Discussion of AC mains isolation transformers

[gererick]

I cut part of the back out of an 8” x 6” junction box, drilled holes for screws, and fastened the box to the output end of the transformer.  I bought two terminal lugs for the transformer, and with my size transformer I can go up to 50 uF in capacitors across the + and - terminals to reduce transverse noise.  On the lugs at the terminals, I paired up a 22 uF 400V Mundorf MCap MKP Classic and a 10 uF 600V MCap Supreme.  I connected two short wires between the + / - terminals and a pair of split bolts that are connected to my power strip.  Between the two split bolts, I connected a .01 uF Duelund Silver Bypass capacitor, a .1 uF 1200 V Jantzen Superior ZCap , a 1.0 uF MCap, and a 2.2 uF 800V ZCap.  These voltages are DC, but I made sure they worked at their respective AC voltages from a safety perspective.  (I tested them for over a week at 24/7 on a Yamaha receiver tuned to an FM station, with no issues but connected at the terminals instead of some at split bolts).  The isolation transformer sits on six Pods from Townshend Audio for vibration control and reduced hum (only four are needed but I don’t have the right spec’s unit on hand).  I plugged it in yesterday and it seems to be working fine with 62+ volts AC at each split bolt.  After measuring, I taped up the split bolts with 2” wide Scotch.Super 33+.  I did not listen yet.  The idea behind the different values of caps is to address a variety of frequency ranges.  I will probably pop open a top and maybe a bottom hole in the junction box to allow heat to escape.  

 

 

[gererick]

I had a small unbalanced isolation transformer plugged into my power strip when the power was unbalanced.  Two digital devices are plugged into that IT.    If my power strip is now getting balanced power, can I still plug an unbalanced isolation transformer into it?

[Speedskater]

2 hours ago, gererick said:

I can go up to 50 uF in capacitors across the + and - terminals to reduce transverse noise.

I hope that value was a typo.

The maximum line to ground value is 0.01 uF.

Typical line-to-line values are 0.1  to 2.0 uF.

Remember the AC power line capacitors need to be 'X' & 'Y' types.

[gererick]

1 hour ago, Speedskater said:

I hope that value was a typo.

The maximum line to ground value is 0.01 uF.

Typical line-to-line values are 0.1  to 2.0 uF.

Remember the AC power line capacitors need to be 'X' & 'Y' types.

 

Regarding "Typical line-to-line values are 0.1 to 2.0 uF", please see One and a half post Jan. 15 with .pdf attachment, and on Jan 17 with photo, my post on page 75 / Feb. 5 asking about the calculation of max value, and Talley4217's reply on Feb. 5 indicating 50uF is the max based on the formula provided by Topaz. 

 

I am at 35.31 uF versus the 50 uF max indicated on 2/5.  I don't know if the 22 uF is worthwhile, though. 

[gererick]

1 hour ago, Speedskater said:

I hope that value was a typo.

The maximum line to ground value is 0.01 uF.

Typical line-to-line values are 0.1  to 2.0 uF.

Remember the AC power line capacitors need to be 'X' & 'Y' types.

Regarding 'X' and 'Y' types, I instead went with rated measurements provided by the manufacturer so that I could use better quality caps.  

 

Email to mfgr:  I am interested in buying quality capacitors, such as Mundorf caps, to go between the black and white wires on the output of an isolation transformer from Topaz.  It is a 91005-31, and it is 5.0 KVA.  The original cap that comes with some versions of the Topaz (including a 2.4 KVA model) for reducing transverse mode noise is the Aerovox 7 uF 250 VAC cap, which is a lesser cap from the standpoint of sound quality.  The value can go up to 50 uF safely, according to Topaz documentation.

 

The isolation transformer will be powering my audio equipment.  I have a smaller Topaz in place at the moment, but want to operate in balanced mode so am going larger.  It is wired for a balanced output.  120V on the black wire at the input, and 0V on the white wire at the input.  60V on the black wire at the output, 60V on the white wire at the output.  The cap would go between these two wires to filter transverse or differential mode noise.

