Modular Power Supply Design (Line 6 M9/13 compatible)

[sinisterguy]

Hey everyone,

A while ago I had the chance to buy a line6 m9 for a decent price, and decided take a chance and get it. I really needed some good delay/mod effects with presets so I didn't have to bend down and fiddle with knobs in the middle of a song. Now, I'm loving it. the overdrives/distortions don't always sound the best, but the delays/mod (which i bought it for) work and sound great.

Until recently, my pedalboard has stayed mostly in my bedroom, so working with the Ac adapter for the M9 and a daisy chain for the rest worked fine. Now, I'm going to be spending more time on the road so I need something more robust. I looked for a commercial supply that had the 9V dc that i needed as well as an AC jack for the M9, but there were next to no options that had the required 9V AC @ 2A.

So, with that in mind, i set out to build my own power supply that a) can power my M9 and b) was robust enough to take on the road c) wasn't ridiculously large and d) was flexible in design. I ended up stumbling across R.G. Keen's spyder design that seemed fairly common. What I didn't find however, was very much detailed information on any implementation of his design. So, I set out to do it myself. I have not built it yet, only drafted the design (I mostly wanted to see if everything would fit in the enclosure without actually buying it first), but I figured that documenting my progress here might help others looking to build their own power supply.

DISCLAIMER: building this design involves AC mains wiring. If you don't know what you're doing, and how to deal with mains AC power, STOP. Learn how to proceed safely so you don't kill yourself. I don't have much experience with mains wiring, but I do have an electrical engineer friend to consult with. If you can find someone similar, I suggest you do.

Specs

8x 9V 300mA DC isolated outputs (2.1mm jacks)
1x 9V 2A AC isolated output (2.5mm jack)

Enclosure Size: (L) 6.3" x (W) 4.1" x (H) 2"

Rendering

**the grey box in the background is to see the size of the transformer (I couldn't be bothered to model it myself

PCB Layout
When I started I wanted the design to be modular. For my personal supply, besides the 1 9V AC output, I only needed 9V DC, so I designed 1 large board (see below) rather than a bunch of modules.

Large Board:


However, because of the finned design of the enclosure, it would be really easy to build several ~1"x4" (it has to be a little less than 1" to fit 4 modules in) modules that you could build and slide in/out depending on the needs of your pedal board. Here is an example of a 7-9V adjustable module using an LM317. R1 and R3 are 1.1K, R2 and R4 are 240 ohms and the trimpots are 500 ohms.

7-9V module:


**Note: the space on the left hand side of the boards is so that there will be plenty of clearance for the DC jacks on the inside of the case.

You could also easily build an 18V module that joins 2 9V outputs, or an ultra-clean module that adds extra filtering, or an 18V output with a switch for 12V and 9V, the possibilities are really up to you. All you have to do is find a schematic and make sure it fits in on a ~1x4" board

Bill of Materials (For an 8x 9VDC and 1x 9VAC)
8x 220uF caps
8x 10uF caps
8x dip4 bridge rectifiers
8x 78L09 regulators
8x 5mm pitch 1x2 screw terminals
8x 2.54mm pitch polarized headers
8x 2.54mm pitch polarized connectors
8x 2.1mm isolated DC jacks
1x 2.5mm isolated DC jack (for AC power, I'm also going to probably paint this one a different colour)
1x Hammond 1455n1602 enclosure
1x Weber WPDLXFMR-1 transformer
1x IEC jack
1x 0.5A fuse
1x fuse holder

misc: screws to mount transformer, hookup wire

Notes
- A fuse is not included in the schematic, but don't forget to include it
- don't forget to ground the IEC connector to the chassis
- heatsinks might be a good idea on the regulators if you're drawing a lot of current
- the 2.5mm jack can be wired straight to the 9V 2A winding on the transformer
- A WPDLXFMR-2 is 2.67" tall and unfortunately there are no 1455 series enclosures taller than 2". sorry for the non-120V mains crowd
- the AC windings go in the screw terminals, and the DC output goes through the polarized connector

Board Mounting Options
- the fins on the inside of the enclosure are 2mm, so if you're etching your own PCB, use 2mm board
- I'm probably going to have the board professionally fabricated to increase robustness on the road. most of the cheap pcb fabs charge more for 2mm board, so I'll use standard 1.6 mm board and use a couple dabs of hot glue to keep the board from sliding around

