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Is the noisey transformer just one unit? Would a torroidial transformer have less physical noise?</div>
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Or if it is vibration related maybe mounting it with rubber washers and making the electrical contact with wires?</div>
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Or move the units away from where the mic can pick up the noise?</div>
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Not my area of expertise, just wondering if there may be a simpler solition.</div>
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Ed</div>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> Synth-diy <synth-diy-bounces@synth-diy.org> on behalf of Ben Stuyts via Synth-diy <synth-diy@synth-diy.org><br>
<b>Sent:</b> Thursday, 09 July 2026 17:39:07<br>
<b>To:</b> cheater cheater <cheater00social@gmail.com><br>
<b>Cc:</b> synth-diy <synth-diy@synth-diy.org><br>
<b>Subject:</b> Re: [sdiy] Converting rack mount to DC input?</font>
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<div class="PlainText">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.<br>
<br>
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.<br>
<br>
Ben<br>
<br>
> On 9 Jul 2026, at 18:23, cheater cheater <cheater00social@gmail.com> wrote:<br>
> <br>
> Thanks. A few questions:<br>
> <br>
> What if only some of the rails are connected, but not the one used for<br>
> steering the relay (a fault)?<br>
> <br>
> Relays are kind of expensive, how much do you think that could end up costing?<br>
> <br>
> If they don't get cycled a lot at all, wouldn't they end up getting stuck?<br>
> <br>
> On Thu, Jul 9, 2026 at 5:57 PM Ben Stuyts <ben@stuyts.nl> wrote:<br>
>> <br>
>> 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.<br>
>> <br>
>> Ben<br>
>> <br>
>>> On 9 Jul 2026, at 16:06, cheater cheater <cheater00social@gmail.com> wrote:<br>
>>> <br>
>>> In order to provide the bridging functionality it has to have at least 8 pins.<br>
>>> <br>
>>> On Thu, Jul 9, 2026 at 1:41 PM Ben Stuyts <ben@stuyts.nl> wrote:<br>
>>>> <br>
>>>> Perhaps a 4 or 5 pin XLR connector is an option? They are not that expensive, and lots of ready-made cables are available.<br>
>>>> <br>
>>>> Ben<br>
>>>> <br>
>>>>> On 9 Jul 2026, at 10:18, cheater cheater via Synth-diy <synth-diy@synth-diy.org> wrote:<br>
>>>>> <br>
>>>>> One way to have DC input, but retain the capability of using the<br>
>>>>> internal power supply, is to have a 4P2T switch for configuration.<br>
>>>>> <br>
>>>>> It seems that 4P2T switches are super expensive, especially if they're<br>
>>>>> supposed to withstand, say, 1A.<br>
>>>>> <br>
>>>>> So I started looking around. TLDR: classic pcie 8-pin power connectors<br>
>>>>> are probably the best, and also the cheapest.<br>
>>>>> <br>
>>>>> My first thought was to look at PCIE x1 slots. The cheapest advanced<br>
>>>>> connector on earth, for 0.4 Euro at unit price, you get a connector<br>
>>>>> that handles 1.1A per pin as per eg this document, page 6, 4.4<br>
>>>>> <br>
>>>>> <a href="https://cdn.amphenol-cs.com/media/wysiwyg/files/documentation/gs-12-233.pdf">
https://cdn.amphenol-cs.com/media/wysiwyg/files/documentation/gs-12-233.pdf</a><br>
>>>>> <br>
>>>>>> 4.4 CONTACT CURRENT RATING<br>
>>>>>> 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.<br>
>>>>> <br>
>>>>> The connector has 36 pins, so while I don't think it would handle 36A,<br>
>>>>> I'm sure it would handle something like 2A, especially if you share<br>
>>>>> pins. You can even leave pins empty to prevent shorts during<br>
>>>>> insertion.<br>
>>>>> <br>
>>>>> You could put the connector out the back, and either insert a plug-in<br>
>>>>> "card" (really just a small edge connector with wires soldered on)<br>
>>>>> that provides DC, or a pass-through "card" that shorts some pins<br>
>>>>> together to carry power from the internal power supply. And now<br>
>>>>> instead of $20-30 per unit, this costs $1 per unit. My main question<br>
>>>>> is how I would fix the connector, but maybe a simple screw hole in the<br>
>>>>> connector that mates with a threaded hole in the case could do the<br>
