Discussion of AC mains isolation transformers

[rickca]

Thanks, Alex. I ordered two of them, and they are indeed nicely built.

@Jud those things are just empty cases, right? Are you building the power strips yourself?

[Jud]

@Jud those things are just empty cases, right? Are you building the power strips yourself?

 

You can get the cases separately if you want to build your own, but these are fully built power strips. No DIY beyond finding IEC cords to plug into them.

[rickca]

Thanks, Jud. I see if you scroll down they do offer 4-8 outlet finished product. The long 8 outlet power bars at the top of the page are unpopulated cases, that's what confused me.

[jabbr]

 

The differences in AC cables could well be the interaction of the cable and the effects of crud coming back from the transformer either as a reflection of RF, low end harmonics, diode pulses and on.

 

Louis Motek of Lossless Audio in this article explains that their (and would assume everyone else's) AC power cable consists of a T network of resistance and in parallel, capacitance, not just in one value but more or less an infinite number of these networks in the cable. As RF frequencies move through the cable, they are affected by the RC networks and are attenuated to a degree depending on the geometry of the cable and clearly the marketing spin to add some spice.

 

.

 

I have a hard time understanding how such relatively low resistances and capacitances would have a significant effect on the ability of the power supply to filter everything but D.C. out -- flip side: shouldn't a properly designed power supply obviate any effect between reasonably well constructed AC cords?

[Superdad]

... shouldn't a properly designed power supply obviate any effect between reasonably well constructed AC cords?

 

Well we think that an RC snubber on a transformer secondary does, by reducing trans ringing back to the wall, reduced the impact of AC cord variations.

 

And the choke filter in our JS-2, by conducting over virtually the entire AC wave cycle (and in combination with Schottky diodes) GREATLY reduces harmonics going back to the wall. So I personally find AC cords have almost no impact on SQ for devices powered from the JS-2.

 

But look at a typical power amplifier: Non-regulated PS and big diodes kicking harmonics back to the wall. No wonder AC cords interact especially strongly with power amps.

 

A regulated, choke-filtered PS for a big power amp will be bigger than the amp itself (though to be fair, most of the real estate in a power amp is already taken up by the power supply.

 

Here is one shot of the interior of the 730W (4 ohms) Hovland Stratos monoblock. Half this 90-pound amp is the power supply (the quasi-C-core trans is suspended in a yoke under the center-front aluminum plate).

 

[Superdad]

Pizza, thick or thin?

 

As long as it's not square in a pan! And no fork and knife please.

[One and a half]

The other transformer manufacturer that used to , maybe still does, don't know, supply balanced transformers to Equitech is Electronetics in Everett, WA.

 

They probably have a standard range of transformers to choose from but have elected not to show them on the website.

[jabbr]

Well we think that an RC snubber on a transformer secondary does, by reducing trans ringing back to the wall, reduced the impact of AC cord variations.

 

And the choke filter in our JS-2, by conducting over virtually the entire AC wave cycle (and in combination with Schottky diodes) GREATLY reduces harmonics going back to the wall. So I personally find AC cords have almost no impact on SQ for devices powered from the JS-2.

 

But look at a typical power amplifier: Non-regulated PS and big diodes kicking harmonics back to the wall. No wonder AC cords interact especially strongly with power amps.

 

A regulated, choke-filtered PS for a big power amp will be bigger than the amp itself (though to be fair, most of the real estate in a power amp is already taken up by the power supply.

 

Here is one shot of the interior of the 730W (4 ohms) Hovland Stratos monoblock. Half this 90-pound amp is the power supply (the quasi-C-core trans is suspended in a yoke under the center-front aluminum plate).

 

[ATTACH=CONFIG]30506[/ATTACH]

 

Ok, choke filter is a great thing. Limits inrush current for big caps on turn on.

 

You need to be careful with RC snubs if you want to limit leakage current. An article that I posted a little while ago discusses this.

 

Amps (usually) don't need really tight regulation -- choke input filters have to handle current but with Class A designs, the H value can be lower without creating instability. Large caps, and yes high & broad cap bandwidth are important. Indeed cap multipliers can be considered to get really high effective values. In this setting it's hard for me to understand how a good AC cable can affect sound, particularly of *that* component. But again, good transformers, chokes and large caps are what make well designed amps heavy -- pay by the pound

[fob69]

Hi,

 

About separated AC lines : is there really a benefit ? I did a test and a CPL network connect easyly goes from one line to an other over the main electrical switch board.

Are they the some efficient board equipments for HF isolation between lines ?

 

Thank you,

 

Bernard

 

 

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Tplink optical bridge/etalon streamer/audiogd nfb29/linn klout/athom sirrocco + athom rafale v38 hypex

[asdf1000]

My recommendation is to use a simple power strip with NO filtering or surge suppression, the Topaz does it much better than what will come in almost any power strip. I plug EVERYTHING into thepower strip. This dramatically cuts down on the impedance between boxes, significantly lowering noise generated by leakage loops.

 

John S.

 

Hi John, just a quick clarification/question on an earlier recommendation of yours.

 

If you have a power strip which has no filtering between the outlets but does have a circuit breaker and on/off switch at the inlet, is this inlet protection of the power strip going to contribute to increasing the impedance between the outlets/boxes on this one power strip?

 

And thus contribute to increased noise generated by leakage currents?

 

Assume this powerstrip is plugged into a high isolation transformer like the Topaz (an Elgar in my case).

