[Syrah]

So I have both a Signal Transformer DU-2 and an SU-3.  The DU-2 is a 1:1 isolation transformer that can be wired for balanced power, it has dual windings.  It is the one used in the Risch formula.

The SU-3 is a 120/240 step up / step down.  It has been sitting in my closet.

I read on another forum that the best thing to do is to first pass the signal through an isolation transformer and then through a balanced power transformer.  I thought the DU-2 did both tasks together.

Would there be any advantage to my using both of these?

I could put 240V into the SU-3, step it down to 120, then put it through the DU-2 to make it balanced.

That's a lot of iron in my living room.  I read somewhere that stepping down the 240 to 120 will lower my impedence which I suspect is a good thing (i.e. more juice).

I've never really preferred iso trannies / balanced on my power amps, but it seems to work better with other gear.  My PSAudio P300 is great fed with balanced power going into my AC turntable motor.  Paul (PSAudio) tells me the P300 likes balanced power.  None of his newer units do, as they all work on the hot side only.

Other than the free workout I'd get hauling the SU-3 out of my closet plus my time, I don't have much downside in trying this if you guys think it could help.

Thanks for any comments and assistance.

[Syrah]

Sorry to pile on to my own post, but part of my new thinking stems from something my sparky told me when he was last over.  I previously thought that, since my house was powered with two 120v supplies that it was necessarily balanced power.  He told me no, it's just a center tapped transformer with two 120v lines, which is not the same as two lines out of phase.

Just when you think you've figured it all out...

So, I guess I would be putting unbalanced stepped down 60/60 into the DU-2 on the primaries, and wiring it to get balanced power on the secondaries.

[Speedskater]

If you have a US type power system, almost all home have a center-tapped 240/120V single phase system.
Note that the NEC has special rules for balanced power.
I'm not sure that you can run the SU-3 backwards. The output voltage might be a little different.
If your sparky can run a 240V circuit to the transformer, that would be good.
Either way only use one transformer.

Go to page 21  of this Middle Atlantic white paper for the hook-up. Also have Mr. Sparky read the addendum.
http://www.middleatlantic.com/resources/white-papers.aspx

[jea48]

So I have both a Signal Transformer DU-2 and an SU-3.  The DU-2 is a 1:1 isolation transformer that can be wired for balanced power, it has dual windings.  It is the one used in the Risch formula.

The SU-3 is a 120/240 step up / step down.  It has been sitting in my closet.

I read on another forum that the best thing to do is to first pass the signal through an isolation transformer and then through a balanced power transformer.  I thought the DU-2 did both tasks together.

Would there be any advantage to my using both of these?

I could put 240V into the SU-3, step it down to 120, then put it through the DU-2 to make it balanced.

That's a lot of iron in my living room.  I read somewhere that stepping down the 240 to 120 will lower my impedence which I suspect is a good thing (i.e. more juice).

I've never really preferred iso trannies / balanced on my power amps, but it seems to work better with other gear.  My PSAudio P300 is great fed with balanced power going into my AC turntable motor.  Paul (PSAudio) tells me the P300 likes balanced power.  None of his newer units do, as they all work on the hot side only.

Other than the free workout I'd get hauling the SU-3 out of my closet plus my time, I don't have much downside in trying this if you guys think it could help.

Thanks for any comments and assistance.

What will you be connecting to the output of the transformer/s? Total connected load?

http://pccomponents.com/datasheets/SIGNAL-DU.PDF

The DU-2.
Each of the two secondary windings has a maximum full load amp (FLA) connected load capability rating of 9 amps each. This rating is based on the size of the wired used in each of the windings.

If the two windings are configured in parallel with each other then the FLA rating is 18 amps max.

If the two windings are configured in series with each other then the FLA rating is 9 amps max.

So if the transformer is configured for a 60V 0V 60V = 120V output, (Balanced as some call it) the FLA continuous rating of the transformer secondary is 9 amps max.
Anytime a 60/120V grounded AC power system is used the load connected to the two ungrounded 120V secondary output legs must be GFCI protected. NO Exceptions!