 

My equipment draws about 1,100 watts when all equipment is on and music is playing.  The caps should not total more than 50 uF.  I could use one, or several, caps to get to the 50 uF.  You have Supreme EVO oil caps that are rated for 550VAC from 6.8 uF up to 15 uF, some from 18 uF to 27 uF at 480 uF.  Your 33 uF and 47 uF caps in this product are rated at 410VAC for dielectric.  Your Supreme EVO Silver Gold has a similar number of caps with these VAC ratings for dielectric.  Would these caps be suitable for what I am considering?  If helpful, below is the relevant documentation."

 

Reply:  "Thanks for your feedback at all and interest in our range.  It is a very specific use to bypass the transformer but I think we have some benefits ones for your project.  We have some cooperation’s you have nearly same layout for transformer & power supply circuit.

 

My first idea is the TCAP47-600 but at least 100VAC … not reach the minimum requirement.  The supreme-evo caps like SEO-47uF or SESGO-47uF are great performers J (especially in cross-over settings)

 

… but from my point of view the supreme classic winding technology (biggest metalized surface with lowest possible inductivity) could have the main benefit you are looking for.      I would start with 1x SUP8-10uF and after 20x-30x hours I would bypass a MCAP400-22uF for 1:1 compares."

 

 

[Speedskater]

4 minutes ago, gererick said:

Regarding 'X' and 'Y' types, I instead went with rated measurements provided by the manufacturer so that I could use better quality caps.  

Using only 'X' and 'Y' type capacitors is a safety requirement!

 

I think that you are getting into dangerous territory.

[gererick]

1 hour ago, Speedskater said:

Using only 'X' and 'Y' type capacitors is a safety requirement!

 

I think that you are getting into dangerous territory.

Is it a fair question to ask whether the capacitors in my amps, which draw 400 watts each, should be X or Y rated as a safety requirement also?

[Superdad]

1 hour ago, gererick said:

Is it a fair question to ask whether the capacitors in my amps, which draw 400 watts each, should be X or Y rated as a safety requirement also?

Well if you are talking about capacitors placed directly across AC mains (line-to-neutral X-types, or line-to-ground Y-types) those are indeed very specific applications where the cap must be capable of withstanding very high peak impulses (thousands of volts) and be designed to fail either as a short (X-types) or fail open (Y-types). 

Don't substitute, don't mix them up, and don't electrocute yourself! 

[gererick]

7 hours ago, Superdad said:

Well if you are talking about capacitors placed directly across AC mains (line-to-neutral X-types, or line-to-ground Y-types) those are indeed very specific applications where the cap must be capable of withstanding very high peak impulses (thousands of volts) and be designed to fail either as a short (X-types) or fail open (Y-types). 

Don't substitute, don't mix them up, and don't electrocute yourself! 

On Jan 17, One and a half showed a photo of a 7 uF Aerovox brand cap with a part # beginning with W43A250, as outfitted from the Topaz factory, wired from line to neutral at the outlet (mine is line to line, hot to hot and not to neutral due to it being wired as balanced output).  The high peak impulses you referenced are potentially an issue, but apparently Topaz felt the transformer did a fair enough job suppressing them as part of its inherent capabilities in that regard (I don’t think the Aerovox was an X type, but may be wrong).  Or perhaps X type caps were not as prevalent when Topaz was shipping units outfitted in that fashion.  X type caps would be a safer and proper approach, and the higher quality caps I’ve used may not make an improvement in sound quality. 

[rah50]

Looking for another Topaz, I came across these inexpensive Chinese balanced isolation transformers, are they worthwhile at all?

 

https://www.aliexpress.com/item/32708862586.html?spm=a2g0o.productlist.0.0.33e8dcc8HBW6q1&algo_pvid=ec371580-9b85-4a3e-807e-69fe7e157a43&algo_exp_id=ec371580-9b85-4a3e-807e-69fe7e157a43-15&pdp_ext_f={"sku_id"%3A"12000026896400895"}&pdp_npi=2%40dis!USD!!107.09!!!89.43!!%400b0a555e16522097277038465e4b2a!12000026896400895!sea

[oneguy]

I don’t have any experience outside the MGE/Topaz and Eaton realm but I think it may be hard to comment on that product without knowing the specs of transformer.

