Building an isolated power supply

[balazs.bencs]

Hey folks,

I scratched my head a lot lately because I needed a power supply for my smaller pedalboard and I didn't want to buy a new one because they are so expensive, so I figured that I have to do something DIY.
I really liked the idea of the Gigrig power supply thing, where they have a power supply, distributors and isolators for clean power. Since I had a 12V 1.5A PSU (it was for an old LG TV media player box) in the drawer, I thought I might build an "isolator" similar to the Gigrig one, and I thought I will share with you what I did, so everyone can build one and learn from each other.

So the schem looks like this:



Not a lot to it, but there are a few things I learned to get to building it:

- I had a 12V supply at hand, so I wanted to buy a 12V to 9V converter with isolation, you can change that for whatever PSU you have at home. The GigRig isolators use a Recom RN-0909S DC-DC converter so that you can isolate 9V anywhere in your chain.

- The PCB design was made with that 9V to 9V converter in mind, but there are a ton of others too with the same packaging (DIP8), so look around - what you can buy cheaper is going to determine a lot of things. Mine changed in the process too, because I found a 12V to 9V converter locally way cheaper than online prices (Aimtec AM1PS-1209S-NZ), but had the same packaging and pinout.

- When looking for converters, make sure you have enough power for your needs (110mA for my needs were more than enough), and important to check the switching frequency. Mine was between 100kHz and 300kHz, so way out of audible range.

- The chokes in the schematic came from the datasheet of the converters, I don't think you really have to have those for pedals, but I wanted to try them out, I used SMD inductors - they are easy to solder and not too big. I think one of the boards I just jumpered the inductor after the DC converter and worked and sounded identical to me.

- I saw something similar to C4 in a couple of designs, but I ended up not using it in my build - you can experiment there if it's going to change anything.

Here's the PCB that I quickly drew up with Eagle and ordered a bunch from JLCPCB, they work fine. (oh and I used the EasyEDA online designer tool, which can panelize eagle PCB designs, so I got 5 boards with 4 of these panels - 20 boards for 2$)



Summary: I think these converters are really cool, I think my Klon clone sounds way better - I don't exactly know why, maybe cause of the type of the PSU - this one is switching, my other Palmer isolated PSU is toroidal transformer based. My pedals are working really good with this PSU solution.
If you have an AC-DC adapter somewhere in the garage that is small and can be used for pedals, I think this solution is great and saving electronic devices.

What do you guys think? Let me know your thoughts!

[Travis]

Looks cool. So it’s an AC input?

Looks like ground is isolated between outputs, which seems better than other (non transformer based) PSUs I’ve seen

[balazs.bencs]

Nope, this one is DC input, I had a 240V AC - 12V DC adapter that I wanted to use for pedals, so this is just a DC "isolator" module.

The DC input voltage is dependent on what DC-DC converter you use (it can be 9Vin-9Vout, or 12Vin-9Vout or even 5Vin-9Vout)
These DC-DC modules are fully isolated, with no shared grounds, so it's going to be really clean power for pedals.

Maybe I will do a 1 DC input, 5 DC 9V output PCB design with DC jacks on the board, maybe with a smaller enclosure in mind, this was just an experiment to see if it works.

[PMowdes]

This is really interesting.  i've been wanting a multiple output psu for a while and refuse to pay the horrible prices for the stock offerings.

What are the limitations?  l'm guessing you could string multiple outputs to the design so long as the current draw doesnt exceed your adapter???

[balazs.bencs]

You are right, the whole idea is based on the fact that your AC-DC adapter can put out enough power. I guess this is not a huge obstacle these days, you can easily find an affordable AC-DC adapter which is small in size but can put out something like 12V/3A or something similar. (ebay is filled with them)

Also, I forgot to mention that for example in this day and age where USB chargers are everywhere, you can easily build a PSU, where the input voltage is lower than 9V because you can easily buy 5V to 9V DC-DC converters too, and boom there you have clean power.

On youtube, I saw this pedal PSU which is based around this idea, where you can power the PSU with a phone charger or a power bank, but will put out 9V DC.
https://missionengineering.com/shop-2/products/power/power-529/
I'm pretty sure that they have something similar setup, with isolated DC-DC converters from 5 to 9 V, and you can easily do this with this design too. It really depends on what converter you buy.

