Guitar Pedal Board PS

[kill_switch]

Hello all.
I'm building a power supply for a guitar pedal board (as the subject says), And I'm looking for a little help. I'm looking for an output of 9VDC, and around 1800mA. 6 Pedals and a LED lighting effect just for touch. Also what type/value should I use for protection. 3A Automotive Fuse?


What I got

• 10:1 Transformer
• 1N40001 Diodes for the FWBR
• 3mm LED's 20mA

What value will I need for the Capacitor to get 1800mA? Or does the transformer make this decision for the cct.

The Vin is standard 120VAC.

 

[Torben]

Hello all.
I'm building a power supply for a guitar pedal board (as the subject says), And I'm looking for a little help. I'm looking for an output of 9VDC, and around 1800mA. 6 Pedals and a LED lighting effect just for touch. Also what type/value should I use for protection. 3A Automotive Fuse?


What I got

• 10:1 Transformer
• 1N40001 Diodes for the FWBR
• 3mm LED's 20mA

What value will I need for the Capacitor to get 1800mA? Or does the transformer make this decision for the cct.

The Vin is standard 120VAC.

What is the schematic you plan to use? So far it sounds like you're not planning on any regulation, which I would think is a bad idea to exclude as you'll end up with a noisy, saggy supply. I think for your purposes an LM150 or maybe LM317T would work. You work out the capacitor value from the ripple produced at your worst-case current draw and the dropout of the regulator. The regulator also gives you output short-circuit protection and current limiting, so that if something should short the outputs, you don't suddenly have a huge current flowing and melting things.

The VA rating of the transformer is important. At two amps a 10:1 audio transformer will melt. I assume you have a power transformer? Is the output centre-tapped? i.e. does the output side just have 12V-0V, or is it 12-0-12 or 6-0-6, or what?

Build the thing to handle 2 amps happily. Gives you a bit of headroom and using 2 instead of 1.8 just makes the math easier.

Check out http://www.geofex.com for one pedalboard supply idea. Click 'FX Projects' in the menu on the left and then scroll down to the pedalboard supply project under miscellaneous. It's a very bare-bones supply but might help. It does include the option to simulate a dying battery, if you like that sound.

My notes on power supply equations are in storage right now but there are plenty of gurus on this board who can help you out.


Torben

 

[kill_switch]

Well I found a 9VDC adapter I use for my Boss Pedal in a moving box from last year and I took it apart.

The transformer had no markings, all the diodes were 1N4001 (FWBR) and had just A capacitor. 1000uF, 16V. Thats it.

The transformer only has 4 posts, so no center tap. The board says its connected to the N and L posts. So I'm guessing 12-0


That link does have a pedal power supply schematic.

The board is designed with flexibility in mind. As it sits, the board accepts a 12VAC/1A flatpack transformer and has enough filtering and heatsinking to put out 1/2 A or so of very clean 9V

So I would have to get a XFMR with a rating of 12VAC and 2A right? In order for it to work for my needs.


Thanks for that site. I've spent nearly 2 weeks looking before I came to my senses and came here.

 

[Torben]

Well I found a 9VDC adapter I use for my Boss Pedal in a moving box from last year and I took it apart.

The transformer had no markings, all the diodes were 1N4001 (FWBR) and had just A capacitor. 1000uF, 16V. Thats it.

The transformer only has 4 posts, so no center tap. The board says its connected to the N and L posts. So I'm guessing 12-0

What is the amp rating of the adaptor you took apart? What do you measure when it's running with no load?

So I would have to get a XFMR with a rating of 12VAC and 2A right? In order for it to work for my needs.

At a bare minimum, yes. Transformer secondaries (the coils on the side with the load; the primary coil in this case is connected to 120VAC) have VA ratings, which means volts x amps. So to run 12VAC at 2 amps you'll need a bare minimum of a 24VA transformer. Don't confuse that with a 24VAC output--you want 12V at 2A, so at the very least 24VA. You don't usually specify the 'AC' part when dealing with transformers since they only really work on AC anyway, so it's redundant. I say bare minimum because the current requirement will be increased by the filter capacitor and other factors. I don't think a 24VA transformer would be big enough for a full-time 2A load.

I'm also not convinced that the 1N4001s are up to the job of running a bridge for a 2A load. I don't really know enough about it to be sure but to get 2A out at DC, I think they're going to have to go well over 2A at 60Hz to charge the filter cap. I would think of getting a properly sized bridge rectifier for this.

I don't know what your requirements are but for a clean supply you will need a few more things yet, like a regulator, bigger filter cap(s), maybe a bleeder LED for the filter caps. When selecting the components, think about what the worst possible situation you'll run the thing in will be. If you're on stage, power is likely to be buzzy, jumpy, and otherwise horrible. In different homes, at different times of day, line voltage will go up and down. If you pick all the parts intending to make the thing put out clean power in the worst conditions you expect, it will always do the job.

Anyway, hope this helps a bit. I'm just a hobbyist so if I'm wrong about something here I'm sure one of the local gods will be along to set you straight.

Oh yes. I'm not qualified in any way, shape, or form to instruct you in working with mains voltage. It can hurt you badly or kill you. I know you know this, but still. Be careful. Hell, i'm not qualified to build these things for myself, but when I do it anyway I am super-careful about grounding, insulation (no tape; heat-shrink tubing and insulated spade clips all the way) and fusing. And I ask people who do know what they're doing for review.

Torben

[Edit: Typo fix.]