[JohnSwenson]

2 hours ago, rah50 said:

Looking for another Topaz, I came across these inexpensive Chinese balanced isolation transformers, are they worthwhile at all?

 

https://www.aliexpress.com/item/32708862586.html?spm=a2g0o.productlist.0.0.33e8dcc8HBW6q1&algo_pvid=ec371580-9b85-4a3e-807e-69fe7e157a43&algo_exp_id=ec371580-9b85-4a3e-807e-69fe7e157a43-15&pdp_ext_f={"sku_id"%3A"12000026896400895"}&pdp_npi=2%40dis!USD!!107.09!!!89.43!!%400b0a555e16522097277038465e4b2a!12000026896400895!sea

The whole reason for being of the Topaz type transformers is that they have extremely low capacitance between primary and secondary. This transformer is toroidal which has the opposite properties, very high capacitance between primary and secondary. The only way to try and get lower capacitance out of one is a one or more shielding layers inbetween primary and secondary and those need an electrical connection and I do not see that in the pictures.

 

So my guess is that this box is about as far from a Topaz as is possible to get.

 

John S.

[oneguy]

Yep, more than likely

[rah50]

5 hours ago, JohnSwenson said:

So my guess is that this box is about as far from a Topaz as is possible to get.

 

John S.

 

Does it get any points for being "Balanced"?

[One and a half]

15 hours ago, rah50 said:

 

Does it get any points for being "Balanced"?

When using off the shelf split phase toroid versus a Topaz or Equitech transformers the difference was dramatic.

Equitech use toroidal transformer,  it is bifilar wound, close coupled with a screen between. What happens is the heat still needs to escape, so the physical size increases to the next size up to dissipate the heat.

 

The other issue is to provide a true balanced output the either end of the output to the centre must be very close less than 2V within each other and the regulation also increases the size. Since amplifiers draw pulsed currents, regulation on the transformer becomes critical as to how the balancing occurs. All that is not simple.

 

From memory the Equitech 1000 VA transformer is about 25cm diameter, a regular 1500VA is 2/3 that.

[rah50]

Curiosity satisfied!

[gererick]

Would it be okay to plug an unbalanced topaz isolation transformer into a power strip that is fed by a balanced one?

[Speedskater]

On 5/10/2022 at 12:08 AM, gererick said:

On Jan 17, One and a half showed a photo of a 7 uF Aerovox brand cap with a part # beginning with W43A250, as outfitted from the Topaz factory, wired from line to neutral at the outlet

That's from over four decades ago! Electrical safety has gotten more serious since then.

[Speedskater]

Interference expert Henry Ott (RIP) wrote in his big book on power line filters:

The performance of an AC power line filter is as much, if not more, a function of how and where it is mounted, and how the leads are routed, as it is of the design of the filter.

 

The filter should:

a] be mounted close to the point where the power line enters the chassis.

b] the wire grounding the filter to the chassis needs to be very short.

[gererick]

17 hours ago, Speedskater said:

That's from over four decades ago! Electrical safety has gotten more serious since then.

Okay, thanks.  
 

From an earlier post on pg 1 of this thread,  a .0005 pF capacitance isolation transformer is “a very good surge suppressor as well. Most of the energy in high power surges is contained in high frequency components, which get suppressed by the low capacitance, thus it is quite an effective surge suppressor without needing any other special circuits to achieve this.” 

 

As my caps are at the output end, the thousands of volts referred to in Superdad’s post should be suppressed after passing through the transformer.  Perhaps that is why Topaz felt comfortable installing Aerovox caps there, the same place I have mine. 

 

I had a surge a year or two ago.  The surge took out my porch light , at least two outlets including a GCFI, a fuse in my tankless hot water heater, some light bulbs, a receiver in m a ceiling fan, tripped breakers and I don’t remember what else.  (this has happened once in 21 years here).  I have an isolation transformer for my two audio/video systems.  None of that equipment was affected, and no fuses blew.  The caps should be okay for a short period as relates to safety, and I’ll unplug it before a storm rolls through.

