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Discussion of AC mains isolation transformers


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Folks, forgive the newbie question, but I'm lost a bit in the various wiring scenarios for the Topaz Ultra Isolation transformers.  

 

I've tracked down a 91018-31T and 91002-31 on eBay.  I'm US-based (120V) so I have H2/H4 (neutral) jumpered and H1/H3 (hot) jumpered on input, and X2/X4 (neutral) jumpered and X1/X3 (hot) jumpered on output.

 

My question is where to wire ground on input and output.  On one unit, ground was jumpered to H4 (neutral) on input and X4 (neutral) on output.  On the other unit, ground was only connected to X4 on output (not jumpered to H4 on input)

 

Should ground stay floating from the primary and secondary, or should it be grounded to the secondary or should it be grounded to both primary and secondary?

 

 

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Thank you @One and a half!  I appreciate the quick reply.

 

To confirm, leave neutral on the  primary disconnected from ground, but connect neutral on the secondary to ground. Ground and shield should be continuous through the transformer (per the graphic).

 

Can you add some color on the motivation/implications of leaving neutral disconnected from ground (except at the main panel)?  Is the intent of connecting neutral on the secondary to ground to mimic the same connection at the main panel?

 

 

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7 hours ago, Speedskater said:

Oops, with regard to:

(with the exception of the secondary of an isolation transformer)

This only applies if the transformer is wired as a Separately Derived System.

 

 

That makes sense for an isolation transformer.  There is no return path from neutral to ground in the panel otherwise.  The regulation also makes sense, since you want the return path to ground to be at the panel, and not get cut short

 

Thank you for the context and information!

 

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  • Superdad changed the title to Discussion of AC mains isolation transformers
  • 1 month later...

After checking (and double checking) that my downstream equipment would be happy with balanced power, I rewired my Topaz 91002-31 for balanced power (+-60V on hot/neutral output lines) and things are working great!

 

As others have mentioned, all the buzz/clicking from my transformer has gone away.  It is still warm (no longer hot) but pretty much silent (I have to lean in to ~10" to hear a very muted/quiet buzzing).  It definitely seems like it is running cooler to the touch

 

Hard to tell if it is a change in power quality or the elimination of the background buzz from the IT, but things are definitely sounding better.

 

Now to rewire the Topaz I use for my digital zone balanced and hopefully get rid of that buzz as well

 

Appreciate the information and coaching from those far more expert than I.  It's great to know enough about how these things work to have the confidence for this type of rewiring job.

 

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Confirmed that I got the same impact/benefit with my second Topaz isolation transformer (a 91018-31T this time)

 

I also finally got around to using my KillAWatt to measure power factor.  Coming in at 0.7 with the linear power supplies and class AB amps I have connected to the first unit.  I'm out of hobby time this weekend, but on the list is to measure the PF going into the Topaz to see how well it is insulating the rest of my house from the heavy PF load from the amps and LPS

 

I did have time for one other quick experiment.  I just got some BK Precision 1604A isolation transformers to help isolate some smaller switching supplies.  These buzz quite heavily.  Naively, I would have thought that plugging them into the balanced output of the topaz would impact them as well, but the buzzing is the same whether plugged into balanced power or normal power.

 

I just added cracking the case open to see how these guys are wired internally (does anyone have a wiring schematic for the 1604A's?)

 

 

 

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Thank you, that’s great info!

 

i did end up cracking open a 1604a last night and can confirm two wires in and two wires out (floating shield as expected)

 

The interesting thing is the two point mounting scheme they use for the heavy transformer. One of the mounting brackets had been bent (presumably in transit). A little muscle action and the mechanical buzzing went way down.   A reminder that these transformers definitely have a mechanical aspect to them. 

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A question for those that have played with a capacitor across the output terminals of their Topaz isolation transformers.

 

One of my Topaz units has a large capacitor connected to the hot and neutral lines on the output (when I switched to balanced configuration, now connected to +-60V lines).  Reading through the Topaz manual, it looks like these are there to minimize transverse-mode noise.

 

I practice, how does transverse-mode noise manifest itself (if at all) in an audio system?  Given the importance of the ground and voltage reference, common-mode noise reduction makes a huge amount of sense to me (which is why I have a couple of the Topaz IT's).  I'm trying to get my head around transverse-mode noise, both in a conventional Hot-Neutral configuration (Neutral connected to ground at the breaker box, and at the output of the transformer), and in a balanced Hot-Hot (+-60V, center tapped ground) configuration.

