Volume control for chinese lightsaber

I've got a cheap chinese lightsaber and want to make some adjustments to it. The item looks great but its volume is too loud and my neighbours get mad when I switch it on. It doesn't have any way to control it. I contacted the seller and confirmed that there was no internal control.

I'm not an expert in electronics, I only know basic teoric concepts and how to use a soldering gun. My first idea was to install a potentiometer between the control board and the speaker, because there is some space behind the speaker, but after I searched this site I discovered it was a bad idea, that the sound will be distorted, the amplifier could break and there would be unnecessary power consumption in the resistance. At least that is what I understood.

I've tried to locate the amplifier, but it doesn't seem easy to make mods to the PCB, as it is really small and it fits in the hilt without much free space.

So the question is, considering that controlling the volume at the amplifier input is not an easy option, and that the system itselt is not a Hi-Fi and small distortions could be accepted, will installing a potentiomenter be dangerous and break the amplifier? What about a voltage divider?

If the risk is too high, could I simply take the speaker off? Altghough I think it can sound silly asking this, I read in another question that it could break the amplifier too, due to infinite resistance. I really don't know if that responses only related to guitar amplifiers or if it applies to small ones.

The speaker specs are 8 Ohm 2 W, 20 mm in diameter, while the battery is 3.7 V 2000 mAh.

The cables on the left down corner of the PCB go to the speaker; the right side ones go to the leds. I cannot extract the PCB more than that without cutting any cable, I hope this helps.

• Take a photo of the board and add it to the post. – Justme May 7 at 20:23
• Hard to say anything without seeing the board/circuit but I would start with putting a series resistor (e.g. 8R2/2W) between the amp's output and the speaker. It will reduce the speaker's power about 75% (From V²/R to V²/4R). it could break the amplifier too, due to infinite resistance. this applies to only tube amps and mostly high volume levels. – Rohat Kılıç May 7 at 20:30
• I dont't think this thing uses tube amps :d, thank you. It makes sense now. – peterfh May 7 at 21:01
• If those three ICs on the left had a part number we could probably tell you what to replace to lower the amplification. One is undoubtedly an op amp (audio or otherwise). – Passerby May 7 at 21:46

For that kind of gadget, it's almost certain that the amplifier is a class D.

Therefore you can simply add a resistor in series with the speaker and this should do the trick. The bigger the resistor the lower the volume. This should not damage the amplifier. Just make sure that you are using a resistor with a decent power rating.

• I'd suggest something like 16 ohms, giving about 1/3 the voltafge or 10dB less volume, but feel free to double it or even go to 100R to be a good neighbour. – Brian Drummond May 7 at 20:37
• @BrianDrummond, these specs are for a fixed resistor or a potenciometer? – peterfh May 7 at 21:17
• Fixed is probably good enough. Or two fixed, if you can fit a tiny switch. – Brian Drummond May 7 at 21:23
• Ok, thank you @BrianDrummond – peterfh May 8 at 13:24