[SoundStage!]Planet Hi-Fi
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October 2002

Powerware 9125-1500 Uninterruptible Power Supply

While searching for a replacement battery for a small uninterruptible power supply (UPS) that supports my personal computer, I discovered a larger, more advanced unit named the 9125-1500 from a company called Powerware. This particular unit was also listed as a UPS, but more specifically an "online double conversion UPS." This unit was designed to address the nine most common power problems that plague the office environment and protect your system from their deleterious effects: power failure, sags, and surges; under- and over- voltage conditions; electrical line noise; frequency variation; switching transients; harmonic distortion. According to the Powerware website, the 9125 series UPSes "provide protection from noise, frequency variation, harmonic distortion, and switching transients that other technologies fail to address." For a detailed explanation of each of the problems I've listed, visit the Powerware website at powerware.com.

After learning more about what the statement above means exactly, I realized that the Powerware 9125 series units, in theory, should perform very similarly to the PS Audio Power Plants. Both products take AC from the wall, convert it into DC, store some in a reservoir, and convert it back into AC to power the equipment, hence the term online double conversion. Although in principle, they are similar products, there are substantial differences between the two products in both internal and external design.

In my mind, there are three significant differences that need to be highlighted:

  1. The Powerware 9125 stores DC power within a large rechargeable and replaceable battery located inside the unit (accessible from behind the removable front panel), and is therefore, capable of providing battery-only power for an extended period of time. The PS Audio Power Plant stores DC within large electrolytic capacitors and cannot provide battery-only power for extended periods of time.

  2. The Powerware 9125 uses two internal conventional fans for cooling. These two fans produce significant amounts of audible noise. The PS Audio Power Plant uses metal heatsinks attached to the side of the large chassis along with a small fan to dissipate internally generated heat, allowing it to run fairly silent.

  3. The mid-sized Powerware 9125-1000 is rated to deliver 700 watts and costs $900 USD (street price around $560.) The similarly rated PS Audio P-600 (600 watts, 720 watts max current draw) costs $2400.

While the PS Audio Power Plant also lists numerous other beneficial features such as user selectable Multi-Wave patterns and output frequencies, and higher-quality AC Power Port receptacles, I have not auditioned a Power Plant in my own system. Therefore, I cannot list them as significant differences, as I do not know whether Multi-wave and Power Ports make significant improvement to the sound.

Do I need it? Who reads manuals nowadays?

After pulling out the manuals and locating the technical specifications of my audio and video components, I added up the stated power requirements and determined the best model for my current and future needs would be the Powerware 9125-1500. It’s a 1500V/1050W model with a retail price of $1200. The entire 9125 series is offered with either off-white or black casings. I chose black to match the rest of my components and found one in stock at TechDepot.com for $743 plus $25 shipping. I felt pretty secure purchasing from this website as they are affiliated with Office Depot. They also offer a 30-day money-back guarantee (minus the cost of the original shipping AND return shipping).

The 50-pound unit arrived promptly, and I immediately skimmed the user manual and hooked up the 9125-1500 in order to break it in for a couple of days before I critically listened to its performance. The unit is fairly straight forward to set up, but I recommend keeping the manual handy, as the front-panel indicators are not intuitive. In addition, getting into the menu to change various settings, such as turning off the audible alarm, can be frustrating as it requires overly complicated combinations of buttons and pauses/waiting time. I’m not surprised, as this unit is geared for IT engineers, not anxious audiophiles. But most folks should have no problem reading the front-panel LEDs that indicate the present % of voltage draw and the system status (drawing AC power from the wall, battery power only, power on/off/standby.)

After locking in my desired settings, I plugged in my entire system using all six heavy-duty AC receptacles on the rear of the unit (with the help of an additional six outlets provided by my Chang Lightspeed power-line conditioner plugged into one of the six receptacles.) After managing and securing the jungle of power cords leaking out from behind the unit, I powered up the 9125-1500 to begin charging the internal battery. Powerware recommends keeping the unit powered and running for at least 18 hours when charging the batteries for the first time. Once the batteries are fully charged, they rarely fall below their stated max capacity during normal operation because as DC from the batteries is converted to AC and consumed by the components, the unit simultaneously takes raw AC from the wall, converts it to DC, and taps off the battery’s DC supply until it is full again.

As I had stated earlier, this unit is fairly loud. Two small motor-driven fans located behind the faceplate take in cool air, pass it over and around the unit’s internal parts, and eject the warm air back out through two air ducts located on the rear panel. This safety system successfully keeps the unit operating at or close to room temperature. And while this is an effective and cost-efficient cooling method, the down side is noticeably high levels of noise -- enough that the increased in-room noise floor distracted me from concentrating on a DVD under normal listening conditions and volume.


