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Years ago I build a mobile speaker with a battery inside but because of the battery dying, I decided to try to run it off USB power. The speaker is an old Creative T40 speaker and they run on 27 V so I tried to run this off a step-up converter, going from 5 V to 27 V.

The problem is that when I do this, the speaker works but I get these blobs and humming all the time. I'm not sure why this is happening but my guess is that the output voltage is not stable, so I think I need a smoothing circuit of some sort.

There is also a Bluetooth receiver connected to the same USB power line. This might influence the voltage as well. But I'm not sure.

What would you guys recommend I do? Is this possible at all, stepping up the voltage this high?

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    \$\begingroup\$ Please show a schematic of your boost converter circuit. \$\endgroup\$
    – Andy aka
    Commented Mar 24, 2023 at 14:47

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The Creative T40 single speaker produces 14W. It might draw 28W from 27V. Your voltage booster must produce 28W from your 5V (USB?) which is a current of 28W/5V= 5.6A plus any heating caused by poor efficiency. USB cannot produce 5.6A or more and maybe the booster also cannot have an input of 5V at 5.6A or more.

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  • \$\begingroup\$ If I hook it up to my power supply it shows that it's only using 0.8 amps. This is not while playing but I think that 28w is a full volume. On paper devices are often rated at much higher watts. Also the speakers works fine while playing music, the music sounds good but it has these consistent blobs, also at low volume. So let's assume I have enough power but the blobs still persist. \$\endgroup\$
    – Tok_Tok
    Commented Mar 27, 2023 at 7:31
  • \$\begingroup\$ Music has loud parts that have fairly short duration. If the loud parts are short enough that a charged capacitor can power the amplifier then music sounds fine. I think your blobs are loud durations that completely discharge the capacitor leaving severe distorted blobs because the power supply max current is too low. \$\endgroup\$
    – Audioguru
    Commented Mar 27, 2023 at 16:27
  • \$\begingroup\$ I tried adding a capacitor but the only ones I have a from a PSU from a desktop pc. Those are 400v and 370f. I hoped that would help but it doesn't, but getting the right caps might work? How my fahrads would you recommend? \$\endgroup\$
    – Tok_Tok
    Commented Mar 28, 2023 at 7:34
  • \$\begingroup\$ Your speaker needs a 27VDC at 1A power supply. \$\endgroup\$
    – Audioguru
    Commented Mar 29, 2023 at 0:53
  • \$\begingroup\$ So I've just hooked up my power supply to the inverter and set it so 5v. The blobs and noises are gone and it says it draws 1.6A. My usb adapter says it can deliver 3A so that should be more than enough. So why do I still get these sounds? Won't a filter help in this case? \$\endgroup\$
    – Tok_Tok
    Commented Mar 29, 2023 at 9:58

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