Replace internal switching power supply with external?

I have a Lucid 88192 converter that has this hum coming from it.  I took the lid off and was saddened to see a cheap $28 GECA40-12 switching power supply buzzing away in there.  I'm wondering if it would benefit me to replace the power supply with decent external power supply?  It is 12v so there is an abundance of options.

Just to clarify also, this is a single 12v 3.3A supply. 

dysenterygary said:

I have a Lucid 88192 converter that has this hum coming from it.  I took the lid off and was saddened to see a cheap $28 GECA40-12 switching power supply buzzing away in there.

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So you can literally hear it? If it really is making an audible noise, something is wrong with it. An audible noise would suggest something wrong with the magnetics maybe. Or something is drawing too much current.

Using an external supply is compelling or possibly necessary if you do not want to or cannot design the circuit being powered around the SMPS. But in case, it looks like a nice mostly digital piece of gear that was probably designed with an internal SMPS in mind.

You might replace the SMPS but keep it internal. Maybe replace it with a newish MeanWell supply like PS-45-12 which looks like it's a drop in replacement (even the mounting holes are the same).

I wouldn't be surprised if "only" a re-cap would suffice. Going by photos i could find of that power supply, it has CapXon electrolytics (aka Crap-xon), which are bound to fail. Then again, any cap that says "vent" on the sleeve, falls into that category, in my book.

That being said, "hum" is usually associated with low(er) frequencies, so if the primary (mains-side) cap is cooked and lost capacitance, that's prone to passing through some mains hum (100-120Hz) to the secondary, if not even excite some of the magnetics, as the PWM controller struggles to compensate for that.

squarewave said:

So you can literally hear it? If it really is making an audible noise, something is wrong with it. An audible noise would suggest something wrong with the magnetics maybe. Or something is drawing too much current.

Using an external supply is compelling or possibly necessary if you do not want to or cannot design the circuit being powered around the SMPS. But in case, it looks like a nice mostly digital piece of gear that was probably designed with an internal SMPS in mind.

You might replace the SMPS but keep it internal. Maybe replace it with a newish MeanWell supply like PS-45-12 which looks like it's a drop in replacement (even the mounting holes are the same).

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Yes, I can literally hear it.  I don't own any other piece of recording equipment that has a switching supply, so I did some quick googling and one of the first things I see is; "Not good for sensitive electronic equipment"....  0_o    Since converters are THE most sensitive electronics in recording (at least in my studio), wouldn't this be the last place I'd want to find one?

I think I will look into replacing it with a linear PS if I can make it fit.

Khron said:

I wouldn't be surprised if "only" a re-cap would suffice. Going by photos i could find of that power supply, it has CapXon electrolytics (aka Crap-xon), which are bound to fail. Then again, any cap that says "vent" on the sleeve, falls into that category, in my book.

That being said, "hum" is usually associated with low(er) frequencies, so if the primary (mains-side) cap is cooked and lost capacitance, that's prone to passing through some mains hum (100-120Hz) to the secondary, if not even excite some of the magnetics, as the PWM controller struggles to compensate for that.

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The caps are definitely not the best,  but what I found odd is that all of the large caps are glued to each other and to the board with some kind of yellow glue/epoxy stuff.  A few of the large resistors also have a dose of the glue.

I put my ear as close as I was comfortable with and the hum definitely seemed like it was coming from the "big" yellow transformer. 

The glue is, at least in theory, intended to help prevent the bigger two-legged components from moving / vibrating in transit or whatever (which would lead to solder joints or the copper traces fatiguing and breaking).

Trouble is, the cheapo light-brown glue, with time and temperature, tends to turn dark, brittle, corrosive and conductive.

https://www.badcaps.net/forum/showthread.php?t=34692

The complaint about switching supplies is generally  not hum or mechanical noise.

I did have to redesign one switching PS because the (small HF output) transformer buzzed, not hummed, but that was an exotic design where a single switcher IC was generating two different regulated output voltages. It worked adequately as a PS but the mechanical noise was audible outside the closed rack package so unacceptable for a premium SKU.

I ended up reconfiguring the PS to only regulate a single rail (using a more conventional well potted inductor), combined with a simple pass regulator for the lower rail voltage. It was then quiet as a church mouse.

I suspect the problem was the exotic transformer, either marginal for magnetic flux and saturating, or just poorly made (it was not potted). It was single sourced so I didn't have other options to try.

