A/C Isolation Transformers

[March Audio]

I'm still thinking the field can dump an instantaneous current higher than what's available on the line, to fill a monentary request...

But I'm susceptible to moments of WrongThink.

I agree that what-goes-in is greater than the-usable-what-comes-out over time for all the reasons listed above.

Blow up a balloon (create the field), you can get the about the same energy and amplitude out of it over time or pop it for an exciting instantaneous bang...

I think the voltage will drop. In any case there seems to be an assumption (or its marketed as) that there is a requirement to supply enormous amount of instantaneous current from the mains. What we have measured so far is a relatively stable pulsed current draw which is essentially the reservoir caps charging. The caps is where the requirement is and where the current is supplied from when the ac cycle is a low/zero volts.

Just to gather some more info on this I am going to get my Onkyo AVR blasting at ear bleeding volume on all 7 channels and measure the dynamic mains current. Lets see what we see

 

[RayDunzl]

Just to gather some more info on this I am going to get my Onkyo AVR blasting at ear bleeding volume on all 7 channels and measure the dynamic mains current. Lets see what we see

That sounds like fun.

Got your ear protection handy?

How will you make the measurement?

 

[March Audio]

That sounds like fun.

Got your ear protection handy?

How will you make the measurement?

I am actually a qualified noise officer so yes !

Measurement will be made the same as before, current probe around live cable attached to scope.

 

[Speedskater]

The SouthWire Romex® is probably the best NM (Non-Metallic) cable available in the US. Other budget brands tend to not fix the conductors in place. Which is a Bill Whitlock concern. Mr. Whitlock also writes that Romex® is better than typical US metal conduit wiring jobs.

In the distant past some US Non-Metallic cables had smaller Safety Ground conductors. I think that even more recently this was true in Canada.

 

[RayDunzl]

The SouthWire Romex® is probably the best NM (Non-Metallic) cable available in the US.

My wire just arrived - I don't have a micrometer, but after snipping off an inch and stripping, the three conductors are indistinguishable, 10AWG.

Orange outer jacket, paper liner, clear wrap over the insulator of each hot and neutral, and a fold of paper over the bare ground.

Other budget brands tend to not fix the conductors in place.

I don't see any evidence of that on this cable.

Resistance reads somewhere around .1Ω, allowing for meter leads, so it meets spec for the gauge, and all three conductors conduct.

Anyway, it'll work.

 

[Speedskater]

On generic Non-Metallic cable (he called it Romex but I think that it was generic) because Bill Whitlock's measurements with real Southwire Romex® were much better,
Dale Shirnk wrote:
The real surprise was the Romex cable. Even though the ground is between the two current carrying conductors, apparently the paper spacers don’t do a very good job of keeping it centered. With the 30 Amp pulse test it generated 433 mV peak of noise on the ground wire. I also tried making some bends both across the flat dimension and across the edge, and these had little effect on the measurement.

 

[Rock Rabbit]

• Isolation transformers don't store energy every cycle total flux must be zero...fortunately
• Don't make better line regulation, it stay the same + the load regulation of the transformer...nothing better.
• Line resistance stay the same
• You're not gonna get better specs than the mains pole pig transformer
• They are not line filters, they don't even work at high frequency (they are transparent for hf ...an audiophile dream)
• The inter windings capacitance ruins your dreams of filter or full isolation action at high frequency

For example 1 nF capacitance is some 2.6 Mohm @ 60 Hz then only 2.6 Kohm at 60 kHz...typical iso transformer (eevblog example,...and what I have measured)
Edit: really good iso transformers can go as low as 0.0005 pF
https://www.head-fi.org/threads/top...ansformers-for-affordably-clean-power.857448/

 

[pma]

Assuming a reasonably/properly sized isolation transformer at the equipment rack, what is good or bad about them in general?

Do they "store" any energy?

Provide a little impedance advantage or detriment?

HF line noise reduction?

What is the inrush current rushing into when you first power it up?

Why do I have one?

Their biggest advantage is that they break the groundloop and you get rid off hum/buzz trouble that is a result of ground currents flow through signal ground (cable shield etc.) especially if you connect two class I components. Isolation safety transformers have low capacitance between primary and secondary so even capacitive currents are reduced to minimum. These transformers help during sensitive measurements or in a real audio setup.

This is my 250VA safety isolation transformer, 230V/230V, that I use mostly during measurements. See there is no protective earth pin at the outlet. This breaks the possible loop.

I can see these very basic issues are generally not well understood, as I can see so many posts dealing with audible hum/buzz after the components are interconnected.

 

[Wes]

If you have extraneous noise - from outside the circuit the isolation transformer is on - then you may benefit from one.

You can find a quality Topaz unit used. They used to be ~~ $600 but I think audiophools have driven up the pricing.

I may have some notes I collected (from people who ought to know) - if anyone wants me to post them, LMK.

 

[GUTB]

I got a small 500VA balanced isolation transformer from AliExpress: https://aliexpi.com/19Xn

Used with my DAC, phono, preamp and CD transport. I found that it provided a noticeable boost to sound quality.