>>>>> trick.<br>
>>>>> <br>
>>>>> A pcie x1 port is 25mm long, so it can fit upright in the back of a 1U<br>
>>>>> rack unit, which is 45mm, so it doesn't take up much space either.<br>
>>>>> <br>
>>>>> The cheapest one that can be found at Mouser currently and can be<br>
>>>>> bought in low volumes is roughly 0.4 Euro.<br>
>>>>> <br>
>>>>> <a href="https://www.mouser.at/ProductDetail/Amphenol-FCI/10018783-10200TLF?qs=V%252BXmToedwojeZUI4fPwmPA%3D%3D">
https://www.mouser.at/ProductDetail/Amphenol-FCI/10018783-10200TLF?qs=V%252BXmToedwojeZUI4fPwmPA%3D%3D</a><br>
>>>>> <br>
>>>>> Qty. Unit Price Ext. Price<br>
>>>>> 1 € 0,439 € 0,44<br>
>>>>> 10 € 0,372 € 3,72<br>
>>>>> 25 € 0,332 € 8,30<br>
>>>>> 100 € 0,316 € 31,60<br>
>>>>> <br>
>>>>> By making the connector require a dummy plug to connect the internal<br>
>>>>> power supply into the circuit, it makes it impossible to connect both<br>
>>>>> DC power and mains AC, so that makes the design intrinsically safe<br>
>>>>> without using switches.<br>
>>>>> <br>
>>>>> Alternatively to a PCIE connector I could use some panel mount plug<br>
>>>>> with 8 pins, have 4 pins for DC input, and have the other 4 pins carry<br>
>>>>> power from the internal power supply, and similarly use a shorting<br>
>>>>> plug to use the internal power supply.<br>
>>>>> <br>
>>>>> Circular DIN connectors start at about 8 Euro per pair of socket and plug.<br>
>>>>> Circular metric aren't better.<br>
>>>>> MIL Spec connectors seem to be cheaper. But the mouser search sucks,<br>
>>>>> so I can't find them by number of pins.<br>
>>>>> <br>
>>>>> PCIE 8-pin power connectors are real, real cheap - 10 cents a piece.<br>
>>>>> They're latching (no need for screws and stuff). There doesn't seem to<br>
>>>>> be a panel mount version, but one could mount a through-hole connector<br>
>>>>> to a pcb, and have the pcb have screw holes for mounting to the rear<br>
>>>>> panel. They handle high power - 150W meaning 3A per pin (half the pins<br>
>>>>> are return pins). Seems like a winner to me. They're also tiny so they<br>
>>>>> will easily fit in the back of a 1U unit even vertically. The biggest<br>
>>>>> pain here might be making the rectangular hole and having it look any<br>
>>>>> good. might be a case for custom die, maybe a small steel job that<br>
>>>>> uses two bolts to screw together the two cutting parts through the<br>
>>>>> sheet metal.<br>
>>>>> <br>
>>>>> "Pin and socket" connectors are the same kind of thing, just not<br>
>>>>> specifically PCIE 8-pin. Still cheap at roughly 20 cents a piece...<br>
>>>>> useful alternative if more than 4 rails are necessary.<br>
>>>>> <br>
>>>>> D-sub connectors carry up to 3A... and are very cheap and can do panel<br>
>>>>> mount of some sort. But I'll be damned if I use one of those cursed<br>
>>>>> things for power.<br>
>>>>> <br>
>>>>> Automotive connectors seem inexpensive too, but I haven't really<br>
>>>>> looked into them much other than a quick parametric search.<br>
>>>>> <br>
>>>>> I wonder what everyone thinks of this.<br>
>>>>> <br>
>>>>> On Tue, Jul 7, 2026 at 6:39 AM cheater cheater<br>
>>>>> <cheater00social@gmail.com> wrote:<br>
>>>>>> <br>
>>>>>> Don't you think this may have had something to do with you<br>
>>>>>> distributing AC power, rather than DC with 0V potential?<br>
>>>>>> <br>
>>>>>> On Sat, Jul 4, 2026 at 11:33 PM Mattias Rickardsson <mr@analogue.org> wrote:<br>
>>>>>>> <br>
>>>>>>> Den lör 4 juli 2026 14:23Florian Anwander via Synth-diy <synth-diy@synth-diy.org> skrev:<br>
>>>>>>>> <br>
>>>>>>>> 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.<br>
>>>>>>> <br>
>>>>>>> <br>
>>>>>>> This reminds me of a somewhat similar issue I had many years ago:<br>
>>>>>>> <br>
>>>>>>> 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.)<br>
>>>>>>> <br>
>>>>>>> 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.<br>
>>>>>>> <br>
>>>>>>> /mr<br>
>>>>>>> <br>
>>>>>>> ________________________________________________________<br>
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>>>>> <br>
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>>>>> This is the Synth-diy mailing list<br>
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