Apogee da16x SMPS noise/whining

[lauritz]

I just replaced the electrolytics in the SMPS of my Apogee DA16x converter. All works fine, but after warming up the converter now makes a whining noise (around 4500 Hz) too loud to be ignored, since the converters are in my small control room close by the mixer and workspace. It did'nt do it before, but the biggest cap was starting to bulge and I thought that I would just replace all 3 caps at once. The noise is specifically coming from the inductor (see picture - red laquored thread standing next to the 2 electrolytics ) and i've tried to put some glue on it and some other white elastic goop too, but it does'nt seem to do the job. It was also glued to the neighboring electrolytic before i started messing with it.

Does anybody have a hint as how to get rid of the noise? It's very annoying

all the best
Lauritz

 

[scott2000]

I'm guessing you replaced whatever caps with equivalent specced ones (esr, etc.)? It was quiet before recapping??

 

[dreamix]

Dont have an answer but they do sounds alot even when working fine, some high frequency noise

 

[lauritz]

I'm guessing you replaced whatever caps with equivalent specced ones (esr, etc.)? It was quiet before recapping??

Thanks. I put in some decent quality capacitors, but did not actually check the ESR value...just capacitance, temperature and voltage. So maybe that could be the problem...i'll have another look at the ones i pulled out later today, To see the specifications.

 

[lauritz]

Dont have an answer but they do sounds alot even when working fine, some high frequency noise

They do make some noise, but this is something completely else. I have an AD16x that i also re-capped and that is super quiet compared to the one with this problem

 

[lauritz]

I'm guessing you replaced whatever caps with equivalent specced ones (esr, etc.)? It was quiet before recapping??

Problem seems to be solved....switched the 2 two smaller caps back to the ones i pulled out - they connect directly with the coil. I looked them up and they are indeed ultra low ESR capacitors. The ones i put in are also low, lower ESR than i can measure with my multifunction meter (below 0.01 ohms), but apparently not low enough.

Left the big capacitor in, which was the bad looking one in the first place. It's sitting right where the 250 AC enters and does'nt seem to cause any trouble.

Lesson learned on ESR! Thanks much for the input. Very happy not listening to that 4500 Hz squeel.

 

[Khron]

I looked them up and they are indeed ultra low ESR capacitors.

If you go TOO low with the ESR of the new ones, that can throw the feedback / compensation network out of whack, leading to such instabilities. "Too much of a good thing", if you will...

 

[lauritz]

If you go TOO low with the ESR of the new ones, that can throw the feedback / compensation network out of whack, leading to such instabilities. "Too much of a good thing", if you will...

Ok, so the replacement caps could have been too low as well. I'm not used to working with these SMPS. I've never payed much attention to ESR specs working with linear supplies or analog electronics in general...and never experience any trouble in that regard....i like to think But it is obvously very important in this case with the converter

Weird that the other converter (AD16x) which was also recapped, with the very same new capacitors, is working without noises or anything. But they are built in different years, so the power supply design may have changed i guess.

Thanks for the info!

 

[Khron]

I've never payed much attention to ESR specs working with linear supplies or analog electronics in general...and never experience any trouble in that regard.

... Because it's next to irrelevant in those cases Although too-low ESR on the output of linear regulators (especially low-dropout ones) CAN upset them too.

Weird that the other converter (AD16x) which was also recapped, with the very same new capacitors, is working without noises or anything.

Well, component tolerances could play into that too, but anyway...