Post Summary - Longer than necessary but (1) Zalman ZM850-HP is also extremely silent and nearly perfect (4-pin 12V cable shorter than other PSU's and does not allow optimal cable management in certain circumstances) & (2) justifying PSU overkill in the name of silence
Although I rarely post, my quest for quiet PC's has been ongoing for years and I share the enthusiasm of this site. I say this b/c the satisfaction with my recent purchase (installed this week) of the Zalman ZM850-HP was going to result in a general post in the power supply forum about this PSU perhaps being the new silent king (& suggesting that SPCR review it, especially since it's inclusion in commercial PC spec'd by SPCR, the Extreme Gamer 22DBA). Well, no need to say that now given this review.
(1) While I cannot attest to the 1k version, the ZM850-HP is silent. As a frame of reference, I have what I would refer to as a silent Seasonic S12 (500w) in an HTPC. I was hoping to accomplish similar silence with a higher output PSU. The ZM850 is just as quiet as the Seasonic. In short, when you turn them on, even outside of a case, they are inaudible.
And, certainly, not all high output PSU's can say the same despite marketing representations. Having seen the Cooler Master 850w on sale for $70 AR and reading numerous reviews indicating that you could not hear it, I decided to purchase the unit. After going through 3 of them due to their noise level (quality control is poor, customer service was poor (~2 months to do 2 cross-shipped RMA's, and CSR's (or should I say CSR - they seemingly have 1) misrepresented the status of the RMA's) and the noise level on none of the units was anything near 16db as represented by Cooler Master....in fact, I could hear the fan 10-15ft away and it was the loudest part of a PC with 6 speed controlled fans and 2 x 8800GTS 512mb), it was time to end the frustration and start anew. A weekend of research led me to two units - Silverstone ST85F (completely modular) and the Zalman ZM-850-HP (partially modular....I started researching the 850 after I saw its inclusion in the 22DBA). While most reviews indicated that the ST85F was extremely quiet (& could not be heard when powered up), I was concerned by a few reviews that found it quiet but certainly audible. The few reviews of the ZM850-HP all commented on how silent it was (& a quick PM to someone who posted on this forum who purchased the zm850 also confirmed its silence). Another factor was that the fan rpm increased at an earlier load output than the Zalman and, iirc, at a much steeper incline (such that it's max rpm kicks in much sooner than Zalmans). Despite the price (ST85F was about $50-60 less AR) differential, and the steep price of the Zalman, I went for the Zalman. I couldn't be more pleased. Well, actually, 1 issue - the 4-pin ATX 12V cable is not long enough to permit optimal cable management in instances where the PSU is at the bottom of the case and the 12V MB header is at the top of the MB. With the prior PSU's (an ultra V-500 & the Cooler Master), I could snake this cable behind the motherboard plate and over the top to the input....the cable on the 850 is not long enough so for now it spans over the video card, cpu hs/fan, etc. although I've ordered an extension cable to resolve this.
(2) When deciding to replace the Cooler Master 850, I considered purchasing a PSU with lesser output in order to increase the likeliness that I would once again find a PSU that provided blissful silence & it would save me some $. After all, SPCR's top-rated silent PSU's were 650 or less. And, I know my setup does not require an 850w PSU (Athlon x2 89w version at 2.6ghz, 4gb DDR2, 2 x 8800GTS 512mb, 1 7200RPM HD (the 2 platter WD640), 2 optical drives, 6 fans & a flash card reader). In fact, a power calculator indicated as moderately reliable by others seems to suggest the draw would be ~400w. Alas, I felt it proper to consider the rpm of the fan of a psu that was drawing 400w +/- 100w (ie. I'm not sure how accurate the power calculator was & didn't want to break out the math so I used that as a margin of error) and not the rpm at idle or less. As indicated by SPCR, most of the top-rated PSU's are far from silent when drawing a significant load in the 400-500w range and none of them were at 500w or above (see http://www.silentpcreview.com/article834-page5.html
). After such consideration, I felt that it was only with a 750 or higher PSU that I could "safely" (ie., increased probability that I would not pay 15% restocking fee to return my "silent" PSU b/cit's loud when playing games) have a silent PSU. In short, I wanted a PSU that could put out the wattage drawn by my setup without needing to increase its fan speed (I also took into consideration that the maximum efficiency of many PSU's that I researched were at the 35-60% load range so you get that as an added benefit - however negligible). That being said, I did come across others who share this theory although I'm not sure it's been widely adopted b/c of the simple fact that before the Zalman line, most high output PSU's just weren't quiet enough for such a consideration. I think the Zalman ZM850 & 1k certainly make such consideration appropriate.