PowerPlant vs. Double Conversion UPS


I’m curious what’s the difference between a power plant and a double conversion UPS?
Double conversion UPS do the same thing as the power plant, converting AC to DC and back to AC, for quite a bit cheaper than the power plant.

Double conversion UPS such as these:

Tripp Lite SmartOnline 120V 1kVA 900W Double-Conversion UPS

Tripp Lite 1000VA Smart Online UPS

They can be loud, but I have one here modified to use a large low speed fan that doesn’t make any noticeable noise at listening position.

Thanks ahead for the insight

(Speaking for myself, not for PS Audio)

Most UPSs don’t make anything near a sine wave, the cheapest make square waves, the slightly better make few steps to approximate a sine and most of the ones that claim something like “True Sine”, etc. are just a better approximation, but still with many small but sharp edges, those edges are a lot of noise, if you filter the edges out you loose the ability to respond quickly to changes in current draw. Most audiophile power supplies take huge gulps near the peaks of the input power so they are very sensitive to the instantaneous current available.

(See https://forum.psaudio.com/t/power-cord-for-dsd-sr/5445/21 or https://forum.psaudio.com/t/power-cord-for-dsd-sr/5445/30 )

There are some audiophile online USBs, I have one and it isn’t bad for low current devices and I never hear it’s fan, but for amps the efficiency of double conversion is too low and the lack of instantaneous current delivery would be a real problem.

Note that the Tripp Lite 1000VA Smart Online UPS has different outputs: “Pure Sine Wave” in “Battery Mode” and “Sine Wave” in “AC Mode” And it’s output regulation is +/-2% in “Line Mode” or “Battery mode” and +/-10% (!) in “Economy Line Mode”. What they mean by Pure Sine Wave and Sine Wave isn’t clear, but 2% distortion leaves a lot of room for high frequency edges.


I have both … a P20 regenerator as well a 3Kva double conversion “pure sine” UPS.
The UPS can be set in “bypass mode” (or where it basically feeds from the grid; with a 10 or 20ms changeover should the mains fail); OR in double conversion (online) mode, thus feeding my P20 via batteries 24/7.
So here’s the thing: P20’s own “power improvement meter” reports less of an improvement when fed in double conversion (battery) mode.
So there is no doubt in my mind that a decent double conversion UPS improves the power quality to some extent but nowhere near the level of control and improvement of the P20.

Ted’s right. Moreover they use a class D output stage and cannot handle power factors of less than 1 without even more distortion. If you try and power anything with a PF of 0.7 (common for amps and preamps) you’ll get a nasty divot out of the peak of the sine wave under any heavy current use. These are fine as intended, as battery backups, but not to replace a real regenerator like a Power Plant.


Thanks for the insights Ted, and Paul.

I was afraid of this… my wallet ran away, let me chase it down, once I catch it I’ll order probably a P12.

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I’ve been told by someone with a deep background specializing in clean power optimization for pro audio that the Eaton 9PX, which he describes as a “full on line inverter system with regulation” to provide less sine wave distortion and 1/3 the high frequency noise of the ps audio regenerators.

I’m not trying to stir things up – just trying to come to an understanding of the Power Plant – UPS comparison. (I own a P12 btw)

Can you prove @willco that statement with some spec’s or measurements, it is a rather interesting point…! I had the same thoughts as @falling_leaves before I stuck my credit card in the machine at the dealer… I actually was looking at that Eaton 9PX…! Believe it or not…!

I’m hoping to get some apples to apples specs between the latest PS Audio Power Plants and the Eaton 9PX.

PS Audio provides much more complete and meaningful specs to the public than does Eaton. I’ve written Eaton for more detail – for instance what is their output impedance-- which seems like an important spec for an inverter?

My source who uses the 9PX in his power optimization work says he concluded (with 18 years looking at everything on the market) that the Eaton is the best out there for audio. I’m not sure if he’s compared it yet to the recent Power Plants. I’ll ask him.

You said your friend is in pro audio, correct? To me that indicates a difference in priorities - specifically, if you’re recording or mastering a track, losing power is potentially catastrophic. If you’re listening to music at home for fun, losing power is an inconvenience generally.

Regarding his comment on sine wave distortion, unless I’m reading things wrong it seems like the Eaton is nothing special in this measurement? This is from their manual:

Output voltage distortion THDV% in normal mode:
a. Linear load: <2% linear load
b. Non-linear load: <5%

Here’s our measurements for output distortion:

Output Distortion (Resistive Load) <0.5% // 0.1% typical
Output Distortion (Reactive Load) <0.5% // 0.1% typical

At a glance I didn’t see any specs listed on the Eaton page regarding high frequency noise, so it’s tough to make a comparison there.

Not to say your friend’s experience is wrong or incorrect in anyway. If he has done his homework and he prefers using the Eaton 9PX, you won’t find me arguing with him on it. Personally, though, I see more downsides to a UPS than upsides.

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Good points. He is from in the pro world, but also high end home theater world.

He did say the Eaton’s distortion is less than 1%. I don’t know if that’s the same THD spec as you site or not? It’s hard to get parallel specs (and much of anything direct from Eaton’s info.)

He also mentioned common and normal mode noise being very low (in mV) from the Eaton. Does PSA measure this? Thanks

For home theater, too, a UPS makes sense - projector bulbs do not like suddenly losing power. It can impact their overall lifespan.

As you said, it’s tough finding apples to apples specs. I checked with one of our engineers and we don’t measure common and normal mode noise in our Power Plants.

Just reading this for the first time. Having interesting discussion (more of a fight) on another platform about just get a UPS.

Welcome @brian.fitterman !

UPS is a different animal. Sure it will keep the power on but the increase in impedance is worse than direct to the wall.

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Hi, I read a lot about using a UPS for a stereo and signed up to this forum in order to join in the interesting topic.

A UPS should be avoided on any hi-fi equipment at all costs. The impedance/voltage drop of UPS’s is really bad for high peak current or high inrush current. A surge protector does however make sense probably.

Luckily, I live in Denmark. We have some of the most stable AC mains in the world. There is about 20 minutes of power outage on average per year. That does not mean every year necessarily, because I have merely experienced a few 1-hour power outages during my whole life.

You can also read my more detailed reply here:

Thanks for this wonderful forum.