Like I said earlier. I have not built this design yet, so there are no guarantees at this point. I'm also open to suggestions and/or corrections. This is more of an enclosure design project more than anything else. I understand the concepts, but don't know the first thing about good power supply design other than what I read in R.G.'s articles so if there is something that could be improved, by all means, say so. I hope that this project becomes a good resource in the future for those that want to build a customizable, clean, isolated power supply for their pedals. And if anyone happens to build this before I do (I probably won't get to it until the middle-end of july), I'd love to hear about it.

a zip file containing all the schematics, board layouts and google sketch up model can be found here:
http://www.2shared.com/file/1iQlD3f3/Power_Supply_Files.html

[Cliff Schecht]

Cool looking project. I dig the detailed mockup, something that would probably save myself and many others around here a lot of headaches when actually putting boards in boxes!

I do think the 8 isolated DC jacks aren't really necessary. While the valiant efforts that many put in to eliminate ground loops are commendable, IME this is not really necessary. I run four distortions and a compressor pedal (not at once!) on my board using a single well filtered power supply and don't have any problems with hum. The singer in my band uses the same PSU I use and also doesn't have a problem. This isn't meant as a knock at RG's design or to what you are doing, just something that I noticed isn't really necessary if you have a clean 9V power source to work with. With that said the isolated voltage is nice if you want a quick 18V or need isolated power for fuzz pedals and such..

[head_spaz]

I really like what you've done so far. Very clean and well-thought out.
I do have a few minor suggestions that might be worth your consideration before you commit to pcb.

1.) I suggest you take a close look at the data sheets (various regs / LM317 especially) and note what they have to say about reverse-biased "protection diodes" for the circuit in case of unexpected power loss etc. -- because regulator damage often occurs whenever the input voltage drops below the output voltage. External capacitance (in pedals) actually increases the risk of failure.

2.) I suggest adding low value tantalum or film caps (.01uF ~ 1uF) on BOTH the input, and output, as near as physically possible on EACH regulator IC. Regs are well known, if not prone, to high frequency oscillation, and it's a common source of "phantom hiss" in sensitive audio circuits. Believe it!

3.) Optional - I would use adjustable regulators with trimmer pots to allow for voltage adjustments.

4.) TIP: You can never go wrong using heatsinks on the regs! A heatsink is better than no heatsink, and bigger is better!
For live performance, it needs to be as bulletproof as possible, especially if it's wearing your AWESOME name! Right Luke?
And if you decide against this, at least consider laying the regs down, using the pcb for a little extra dissipation. It's better than nothing. Still, heatsinks are better. That's what they're made for!
This Futurelec TO220 would probably fit your layout as is:


My philosophy is: "Anything worth doing, is worth overdoing!"

But whatever you do... don't let the magic smoke leak out.

Good luck,
~D

[sinisterguy]

Cool looking project. I dig the detailed mockup, something that would probably save myself and many others around here a lot of headaches when actually putting boards in boxes!

I do think the 8 isolated DC jacks aren't really necessary. While the valiant efforts that many put in to eliminate ground loops are commendable, IME this is not really necessary. I run four distortions and a compressor pedal (not at once!) on my board using a single well filtered power supply and don't have any problems with hum. The singer in my band uses the same PSU I use and also doesn't have a problem. This isn't meant as a knock at RG's design or to what you are doing, just something that I noticed isn't really necessary if you have a clean 9V power source to work with. With that said the isolated voltage is nice if you want a quick 18V or need isolated power for fuzz pedals and such..

I agree. In all the venues I've played, I've only ever had 2 instances where hum/noise was an issue. But I was thinking more about flexibility like you were saying. In the future if I need an 18V output, a 12V output, -9V output and a +9V output, I could do so fairly easily. Not that I'd ever need all that, but hey, you never know.

[sinisterguy]

I really like what you've done so far. Very clean and well-thought out.
I do have a few minor suggestions that might be worth your consideration before you commit to pcb.

1.) I suggest you take a close look at the data sheets (various regs / LM317 especially) and note what they have to say about reverse-biased "protection diodes" for the circuit in case of unexpected power loss etc. -- because regulator damage often occurs whenever the input voltage drops below the output voltage. External capacitance (in pedals) actually increases the risk of failure.

