[sdiy] Converting rack mount to DC input?

Fri Jul 10 17:58:17 CEST 2026

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

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________________________________
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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>>>>> ________________________________________________________
>>>>> This is the Synth-diy mailing list
>>>>> Submit email to: Synth-diy at synth-diy.org
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>>>>>
>>>>
>>>
>>
>

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