 

Does your Tripp Lite power strip have a circuit break at it's inlet? And on/off switch?

 

Many thanks for your help again

[YashN]

Well we think that an RC snubber on a transformer secondary does, by reducing trans ringing back to the wall, reduced the impact of AC cord variations.

But look at a typical power amplifier: Non-regulated PS and big diodes kicking harmonics back to the wall. No wonder AC cords interact especially strongly with power amps.

 

And there's no Transformer snubber for most of these amps either!

 

I've looked over around 10 audio pieces of equipment like that, and none except perhaps a Pioneer DVD player attempt any ring damping right after the transformer.

 

So, one thing I want to do when I rebuild my project studio is to re-do all the power supplies.

I will most probably include a snubber for my SET Tube amp as well.

[YashN]

Well we think that an RC snubber on a transformer secondary does, by reducing trans ringing back to the wall, reduced the impact of AC cord variations.

 

Now that's interesting because I could probably retrofit a snubber into my SS amp and then do an A/B between the old power cord and my DIY one and hear if there's still a difference.

 

Problem: I don't know where the original power cord is

[sandyk]

Now that's interesting because I could probably retrofit a snubber into my SS amp and then do an A/B between the old power cord and my DIY one and hear if there's still a difference.

 

Problem: I don't know where the original power cord is

 

You could try John's typical 2.2nF and series 330 ohm resistor across the secondary winding and see if you can hear a difference.

[YashN]

You could try John's typical 2.2nF and series 330 ohm resistor across the secondary winding and see if you can hear a difference.

That's precisely what I meant to do, but in addition, compare the original power cord with my DIY one after the fact to hear if there's any immunity with respect to that.

[jabbr]

Here are a couple of papers:

http://archive.eetasia.com/www.eetasia.com/ARTICLES/2004NOV/B/2004NOV16_POW_TA.pdf?SOURCES=DOWNLOAD

 

 

http://coefs.uncc.edu/mnoras/files/2013/03/Transformer-and-Inductor-Design-Handbook_Chapter_17.pdf

 

In particular, in the first the value of the Y capacitor correlates with reduction of EMI but also leakage current. Of course this is for a different design with a secondary transformer, nonetheless same principles apply.

[ted_b]

Silly question, but under the heading of Barrows' "everything matters" does it truly matter on a , say 12 outlet clean power strip, where you put your most prized sources (i.e near the cord or opposite end). This is silly but I've heard weirder.

[Cornan]

Anyone on this thread who knows If this £290.- 1500 VA balanced power supply would be something good or not instead of a filtered power strip?

 

http://www.airlinktransformers.com/balanced_power_supply/standard_balanced_power_supplies/BPS1502/

 

 

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[One and a half]

Anyone on this thread who knows If this £290.- 1500 VA balanced power supply would be something good or not instead of a filtered power strip?

 

Standard Balanced Power Supplies: BPS1502: 1500VA 230v to 230v CTE Two schuko sockets

 

 

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It's an isolation transformer , not a balanced transformer.

[Superdad]

Anyone on this thread who knows If this £290.- 1500 VA balanced power supply would be something good or not instead of a filtered power strip?

 

It also has an inrush current thermistor on it. I don't know if those are a problem or not.

[jabbr]

It also has an inrush current thermistor on it. I don't know if those are a problem or not.

 

Nelson Pass uses those in his amps FWIW -- I'd assume he doesn't think a problem.

[Cornan]

It's an isolation transformer , not a balanced transformer.

Thanks One and a half! I was a bit confused as well. They call it a balanced power supply and it is under the Audio/Balaned Power menu...but on the specs they are also mensioning safety Isolation transformer. I am all new to this Isolation transformer thing and do not even know the difference between it andva balanced dito. I can just tell that it looks like a good build and fairly priced. Any opinion if it is a good choise or not?

 

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[Cornan]

It also has an inrush current thermistor on it. I don't know if those are a problem or not.

Thanks Alex! Hmmm...that would be a current limiter right? Why could that be a problem?

 

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[ElviaCaprice]

I can just tell that it looks like a good build and fairly priced. Any opinion if it is a good choise or not?

 

 

Where are the measurements? JS already said if it doesn't provide good measurements it's probably not a good solution.

[ericuco]

Got my Kill-a-Watt meter today and tested one of my mono block (nCore Class D) amps.

 

With limited testing, the amp was at 16-17 watts at normal listening volume & 20-21 watts at a volume somewhat higher, too loud for normal listening but no means painful. Besides my ESL's don't get too loud.

 

So I am thinking a Topaz 250VA (91092-32T) or 500VA (91095-32T) would work.

 

 

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[guzmanatm]

Here is a nice 500VA unit for $120 which has a cord and a duplex outlet. Nice size for front end gear.

Topaz Line Noise Suppressing Ultra Isolator 91095-12 | eBay

...

Forgive me if this is a silly question . . . Let's say I have a Topaz unit with duplex outlet, and I only need to power two devices-- an LPS-1 feeding a bus-powered DAC/amp, and a laptop. Would it be better to connect both devices directly to the two outlets on the Topaz, or connect a power strip to the Topaz and plug both devices in to the power strip? I'm asking because I've read posts stressing the importance of connecting all devices to one strip. I'm not sure whether connecting both devices directly to the Topaz would defeat some of the purpose of using the isolation transformer to begin with.