I've seen that before for LM317 designs, but I haven't seen it on LM78xx. Why is that? Would it still be necessary if I only used a LM78l09?

2.) I suggest adding low value tantalum or film caps (.01uF ~ 1uF) on BOTH the input, and output, as near as physically possible on EACH regulator IC. Regs are well known, if not prone, to high frequency oscillation, and it's a common source of "phantom hiss" in sensitive audio circuits. Believe it!

looking at several data sheets and power supply designs, this makes sense. Is there any particular reason for tantalum or metal film over ceramic or any other type?

3.) Optional - I would use adjustable regulators with trimmer pots to allow for voltage adjustments.

I might do that. I was wondering though if I wanted an 18V output, would it be better to join 2 11V AC secondaries and regulate them to 18V, or to take join 2 9V DC outputs after they've been regulated

4.) TIP: You can never go wrong using heatsinks on the regs! A heatsink is better than no heatsink, and bigger is better!
For live performance, it needs to be as bulletproof as possible, especially if it's wearing your AWESOME name! Right Luke?
And if you decide against this, at least consider laying the regs down, using the pcb for a little extra dissipation. It's better than nothing. Still, heatsinks are better. That's what they're made for!
This Futurelec TO220 would probably fit your layout as is:


My philosophy is: "Anything worth doing, is worth overdoing!"

makes sense. For the extra couple bucks, its worth having the extra protection. There is still plenty of room for them in the layout too.

[R.G.]

1.) I suggest you take a close look at the data sheets (various regs / LM317 especially) and note what they have to say about reverse-biased "protection diodes" for the circuit in case of unexpected power loss etc. -- because regulator damage often occurs whenever the input voltage drops below the output voltage. External capacitance (in pedals) actually increases the risk of failure.

I've seen that before for LM317 designs, but I haven't seen it on LM78xx. Why is that? Would it still be necessary if I only used a LM78l09?

Some app notes for the 78xx regs do have that in there. I don't know why it isn't universal, but it's a definite exposure on any regulator. If the input is suddenly dropped faster than the load can suck down any output capacitance (including the several 1000uF caps that may be inside the load/pedals  ), the output cap forward biases the junctions in the regulator and can burn them out. It is most definitely necessary on 7800 regulators.

looking at several data sheets and power supply designs, this makes sense. Is there any particular reason for tantalum or metal film over ceramic or any other type?

Tantalum, multilayer ceramic (MLCC), and stacked-foil caps have quite low ESRs. This lets the capacitance be more effective. Generally the ESR is what dominates this particular aspect of output capacitance, so you can get it with low-ESR caps or much bigger standard electros. The National Semi app notes generally note a 1uF tantalum or a 22uF standard polarized as equally effective.

I might do that. I was wondering though if I wanted an 18V output, would it be better to join 2 11V AC secondaries and regulate them to 18V, or to take join 2 9V DC outputs after they've been regulated

It's simpler to stack two 9V outputs. The input switching is more complicated, as are the power calculations to make one output run without overheating if you switch input secondaries.

[sinisterguy]

So I finally got around to building this project. I've been collecting the parts gradually over the summer as my income has been limited (or rather, quickly spent on wedding expenses).

I ended up going with the recommendations from this thread and I redid the layout to include the protection diodes and tantalum caps for extra high frequency filtering. I can post the final eagle board and schematic files if anyone is interested.

Here are some pictures of the build so far. I think that this enclosure is pretty much the absolute smallest I could have been for this project.

all the parts ready to be assembled:


here's the test of the first section of the board:


and the final module:


So far, I've got the boards done and mounted in the enclosure along with the transformer. More pictures to come when I get home from work.

[maroonedwizard]

Really amazing schematics sinisterguy. Are those made with Eagle ? Did you made the rendering using Pov-Ray ?

I am a little bit puzzled about what exactly the "isolated" means .
By your design, you are creating a separate ground for each 9V output that none of them is communicating to each other. If you now power up your pedals using all or some of the power supply's outputs don't you just essentially connect all the grounds together since all the pedals share the same ground through the In/Out signal jacks ?
Or maybe I got all this wrong and " isolated " means isolation from the grid's ground. But if that's the case why bother and make all these separate outputs with separate regulators ?