FELICIA - A DIY Balanced Power Conditioner

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FELICIA - A DIY Balanced Power Conditioner
« on: 17 Apr 2005, 11:00 pm »
EDIT-6/26/07 Because of the bulk, power constraints, and limited availablility of appropriate transformers at low cost for the Felicia conditioner, I personally feel it is advisable for diy folks to devote their powerconditioning efforts to other available topologies. The 'Felix' conditioner, based upon reasonable cost, easily available common mode chokes and X capacitors provides similar results and is easily implemented -

This is an extension of Jon Risch's SQ&D iso trans project -

What has been added is balanced power in addition to power conditioning. The project is called Felicia in honor of JoshK's wife who has shown tremendous indulgence while Josh and I have experimented.

Thank you Fryman for providing this udated schematic!

All transformers must have dual 120/240 primaries.
Breakers may be substituted for fuses.


1. The input 'hot' line should be fused to reflect the maximun draw allowed for the input transformer. In the case of the 175va Signal transformer initially reccomended, for the single output, it should be a 1amp fuse, reflecting the downrating required by the series connection of the primaries down to 88VA. In versions 2 & 3 where the input primaries are configured in parallel, a 2amp fuse should be used reflecting that 175VA rating. As the transformer is an EI core feeding a 'small' capacitance of 15uf, that rating should not cause turn-on surge tripping.
Also, if the unit is plugged into a large draw component, like an amplifier, you want the fuse to trip rather than have the transformer go into meltdown.

2. All output lines should be fused on both legs, as they are both now 'hot'. If the intended component is has both lines fused and switched internally, you may forgoe this, but frankly, you never know what you'll plug into what, so I'd include it regardless. Sort of a belt and suspenders approach. The fuses used should be exactly those in the component you intend to power.

3. When working on components with the cover off, NEVER have it plugged into a balancing transformer. Do your mods or troubleshooting with the component pluged into a conventional single phase line for safety reasons, if the unit has to be powered.

4. A component plugged into any balancing transformer, whether Felicia or commercial unit, when not powered, should be unplugged or taken out of the circuit via a dpst switch on both output lines. The reason is that unless the components switch is a dual pole, ie switching both lines, the formerly neutral line will have leakage to ground which is not balanced by leakage from 'hot' to ground. You'd be unbalancing you balanced leakage and significantly defeating its purpose..

5. Again, applying to both Felecia and commercial balancing transformers, NEVER use any balancing transformer with older component that may have neutral tied to the chassis. Although this has been a UL no-no for over 20years, some golden oldies do internally connect neutral to the chassis assuming that the neutral line is grounded. You can check this with a ohmmeter by making sure you've an open circuit between both (either) blades on the powercord plug and the chassis with the unit turned on but not plugged in.

6. Chassis - Obviously, as the balancing requires a ground, the implementation requires a grounded 3 prong power cord. If Felicia is housed in a metal chassis, the chassis must also be grounded. There is no problem with housing Felicia(s) in a non-metalic chassis. But any magnetic fields from the transformers can cause hum in other components if Felicia is located in close proximity. So obviously, if you use a wooden box, etc... make the connecting powercords long enough so that the Felicia won't cause interference.

I've opened a constructor's thread here -

A note to constructors in countries with 220-240VAC mains.
A 240v balancing conditioner is actually a bit more straightforward than for 120v given the same dual primary transformers. The transformers do not need to be downrated.  If interested please open another thread on the Lab. I've no familiarity with electrical codes in your countries!!!
« Last Edit: 26 Jun 2007, 01:28 pm by Occam »


FELECIA - A DIY Balanced Power Conditioner
« Reply #1 on: 18 Apr 2005, 01:37 am »
and how it works -


no.... actually this is a unique configuration that attracts Maxwell's Daemons, which just gobble up the noise.

transformers are the best devices for purging common mode noise. The big sucker capacitor, isolated galvanically doens't raise concerns over leakage, converts differential noise to common mode noise, and since it bracketed by transformers....
EI core power transformers have much lower bandwidith than torroids, which when you only want to pass 50/60hz is a good thing.
Split bobbin or interwinding shielded transformers (like the better commercial balancing toroids) have minimal capacitive coupling between primary and secondary and tend not to pass noise through windings.

Felicia is not dc coupled, there is no path for entering dc on the mains line to exit from Felicia  :) While transformers are AC coupled (within their bandwidth) they do not pass dc. The optional resistor accross the secondaries, is there to preload and stop under some circumstances any humming of Felicia's own transformers. The current 'in process' Felicia, with its specific transformers and cap, has no resistor and doesn't hum, at all. Felicia's dual bobbin EI core transformers are far less succeptable to dc induced distorion and humming than the typical toroid.
While Felicia would certainly address any dc induced hum from a component's transformer, a simple dc blocker is simpler.

DOH!!! Dunno how I could forget (with the thread title and all) but the dang thing produces BALANCED power! This is a very good thing. For some info visit the equitech, bpt, alphacore, blue circle.... and they will all extoll the technical merits of balanced power. Each will also tell you why their specific implementation is best.


Reasons not to build Felicia
« Reply #2 on: 18 Apr 2005, 03:51 am »
Reasons not to build Felicia

You are likely to electrocute yourself.

Your time and efforts are  too valuble to be squandered on such a project, and/or better spent elsewhere.

If you've already a big balancing conditioner which powers all your source components (and possibly your amp), what you might want is additional isolation between components. You've already got the balancing part down. If you want to provide isolation between source components, buy/build/DIY an inductor/cap AC linefilter ala Jon Risch -

KevinP at DiyCable sells a 2 filter board, and components for this purpose-

This is what Equitech is doing for their newer offerings.