At first, I was tempted to call it quits and send the unit back to the retailer. But my initial observations during the break-in period were positive. I heard more natural and distinct dialogue through DVDs and larger more spacious overall sound when listening to music. The picture on my 43" Hitachi RPTV even looked a bit brighter, with increased color saturation and less noise throughout the viewing area. So I decided to try to reduce the level of noise emanating from the fans by placing the unit upright with the supplied footers/couplers. No good. I tried stuffing foam between the fans and the faceplate. Not enough. I even tried building a sound absorbing housing around the entire unit using cardboard and open-cell foam. Good, but again, not enough. During the quieter hours of NYC (weekdays after midnight), I could still hear the fan motors whirring away. It was beginning to drive me crazy.

Finally, I came up with an idea that was certain to significantly reduce or perhaps even eliminate the high levels of excess noise that I heard from the unit. First, I printed out instructions for building a DIY power cord off the AudioTweaks.com website. This particular cord is called the VenHaus power cord. The parts are easy to locate, and the cord requires little effort to assemble. Cost is minimal, and best of all, it sounds surprisingly good considering mine is 16 feet in length. (I substituted the Marinco 3201 IEC connector in the original design with a Marinco 5269 straight-blade receptacle, making my version essentially a high-end extension cord.) Second, I drilled a small hole in the wall separating my living room (listening area) and my bedroom. Third, I moved the Powerware 9125-1500 into the bedroom and positioned it close to the recently drilled hole. Lastly, I connected my Chang Lightspeed power-line conditioner to the female side of the VenHaus extension cord and fed the three-prong (male) side of the cord through the hole into the bedroom, slipping it into one of the receptacles on the rear of the 9125-1500. I then powered up the 9125-1500, waited for the automatic system diagnosis to finish, and walked back into the living room.

Silence…beautiful silence. The solution worked! How could it not? And now I was ready to get down to some serious listening.

Somebody’s awfully quiet today. What’s up?

The Powerware 9125-1500 is no take-it-on-faith tweak. I did not have to convince myself of the beneficial effects of the UPS, as I occasionally do when auditioning questionable accessories or even some highly touted (or should I say, highly marketed) cables. Right out of the gate, I heard a significant reduction in my audio system's noise floor, which I attributed to the UPS’s ability to remove power-line noise, interference and grunge that were apparently riding along the AC line into the delicate and sensitive circuits of my components. This quieter background allowed me to hear more information, more focused music, more clearly defined notes, and to my ears more natural-sounding music. High-frequency hardness and glare and slight raggedy outlines around brass and strings during loud passages were attenuated to a degree that I did not know was possible with my system. After incorporating high-end power cords, a line conditioner, and some parallel shunt filters, I was under the impression that I was capturing or rejecting most of the backdoor EMI/RFI that was trying to get into my system. But the UPS provided incremental sound benefit to my existing power-line solution.

Bass expansion was another surprising discovery. While listening to Fiona Apple Tidal [Sony OK67439], I felt the system’s improved low-energy delivery. Electric bass was neither quicker nor tighter, but it certainly was much more powerful, forceful, and voluminous. During some passages, with the UPS in the mix, I could feel the long soundwaves exciting the elements within my listening room, causing the room and many things inside to resonate when they did not before.

Add more bass, reduce some of the perceived midrange and high-frequency forwardness (through power-line noise reduction), and we’ve succeeded in altering the overall balance of the system’s sound. Lou Donaldson's Lou Takes Off [Classic Records DAD 1026] sounded smoother, more fluid, but more coherent without the blending of one note or instrument into another. The UPS did not soften the sound of Donald Bird’s trumpet on "Sputnik" by taking the treble down a notch. I believe the UPS successfully revealed more of the data that resided on the software, more of Bird’s musical essence. It acted as a cleaner that targeted dirt and mold caked up in and around the pits and crevices of the music landscape -- well, sort of. Instead of filling in the depressions with more dirt to even out the surface, the UPS removed excess grit both down at the base of the note and around the top and sides of its peak. Combine this less aggressive but more realistic upper end with a more robust bottom end and I’m left with a more relaxed but no less rhythmic or dynamic presentation.

Unlike the dynamics, the soundstage and imaging capabilities (or potential) did change. Both improved slightly, and less than I had anticipated. From my listening position, the musical picture deepened noticeably, with the space between instruments and vocalists ever distancing. But the width remained pretty much on par with the system sans UPS. With the unit’s impressive reduction in the noise floor, I was expecting to find a corresponding explosion in both soundstage width and depth. It didn’t happen in my listening room. Again, the depth improved, but generally, the sides remained slightly outside the edges of my loudspeakers, occasionally creeping farther out when playing tracks with particularly ambient qualities. "On Green Dolphin Street" from Ernie Watts Classic Moods [JVC JVCXR-0054-2] quickly comes to mind.

It works on TVs too!

Along with vastly improved bass, increased midrange/high-frequency resolution, and a significant reduction in edginess (and at times, sibilance), the last memorable improvement wrought by the UPS was associated with my RPTV. I noticed a brighter, more colorful picture with less prominent video noise. As a self-proclaimed non-videophile (although I am beginning to catch this bug as well), I will keep this part of the discussion brief.