 (It also should be mentioned a 60/120V Grounded AC Power system is not intended for use in a residential environment setting. It is intended for commercial/industrial use where its' use is controlled/supervised by qualified personnel.)

Normally a transformer should not be continuously loaded more than 80% of its' FLA rating. For a power amplifier the rule of thumb is to size the transformer FLA rating for 3 to 5 times of that of the FLA of the amp.

I would recommend you configure the primary, (series the two windings, observing polarity) for 240V nominal. (If you use a 2pole 15 amp breaker at the electrical panel, to feed the transformer, you will not need any overcurrent protection on the secondary of the transformer. I would use #12 wire to feed the 240V primary.)

Configure the secondary for straight 120V nominal out. The two secondary windings paralleled with each other, OBSERVING POLARITY.

You can not leave the 120V secondary output of the transformer floating above ground. For electrical safety, code, you must wire the secondary to become a Grounded AC Power System.

To accomplish this one of the paralleled secondary leads, legs, must be connected to earth. This lead, leg will become the Grounded Conductor, the neutral. It also must be connected to the metal enclosure of the transformer. This is also the same point the safety equipment ground terminal of the 120V receptacle will connect to.
The other lead, leg, of the paralleled winding becomes the Ungrounded Conductor, the HOT conductor.

(Note: Per code the earth connection is the main grounding system, The Grounding Electrode System, for the main electrical service of your home. By code you can connect to any point of the grounding electrode system. I believe in the 2008 NEC the safety equipment grounding conductor can no longer be used as the earth connection for The Grounded Conductor, neutral conductor.)

To be honest if the primary of the transformer will be hard wired, there in not cord and plug connected, a licensed electrician should be hired to wire the transformer.
If you want to use a cord and plug for the 240V primary to mains connection A 250V rated plug and receptacle must be used.

Note: My intention of this post is meant as an outline, general guide, only. Local electrical codes must be followed. 

[jea48]

Sorry to pile on to my own post, but part of my new thinking stems from something my sparky told me when he was last over.  I previously thought that, since my house was powered with two 120v supplies that it was necessarily balanced power.  He told me no, it's just a center tapped transformer with two 120v lines, which is not the same as two lines out of phase.

Just when you think you've figured it all out...

So, I guess I would be putting unbalanced stepped down 60/60 into the DU-2 on the primaries, and wiring it to get balanced power on the secondaries.

I previously thought that, since my house was powered with two 120v supplies that it was necessarily balanced power.  He told me no, it's just a center tapped transformer with two 120v lines, which is not the same as two lines out of phase.

The secondary winding of the utility transformer is a split phase winding.
The outer most two ends of the winding will measure 240Vac nominal. These two leads are the Hot ungrounded Lines, legs, of the transformer split phase, single phase winding.

The center tap of the secondary winding is intentionally connected to earth making it
the Grounded Line, leg, the neutral.

If a volt meter is connected from one Hot Line, leg, to the neutral it will measure 120Vac nominal. Same from the other Hot leg to neutral, 120Vac nominal.
From Hot leg to Hot leg, 240Vac ac nominal.
Another way to say it would be 120V - 0V - 120V. Look familiar? 

http://www.allaboutcircuits.com/textbook/alternating-current/chpt-10/single-phase-power-systems/

http://i.stack.imgur.com/HdUzm.gif

[Speedskater]

Well said, jea48.

[Speedskater]

If I were to do this kind of project with a permanently installed transformer.
I would:
a] Skip the balanced transformer idea. Too many rules and the real world gains are nowhere near what some claim.
b] Use a 240V input and two 120V outputs. With a small breaker box on the outputs.
c] Wire the Safety Ground circuit as a Separately Derived System. (as in the Middle Atlantic paper)

[werd]

I wonder what the VA size of the step down transformer is? Might have been helpful.

