[sdiy] Converting rack mount to DC input?

Tue Jul 14 14:03:20 CEST 2026

Hmm, GX16 is interesting, thank you! Let me see if I can find one with
8 pins easily - that's the minimum that I need (see earlier emails
why: to either supply external DC (+17, -17, 0, 48) or loop back the
internal PSU (half the pins would carry the internal psu's voltages))

That's actually pretty cool because those are small and allow a
circular hole and are easily panel mounted. Thanks, great idea!

On Mon, Jul 13, 2026 at 10:19 PM David Huss via Synth-diy
<synth-diy at synth-diy.org> wrote:
>
> Ethernet has a PoE (Power-over-Ethernet) standard and in its maximum
> PoE++ variant Type 4 switches can supply up to 100 Watts over one
> ethernet port.
>
> HOWEVER: PoE similar to USB-C PD (Power Delivery) negotiates this power
> delivery with the device attached to it and also has some measures to
> detect faulty connections/cables. A self-baked solution may fail
> spectacularily (and consider what happens if someone plugs your power
> supply into an actual network port. Professional networking equipment
> can easily cost mor than most peoples cars are worth..
>
> For this type of DC connection there are dedicated connectors and
> cables. The price ranges and features vary wildly, but a good and cheap
> solution that is tough enough for live-gig is the GX16 5-pin connector,
> you can get a pack of 5 plugs AND jacks (including a shitty
> screwdriver!) for 9 Euros on Amazon. The plug has a thread so it can be
> locked and it is not too hard to solder.
>
> This type of plug has sometimes also be used in mixer power supplies
> that work with outboard power supplies with exactly the requirements you
> have, so it has been done before as well.
>
> Cheers,
> David
>
>
>
> On 2026-07-13 21:24, cheater cheater via Synth-diy wrote:
> > A little more to qualify my question, it's easier to find panel mount
> > hardware for those, can just use a keystone plug, and they take up
> > less space, so easier to fit on the back of a 1U device.
> >
> > On Mon, Jul 13, 2026 at 9:13 PM cheater cheater
> > <cheater00social at gmail.com> wrote:
> >>
> >> Another question - how is everyone feeling about rj-45 as a power
> >> plug? carrying up to 800 mA. I've seen threads where people say
> >> they've been putting 1A through those, per pin. Thanks.
> >>
> >> https://www.eevblog.com/forum/projects/rj12-rj45-rj50-max-current-per-pin/
> >>
> >> https://groups.google.com/g/sci.electronics.design/c/TPGrRTJjReA?pli=1
> >>
> >>
> >> On Mon, Jul 13, 2026 at 5:09 PM cheater cheater
> >> <cheater00social at gmail.com> wrote:
> >>>
> >>> Someone off-list made some comments, and here's what came out of it:
> >>>
> >>> 1. All my devices use balanced audio
> >>> 2. The rack items actually tie together their grounds by using rack
> >>> screws and the rack rail
> >>> 3. I don't know if the rack devices have isolated audio grounds, but
> >>> they're almost fully analogue, except for stuff like LED bar graphs
> >>> and on-off status LEDs for functions
> >>>
> >>> On Mon, Jul 13, 2026 at 4:34 PM cheater cheater
> >>> <cheater00social at gmail.com> wrote:
> >>>>
> >>>> So a person on another forum mentioned that converting the devices to
> >>>> DC input could create ground loops.
> >>>>
> >>>> As a reminder, I would be creating a "DC Bus" that carries +18, -18,
> >>>> 0V, and +48V, and I would wire it in a daisy-chain configuration going
> >>>> from unit to unit. All of those units are in one rack on top of each
> >>>> other.
> >>>>
> >>>> Here's what they said:
> >>>>
> >>>>> If you're intending to run them all off a single raw supply, that could
> >>>>> introduce ground loops. The safest would be a bunch of small
> >>>>> transformers, or one with multiple secondaries. Hammond 229 are
> >>>>> small low profile transformers that could fit in a 1U cabinet.
> >>>>
> >>>> So I've been thinking about this since they mentioned ground loops.
> >>>> Here's what I think.
> >>>>
> >>>> Currently all those rack devices already use a three-prong IEC C14
> >>>> receptacle, with the earth wire connected to the chassis.
> >>>>
> >>>> Instead of the chassis grounding point being connected via the C14
> >>>> receptacle, and through a mains cable, to mains earth, it would now be
> >>>> connected via my DC bus cable, which would have an earth conductor as
> >>>> well.
> >>>>
> >>>> So in terms of ground loops, not much changes.
