DC soldering iron make noise on power supply, please help me design filter

I have a computer AT power supply mounted to bottom of desk. From that, I use to power my computer speakers, and a TS-100 soldering iron. I use a step-up voltage booster on the soldering iron to deliver 24 volts, for the purpose of making the heat-up time faster.

I turn the solder iron on, and my computer speakers get a FART sound through them. It's a low frequency buzz. I figure this was due to some type of severe drop in voltage through a pulse, but I do not know enough about electronics to know what to do. My first thoughts was to put a capacitor near the power input to the step-up power supply that drives the DC soldering iron. I think I need a power filter or coil, but I do not know what I am doing. Attached is a picture from my oscilloscope, that shows the 12v power supply noise. Can anyone advise, please?

Start with the grounds. Does each device have its own ground wire all the way back to the power supply?

The power supply +12v and ground are connected into terminal bus-bar blocks. The speaker +12v & ground is connected to the bus-block, and so is the solder-iron supply +12v & ground.

Try a big capacitor 1000uF or 10000uF if you can get a cheap one.

That scope trace is almost meaningless without the numbers on the bottom line that you cut off in the photo. What’s the 21 ms? The time between the two Y markers? That’s useful if so.

Is your mains frequency 50 or 60Hz?

PS: If that’s a Tek scope, lose the Trigger menu and get something useful by pressing the Measure button.

Ok, I re-did the scope. Here is the picture with the full view. I am USA so, I guess mains is 50hz ? I do not know how to check that.


P_20190215_230557 (1).jpg

You don't know the frequency your country’s electrical grid? If the answer is no, don’t go sticking scope probes anywhere near mains voltage to measure it, it’s too easy to blow up your scope and probably injury yourself in the process.

I seriously doubt a filter will do much to fix that, especially with it powering audio.

How much current is your supply able to provide and what does the iron require? It’s either overloaded or it doesn’t like the inductive load of the boost supply.

I apologize for my ignorance regarding my mains frequency phase. I can not remember when someone asked me that and do not know what or how that affects what I am doing. I only use my probes on DC power.

The AT power supply rated at 20 amps @ 5v, 10a at 12v. I have had it basically forever and used it without problems. I tried swapping power supplies, and get the same results. The current-meter shows me peak current used is 5.54 amps, when the iron starts up and 3.14 after the iron reaches it's programmed temperature. At this point I suspect the weakest part of the link would be the China step-up converter rated for 150w.

There is about 30" of copper 18-gauge cable between the +12v and the step-up converter. There is 24"+ copper 18-gauge wire between my step-up converter and the DC soldering iron.

US is 60hz but I think they allow it to vary a bit now...

Cheap chinese step up converter. Yes, that's likely to be very poorly behaved in my experience, and a high power step up converter is always going to put out too much noise for audio electronics.

Hi There!

Here's what u have to do

Just remove every thing and wire it to a power distribution board (remember to buy a fuse with it) and replace the converter with a more reliable one . And remember one more thing boosting up the voltage and current will spoil the soldering iron so better not to use that . And just buy a new soldering iron with faster heating speed. I would recommend this.


dhanush: And just buy a new soldering iron with faster heating speed. I would recommend this.


The TS-100 is my favorite soldering iron. At about 20 seconds to heat to 310c, and it's the size of a sharpie marker minus the iron tip. There is no other iron that heats faster, equal size or smaller.

I realize I can just run the iron from (6) 18650 battery power, and charge the batteries from the power supply. This would be a cleaner solution.