Tube pedal power adapter question.

[Regan]

Hi everybody,
Is using an ungrounded AC adapter safe on a tube pedal or adapter powered amp? I had a modern HV tube pedal that was ungrounded, and remember reading its ok but I'm still a bit leery about it all.

I have a bunch of 12v AC adapters that I have been thinking about making some super small amps and pedals with using a suitable transformer to up the voltage in the pedal and can't seem to wrap my brain around whether its ok or not.
Thanks
Regan

[DonMoose]

If the secondary is isolated from the line and grounded to the pedal ground, you _should_ be safe.

Look for UL and CE approvals.
Ideally you can find the datasheet and look for whether it's supposed to have passed HiPot or other insulation testing.

[Regan]

Thanks DonMoose,
The secondary is definitely isolated, what has me confused is I can't really see how this is any different than an ungrounded power cord on an amp.
Hot and neutral coming in, no ground and no way to ground the adapters power transformer.
Regan

[Leo_Gnardo]

The secondary is definitely isolated, what has me confused is I can't really see how this is any different than an ungrounded power cord on an amp.
Hot and neutral coming in, no ground and no way to ground the adapters power transformer.

The secondary is "floating" that is not referenced to ground or line or anything else. Think of what we have to do in order to make a "hot chassis" amp safe, run its AC from the secondary of an isolation transformer. The secondary is not attached to the AC line, but derives its power from the oscillating magnetic field within the transformer. You can attach the hot chassis amp to ground, no penalty, just safety (yay!) when operated from the isolation transformer secondary.

Some commercial tube pre's like that big Mesa V-Twin pedal run off a 12VAC transformer. You wind up attaching the pedal to other grounded equipment via the output cable, never heard a complaint of buzz or shock.

Although AC line neutral is supposed to be bonded - firmly attached - to ground ONLY in the AC distribution box for the building, I think you will be able to attach a ground to the chassis of your transformer-powered builds with no problem.

I don't know what would happen if the AC neutral was to be attached to ground away from the distro box. Can't be good, NEC disallows it. And if you attach the hot side, pop breakers or fuses beaucoup quick I hope. Not the thing to do, not at all... Save the sparks for the 4th of July.

If I'm off base about any of this, experts please chime in. Martin? Ginger? Anybody? Safety first. Don't want anybody to get zapped. Dont be the guy on the warning sign.

[Regan]

Thanks Leo_Gnarlo,
I never thought about the grounding through the other equipment, that should provide somewhat of a solid earth ground connection depending on the following equipment having an earth ground I would think. Seems to me then that you really only need one piece of equipment in your chain(probably your amp) that has a true earth ground, I'm probably way off on this and the issue definitely needs more investigation and analysis
Regan