[Occam]

John,

A measured output voltage of 125V from 120V on un or lightly loaded isolation transformer isn't really telling you much. 125v AC shouldn't hurt anything. It will drop as additional load is applied. I doubt whether the cablebox and cdp total over 20watts consumption. Nor would the Teacs demand much power given their efficiency.  If you want a more accurate measurement. plug a lamp with a 60-100watt incandescent bulb into it. You can linearly extrapolate the transformer's  nominal load regulation from that.
Regulation% = 100 x (V@noload - V@ratedload)/ V@ratedload

Assuming that the voltage drops to that 120V output close to the rated load, this 120 --> 125v represents a Regulation of 4.2% quite good, but not unexpected in a well made EI core isolation transformer. There is nothing unusual or suspect about those voltage readings. The larger the transformer, generally, the better (lower) the regulation %.

Neither you or Josh have gotten back with what, which and how any caps are used in the OneAc. Please?

[ludavico]

Occam, thanks for the reminder, I meant to ask you about those caps in the stock ONEAC.  

There are two 4.0 uF 250V caps (I think) and another smaller one on a separate board that connects to the screw contacts on the first outlet.  If you want I can open it up again and check for sure, if these values seem screwy.

I can also take some pictures.  My ONEAC has a giant torodial transformer which is different from what I have seen in pics of other ONEACs.  

I do not hear any buzzing,  but I do feel the case "humming" slightly.  

John

[JoshK]

Occam,

I took a look inside my OneACs and took note of the caps inside.  As far as I could tell, there was no noticeable brand anywhere just a marking "IC" on the cap in a stylized way.

The 5amp OneAC has two 4.0uF 200V 'mkw' caps in parrallel bypass by a small radial cap with a 5w resistor that looks like it is between the outputs of the caps, although I am assuming it is a bleeder resistor.  It was a little hard to tell the circuit because I didn't disconnect the board to trace the bottom as I soldered everything in place.  The 7amp OneAC had two 8.0uF 200V 'mkw' caps instead of the two 4.0uF, otherwise the same.  

There is a small radial cap across the live to neutral lines on the input of the IT.  There is also a green ground wire coming out of the IT in addition the the live and neutral.  Does this mean it is 'center tapped'?

[Occam]

Gents,

Thanks for the info on the OneAc's innards. Josh, if the invite to use your drill press is still valid, we can examine the OneAc in more detail. At this point any comments are speculation.

The IC designation is simply that of Illinois Capacitor, a very good manufacturer. The MKW would inditate a metalized polyester (PET) cap, and the resistor is not necessarily a bleeder, but could be part of a RC snubber to mittigate a resonance. Dunno. I'll contact OneAc and see if I can cadge some schematics.

The size (and increase with increased size) makes me think their purpose might not be soley for noise supression, but for power factor correction, as well -
http://home.earthlink.net/~jimlux/hv/pfc.htm

(Josh, that green wire, indicating ground, is just a likely a connection for an interwinding shield within the transformer, a very good thing. Dunno...)
'

[JoshK]

Absolutely still valid, we'll chat I guess when I get back from the holidays.

[NotoriousBIG_PJ]

Gents,

(Josh, that green wire, indicating ground, is just a likely a connection for an interwinding shield within the transformer, a very good thing. Dunno...)

My oneac cb1115 has a wire coming out from the middle of the transformer that is used to ground an inner sheild.

Biggie.

[Occam]

From a different thread -

I had my 12amp oneac moddified so that it runs in balanced mode now (+60/-60 instead of 120/0). Also a cap was added to each of the recepticles. This mod dropped the already low noise floor even lower. ...

Does the OneAC transformer's secondary have a center tap, or are you running the non center-tapped secondary as floating balanced?

 In an isolation transformer, typically one of the secondary's legs is tied to neutral, recreating that 0-120vac environment. If that conection is severed, the output AC 'floats' with respect to ground [which is usually established via the return leg of the attached interconnects] This yeilds a truly balaced mains supply. If your component is 'approved' for use with an ungrouded AC cord, this approach could yeild substantial benefits.

What components have you connected to your balanced OneAc? Did they perform differently?

Thanks in advance,
Paul

[EProvenzano]

I thought this question would be appropritate in this thread.

Is is wise to add an X rated filter cap across the Pos. and N, inside a power amp (on the IEC recepticle)?
This seems like a good minimalist alternative to creating an external power strip.

Is there a problem with this approach?
Thanks
EP

[JoshK]

I thought this question would be appropritate in this thread.

Is is wise to add an X rated filter cap across the Pos. and N, inside a power amp (on the IEC recepticle)?
This seems like a good minimalist alternative to creating an external power strip.

Is there a problem with this approach?
Thanks
EP

seems a logical approach to me.  maybe someone like Paul who knows a bit more about safety issues can chime in but I don't seem why it couldn't work.

