DIY universal power supply for various outboard gear

[mattmartin831]

I am planning out my studio setup which includes a lot of DIY outboard gear, and I would like to be able to power all of it using one rackmounted power supply unit. I have a SMPS (rated 28V@5A) that I plan to convert to +24VDC with a 48V rail to drive my 8x Neve 1073 clones,  +30/-10VDC to drive my 4x 1176 clones, and +/-16VDC with a 48V rail to drive my 8x API 312 clones, Harrison Ford filters, and SB4000 compressor. I plan to use a boost converter to generate the 48V phantom power rail, and I would use buck converters to create two negative voltage rails from the SMPS and use LM317/337 ICs to regulate the voltage rails to the values necessary for my applications. I have attached a drawing of my overall plan so far, but I have a few questions. Maybe some of you experienced DIYers can offer some advice:

1) I definitely want to make sure I don't damage any of my outboard gear, so would you guys have any advice regarding the values and types of fuses I should use?
2) Should I place rectifier diodes along each rail to make sure current only flows in the desired direction? If so, should I place the diodes at the beginning, middle or end of each current path?
3) I may consider adding a CAPI 500 rack sometime down the road. Would it be smarter to use a second SMPS to source the +/-16V rails in order to provide more current and to keep those rails electrically isolated from the others?

Feel free to point out any potential problems you see that I haven't thought of. I would be very grateful for any help you'd be willing to offer.

 

[Bo Deadly]

I wouldn't do it that way at all. I would use SMPS into common mode chokes and then regulate down inside each piece of gear.

But it's not crystal clear to me why you would do this if all of those pieces of gear already have integrated power supplies.

 

[mattmartin831]

I wouldn't do it that way at all. I would use SMPS into common mode chokes and then regulate down inside each piece of gear.

But it's not crystal clear to me why you would do this if all of those pieces of gear already have integrated power supplies.

It's because none of these pieces of gear have internal power supplies. I am still building the units and wanted to avoid buying 8 power transformers. My thinking was the 317/337s would take the existing ripple voltage from the SMPS (some amount in mV) and bring it down to microvolts to where I hoped it would be insignificant and unnoticeable, but that may not be the case. So you would choose to use chokes to get rid of the ripple altogether then? That may be a better idea.

 

[Newmarket]

I understand the wish to avoid multiple transformers. But the proposed scheme looks fairly complex to me with the addition of buck / boost stages.
Anyway, regarding noise / ripple. You need to condsider both Common Mode noise and normal Differential Mode noise.

 

[mattmartin831]

The boost and buck converters I plan to use are simple to use modules shown in the image attached, which you just need to connect an input and output and adjust a trim pot to the desired output voltage value. I understand these may introduce more ripple voltage, which i hoped would be reduced with coupling caps and LM317/337's post DC-DC conversion. I had not considered those two different types of ripple, would I be able to get rid of both using common mode chokes and bypass capacitors?

 

[Newmarket]

The boost and buck converters I plan to use are simple to use modules shown in the image attached, which you just need to connect an input and output and adjust a trim pot to the desired output voltage value. I understand these may introduce more ripple voltage, which i hoped would be reduced with coupling caps and LM317/337's post DC-DC conversion. I had not considered those two different types of ripple, would I be able to get rid of both using common mode chokes and bypass capacitors?

Well you need to look at what the power rail looks like in terms of noise (under load) to see what you might need in terms of additional DM filtering. Hopefully it might have adequate smoothing on board such that a standard implementation of the linear voltage regs will be sufficient. If you need additional DM filtering then it'll help if you know at what frequency the SMPSU operates ( fixed or variable).

CM noise (that gets converted to DM noise in the circuit) is more 'slippery' to deal with as it's return path isn't clearly defined - parasitic capacitances etc.
Again there's usually some filtering on board.
But you can't really see what problems you might have until you implement the system.

I'd suggest looking at some texts - EMC for Product Designers (Tim Williams) ; The stuff on Henry Ott's website ; Ridley Engineering website ; http://www.we-online.com.

It ain't simple. Alternatively - just build it and see what you get

Good Luck !

 

[Bo Deadly]

I would just buy off-the-shelf AC-DC (not DC-DC) SMPS open frame units, add some large common mode chokes and caps to knock down the HF hash and then mount them in a rack chassis with some CPC connectors. Use a power switch that can handle the high in-rush currents of SMSPs. Than regulate down to the correct voltages inside each unit. That will give you solid clean safe power.

But you need to get the right SMPS. They have be the kind that have isolated outputs if you want to "stack" them to make negative voltages. Look at the block diagrams in datasheets for transformer isolated units. There have been posts about this here before.

The only other thing I would say is build a small version first for the bench and then a medium version to get you going on the rack and as a backup unit and then, if you actually build all of this stuff, you can use that experience to build a proper larger capacity unit.

 

[beatnik]

you could possibly use the GDIY power supply. it a readily available design and I guess it somehow has been tailored for audio devices