[rocket88]

The one I designed with induction is posted in the verified section. It’s not isolated, but it’s filtered. I can tell you that I have 0 issues with it as far as him or crossover.

[balazs.bencs]

Yeah, I know that isolation in a lot of cases is not required at all and for most people, it is not an issue, but I am gigging regularly and I had problems. If you have no problems a filtered PSU is enough, it's much cheaper, no reason to buy expensive stuff.

The Boss tuner that I have on my board is dumping a ton of digital noise to ground and without isolation, even my small pedalboard became noisy when I was using only a low gain overdrive.
Also, in a lot of clubs, where power was crappy (crappy wiring, phase issues, etc) I always had problems with ground loops, etc..

All of my noise issues went away with an isolated PSU, the whole rig is dead quiet now, so that was the main thing that started me to experiment with this.

[monasfx]

For reference the following link of a similar project might come in handy: http://www.muzique.com/lab/9v_iso.htm
Link also contains a BOM.

[balazs.bencs]

Thanks for the link, this is pretty much the same thing. As I said earlier, this is an easy topic, these schematics can be found in the datasheets of the DC-DC converters, I just wanted to show that it works with pedals really well. Btw I had 6-7 gigs with this power supply solution, and it is clean and quiet, no noise (even with high gain pedals) whatsoever, so really recommended!

[monasfx]

Just got all the parts in from TME as they had the cheaper Aimtec converters. So time to build. Thanks for bringing this one up!

[nonost]

 
 That's great! :)

 For more than one output, should I use one of this modules (pcb, little circuit) for each output? It would mean one dc dc converter for each output.

[balazs.bencs]

Exactly right.

[moterrac]

This is really cool, I've been thinking about something along the lines of this for the last week or so as my crappy switch mode chinese power supply dies.

[monasfx]

Works like a charm! Even with an el cheapo 12v adapter there's no hum with one of the pickiest pedals I've build recently (Boob tube). Built it on vero.

[balazs.bencs]

Looks great!

I built a couple since my initial post and my experience is that the inductors are not really necessary. I built a couple where I just jumpered the inductor part on the PCB and to me, it sounded identical.
You can cut costs a little if you leave them out.

[SouthIslandSplit]

Hi Balazs.bencs. Thanks for sharing this! I got some PCB’s made up for a pedal power supply with 8x 9V outs.  Super quiet. Thanks again!

[balazs.bencs]

Nice builds!

I just built a second pedalboard, because I needed more stuff for another band, and I needed more outlets so I figured I'll make more of these, but I wanted it to be more compact.

This is the PCB I made, using a smaller form factor DC-DC converter (Aimtec AM1SS-1209S-NZ), which is basically the same one I used before, but in thinner, standing format. I drew up a small simple PCB and ordered a prototype from JLCPCB:



With this I was able to cut down the size of it, to fit it under the board easily!

I know it looks a bit wonky, lots of superglue and plastic casing... cause I realized it late that I should plan it using PCB mounted DC jacks, but hey, that's where we all learn from our mistakes.
 


The thing works fine, I omitted the inductor after the converter - just used a 2R2 resistor and no problems, it is dead quiet with my pedals.

[nonost]

Looks really cool! Thanks for sharing.

I want to build a vero version as small as possible.

If I'm not wrong:

1) C4 is not that important
2) we can put a 2k2 resistor instead of the output inductor L2
3) D1, C1, C2 and L1 are shared among all dc dc converter' inputs

Am I right? If so it can fit in a 1590B with lots of outputs and that's going to be greaaat!

Also, I'm new with inductors: what specs do we need for this project?

Thank you :)

Cheers!

[balazs.bencs]

I built this thing based on the Aimtec AM1SS-1209S-NZ datasheet, which shows you the schematic for EMI class B:


1) C4 is not needed really..
2) I used 2R2, the smallest resistor that I had, not 2k2!
3) Yes, I figured this should be OK, and looks like it's working fine

For inductors, I just used the 6.8µH/1A in SMD packaging, so that's all. You should be able to find whatever works for you.

Based on the schematic the resistor and the filtering capacitor after the converter are not really needed at all. If you want, you can skip those.