[sdiy] Converting rack mount to DC input?

Thu Jul 9 13:40:46 CEST 2026

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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