Balanced Power

[caffeinator]

Hello, All~

I've long been interested in using a balanced power supply (essentially wiring a transformer to split power from 120V relative to ground to +60 / -60 relative to ground), due to the touted noise reduction benefits.

This results in there being a +/-60 on the normal 'hot' side and a -/+60 on the normal 'neutral' side.  I note that most of the Bottlehead kits I've built appear to tie the neutral and ground together (taking both to chassis ground after the IEC socket input).

This may seem like a dumb question, but to try the balanced power, wouldn't it be necessary to sever the neutral/ground tie?  Also, anyone have experience with balanced power?  Is it worth the trouble?

[Jim R.]

To be safe you really need a DPST power switch, and you'll want to switch both hot and neutral separately, and then connect the earth ground on the IEC inlet to the chassis ground.

As to the effectiveness of balanced power, it all really depends on how noisey your local electric grid (or household wiring is) but it can often make things a bit quieter, but often at the expense of best dynamic response.  Which may or may not be audible or important to you.

Also, both hot and neutral should be fused, which can be a problem in terms of finding room on some of the BH chassis.

HTH,

Jim

[caffeinator]

Thanks, Jim - I hadn't even thought about the switching - that's a great point.  While it's not too hard to find info on the internet about balanced power, and DIY balanced power supplies, few, if any, devote any ink to what happens on the device side of the supply.

I can't perceive a lot of power-line noise in my current residence, apart from transients (clothes dryer switches off, other big draw goes on), which are really not a problem.

Would a 1:1 isolation transformer give any benefits?

[Jim R.]

I don't really know about the 1:1 isolation transformer -- to my mind they are mostly used for eliminating severe ground loop or DC offset problems.  I've never found one of these that negatively effects the sound so none have ever stayed that long in any of my systems.  Of course many people perceive no difference whatsoever, so whose to say one way or another without trying it.

-- Jim

[Grainger49]

I can't find any Bottlehead equipment that ties neutral to ground.  That is properly done at your service panel.  But, you are right, if there was such a tie there would be a problem.

So I see no problem using balanced power with the Eros, Seduction, Paramour (all), Paramount, SEX or any version of the Foreplay.  Those are the ones I looked at.

My PS Audio P300 has a balanced (60V/60V) output and it feeds my Eros/FP 2/Paramours.  All are fine.

I can't tell you if it was the balanced nature of the output or the cleaner regenerated power that made it sound so good when I put the P300 into my system.   I had thought my power was fine and then I got the P300.  I was wrong!  It was a big step up.

Jim,

Great point on the switching and fusing.  I'll look into that for my pieces.  Mostly I just turn the system off at the P300.

Should the fuses be sized 1/2?

[Paul Joppa]

...  I note that most of the Bottlehead kits I've built appear to tie the neutral and ground together (taking both to chassis ground after the IEC socket input)....

None of the kits tie neutral to ground or chassis. That would be dangerous!

We do switch the hot lead, not the neutral lead, in accordance with normal US practice. I agree, it would be preferable to switch both if you have balanced power.

As for the advantages, it is like most noise sources - the effect of using balanced power depends on which of the many noise mechanisms is a problem in your environment. In my humble opinion, the only practical way to tell is to try it - there are too many possible problems and too few ways to test for them.

[Grainger49]

If I have read correctly, balanced power is like balanced interconnects.  Both are good for eliminating, not just suppressing, "common mode" noise. 

[caffeinator]

Hi Grainger,

Thanks for the clarification!  When I was pondering this the other day, I know I referred to an image somewhere (thought it was a CD manual, but can't find it now) that depicted the connected neutral/ground, but can't find it now.  A quick look at my SEX amp shows them separated from the IEC inlet to the PT inputs.  I'll visually check everything prior to connecting if I decide to try balanced power.

I have the pieces to put together a DIY balanced power box (trafo, powerline noise filter, MOV's, caps).  If I get around to it, I'll try to post pix and results.

I can't recall if it was on this forum or somewhere else, but back when I was originally looking into this, another poster offered his suggestion for balanced power - some small, chassis mountable sized transformers wired to convert from regular AC to balanced inside the chassis.  Seems like there was some combo IEC inlet combo that provided for this, but I may be misremembering.

[4krow]

After years of using ALL kinds of power filters, etc, I couldn't be a bigger fan of balanced power. Even though I hold the PS Audio products in high regard, I personally chose a product from BPT. Not only does have the advantage of balanced power, but the transformer has five separate secondary wings with Faraday shields between each, and other forms of isolation as well. This amounts to dedicated power for every outlet. No doubt you can take this on yourself and save money, but I went the quicker route and bout the item used. I wouldn't dream of going back.

[caffeinator]

Thanks to all for the replies.  I think my curiosity is peaked enough to try it and see.

My sincere apologies for the mistaken description of typical Bottlehead practice re: neutral and ground.  Thanks to everyone for correcting that, too.

[RPMac]

I've used a step down transformer to get balanced power to my older Bottlehead equipment for years with no problems. I agree that the wiring should be handled as hot/hot/grd with a DPDT switch.

I don't have any filtering, but believe I get a benefit of isolation from other AC noise. Lots of noise sources on house lines...computer, TV, LED lights, programmable appliances, chargers...

[caffeinator]

After years of using ALL kinds of power filters, etc, I couldn't be a bigger fan of balanced power. Even though I hold the PS Audio products in high regard, I personally chose a product from BPT. Not only does have the advantage of balanced power, but the transformer has five separate secondary wings with Faraday shields between each, and other forms of isolation as well. This amounts to dedicated power for every outlet. No doubt you can take this on yourself and save money, but I went the quicker route and bout the item used. I wouldn't dream of going back.

Plitron makes (or used to) the transformer for the BPT unit.  It is a gorgeous piece of work.  Plitron used to sell it to the public, but the last time I checked they had discontinued that practice.  BPT used to have some good pics on their site of the innards of their unit (can't get their site to load at the moment to see if they still do).  It appeared they followed practice typical of what one sees on DIY sites - the transformer, of course, a powerline filter (they used one whereas I've seen other approaches placing one on each output), MOV's, capacitors...one notable difference was what appeared to be a huge ferrite tube - like an elongated or more like extruded - ferrite toroid around the incoming power line.

Here's a link to one diy approach: http://home.comcast.net/~thomasw_2/CheapskateBP1.html

[4krow]

Yes, they have many options for their products. The ferrite sleeve that you noted may not be essential, but considering the amount of RF now days, I would opt for it. Piltron seems to be in high esteem with a lot of the power guru's. I especially liked the one I bought from BPT, because as I mentioned before, it has separate windings for each outlet, and each winding has a Faraday shield further isolating each winding. Mine weighs about 60 pounds. Now here is the trick to my product. The primary winding is rated at 10 amps RMS, and each secondary winding is rated at 10 amps RMS ass well. You cannot exceed 10 amps RMS for total load from your system. Looking more closely at each component, you will note that they do not draw as much as you might think except for turn on surge. If you turn on the more beefy components after the smaller ones, you will likely avoid any trouble. As it is, my system does not have that much draw to concern myself with in the first place.

[Grainger49]

Greg,

This seems to be an exception to the transformer rule that the volt-ampere product of the primary being equal to the volt-ampere product of the secondary.  But this rule can not be violated.  So something is amiss. 

[4krow]

I thought to be strange as well, but the owner of BPT and I discussed it and he was sure to say that the total amperage of the primary is the actual rated amperage for the whole device.