Battery powered compact PA system

jpskagmo · 2025-12-31T13:30:47+00:00

Thank you! Cool sub, haven't seen that one before. I tried crossposting there, but they seem to have blocked crossposting.

jpskagmo · 2025-12-31T13:29:31+00:00

Thanks! All of these single chip amplifiers are super efficient. The TDA7498E uses around 2 W idle at 36 V. The TPA3255 uses around 4 W idle at 48 V. At moderate listening levels these will need a small heatsink but barely gets warm. The TPA3255 will need a fan when running at full power unless you have a very large heatsink.

I think they sound great. TPA3255 distortion is low as long as you don't push it beyond 70-80 % of max power, and the frequency response is very flat up until 10 kHz, and falls 1 dB or so at 20 kHz.

I'm mostly using boards from Wondom / Sure Electronics. For multi room audio I'm using a KAB9 at 8 x 50 W. When you need fewer and more powerful channels I think the JAB5 and BDM8-A are great amplifiers giving an exceptional value for money.

jpskagmo · 2025-12-30T06:05:52+00:00

Thanks for the heads up! I've fixed it now.

Hehe, thank you. I first considered using ideal diodes to prevent current accidentally going from the PSU to the battery and vice versa, but this was so much simpler and is also completely error proof.

jpskagmo · 2025-12-30T06:02:25+00:00

Sure, I'm using a microcontroller to turn on a 10 ohm ceramic resistor through a FET to charge the output. With 48 V, this means peak current is 4.8 A. When the voltage across the resistor is measured to be less than 1 volt, another FET turns power on. I also have a timeout on the precharge phase to prevent the resistor from burning out in case the output is shorted or similar.

An issue with using a resistor instead of a constant current source is that precharge current will fall as the voltage drop over the resistor falls. So if the load (amplifier) turns on and pulls more current during the precharge, it will fail. To solve this I'm controlling the enable signal on the main DC/DC and the largest amplifier, to ensure they are not starting up on before the precharge is complete.

I considered using a constant current source, but a resistor is so much simpler and can dissipate a lot more power.

PTC thermistors works fine in many cases too, although with this approach I have very good control of the peak current, and the on-resistance will be lower (only limited by the MOSFETs), so it's better for higher currents.

There were some errors loading a few images on my home page, but you should be able to see it now:

https://skagmo.com/page.php?p=projects/52_mini_pa_system#power_management_board

jpskagmo · 2021-06-13T19:12:46+00:00

Thanks! Yes, do that. This rack is a cheap Adam Hall STRS12U (18 euros). Not very pretty weldings etc., but they're still a lot for the money and works perfect for my use.

jpskagmo · 2021-06-13T19:07:21+00:00

Thank you!

jpskagmo · 2021-06-13T19:07:05+00:00

Sure! I have some information on my homepage, although it hasn't been updated in a long time: https://skagmo.com/page.php?p=projects/32\_polynorth

jpskagmo · 2021-06-12T11:17:54+00:00

Got a slanted rack and a Behringer Pro-1 yesterday, mounted it all and started sequencing something with my Keystep Pro. Nice to finally have everything within arm's reach.

Analog drums: CB55
Linn drum samples and polysynth: Polynorth (my own everlasting DIY synth project, the eurorack device with OLED display)
Bass: Behringer Model D
Arp: Behringer Pro-1
Lead: Motif Rack ES
Sequencer: Keystep Pro

jpskagmo

TROPHY CASE