[Speedskater]

The link to the above referenced Signal Transformer DU-2 and an SU-3  transformers.
Notice that the spec VA ratings are KVA.
DU-2 = 2000 VA
SU-3 = 3000 VA

http://www.signaltransformer.com/sites/all/pdf/DU-SU.pdf

[jea48]

Also worth noting is the maximum amp rating of the DU-2 and the SU-3 transformers.

For the DU-2, (2000VA), each winding of the secondary is good for 9 amps max.
So if they are configured in series the max. available amps is 9 amps.
If the 2 windings are paralleled the max available amps is 18 amps.


For the SU-3, (3000VA), each secondary winding is good for only 7 amps each.
So if they are configured in series the max available amps is 7 amps.
If the 2 windings are paralleled the max available amps is 14 amps.

The wire sized used in the windings of SU-3 is smaller than that in the DU-2


 Watts, VA = Volts X amps.
 

[Speedskater]

Oh, I see why. The SU-3 is a 480/240V xformer and the DU-2 is a 240/120V xformer.
So at 240V:
DU-2 = 2160 VA max. 2 KVA nominal.
SU-3 = 3360 VA max. 3 KVA nominal.
But audiophiles may not always wire them that way.
For our purposes we can think of Watts = VA. But if we get technical, their not.

[werd]

My experience with putting transformers in series. By starting from the audio component working towards the local neighborhood. Transformers needs to be at least 10x bigger in VA as they move to the local transformer. The size difference of the the transformers in balanced (or not in front) of that SU3 is too small. It will work but it nerfs the dynamics. Or it will sound dragged down.
I would use the isolation transformer DU-2 and run two 9 amp 120 out phase legs into the isolation and then you will get around 20 amps out in 120.  That is your best bet and it still will not be enough for for some amps.

But great for digital.

That is if you can with that transformer.

[werd]

The least amount of transformers between amps and local mains transformer the better.  For digital and pre amps I think isolations are fabulous, that is what I do. Ideally the best scenario is having the local transformer hanging on a pole in your back yard. Then having the mains hang down into the house That is primo and you will never get any better conditioning than that. The worst is living as far from the local transformer and having underground feeds into your house. I know because that is my situation now. Haha sad .

[Guy 13]

werd,
I would think that outside arial wires from utility transformer would be more prone to
pick-up more interferences than underground -burried wires ????

Guy 13

[werd]

No they are shielded big time and if you run 240 you will cancel any noise at the transformer. Also amp transformers give you good resistance to noise if they are too big for the transformer.

[Speedskater]

Don't recall ever seeing any power company shielded cables. Power lines are not the best radio frequency antennas, but then RF does some strange things.

[FullRangeMan]

The SU-3 is a 120/240 step up / step down.  It has been sitting in my closet.

Its not a transformer, it is a autoformer. Dont use it for hifi, just for your refrigerator.
It offer no protection since it let pass all the tension in/out, it connect your equip to the nearest HV station transformer.

I would never use any transformer at all IMO.

[FullRangeMan]

Sorry to pile on to my own post, but part of my new thinking stems from something my sparky told me when he was last over.  I previously thought that, since my house was powered with two 120v supplies that it was necessarily balanced power.  He told me no, it's just a center tapped transformer with two 120v lines, which is not the same as two lines out of phase.

Just when you think you've figured it all out...

So, I guess I would be putting unbalanced stepped down 60/60 into the DU-2 on the primaries, and wiring it to get balanced power on the secondaries.

You can not do it, 60V + 60V are not 120V.
Electricity is not added as oranges (2+2=4)
There is a vectored formula (about 173 if I remember well) to join two different phases.
There is a loss of about 13% in the biphasic that is your case.

[Speedskater]

But it is a transformer and a nice on at that.
See the link in reply #8

[Speedskater]

You are mixing 3 phase and center tapped single phase math. 60 + 60 still equals 120.