> >>>>
> >>>> However, given that we're talking about LOOPS, the area of the ground
> >>>> loop would be important as well.
> >>>>
> >>>> Currently each rack has a cable going to a power strip.
> >>>>
> >>>> However, with my DC bus, I would be daisy chaining it, so the bus goes
> >>>> to the bottom rack mount device, there's a plug there, then from that
> >>>> plug there's a short cable going 1U above it, and so on.
> >>>>
> >>>> That would create an extremely small area for the devices to create
> >>>> ground loops.
> >>>>
> >>>> I could (and maybe should) additionally put an earthed shield around
> >>>> these wires, in order to shield them from EMI.
> >>>>
> >>>> So in total, either nothing changes regarding ground loops, or it's
> >>>> purely improved compared to the current situation.
> >>>>
> >>>> I would be interested in everyone's thoughts on this matter.
> >>>>
> >>>> Thanks.
> >>>>
> >>>>
> >>>> On Fri, Jul 10, 2026 at 6:03 PM cheater cheater
> >>>> <cheater00social at gmail.com> wrote:
> >>>>>
> >>>>> there's one that's particularly noisy, but there are others that are a
> >>>>> little noisy too, and it adds up. plus the heat just makes the room
> >>>>> uncomfortable to be in. I've gone to great lengths to move all heat
> >>>>> and noise generating equipment out of my day room, including moving
> >>>>> the pcs to another place and connecting everything via fiber optics.
> >>>>> so having 80W less heating my head will be an improvement once more.
> >>>>>
> >>>>> On Fri, Jul 10, 2026 at 5:58 PM el macaco <elmacaco at hotmail.com> wrote:
> >>>>>>
> >>>>>> Is the noisey transformer just one unit?  Would a torroidial transformer have less physical noise?
> >>>>>>
> >>>>>> Or if it is vibration related maybe mounting it with rubber washers and making the electrical contact with wires?
> >>>>>>
> >>>>>> Or move the units away from where the mic can pick up the noise?
> >>>>>>
> >>>>>> Not my area of expertise, just wondering if there may be a simpler solition.
> >>>>>>
> >>>>>> Ed
> >>>>>>
> >>>>>>
> >>>>>>
> >>>>>> Get Outlook for iOS
> >>>>>> ________________________________
> >>>>>> From: Synth-diy <synth-diy-bounces at synth-diy.org> on behalf of Ben Stuyts via Synth-diy <synth-diy at synth-diy.org>
> >>>>>> Sent: Thursday, 09 July 2026 17:39:07
> >>>>>> To: cheater cheater <cheater00social at gmail.com>
> >>>>>> Cc: synth-diy <synth-diy at synth-diy.org>
> >>>>>> Subject: Re: [sdiy] Converting rack mount to DC input?
> >>>>>>
> >>>>>> You could use both rails, i.e. connect the relay coil between the + and - supply. Not + and gnd. If you want anything more fancy you should build some sort of power-good circuit. But that applies to your homebrew connector solution too.
> >>>>>>
> >>>>>> Just look at any general purpose or small power relays from e.g. Panasonic, Omron, TE. They usually have an endurance of millions of cycles. A quick search on digikey shows lots of options, starting at a few euro’s.
> >>>>>>
> >>>>>> Ben
> >>>>>>
> >>>>>>> On 9 Jul 2026, at 18:23, cheater cheater <cheater00social at gmail.com> wrote:
> >>>>>>>
> >>>>>>> Thanks. A few questions:
> >>>>>>>
> >>>>>>> What if only some of the rails are connected, but not the one used for
> >>>>>>> steering the relay (a fault)?
> >>>>>>>
> >>>>>>> Relays are kind of expensive, how much do you think that could end up costing?
> >>>>>>>
> >>>>>>> If they don't get cycled a lot at all, wouldn't they end up getting stuck?
> >>>>>>>
> >>>>>>> On Thu, Jul 9, 2026 at 5:57 PM Ben Stuyts <ben at stuyts.nl> wrote:
> >>>>>>>>
> >>>>>>>> You could use an internal relay for the switch-over. If there is power on the DC connector -> switch over. Otherwise keep the AC rectifier connected.
> >>>>>>>>
> >>>>>>>> Ben
> >>>>>>>>
> >>>>>>>>> On 9 Jul 2026, at 16:06, cheater cheater <cheater00social at gmail.com> wrote:
> >>>>>>>>>
> >>>>>>>>> In order to provide the bridging functionality it has to have at least 8 pins.