 

For those that have researched/played with this stuff, how important/impactful is transverse-mode noise reduction in an audio context?  Is it worthwhile for me to be adding a large cap to the output of my other Topaz IT?

 

 

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Now that I have a couple balanced isolation transformers in place, time to harden the setup against people hurting themselves by plugging things in that don't play nice with balanced power.

 

My understanding from searches and this thread is that the best way to protect against the formally neutral line (now -60V) creating a short to ground is to have a ground fault interrupt breaker between the balanced isolation transformer and the things I'm plugging in.  This is guess work, since I'm not a GFI expert.

 

https://smile.amazon.com/gp/product/B00TQOF3FI/

 

My tentative plan is to get a couple of these, hack off the plug end, and hard wire them to the output of the BIT's (3 outlets per BIT)

 

For those that have gone through this research and come up with a good solution, could you please share your findings and solution, or give feedback on the suitability of the generic GFI tap cord I linked to above?

 

Thank you again to everyone here that has been so generous in sharing their experiences and expertise!

 

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Have you tried tightening the bolts on the unit?  I've been reminded a couple times recently that the mechanical nature of the transformers is a big part of buzzing

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  • 1 year later...

I have 3 Topaz units and all of them generated a bunch of heat and buzzing in my home.  When I switched them to balanced power config, maybe 95% of the heat and the buzz went away (cool and quiet as a cucumber).  

 

Note that not all electrical items (lamps etc) play nice with balanced power, although all my audio equipment (to date) has.  If you're not sure what you're doing, don't experiment, and if you do know what you're doing, make sure you keep civilians in the house from accidentally plugging something into the units that they shouldn't.

 

 

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  • 9 months later...

Fair Warning: Don't listen to a TT7 unless you're ready to trade in a car for one ;)

 

As someone who didn't heed that warning, if anyone in SoCal is looking for some isolation transformers, I've got three in the garage (couple wired to balanced...made a big difference for me) that I'm happy to loan out for folks to try, or sell outright.  Loved them, but the TT7 is something else.

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23 minutes ago, Talley4217 said:

Whatever is in that thing is not worth a car.  I've just been exposed to this.  Is there any information to this?  Nothing is really coming up on google about the product.

 

Here you go... (wow, that was a year ago!)

 

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I should note that my write ups are a snap shot in a long system evolution (Reality Quest).  Those power experiments pointed the way to improvements, that's for sure, but the dedicated line (even with romex) was a huge step forward from what I had before - at the time I put those in several years ago it was one the more significant system improvements I'd heard up to that point (who knows whatever house crap was on the shared line before then).

 

As a quick update, since my TT7 write up last year I moved into a new home, and used the opportunity to upgrade to 6AWG cabling from the electrical panel to my outlet (~20' run, in conduit).  Obviously not possible to do an A/B any more, so I can't speak to impact, but my experience with the Sablon power cords certainly gave me VERY high confidence to go with heavier gauge wiring in the walls.  If you can swing it (and find an electrician to help you with it without laughing at you), a very cost effective way to get a big impact across your system.

 

As FYI I did get the outlet and wiring from Jim.  He spoke about how challenging it was to get the wires connected to the outlet, but that it could be done with persistence.

 

I also have been doing a lot of experiments with power buffering and power regulation. Astonishing how much lift there is to be had by doing everything you can to stabilize power (AC and DC) under dynamic load, external to components and internal to components.  I'm nowhere near the summit on this stuff, that's for sure.

 

I should note that everyone's power experience is very very different, even if the toolkit is the same.  At the end of the day, everyone has a different electrical grid, home wiring, etc, so the best advice is use best practices, and see which best practicers are "bester" in your setup.  Pay attention to these, and try other best practices that double/triple down on that aspect of power hygiene (alas, now that I've moved to a new home/neighborhood, it is time to repeat that process....ug)

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2 hours ago, gererick said:

In your 6 AWG 20' run in conduit, I assume the conduit was PVC or rough equivalent?


I believe it is a metal conduit (on exterior wall of house). There was some improvising going on when trying to get it installed

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