Back to your question, hum is not a common fault from switching PS so should be repairable without redesign.

JR

PS: It is common to glue larger massive parts to PCBs to prevent vibration stress.

PPS: To sniff out mechanical noise you can use a small wood dowel. Touch the suspect component with one end, and put the other end near your ear. Sound will conduct through the dowel. Do not use a screwdriver or conductive metal when probing around inside a product with the power on. 

dysenterygary said:

Yes, I can literally hear it.  I don't own any other piece of recording equipment that has a switching supply, so I did some quick googling and one of the first things I see is; "Not good for sensitive electronic equipment"....  0_o    Since converters are THE most sensitive electronics in recording (at least in my studio), wouldn't this be the last place I'd want to find one?

I think I will look into replacing it with a linear PS if I can make it fit.

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You're conclusion is simply incorrect. Modern SMPS are very good. There is high frequency noise in the 50+kHz range that most electronics do not care about but if used with a sensitive analog circuit chokes and caps can easily take care of that. Sometimes SMPS have fancy low load throttling modes that generate low frequency noise but that's unusually (never seen it myself, only heard about it). Add some regulation (probably not even necessary) and it will be *better* than a linear supply. A linear supply will almost always leak some 60Hz and 120Hz. There is plenty of studio gear that use SMPS. Usually they're external because they can radiate EMI but even inside a rack it's ok as long as you keep it far enough away from sensitive analog circuits. In an extra fancy piece of gear it might be walled off with a metal L divider. Also grounding layout is very important. But your converter thing was certainly designed with all of this in mind. I would assume by default that the designers of your converter unit knew all of this and did the right things to make it work correctly. It has specs right? They can't lie about that.

In your case, it sounds like the SMPS just worn out in some way. No SMPS should make audible noise. For $14 USD you can drop in a replacement (MeanWell PS-45-12) and see (unless you live in some place where it costs $9 million dollars to ship something in). How could you possibly hope for a better solution than that?

dysenterygary said:

Yes, I can literally hear it.  I don't own any other piece of recording equipment that has a switching supply, so I did some quick googling and one of the first things I see is; "Not good for sensitive electronic equipment"....  0_o    Since converters are THE most sensitive electronics in recording (at least in my studio), wouldn't this be the last place I'd want to find one?

I think I will look into replacing it with a linear PS if I can make it fit.

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All of your modern home appliances, computers, pro audio gears, medical, military even aerospace equipments use a switching power supply because unlike a linear power supply, it can deliver more power in a smaller form factor, and it doesn't waste unused energy by converting it as heat. 

That statement about not good for sensitive electronics heavily depends on what kind of switching power supply you select for your application.

Of course you don't use a cheap arse low quality switching power supply, for an example one that cost you $2 @ 1,000 pieces, because it's pretty obvious that the manufacturer has definitely cut corners a lot to sell it at that price tag.

dysenterygary said:

Yes, I can literally hear it.  I don't own any other piece of recording equipment that has a switching supply, so I did some quick googling and one of the first things I see is; "Not good for sensitive electronic equipment"....  0_o    Since converters are THE most sensitive electronics in recording (at least in my studio), wouldn't this be the last place I'd want to find one?

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Possibly not. If you have almost any phantom powered condenser mic there is a good chance it has a from of SMPS inside it to generate the capsule voltage.

Cheers

Ian

I stand corrected!  My next question would be: if switchers are so small, efficient and (most importantly) cheap, why are they not used in everything in the audio world?  <-- genuine curiosity, not sarcasm, to be clear.

dysenterygary said:

I stand corrected!  My next question would be: if switchers are so small, efficient and (most importantly) cheap, why are they not used in everything in the audio world?  <-- genuine curiosity, not sarcasm, to be clear.

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They weren't always this inexpensive.  Now they are widely used.

JR

PS: My first technician job back in the 60s was debugging a new SOTA technology called DC to DC switching power supplies (for a big deal Navy rescue submarine project)... Now it's a mature technology with off the shelf ICs and designs.

JohnRoberts said:

PPS: To sniff out mechanical noise you can use a small wood dowel.

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Might I suggest a glass stirring rod from chemistry class, and a tiny plastic funnel. Jam rod into funnel neck, done.

Glass conducts sound great, vibrates funnel. Ear near, or right on funnel, nice and loud.

Gene