> >>>>>>>>>
> >>>>>>>>> On Thu, Jul 9, 2026 at 1:41 PM Ben Stuyts <ben at stuyts.nl> wrote:
> >>>>>>>>>>
> >>>>>>>>>> Perhaps a 4 or 5 pin XLR connector is an option? They are not that expensive, and lots of ready-made cables are available.
> >>>>>>>>>>
> >>>>>>>>>> Ben
> >>>>>>>>>>
> >>>>>>>>>>> On 9 Jul 2026, at 10:18, cheater cheater via Synth-diy <synth-diy at synth-diy.org> wrote:
> >>>>>>>>>>>
> >>>>>>>>>>> One way to have DC input, but retain the capability of using the
> >>>>>>>>>>> internal power supply, is to have a 4P2T switch for configuration.
> >>>>>>>>>>>
> >>>>>>>>>>> It seems that 4P2T switches are super expensive, especially if they're
> >>>>>>>>>>> supposed to withstand, say, 1A.
> >>>>>>>>>>>
> >>>>>>>>>>> So I started looking around. TLDR: classic pcie 8-pin power connectors
> >>>>>>>>>>> are probably the best, and also the cheapest.
> >>>>>>>>>>>
> >>>>>>>>>>> My first thought was to look at PCIE x1 slots. The cheapest advanced
> >>>>>>>>>>> connector on earth, for 0.4 Euro at unit price, you get a connector
> >>>>>>>>>>> that handles 1.1A per pin as per eg this document, page 6, 4.4
> >>>>>>>>>>>
> >>>>>>>>>>> https://cdn.amphenol-cs.com/media/wysiwyg/files/documentation/gs-12-233.pdf
> >>>>>>>>>>>
> >>>>>>>>>>>> 4.4 CONTACT CURRENT RATING
> >>>>>>>>>>>> 1.1 amp per contact minimum per EIA-364—70, method 2 and PCI Express Connector High Speed Electrical Test Procedure. The temperature rise shall not exceed 30 degree C. Ambient condition is still air at 25°C.
> >>>>>>>>>>>
> >>>>>>>>>>> The connector has 36 pins, so while I don't think it would handle 36A,
> >>>>>>>>>>> I'm sure it would handle something like 2A, especially if you share
> >>>>>>>>>>> pins. You can even leave pins empty to prevent shorts during
> >>>>>>>>>>> insertion.
> >>>>>>>>>>>
> >>>>>>>>>>> You could put the connector out the back, and either insert a plug-in
> >>>>>>>>>>> "card" (really just a small edge connector with wires soldered on)
> >>>>>>>>>>> that provides DC, or a pass-through "card" that shorts some pins
> >>>>>>>>>>> together to carry power from the internal power supply. And now
> >>>>>>>>>>> instead of $20-30 per unit, this costs $1 per unit. My main question
> >>>>>>>>>>> is how I would fix the connector, but maybe a simple screw hole in the
> >>>>>>>>>>> connector that mates with a threaded hole in the case could do the
> >>>>>>>>>>> trick.
> >>>>>>>>>>>
> >>>>>>>>>>> A pcie x1 port is 25mm long, so it can fit upright in the back of a 1U
> >>>>>>>>>>> rack unit, which is 45mm, so it doesn't take up much space either.
> >>>>>>>>>>>
> >>>>>>>>>>> The cheapest one that can be found at Mouser currently and can be
> >>>>>>>>>>> bought in low volumes is roughly 0.4 Euro.
> >>>>>>>>>>>
> >>>>>>>>>>> https://www.mouser.at/ProductDetail/Amphenol-FCI/10018783-10200TLF?qs=V%252BXmToedwojeZUI4fPwmPA%3D%3D
> >>>>>>>>>>>
> >>>>>>>>>>> Qty.  Unit Price  Ext. Price
> >>>>>>>>>>> 1     € 0,439     € 0,44
> >>>>>>>>>>> 10    € 0,372     € 3,72
> >>>>>>>>>>> 25    € 0,332     € 8,30
> >>>>>>>>>>> 100   € 0,316     € 31,60
> >>>>>>>>>>>
> >>>>>>>>>>> By making the connector require a dummy plug to connect the internal
> >>>>>>>>>>> power supply into the circuit, it makes it impossible to connect both
> >>>>>>>>>>> DC power and mains AC, so that makes the design intrinsically safe
> >>>>>>>>>>> without using switches.
> >>>>>>>>>>>
> >>>>>>>>>>> Alternatively to a PCIE connector I could use some panel mount plug
> >>>>>>>>>>> with 8 pins, have 4 pins for DC input, and have the other 4 pins carry
> >>>>>>>>>>> power from the internal power supply, and similarly use a shorting
> >>>>>>>>>>> plug to use the internal power supply.