 

I will be wiring thicker gauge cable from the panel to a junction box with an audiophile-grade outlet.  I will put an audiophile fuse in the junction box before the outlet for additional surge protection, and will plug the transformer into that.

[Speedskater]

7 hours ago, gererick said:

a .0005 pF capacitance isolation transformer is “a very good surge suppressor as well. Most of the energy in high power surges is contained in high frequency components, which get suppressed by the low capacitance, thus it is quite an effective surge suppressor without needing any other special circuits to achieve this.”

Whether that transformer is a good suppressor on not, I don't know.

But that explanation is incorrect.  Nothing get suppressed by low capacitance.

[JohnSwenson]

7 hours ago, Speedskater said:

Whether that transformer is a good suppressor on not, I don't know.

But that explanation is incorrect.  Nothing get suppressed by low capacitance.

A fair amount does get suppressed. In a transformer with with very low capacitance the magnetic circuit is the only way energy gets transferred from primary to secondary. The magnetics used in power transformers are good enough to handle 50/60Hz. By 400 Hz the attenuation is quite strong. Most "surges" that happen on power lines have steep rise and fall times, which means the slow magnetics will suppress most surges on the power line. Of course it is not perfect, I'm sure you could engineer a "surge" carefully crafted  to make it through the magnetics and cause damage. But almost all other suppression techniques have the same issue, that if you work at it you can find some way to get something through.

 

John S.

[NovaInfinity]

I currently have a -31 Topaz with 500VA and I can't fit the entire full chain on it, namely the computer. I can fit everything else including a streamer that my DAC can plug into that I can hook to my computer via ethernet to get the music.

 

My question is, is something like the below enough to isolate the rest of the chain from noise if I put it between my computer and the streamer?:

https://www.digikey.com/en/products/detail/icomtech,-inc./2005674/14837293

 

Or would the signal from the computer either be muddled in some way due to its own power noise or whatever noise it produces will still travel to the streamer and down the chain? I'm not confident I can find something that can fit my computer's large power requirement as well with the .0005 capacitance. Unless there are better options I'm not aware of.

[jas]

Some  use a BK Precision 1604a Isolation Transformer (thanks to Jud if I recall, for the suggestion) on individual components. There are a lot of choices in iso transformers and I don't know the unit you reference, but I can report that I use it between my Mac 27 and a 750VA Topaz Iso Transformer. I thought that I might be overdoing it, so just recently I ran the Mac directly to the Topaz with the BK unit off line and nope, I could hear the difference so the BK unit went right back in. I have read in these pages and on other forum pages that you can't do too much to clean the AC signal and my limited scope experiment supports the contention.

 

I have no comment on the unit you selected, haven't heard it. Hope this helps some.

 

[NovaInfinity]

19 minutes ago, jas said:

Some  use a BK Precision 1604a Isolation Transformer (thanks to Jud if I recall, for the suggestion) on individual components. There are a lot of choices in iso transformers and I don't know the unit you reference, but I can report that I use it between my Mac 27 and a 750VA Topaz Iso Transformer. I thought that I might be overdoing it, so just recently I ran the Mac directly to the Topaz with the BK unit off line and nope, I could hear the difference so the BK unit went right back in. I have read in these pages and on other forum pages that you can't do too much to clean the AC signal and my limited scope experiment supports the contention.

 

I have no comment on the unit you selected, haven't heard it. Hope this helps some.

 

I don't think you read the question right. The problem is my new computer that would be feeding the rest of the chain cannot go on the Topaz and need to go straight to the wall so I'm worried that AC noise and whatever else coming straight from the wall will travel through the computer and to the other isolated components. I'm asking if that ethernet isolator can let me get away with having the computer outside of the isolation. If there are any other solutions that can mitigate that I'm all ears. But as I understand it, you need to have everything on 1 Topaz transformer or there isn't any point. I already have Hammond transformers (alternative BK Precisions) before the DAC and the smaller computer that is getting scrapped soon currently on the Topaz so that isn't the issue here.