is connected to 1 unique Gnd.

Any advice ?
Emmanuel
 
Can't find a datasheet for the TDA1822 - is that the correct part number? what sort of amp is it?
 
Sorry... it is TDA2822.
The problem is not the chip I think, but noise coupling. I made test with other amps, same results. When I use an external amp with its own power supply, there is no noise.
Emmanuel
 
Ah, the TDA2822 has only 24--30dB of PSRR, so it definitely needs a linear voltage regulator all to itself to be "quiet"...
Even the PAM8403 class D chip does a lot better than that (59dB PSRR)
 
Thanks Mark.
I have a few class D chip PAM8403. It is better, but I still have coupling problems.
Is it possible to have 2 fully isolated power rail from 1 battery ?
Emmanuel
 
As I said use a separate linear regulator for a quiet supply - this means you need enough voltage headroom in the first place.

You may still have the issue that the source isn't clean - do you have a schematic for your setup?
 
Hi Mark,

Here is a simplified schematic.
The Teensy board is hooked to a battery pack via USB. My amp is powered via Vin pin (= battery). It works but I get "digital" noise. I tried Analog GND and main GND : no difference. I also tried to add some capacitors.
What regulator would you advise ?

Emmanuel
 
Hi Mark,

Here is a simplified schematic.
The Teensy board is hooked to a battery pack via USB. My amp is powered via Vin pin (= battery). It works but I get "digital" noise. I tried Analog GND and main GND : no difference. I also tried to add some capacitors.
What regulator would you advise ?

Emmanuel
A low drop out linear regulator capable of the current and with a suitable voltage. There are 1000's - I am not a search engine!
Digikey/Mouser/Farnel - they have search facilities.... What battery voltage though?
 
My battery delivers 5V. I'll find a reference for the regulator.

Then you have no headroom for a regulator. I'd suggest separate supplies for Teensy and amp in that case.
Digital and analog audio don't mix well as even a few mV of digital hash can be highly audible. The alternative
is some heavy filtering like CLC or CLCLC using ferrite chokes if the hash is breaking through badly like this.

This has a brief description of CLC filtering, there's probably a site somewhere with design equations if you look
https://www.daenotes.com/electronics/devices-circuits/filter-circuits
 
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