[sdiy] Power supply of a 19" rack

Rutger Vlek rutgervlek at gmail.com
Wed May 15 12:08:47 CEST 2019

Hi Frederic,

When I was touring as a musician I absolutely hated wall warts. They get lost, damaged or unplug at the wrong moments. But my hate is specifically turned towards wall warts for instruments that get packed/unpacked frequently and sit quite prominently on stage. In that sense a 19” rack is different. My 19” rack is rather static, I don’t change it much and certainly don’t make changes while on the road. Also, the back side and power-supply (in whatever form) is well protected by the case the units are mounted in. So in that situation, I’m relatively okay with wall-warts, though there are a few considerations in 19” world:

- some wall warts are heavy and plugging them into a socket may not be enough to keep them there during transport. As soon as they get on the loose inside a 19” case, they might cause problems/damage/unreliability.

- radiation from wall warts…. I’ve always had some worries about interference between wall warts and sensitive cables or devices in my rack. I try to keep them as far as possible from each other. Of course you have the same with internal power supplies, but then you have a more controlled situation. You can design the rack unit for sufficient isolation from the PSU and you the casing can assure radiation will not leak to the outside world.

All together I keep preferring a mains input, though for some devices (desktop units, e.g. a Waldorf Streichfett) it just doesn’t make sense.


> On 14 May 2019, at 10:15, Frédéric (Opensource) <marzacdev at gmail.com> wrote:
> Hi everyone.
> I have not written here for a long time but I keep reading
> the list because of the interest of the topics.
> I am shared between two concepts for the power supply
> of a 19" rack and I would like to hear your opinion both as
> musicians and as instruments makers.
> _Option A: mains_
> Offering a regular 220V / 110V / 100V C14 input at the rack.
> Inside:
> pre-certified switched mode power supply (which adapt for all countries)
> Pros:
> * C13 cables are common and available
> * No need for an external wall adapter
> * Musicians seem to like this (my impression)
> Cons:
> * Certification process (more complex and costly)
> * Design risks (mains inside / grounding / security for users and technicians)
> * Big additional cost
> _Option B: all in_
> Offering a regular 2.1mm DC jack connector that can accept ANYTHING
> like DC/AC from 6V to 16V.
> Inside:
> rectifier + small DC/DC converter or linear regulation
> (depending on the consumption and dissipation of the circuits)
> Pros:
> * Everyone owns needless adapters that could be reused
>    (= environment friendly / less e-waste)
> * Less design complexity
> * No mains inside the rack
> * Simplified certification process
> Cons:
> * Need an external power adapter
> * Need a power adapter that works for the region where the machine is used
>    (simple wall transformers often cannot travel)
> * Musicians don't seem to like it (my impression)
> Question:
> What would you prefer?
> Fred.
> PS: By the way, last hours for the Buzzzy! on Kickstarter:
> https://www.kickstarter.com/projects/1304489933/buzzzy-the-digital-polysynth
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