[sdiy] Converting rack mount to DC input?

Thu Jul 9 15:37:25 CEST 2026

With respect, but is that really *the* standard? A bit of duckduckgo-ing shows me this:

https://pinoutguide.com/Audio-Video-Hardware/xlr6_pinout.shtml

and then there is this…

https://pinoutguide.com/Audio-Video-Hardware/xlr4_pinout.shtml

and of course:

https://xkcd.com/927/

Ben

> On 9 Jul 2026, at 15:02, Mike Bryant <mbryant at futurehorizons.com> wrote:
> 
> The 6 pin XLR is the standard for +/- power transmission.  See last entry on :
> 
> https://www.clarkwire.com/pinouts/xlr-audio-pinouts
> 
> 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: 09 July 2026 12:40
> 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?
>  
> 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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