> >>>>>>>>>>>
> >>>>>>>>>>> Circular DIN connectors start at about 8 Euro per pair of socket and plug.
> >>>>>>>>>>> Circular metric aren't better.
> >>>>>>>>>>> MIL Spec connectors seem to be cheaper. But the mouser search sucks,
> >>>>>>>>>>> so I can't find them by number of pins.
> >>>>>>>>>>>
> >>>>>>>>>>> PCIE 8-pin power connectors are real, real cheap - 10 cents a piece.
> >>>>>>>>>>> They're latching (no need for screws and stuff). There doesn't seem to
> >>>>>>>>>>> be a panel mount version, but one could mount a through-hole connector
> >>>>>>>>>>> to a pcb, and have the pcb have screw holes for mounting to the rear
> >>>>>>>>>>> panel. They handle high power - 150W meaning 3A per pin (half the pins
> >>>>>>>>>>> are return pins). Seems like a winner to me. They're also tiny so they
> >>>>>>>>>>> will easily fit in the back of a 1U unit even vertically. The biggest
> >>>>>>>>>>> pain here might be making the rectangular hole and having it look any
> >>>>>>>>>>> good. might be a case for custom die, maybe a small steel job that
> >>>>>>>>>>> uses two bolts to screw together the two cutting parts through the
> >>>>>>>>>>> sheet metal.
> >>>>>>>>>>>
> >>>>>>>>>>> "Pin and socket" connectors are the same kind of thing, just not
> >>>>>>>>>>> specifically PCIE 8-pin. Still cheap at roughly 20 cents a piece...
> >>>>>>>>>>> useful alternative if more than 4 rails are necessary.
> >>>>>>>>>>>
> >>>>>>>>>>> D-sub connectors carry up to 3A... and are very cheap and can do panel
> >>>>>>>>>>> mount of some sort. But I'll be damned if I use one of those cursed
> >>>>>>>>>>> things for power.
> >>>>>>>>>>>
> >>>>>>>>>>> Automotive connectors seem inexpensive too, but I haven't really
> >>>>>>>>>>> looked into them much other than a quick parametric search.
> >>>>>>>>>>>
> >>>>>>>>>>> I wonder what everyone thinks of this.
> >>>>>>>>>>>
> >>>>>>>>>>> On Tue, Jul 7, 2026 at 6:39 AM cheater cheater
> >>>>>>>>>>> <cheater00social at gmail.com> wrote:
> >>>>>>>>>>>>
> >>>>>>>>>>>> Don't you think this may have had something to do with you
> >>>>>>>>>>>> distributing AC power, rather than DC with 0V potential?
> >>>>>>>>>>>>
> >>>>>>>>>>>> On Sat, Jul 4, 2026 at 11:33 PM Mattias Rickardsson <mr at analogue.org> wrote:
> >>>>>>>>>>>>>
> >>>>>>>>>>>>> Den lör 4 juli 2026 14:23Florian Anwander via Synth-diy <synth-diy at synth-diy.org> skrev:
> >>>>>>>>>>>>>>
> >>>>>>>>>>>>>> Maybe, it's a stupid thought, but...: could it be that a device relies on beeing galvanical separated from other devices. I this case the common supply might clash with the devices concept.
> >>>>>>>>>>>>>
> >>>>>>>>>>>>>
> >>>>>>>>>>>>> This reminds me of a somewhat similar issue I had many years ago:
> >>>>>>>>>>>>>
> >>>>>>>>>>>>> I wanted a Korg MS-20 and a Korg KR-55 to share one external power puck. (Swedish-sold old Korgs had a big external power transformer to step down from 220 V AC to 16 V AC, which is then what the instrument then accepts via a plug with 2 flat prongs that doesn't seem roadworthy with European electrical standards.)
> >>>>>>>>>>>>>
> >>>>>>>>>>>>> So I made a short splitter Y cable on the 16 V AC side and attached both instruments and turned them on. But then I connected an audio cable between them (or audio cables from both units to the same mixer) and I had a blown fuse! It was apparently not okay to connect those two grounds together when running off the same AC supply.
> >>>>>>>>>>>>>
> >>>>>>>>>>>>> /mr
> >>>>>>>>>>>>>
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> >>>>>>>>>>
> >>>>>>>>>
> >>>>>>>>
> >>>>>>>
> >>>>>>
> >>>>>>
> >>>>>> ________________________________________________________
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> >
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