Muthapower

[karbomusic]

The only way I can learn is to put my hands on stuff, make mistakes, rinse & repeat. Since I've built several pedals while getting my feet wet, I have a few builds that work better at 12V and... moving adapers around all the time was becoming a PIA and I wanted to run 9V and 12V at once to simplify things. So I dug through some datasheets, pulled my hair out for a week or two debugging problems and finally ended up with a "hello world" version. I'm sure the big torodial transformer is overkill but there it was on the net asking me to add to cart. I also noticed this strange "QTY" button and if you change it to 2 two transformers show up on your doorstep.

Fair warning that it uses AC mains and I don't know enough to advise. I did at least fuse it so that if it did go into meltdown the fuse would go and at least for now, the metal case is painted and also completely electrically isolated to any of the circuit anyway. I have so few posts to show for anything, I thought I'd share where I stopped.

Final breadboard version after a week of failures and tweaking:



Made miscalc on the heat sink sizes, better said, I forgot to account for them properly and trimmed off on one end to compensate. However, after all the testing with multiple pedals they barely got much above room temperature so I hope it isn't going to be an issue:
                                                                                       


Those LEDs are just tacked in below as I test the soldering job and prepare for fitting. They end up insulated and heatshrunk:
                                                                                       


Almost done, the transformer is a Triad 30V 1.6 Amp / PN: VPT30-830 running parallel @ 15V.
                                                                                       


Final product with the homemade look since my waterslide decals didn't work on black so I drew a cartoon version of the layout instead:


                                                                                       
And it actually works and is quiet as a mouse with my limited testing since yesterday; white LED is incoming power from the Triad transformer, blue is the 9V rail, red is the 12V rail:




To summarize I spent almost two weeks testing pedals and running the rails through the oscilliscope and multimeter trying to get it smooth. Most of that time was taming ripple, ground loops, hum etc. I know the best method is isolated but half the challenge was to see how close I could get unisolated. It was somewhat painful but I learned a lot. If there are any horrible mistakes or safety sins then please forgive. Here is the layout I created which I think is the exact one I built but there could be a mistake there:


                                                                                       

[Jdansti]

Thanks for sharing this!  Great job!  I really like the compactness of it. I came to a similar conclusion and did the same thing a few months ago. Two 9V out jacks and two 12V just like yours. I guess great minds think alike!   I wish I'd used a more compact transformer like yours. Mine was cannibalized from an old wall wart that was used to provide power to light the dial of an old rotary dial telephone. It's really great to leave my pedals and small amps plugged in and just hit the switch to turn everything on and off. Keep up the great work! 

Here are some photos of mine.

[karbomusic]

Thanks. ^That looks like it could handle some pretty serious pedal demands! I like the chrome heavy duty look. Is that an on/off switch on the side? I started to put a switch but was running out of room. Either way, I like how yours looks, nice job.

[duck_arse]

karbon, may I?

what is the voltage out of your bridge rectifier? most of the regulator heat would probably come from dropping the extra. I know it's too late now, as it's all built, but, you could have used the 2 seperate secondaries into 2 bridges and filters, providing 2 isolated supplies, lower volts in, less heat out, smaller volts filter caps. and if you'd swapped the lm317's for 7812 and 7809, you'd save a few parts, board space, case etc. and you could have "sag" outputs using the lm317.

that's my 2c, as you were ....

[karbomusic]

Voltage out is 15V (edit I see you said rectifier and I can't remember but the rect isn't warm at all IIRC) but I was just following the spec that said wire it parallel to get 15V/1.6A so I really didn't know any better. I'm not seeing any heat but haven't pushed it to its limits yet. I had played with the 7812 early on but was using a different transformer that couldn't handle the load and when I ended up with the new transformer using the 317 I never got back around to the 7812; so many parts so little time to try stuff out. The only thing I hate right now, is I don't know what I don't know based on previous experience.

And yes you absolutely may. I'm here to learn so don't hesitate to teach.

Oh yea, I had it hooked to the DC scope/histogram for a few days, I haven't seen it sag any yet but I'm sure it's entirely possible. I had lots of similar issues with the first transformer I used because it was obviously too small for the job I was giving it.

