The unglamourous part of the project is the power supply.
For the past four years the power supply unit (PSU) has been housed in a plastic case, which used to carry car jump leads.
In fact, it's hosted the PSU and the rear-panel connectors through the development and testing phase of the project. But now that time is over and I need to move the PSU to a new home and rewire the rear-panel connections.
Power Struggle
There is no room left in the rack enclosure for the PSU so the plan has always been for a separate case for the PSU.
PSU Requirements
Ventilation - It gets warm.
Main PCB - 110mm x 110mm
Transformer - 74x66x73mm (WxDxH)
Minimum internal dimensions - 120x200x80mm
Power switch accessible on front panel.
Power On Through
One problem with having a PSU that is tucked away out of reach is that turning the power on and off could be annoying. I thought of several solutions to this, but the one I like best is to have the power switch on the front panel of the SS30-M and loop the live wire through from the PSU for switching.
To do this I need a live wire out from the PSU into the SS-30M then onto a switch before returning back to the PSU. Most important here is that the connector out of the PSU is safe. No live pins. Also, I don't want there to be any doubt that this is not a normal mains inlet. It will short out a normal supply so using a domestic main connector is a no-no. After looking around a bit I decided to use Neutrik PowerCon connectors. You get different designs for input and output and they are safe. I found knock-off cheaper copies from China too.
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| PowerCon connectors from eBay |
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I got these and made up the cable.
This is the drawing of the panel connector
Drawing+NAC3MPA-1-WOT.pdf
Mains Event
The next step was supposed to be a choice of PSU enclosure. Instead, after a bit of research, I decided to make another temporary case. I was heading towards making or designing and having made, a bespoke enclosure and that would have taken too long. Too long in the sense that it would have delayed the making of the SS30-M. I was also keen to re-house the PSU in the final configuration so I could see if there were any issues and prepare the way for a better case later on.
I looked around my garage and found a three-bottle, wooden wine case which was an ideal temporary solution.
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| Rjoca, if you must know |
The nice thing about this box, as well as being wooden and thus easy to work and the right size, is that it has a hinged lid, with a catch. This makes it easy to open and close, but one disadvantage is that the wood is fairly thick, which makes it hard to mount some of the components and connectors.
I decided to reuse the original back panel again but this time with only the power connectors. That meant a bit more vandalism of the original SS-30.
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| Original SS-30 rear-panel marked up for cutting and components unscrewed |
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| Main panel side of temporary PSU no.2 under construction |
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| Finished mans panel with original switch and lamp. |
On the other side of the box, I had to create a panel to mount the Cliffcon Miniature ZC connector. Again I looked around the garage and found a nice strip or thin, polished metal (originally something to do with a kitchen unit I think) which was cut down and drilled.
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| Power Output side of the temp PSU no.2 |
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| Power Output with cable connected |
Once the connector mounting was done it was onwards to wiring it up. The power regulator PCB has a connector header and obviously i wanted to reuse that, which meant the wires from the actual synth had to be cut at last.
And I had to decide which wires go to which pins.
And I decided to do a good job, with heat-shrink and everything.
When all is ready, I throw this switch
Whilst I'm still working on the rest of the main enclosure I don't want the front-panel mains power switch in there. Hence I've made a temporary switch box and that's the PSU temporary PSU no.2 all done!
Burly Chassis
The following is just some notes on a PSU case.
e.g.
http://uk.farnell.com/multicomp/mb4/box-abs-black/dp/301279
but that has no ventilation,
Or in metal
http://uk.farnell.com/multicomp/mc001134/enclosure-ip65-aluminium-alloy/dp/2544965
also no vent
Options:
1. Standard electronics project case - e.g. Hammond
http://www.hammondmfg.com/pdf/1454P.pdf
2. Aluminium amplifier case - e.g
https://diyaudiostore.com/collections/chassis but other options on eBay from China
3. 19" rack case - 3U - Too much
4. laser cut enclosure in wood/perspex
The laser cut option wins because:
- Exact sizing is a given
- Can cut in ventilation slots
- Cheap
- Can cut in exact holes for connectors etc.
- Can etch in legends and logo
Here's an online tool to deisgn a case ready for laser cutting.
http://www.makercase.com/
"MakerCase
lets users create cases with flat edges or interlocking edges using
finger joints or t-slots for retaining nuts and bolts. "
This is the kind of plan you get.
This site shows how the nuts are held into the t-slot and then it all fits together.
http://store.curiousinventor.com/blog/how-to-make-cheap-lasercut-custom-boxes-for-your-diy-electronics/
It seems a bit shonky though. You have nuts protruding as well.
This is another one done with wood and perspex
http://www.instructables.com/id/AutoCAD-to-Trotec-Laser-I-Made-It-at-TechShop/
I'm
really not sure about having metal nuts all over the sides of the case
when there's no way to earth them. There's mains inside and I'd like it
to stay there.
For Inkscape this guy has a plug-in
http://www.instructables.com/id/The-Ultimate-Guide-to-Laser-cut-Box-Generators/
Finger
joints will create a basic shape, but I would still need some way of
holding it together without, again, ending up with lots of exposed metal
on the outside.
Gluing three pieces into a U shape and the other
three into another U reduces the need for lots of bolts. All the
connectors and switches etc would have to go on either side of one U so
the other could be removed without un-wiring anything. Holes can be cut
to allow bolts to through to right-angle brackets which are then fitted
into nuts.
