Guitar Pedal Power Supply

[nazaroo]

Project Goals:


To design and build a reliable, high quality, heavy duty power supply
in a small size that can power 10 – 20 typical guitar pedals,
replacing 9 volt batteries and/or multiple wall-warts.


This would substitute for a typical $150.00 commercial unit,
available at music stores or on the internet.


Circuit Design:


A transformer-based supply was chosen, to reliably deliver the current and power required, rather than a lighter but less reliable and/or noisier 'switching supply'. The simplicity of the design, coupled with independent regulators will make a low-maintenance unit that delivers clean D.C. Power and very low noise. (See circuit diagram).


Full-wave rectification with de-rated parts and a wide safety margin for voltages and current was chosen, since consistency of voltage is needed, while the number of guitar-pedals and their power-needs will vary greatly and be out of the control of the designer. The unit must perform consistently under a wide variety of loads.

Important: Each Regulator was mounted on a small heatsink to allow it to operate at high current values.

Guitar pedals range in current-draw from as little as 10 mA to as high as 100 mA.

Using a daisy-chain cable to connect them in parallel,
means the currents will simply add up.
Each regulator can handle a maximum of less than 1 Amp,
so load each branch accordingly.

Examples: (actual measured current draw)

Distortion + (BOSS) - 10 mA
Chorus Factory 7 (Digitech) - 90 mA
Main Squeeze (Digitech) - 80 mA
Accoustic Simulator (BOSS) - 20 mA
Noise Reducer (Behringer) - 30 mA
Ultra Temolo/Pan (Behringer) - 15 mA
Reverb RV600 (Behringer) - 90 mA
Digital Delay DD400 (Behringer) - 95 mA

Dual branches were chosen, to lessen the load on each branch, and further isolate various pedals from each other, when connected.
Also, in case of part-failure, one branch alone can easily drive at least 10 typical guitar-pedals so that the unit can continue in use until one branch can be repaired.

Long A.C. Mains chord and power-lines were chosen, to allow a physical distance of up to 3 feet from pedal area and/or signal cables, and to allow convenient connection to A.C. Supplies located anywhere on stage.


An indicator light was added to reveal power-on condition.
A heavy metal box which can endure abuse was also chosen, to support the weight of the transformer and protect circuitry.

[Emerson Prado]

Hi there,
One question: why negative regulation and positive ground, instead of the other way round? Most pedals go negative ground - wouldn't it be better to follow suit?
There are a few positive ground goodies, specially some fuzz boxes. The dual section design could be used to power both positive and negative ground pedals, though you'd lose the backup feature. Well, you can't power positive and negative grounded pedals with the same supply at the same time anyway.
Best regards,
Emerson
Edit: BTW, I use a 7809 regulated power supply in my set, and it also powers my active instrument. It's a bass guitar, an overdrive and a wah pedal, and the PS does pretty well with them.

[nazaroo]

Originally Posted by Emerson Prado

Hi there,
One question: why negative regulation and positive ground, instead of the other way round? Most pedals go negative ground - wouldn't it be better to follow suit?

Not sure what its like in South America,
but everything I have here in Canada (three different brands)
has -ve tip and +sleeve (ground).

There are a few positive ground goodies, specially some fuzz boxes. The dual section design could be used to power both positive and negative ground pedals, though you'd lose the backup feature. Well, you can't power positive and negative grounded pedals with the same supply at the same time anyway.
Best regards,
Emerson

Edit: BTW, I use a 7809 regulated power supply in my set, and it also powers my active instrument. It's a bass guitar, an overdrive and a wah pedal, and the PS does pretty well with them.

You've got me stumped. Sure a few pedals may be +ve hot,
but I haven't seen anything like that for decades.

[i2k92]

IMHO, the most important thing for effect pedal PS is availability of multiple isolated voltage supply (connected to different transformer secondary, ala Voodoo Lab Pedalpower) as some pedal doesn't like to share supply with another pedal (at least some fuzz boxes and EHX microsynth).

As with Emerson, I don't see any reason to have a negative supply, it's better to have 2 isolated positive supply.

Try to use LM317, which supposedly cleaner than 78xx.

[Emerson Prado]

Originally Posted by nazaroo

everything I have here in Canada (three different brands)
has -ve tip and +sleeve (ground).

Yes, definitely all pedals have negative tip and positive sleeve. But sleeve isn't the same as ground, even if it's connected to the cable shield. In regular pedals (vast majority), the tip (negative) is connected to ground inside the pedal. In the case of those fuzzy boxes (not all), you have the sleeve (positive) connected to ground.
In practice, this doesn't make much difference, since the power supply is isolated anyway. For the same reason, using 78XX or 79XX ends up being the same thing. It's just a good thing to keep in mind when connecting several pedals and supplies. It just brought up my curiosity that you deliberately chose a negative regulator.

Originally Posted by nazaroo

You've got me stumped. Sure a few pedals may be +ve hot, but I haven't seen anything like that for decades.

Yes, they're quite rare. But there's a vintage trend among guitarists too, so it's fairly possible you get through one of these sometime. I know a Brazilian factory which supplies a lot of those. Just double check before you plug it in.

[Emerson Prado]

Originally Posted by i2k92

IMHO, the most important thing for effect pedal PS is availability of multiple isolated voltage supply (connected to different transformer secondary, ala Voodoo Lab Pedalpower) as some pedal doesn't like to share supply with another pedal (at least some fuzz boxes and EHX microsynth).

IMHO, the most isolation one would need is two PSs, and only if there are both negative and positive ground pedals. If he only has negative ground ones, I don't see a reason for isolation.

Originally Posted by i2k92

Try to use LM317, which supposedly cleaner than 78xx.

Good hint. I'll try that too!