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Power Supply Question

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Power Supply Question

Postby Jay Menon » Sat Feb 18, 2012 9:35 am

All the pedals on my board are 9volt DC regulated, except one which requires a 12 volt un-regulated (or an 18volt regulated) supply. The pedal's current draw is 35mA at 9VDC.

From the manufacturer's website:

An un-regulated +12V AC to DC adapter rated at 500mA is required based on the following: The ETHOS provides filtering circuitry that removes the noise (60 Hz Ripple) from typical AC to DC unregulated power adapters. This filtering circuitry develops a voltage drop across it, so the adapter voltage becomes +9VDC by the time it reaches the ETHOS analog circuits. Additionally, an unregulated +12VDC supply (not a regulated supply) is required due to the fact that it actually outputs 15 to 16 volts with the ETHOS load. This higher voltage provides the adequate headroom for the ETHOS to operate correctly. Using a +9VDC AC to DC external adapter will result in poor ETHOS performance.

I found this: http://www.effectpowersupplies.com/diago-9v-to-18v-adaptor-1169-p.asp

It seems to be usable with a 9v daisy chain, and will increase voltage from 9v to 18v, maximum current output 30ma.

From my elementary electronics it should work since, at 18volts, 17.5ma should be adequate for the pedal, so this actually gives me 12.5ma reserve current draw (please correct me if I'm wrong).

Yet the manufacturer seems to be quite keen on maximum headroom (they supply a 12V unregulated adapter with 500 ma).

This adapter would however, simplify the power supply to my pedal board. Expert advice most appreciated.
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Re: Power Supply Question

Postby 4TrackMadman » Sat Feb 18, 2012 11:05 am

Jay - what about the 9v adapter - does that power the 12v effect in question? Might want to try that, I don't think there'll be any harm done. I recently used 9v adapter on a 12v pedal and had no trouble , I guess difference in current wasn't that big or they went up in specs just to be on the safe side.
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Re: Power Supply Question

Postby agent funk » Sat Feb 18, 2012 11:47 am

Just to be clear, is the current draw of the pedal from the manual, or did you measure it? It's just that seems a lot less than what they are saying you need the power supply to be capable of. I mean 500mA needed for a 17mA pedal!
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Re: Power Supply Question

Postby Jay Menon » Sat Feb 18, 2012 10:10 pm

I'm thinking - if the current requirement is 35ma, then wouldn't that amount of current be required irrespective of what voltage comes in to play...?
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Re: Power Supply Question

Postby ef37a » Wed Feb 22, 2012 5:20 am

The actual current draw of the pedal is immaterial so long as the DC suppy can deliver about 16volts at a few tens of mA. A "12 volt" 500mA supply is specified probably because that equates to a 6va ish transformer and mains traffs don't really get much smaller! Also a 12/500mA supply fits in with their dynamic re the onboard regulation.

There is likely a polarity protection diode in the line so that is a loss of ~0.7V then a 78style regulator needs at least a 3volt, better 5volt differential so that soaks up the 15-16volts input stated.

A 12volt regulated supply, best a SMode type should be ok but there is a chance that the regulator in the pedal would dropout or be a bit unstable. Simpler to just go with a bog standard unregulated 12volt supply.

It really is about time manufacturers standardized on 12 or 24 volt regulated supplies at X amps DC i.e. multiples of 12volt sealed lead acids. Getting any other internal voltages pos or negative is now beer into water.

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