[NotoriousBIG_PJ]

My 12amp oneac had 2 large oil caps, one from the left wire out of my oneac and one from the right wire out of my oneac, and then hooked up to the various recepticles.  These rolled off the highs and were removed, but now the noise floor in my system isn't as low as it was. Any suggestions on caps I could put in their place?

What about something like this? http://www.referenceaudiomods.com/Merchant2/merchant.mvc?Screen=PROD&Product_Code=NOS_P80_325_CAP&Category_Code=NOS&Product_Count=1
I like those because no soldering involved heh. I'm not sure what kind of uf I should be going for, and how much better regular caps are.

Biggie.

[Occam]

Notorious - I'm not sure how those two oil caps are wired. Are the caps in parallel or in series to the Hot and Neutral outputs? Does transformer secondary have a single set of outputs? What are the values of the present oil caps?

But assuming the the OneAc has a single pair of secondary wires, and both present caps are wired in parallel accross those secondary leads -

That LeClanche Paper/Foil in Oil cap is absolutely gorgeous, in a retro, RUR (a 30s Chech science ficton silent film), sort of way.
Their construction well might be ideal for this application. Its no more expensive than the other bespoke alternatives, and they are operating well within their  AC specifications.  They are as scarce as hen's teeth.
If you get one, remove  the output caps, and wire the LeClance accross the output of the transformer's secondary, prior to their connecting with the Hot and Neutral of the outlet.
Ideally, you'd bring the reconfigured OneAc up to full voltage with a Variac,  first with no load, then with a 100watt incandescent bulb, and check after 30 minutes that the cap is not overly hot. These are NOS caps, and should exercise care. Wear glasses. But I wouldn't expect the worst to happen.
These caps seem like they could be wonderful for this application, and I really want to hear your evaluation, if you choose. I've no direct experience and am as curious as you.

[NotoriousBIG_PJ]

The balancing of my oneac was done by hooking up resistors to the two output taps of the transformer attached to the ground wire. Interestingly enough if the oneac heats up too much, it unbalances.

Thanks,

Biggie.

[Occam]

...The balancing of my oneac was done by hooking up resistors to the two output taps of the transformer attached to a ground wire. The stock recepticles needed a piece of metal stripped to make this work. Interestingly enough if the oneac heats up too much, it unbalances.

Please don't do that....
If I'm following this, you're explaining how someone modified your OneAc for balanced operation.  Establishing a ground reference via a resistive divider is well and good for signal levels. but it does not establish a power ground! If that resitive 'power ground' is not tied the mains ground, it provides no saftey ground whatsoever. If that point is tied to ground, it will simply pollute your ground with differential noise that additionally reflects whatever non-linearity are in the transformer, and any mismatch between the divider resistors. It seems the worst of all possible worlds. I'd initially thought you balanced modification was simply not tying one of the outputs to neutral, and leaving a floating balanced output. This is something I'm experimenting with....Without a real center tap, a point you can tie either a POWER ground ground, or a real technical ground (like a copper rod driven into treated eart, connected via heavy copper) you don't have balanced power, and what I think is your configuration, scares the crap outta me! (I could be wrong)

If I'm following this, the mod consists of that resistive divider network establising your 'balanced ground', the 2 oil caps from your balanced outputs, to this putative ground, Y caps. Additionally, you've those 1uf (microfarads) caps accross the balanced live lines as X caps on your outlets.

Please respond, and in the meantime, stop using the modded OneAc, unplug it.

[NotoriousBIG_PJ]

Interesting.

Biggie.

[Occam]

Is that midpoint of your resistive divider tied to a real ground, either at the walll socket or a techinical ground?

I'm not concerned whether you measure 60v ac from each of the balanced legs to your resistively derived ground or not. I'm concerned with safety issues. I'm concerned with noise you have on that 'ground' in comparison to a real ground. As you've said, it looses balance under high loads. You're just seeing the imbalace on a gross level. Its simply not balanced and an examination of that 'ground' under dynamic conditions will clearly show that.

If you're convinced that this resistive divider is your route to whatever benefits balanced power provides you, discuss whatever mods with the person who came up with this scheme.  It is unknown to me. I'm speaking as facilitator of the Lab Circle, and I consider futher discussion without resolving the safety issues to present a danger to the participants.

[NotoriousBIG_PJ]

The first shows the "balancing", the 2nd how it is grounded. I certainly would not want to use a unit that is proven to be unsafe.

Biggie.

