How to build a balanced power supply?

[Bas Horneman]

Currently the mains in my house does not have a safety earth (Until not so long ago Dutch houses only had them in bathrooms and kitchens.)

So will something like a balanced power supply actually have advantages? I can imagine that having my dac, phono preamp and linestage etc. all attached to the same psuedo earth will prevent possible ground loop problems.

In my case I could just omit the center tap to safety earth connection?

[poynton]

Something like this was tried a year or 2 ago by Ray on the humungous CD 63 / 67 thread.

It's now on his website.

Balanced Power Source



Andy



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[zigzagflux]

Surprising a ground was not required just a few years back. I assume the utility has grounded the supply at the transformer, but just not required bonds at your panel? I can't imagine the enclosure of your panel is actually floating. Is it tied to neutral (if one is provided)?

A shielded isolation transformer is really all you should need, but I would definitely try to find a way to give yourself a grounded secondary. Maybe grab a tap off your water service or something. I'm not convinced on the need for balanced power when the transformers you connect it to are not balanced. I prefer the grounded neutral / hot method and finding the high capacitance lead on each downstream power transformer I use. That lead connects to the neutral.

I have an AC drive feeding my well pump. It spits out copious amounts of noise. Until I used a C-core power transformer for my D/A, I never had any noise issues. Split bobbin or shielded were sufficient. Once I installed the shielded transformer (1500 VA for the entire system), all was silent as could be. Maybe someday I'll swap out the C-core.

Technically, balanced power is not permitted in a US residence. Next comes many posts with 'hang the code' and 'I've been doing it for years'

[Steve Dunlap]

Originally Posted by zigzagflux

Technically, balanced power is not permitted in a US residence. Next comes many posts with 'hang the code' and 'I've been doing it for years'

Isn't that what our 220 system is?

[zigzagflux]

It is, but split 240V is not the subject here. Bas has generated 120V single phase with the midtap grounded (60-0-60). The desire is to plug either DIY or commercial products into this supply. These products are designed for 120V operation and have either 2 or 3 wire plugs, typically polarized.

NEC Section 647 specifically addresses this application. Requirement #1:

"The system is installed only in commercial or industrial occupancies."

There are many other requirements that I suspect no DIY'er has bothered to follow. Just ground the center tap and away you go.

[sumaudioguy]

This has worked well in the past as the mains are balanced at the 240 volt lines.

[Speedskater]

Note: The two circuit breakers in the above 240V input schematic need to be interlocked.

[event horizon]

Originally Posted by Bas Horneman

So will something like a balanced power supply actually have advantages?

I have a PS Audio P600 Powerplant & the output of that is a balanced 120V 0V 120V output. I believe that the same is true of the american version which would be similar to what you are planning, the only difference being a 1 to 2 ratio step up transformer just before the output.

I couldn't actually say if this has advantages over the standard system as there is the Powerplant already doing it's own clean up of the mains

[damacles]

Hi

I'm not sure about in the US but in the UK having an isolation transformer in this manner gets around the "Code" as its an isolated supply.

I think the same would be true in the US as if it were'nt
the code would apply to high voltage supplies in tube amps etc these can be up to 1500Vdc.

Ben Duncan has a compendium of articles entitled "high quality mains audio supplies" which extols the virtues of the balanced supply.

Dam

[star882]

Most power inverters are balanced output since it simplifies the design.