Class D amp + AA battery = voltage drop

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emmanuel63

Well-known member
Hello,

I have finished a little synthesiser with a Teensy 4.0. I use a little class D amp (pam8406) with a 4 ohm speaker. The synth is powered with 3 x AA batteries. When playing clusters of notes at full volume, the teensy shuts down and restart. I am pretty sure the amp sucks so much current and the voltage drops. Do you think it is safe to add a 1000uF cap on power lines ? Or maybe I could use a 8 ohm speaker ?
Emmanuel
 
Try 4 NiMH rechargable AA batteries (about 5.3V), which should have better high current handling. 3 x alkaline AA is only 4.5V and thus much closer to undervoltage cutoff, and the max current is less than with good NiMH cells.

1000uF is not going to help a continuous overload much. 8 ohm speaker will help of course.

Another issue to be aware of is that many cheap black plastic AA battery holders are riveted construction rather than spot-welded, and can drop significant voltage at high current in the rivet joints. I wouldn't recommend these for more than 100mA.
 
For similar setups I am using successfully small powerbanks. There are types with around 1000mAh or so which do not turn off when only small power is taken. You get stable 5V from it.

4 freshly and fully loaded NiMH cells could exceed the limit of 5.5V input voltage of the Teensy.
 
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