[Occam]

Notorious,

No, I don't think it particlarly dangerous, just a bit ill considered. That derived ground between the 4 resistors connects to your other green wires (which indicate the mains ground, and assuming, the wall's ground is intact to that chassis 'starground', it seems? ok.
I think I understand the modders intent. The idea was to provide that derived ground with the resistive divider, and provide a lower impedance path for differential mode noise to that ground via the bypass oil caps. And what you seem to have found, is that they work too well, injecting noise into your ground to pollute your components connected to that same ground. Hence, you removed them. With that functionality gone, what you are left with is a resistance across the secondaries, which pre-loads the transformer (this is often a good thing with power conditioners because it oftem moves the inductive elements into a better perfoming part of the magnetization curve, and it can also ameliorate humming from the transformer.), but the resistors are simply injecting differential noise into ground (and an ac component to the extent of any resistor mismatch) along with consuming power, The noise you inject into the ground is exactly that noise you're trying to reject by this balancing scheme. Even in the best of circustances you simply removed the noise from your 'hots' and impressed them on your ground.

Use the proper components for the proper task-
You use the isolation transformer to deal with common mode noise, that is what they are for, and nothing to my knowledge works better,
You use an X cap, accross the line capacitor, to deal with differential noise.
If you want a real balanced powerline, you need a center tapped secondary.
If you want to pre-load your powerconditioner, plug an incandescent lamp into it, or find the resistor load accross the lines (not to ground!) that optimizes performance/quiet for your specific load.

[NotoriousBIG_PJ]

Ok, thank you.

Biggie.

[Occam]

So if I remove the resistors and the ground wire that is attached to them, do I need to do anything else to restore the oneac to its normal state?
"use an X cap, accross the line capacitor"  Can you go into more detail about doing this?

AC VOLTAGES CAN BE AND ARE LETHAL.  IF YOU'RE NOT FAMILIAR AND COMFORTABLE WITH SAFTEY PROCEDURES, DO NOT ATTEMPT ANY MODIFICATIONS.

I'm assuming the following -
1. the capacitors mounted on the outlets have the same (or better) rating and similar capacitance to those mounted on the board that originally came on the stock unit.
2. the caps mounted on the outlets are wired 'accross the line' as X caps, from Hot to Neutral.
3. the resistor string consisting 4 220K resistors is roughly equivalent to the bypass resistor on the original board, which I assume is there to discharge those X caps when unplugged.
4. From picture #1, those black and white wires from the transformer secondary, are connected to the same  3 white and 3 black wires, respectively, that connect to the 3 outlets as shown on Picture #2.
5. From picture #2, that the 2 green ground wires connected to the central ground post has one coming from the ground of the powercord and the other is from the transformer's shield.
6. the wiring of the transformer is correct? The wave form of the black output wire (by convention Hot) is in phase with the input Black? wire to the primary, the wire that comes from the narrow (Hot) blade of your powercord. (I show how to check it further down)
7. The original circuit breaker/switch or fuse is intact and wired as original.
If any of the above statements are not true, do not proceed.

[If someone has a the same OneAc, CB1115,  could they chime in and let us know the specific values for the components on the removed board?]

Looking at your picture -
http://www.notorioussource.com/oneac1.JPG
1.Remove the white wire from the secondary's output terminal. At the other end, where it fans out to those 3 white wires connected to neutrals on the outlets, disconnect them from the outlets and remove the whole harness.
2. snip the white wire coming off the bottom of the 'V' formed by the 4 resistors.. Connect that free end of that white wire to the terminal of the secondary output where you previously disconnected the OTHER white wire. You are reestabliching the output ground-neutral bond that the OneAc originally came with.
3. You are now left with no connection to the neutrals on your outlets. You've a choice -
Runs white 'star' wires (3)  from the groundpost to the neutrals
or
use wires to connect the neutral and ground (black wire) of the outlets, themselves.

If you've any questions or anything isn't clear, PM me. We're talking leathal voltage here..

When the reconstructive surgery has been completed, make sure nothing that shouldn't be is touching. Be sure to remove your pliers (it sounds funny but I've done it). Put the cover back on.

First check that your wall polarity on the outlet that you plan to plug the unit into is correct. The voltage between the wide blade entrance, neutral, and the ground (circular bottom hole), must be very close to 0. The voltage between the narrow blade opening (hot) and neutral, should measure you wall voltage, 120v AC +-. You should measure that same line voltage between hot and ground. If not, stop, and call an electrician, or your landlord, as your outlet is miswired.

Plug the unit in. Turn it on. If it doesn't trip the breaker or blow up, perform the same test on the OneAc's outlets that you did on your wall outlet.
Now you must check verify that both outlets, wall and conditioner, are in phase. If they are not, the potential shock hazard danger is substaniially increased in the event of powered components not all being fed from the conditioner. Measure the voltage between the narrow blade entrance. on the wall outlet of the duplex that isn't supplying the conditioner, and a conditioner's outlets 'hot'. If you get a minimal voltage, you're ok. If you measure close to 240V AC, your modder has miswired your transformer out of phase.

Assuming everything is sympattico, plug in a lamp..... Then remove the lamp and start trying audio components....

[NotoriousBIG_PJ]

This assumption isn't true:

3. the resistor string consisting 4 220K resistors is roughly equivalent to the bypass resistor on the original board, which I assume is there to discharge those X caps when unplugged.

Biggie.