NS2 humming power supply

[adoors]

Hi All,

It seems like my 2 months old NS2 developed a humming power supply today. It didn't make any sound before while idling. Nothing has changed in the setup. I searched the forum and found some members complaining that but I don't know if this is common. Is there something I can do about it (other than returning it to the shop and waiting for a replacement)?

Cheers
Marcus

[drezz]

The hum you are hearing is from the internal power supply, it comes from the transformer that is situated on the power supply PCB. It is an entirely acoustic thing; this hum does not reach the audio signal in any way, as you have found out. The hum is normal and does not indicate a fault or an upcoming problem. It is not a serviceable issue. Almost every unit that operates with a transformer with an iron core that is connected to the mains AC generates some level of acoustic hum. The hum/buzz is purely mechanical and is caused because the 50Hz or 60Hz Mains AC voltage is "shaking" the iron in the transformer core (also known as magnetostriction). I really can't say why sometimes the Nord power supply does this and not others, it may be because we use a power transformer that is built like a tank (to get the reliability Nord wants)....

Bless,

Pablo

[pterm]

This all makes me wonder whether Nord will move (has moved with NE5?) to a power supply without a transformer. Audible noise and electromagnetic noise are important design criteria for medical equipment, so I looked into medical-grade switching power supplies...

The KMT40-51515 produces +/-15V and 5V at 40W output power and might be a good fit for Nord http://us.tdk-lambda.com/ftp/Specs/km.pdf
<edit> This power supply allso has 90V-264VAC input range from 47-440Hz, so would be globally compatible.</edit>

This might not be a serviceable issue on existing product, but design solutions exist to address both the audible hum and audible-band electromagnetic interference issues inherent to transformer-based power supplies.

Something for the NS3 wishlist maybe.

[pablomastodon]

I'm curious to know what "medical-grade" power supplies cost...sounds scary...

Agreed that worldwide compatibility would make life easier in many situations.

Bless,

Pablo

[pterm]

I'm curious to know what "medical-grade" power supplies cost...sounds scary...

I used medical-grade for a starting point.

Obviously, Nord wouldn't need the isolation and certifications necessary for true medical-grade, so the price would not be as high. As it is, the part I mentioned costs $55 (USD) if buying only 10 pieces from distribution (Digi-key). http://www.digikey.com/product-search/e ... MT15-51515. Nord would get volume discount and likely buy direct for further discount. Not too scary on a $5K keyboard.

Also, I did some further reading, and these supplies might contain a transformer, but the transformer runs at a high frequency, (not at mains frequency) so it is out of the audible band and much smaller.

[Mr_-G-]

I'm curious to know what "medical-grade" power supplies cost...sounds scary...

They cost an arm and a leg.

[pablomastodon]

good one, Mr. G!

[stuartoMVF41000S]

It would be a mistake to use a transformer-less power supply. If you look at high-end audio equipment they all use transformers. The circuit is simple to get clean DC using a transformer. AC in goes through an AC line filter, then to the transformer which provides electrical isolation and steps down the voltage, then to a bridge rectifier with snubbing capacitors to reduce the switching noise, then through filter capacitors to reduce any AC ripple, then to a voltage regulator. If you want the safest, most reliable, and lowest electrical noise power supply you use a transformer. Everything I have read in electronics have said that the only reasons transformer-less power supplies are used is to reduce cost and weight. They are inherently unsafe and electrically noisier. See "The Art of Electronics Third Edition" by Paul Horowitz and Winfield Hill.

[stuartoMVF41000S]

I should have elaborated that the bridge rectifier converts the AC to DC and the snubbing capacitors reduce the switching noise from the diodes that make up the bridge rectifier.

[pablomastodon]

may I quote you on that?

bless,

pablo