Thanks for the advice, I appreciate!

[Jdansti]

Thanks. ^That looks like it could handle some pretty serious pedal demands! I like the chrome heavy duty look. Is that an on/off switch on the side? I started to put a switch but was running out of room. Either way, I like how yours looks, nice job.

Thanks!  Yes, I had a spare DPDT stomp switch and it's easily rated for the voltage and current. It was a squeeze to get in, but I made sure I insulated all of the lugs on the switch, mains power connector and fuse holder. I also made sure that the lugs weren't touching each other or any components.  I grounded the enclosure to the ground lug on the power connector, so that if a 120V line wire accidentally touched the case, it would short to ground and blow the fuse.

Speaking of that, I can't tell whether you used a two or three prong power connector. If it's two prong, you won't have a ground wire going back to the mains breaker panel, and your metal enclosure could potentially become energized if the hot AC wire were to accident come into contact with it.

[karbomusic]

Thanks. ^That looks like it could handle some pretty serious pedal demands! I like the chrome heavy duty look. Is that an on/off switch on the side? I started to put a switch but was running out of room. Either way, I like how yours looks, nice job.

Thanks!  Yes, I had a spare DPDT stomp switch and it's easily rated for the voltage and current. It was a squeeze to get in, but I made sure I insulated all of the lugs on the switch, mains power connector and fuse holder. I also made sure that the lugs weren't touching each other or any components.  I grounded the enclosure to the ground lug on the power connector, so that if a 120V line wire accidentally touched the case, it would short to ground and blow the fuse.

Speaking of that, I can't tell whether you used a two or three prong power connector. If it's two prong, you won't have a ground wire going back to the mains breaker panel, and your metal enclosure could potentially become energized if the hot AC wire were to accident come into contact with it.

Ah thanks! It's only 2 prong currently. Due to that, I tried to make do and it would pretty much have to come unwound from the terminal  (I twisted it so if the solder melts it stays put), then would have to melt through a few layers of heat shrink then through 4 coats of plastidip that the internal is coated in. I'm hoping the fuse would certainly go before that happens (notwithstanding the pre fuse live terminal). I know would be better if it went back to earth; just wanted to list what I did try to do as an FYI. I  think I'll possibly change this one over. I think I might have room to do that actually now that I think about it.

[duck_arse]

ahh, see, now I'm the dumb one. I missed if you said you had the secondaries in parallel, I was thinking they was in series.

and by sag, I meant you could have the lm317 with an external variable control, so you could wind the volts on or off.

[karbomusic]

Ah, I see, makes sense. The two trim pots dial in the two voltages but they are obviously internal. Did you mean make those external or add one just after the rectifier? Sorry for the denseness.

[Jdansti]

It's good that you have everything well insulated. Just to pass on some information about grounding and potential hazards, if the mains hot wire were to come into contact with the enclosure on a two wire system, there's no guarantee that the fuse would blow. In order for the fuse to blow, you have to have a complete circuit. If the enclosure isn't connected to ground, there's not a complete circuit. The danger is that a person touching the metal enclosure and something that's grounded, like a guitar or amp, would complete the circuit with their body and receive a shock. The fuse in your situation protects against an overload on your transformer and from a short between the mains hot and neutral, but not against a shock if the mains hot wire were to come into contact with the enclosure.

There are such things as two wire systems that are double insulated, but that doesn't apply in this case.

Do I think that you're in immediate danger?  No.  I just wanted to point out what I understand as the standard way to wire such a system. As you said, you've got it pretty well insulated, but things happen.

[karbomusic]

In order for the fuse to blow, you have to have a complete circuit. If the enclosure isn't connected to ground, there's not a complete circuit.

Do I think that you're in immediate danger?  No.  I just wanted to point out what I understand as the standard way to wire such a system. As you said, you've got it pretty well insulated, but things happen.

As I was running things through my mind after your previous post it "clicked" with me about the fuse not being foolproof. It would be rare but I am of the camp of accounting for the near impossible whenever possible so I'll likely change it to three prong if I can get it to fit. Thanks again for all the info, it's good to be reminded of the critical safety stuff and is appreciated.

[Jdansti]

You're welcome. Again, great job-have fun with it!