While watching DVDs on my Hitachi 43" RPTV through my Panasonic DVD-H1000 DVD player, I noticed a slight reduction in snow throughout the screen acreage that helped finely tune the picture’s clarity. This also helped firm up the images, lending a sort of stability to scenery. Before, if I scrutinized the picture from a few inches off the Plexiglas screen protector, I could see some image shake and instability during scenes where objects remained stationary for a few seconds or more. With the UPS in place, there was still that sense of a vibrating picture up close, but to a lesser degree. More obvious was the UPS’s ability to increase both brightness and color saturation. This result prompted me to enter the television’s menu and bring down the brightness and color settings a notch or two. For those who had upgraded their video cable from the freebie that comes in the box to a decent after-market cable such as Monster Cable M500V, the improvements rendered by the new cable would be quite similar to the improvements I had seen when powering my RPTV from the 9125-1500. They were impressive.

Unplug me

Fortunately, and unlike many competing UPSs, the Powerware 9125 series allows the user to defeat the audible alarm that sounds when the unit detects a break in the incoming AC stream. For computer network technicians, this is a valuable feature in that it could alert the staff that power has ceased and their critical equipment is now being powered exclusively through the UPS’s internal lead-acid batteries. But the unit does not allow the user to easily switch the power sourcing from online double conversion (wall AC to battery DC to component AC) to online single conversion (battery DC to component AC.) In order to test how the unit sounds in battery-only or online-single-conversion modes, you have to place the unit into standby mode and then remove the three-prong plug from the wall. This action will automatically trigger the unit to move into battery-only mode. LEDs on the front panel confirm the unit is running on batteries only, and indicate the percent charge remaining in the cells.

Evaluating the sound while running the UPS in battery-only mode was exciting but somewhat disappointing. Overall, music sounded even more liquid and lush. I really enjoyed the gracefulness of the sound through the UPS, the slight removal of the electronic character that most modern recorded CDs contain in their sound. The complete isolation of the system’s power source from the rest of the power grid/network allowed the noise floor to practically diminish into nothing. This was a noticeable improvement over the already impressive results via double-conversion mode. But, and this was my only concern regarding battery-only mode, the bass appeared to loosen up a bit. While double-conversion mode maintained the low-frequency status quo, single-conversion mode seemed to let the bass get away. It sounded just as full, but not quite as fast, taut or defined. Pitch appeared to suffer somewhat as well.

It took me a long time to zero in on these effects, as they are subtle and not nearly as obvious as the benefits provided by the UPS. My buddy Marc seems to think there may be internal restrictions placed on the amount of power that can be drawn from the batteries at any given time while running in battery-only mode. It could be a precaution or a limitation designed to maximize the value of the fixed amount of power stored in the batteries. Remember, this unit was originally designed to provide back-up power for computer networks. A key priority for the unit’s design was probably maximizing battery run times. Marc thinks Powerware has built logic into the unit that senses when the unit is receiving constant AC from the wall. When this happens, it proceeds to lift the "floodgates," thereby allowing the components to "drink from the well as needed." He may be right. Unfortunately, I was unable to confirm this with Powerware.

Another issue is the question of battery run time. In battery-only mode, with my audio only system playing music at normal listening volumes, I received approximately 30 minutes of playing time before the LEDs went out and the fun stopped. Powerware does offer additional outboard batteries called Extended Battery Modules (EBM) that can be connected to any 9125 series UPS for increased run time (up to four additional EBMs.) Physically, the EBM is identical to the 9125 series UPS, except for the LED front panel. And according to the Powerware literature, when attached via its umbilical cord, a single EBM should quadruple the system’s run time and two additional EBMs should provide 7x the run time of the UPS’s internal batteries alone. They list for $439 each, with a street price around $275.

Take this hammer; we’re going to make a big sacrifice

What do I think? I think it’s obvious. If you can make the sacrifice, you will be rewarded. The Powerware 9125-1500 UPS is a fantastic product and I recommend giving it a test drive in your own system as long as you can defeat the heavy fan noise. While I was able to get around this problem by relocating the unit to another room, some audiophiles may not have this luxury or the requisite patience. Be creative -- it’s worth it. I’m thinking of purchasing an enclosed rack with air-tight doors and seals normally used to prevent dust and contaminants from getting into sensitive rack-mounted equipment.

When used in online-double-conversion mode, I discovered it to be a win-win proposition. I cannot universally recommend battery-only mode as I have reservations regarding the effects on bass quality. But everybody’s situation is different, and I’m certain each user will receive varying results -- even some drastically different from mine. As for the Extended Battery Modules, they depend on your results using battery-only mode. If it works well for you, consider adding an EBM or two. As for me, I’m going to keep trying different configurations, but mostly, I'll be sitting back and enjoying the silence.

...Greg Kong

Powerware 9125-1500 Uninterruptible Power Supply
$1199 USD.
Warranty: Two-year limited.

Invensys plc
Carlisle Place
United Kingdom
Phone: +44 207 834 3848
Fax: +44 207 834 3879

Website: www.powerware.com


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