Pass Labs X600.5 Monoblock Power Amplifiers
Figure 1. The X600.5 meter measures current draw. Some people wish the meter light could be turned off.
I like it.
The Parasound Halo JC 1 monoblock power amplifiers in my two channel reference quality audio system were recently replaced with Pass Laboratories X600.5 monoblocks. The X600.5's higher power reserves, faster transient response and lower noise characteristics facilitated a more realistic stereophonic sound stage with heavier images, greater delineation of space between images, greater image stability, greater detail, greater clarity and spectacular bass response. The X600.5s are nearly 2.5 times the cost of the JC 1s. In terms of enhanced stereophonic performance, I do not think that I paid a diminishing returns penalty with this purchase. In terms of listening pleasure, I think the X600.5s are the best audio investment I have made to date.
A few words regarding the design philosophy behind the X600.5 provide some insight. The following is taken from the X600.5 manual:
"The X.5 Series amplifiers have the tremendous dynamic range (>140 dB) to do justice to the high-resolution digital recordings of the 21st Century and the elegance to retrieve the micro dynamics offered by the most sensitive loudspeakers. The simple but powerful circuitry moves easily from total silence to explosive transient and back to silence without a trace and without information loss. Very unlike conventional high power amplifiers, they provide this level of power with a subtlety befitting some of the better tube amplifiers. This performance is consistence across the audio spectrum and the amplifiers are unconditionally stable into all speaker loads."
"Listening to my amplifiers is like listening to tubes, but without the hassle." - Nelson Pass
The Luminous Meters
My meter needles remain stationary unless heavy bass content is playing. For example, on Whitney Houston's "My Love Is Your Love" ("Greatest Hits" CD) the meter needles moved back and forth about one millimeter. The movements were in synch with the song's Reggae-ish bass beats.
The owner's manual does not specifically address break in requirements. It only mentions that the amps require an hour to fully warm up. The Pass Labs website states the following regarding break in:
"Most improvement comes in the first 24-36 hours, after which the amps will continue to improve as long as they are left on."
The dealer recommended playing music for five days straight before doing critical listening. Music was supplied by analog and digital media during listening sessions and by a tuner at other times.
Right out of the boxes, the X600.5's increase in overall clarity, detail and sound stage characteristics over the JC 1s was immediately obvious. I was not pleased with the initial bass performance, which seemed disjointed from the rest of the sonic presentation and which did not have anywhere near the JC 1's bass speed, bass clarity, bass detail and bass articulation. The X600.5s did produce more tactile sensation. It took four days of playback for the X600.5s to equal the JC 1's bass presentation. After eight days, the X600.5's bass performance exceeded that of the JC 1s. I have not heard any changes or improvements, in any performance aspect, since the eighth day.
Figure 2. Two big boxes showed up at my door exactly one week after placing the order.
The temperatures quoted in this section were taken after break in was completed (eight days on continuously, 145 hours of music play). The room temperature is maintained at 72 degrees F.
Figure 3. Temperature measurements were taken with a group of Accurite digital thermometers (made in
Red China (get over it), and purchased at Walmart for $5 each (get over that too!)).
Figure 4. I had just enough room, 3/8" on each side, to slide in the 19" wide X600.5's. I found out that
those aggressively sculpted heat sinks are big for good reason.
The X600.5s draw more idle current than the JC 1s, but run cooler than the JC 1s when idling and just a little hotter than the JC 1s when playing music. The X600.5s generate more heat, but dissipate that heat over a much larger case and much larger heat sinks. The JC 1s are biased into class A for the first 25 watts compared to the X600.5's first 80 watts. The X600.5's case encloses 3,895 cubic inches compared to the JC 1's 2,173.5 cubic inches (increase of 79%). In addition to larger size, the X600.5 case is much thicker and heavier, 132 pounds compared to 64 pounds for the JC 1. The current draws for the JC 1 and X600.5 are shown in table 1.
Figure 5. The X600.5s are installed in a Salamander Synergy Triple 30 audio credenza with an open back and
metal mesh doors and sides.
Figure 6. Quiet (29 dB) fans were installed above the X600.5s, but they are not required during normal
operation. I cannot hear the fans when music is playing and can barely hear them when no music is playing.
(Refer to figure 5 for component location references.) During idling and playback at reasonable levels (85-90 dB-C) the X600.5's heat sinks and the cases of the other components do not reach unsafe temperatures. The X600.5's heat sinks reach an average idle temperature of 117 degrees F. The XP-25 preamp above the left X600.5 reaches a case temperature of 104 degrees F. The XP-25 preamp power supply above the right X600.5 reaches a case temperature of 95 degrees F. The components in the middle, going from top to bottom, reach temperatures of 96, 96, 94, and 85 respectively.
After four hours of playback with material with moderate to heavy bass content, The X600.5's heat sinks reach an average idle temperature of 127 degrees F. The XP-25 preamp above the left X600.5 reaches a case temperature of 108 degrees F. The XP-25 preamp power supply above the right X600.5 reaches a case temperature of 98 degrees F. The components in the middle, going from top to bottom, reach temperatures of 99, 99, 90, and 89 respectively.
The temperature on the top of the equipment cabinet reached 75 degrees F during idling and 77 degrees F during music play. The X600.5s do not dump a lot of heat into my 3570 cubic foot living room (21'L x 17'W x 10'H). I did not find them to be the "space heaters" that others have complained about.
Turning on the fans while playing music lowered the amp heat sink temperatures by 5 degrees F and the case temperatures of the other components by 7 to 9 degrees F. I would only run the fans in situations where I needed to play music for many hours and days continuously, such as when breaking in a new component.
Figure 7. The fans are turned on and off with a radio frequency remote controlled outlet switch.
An infrared outlet switch would have provided the convenience of using my universal remote to turn the fans on and off, but I would have had to put the switch in a line of sight location rather than out of sight behind the cabinet.
Fan model and vendor: PQ Fan, HomeTheaterCooling.com.
Outlet switch model and vendor: Westek RFK306LC, Home Depot.
15 Amp White Triple Adapter: Leviton R52-00531-00W, Home Depot.
I usually can find something to complain about with regard to construction quality and/or aesthetics, but I'm stumped here. I could nitpick about my preference for black-faced components, but my amplification gear is behind black metal mesh doors...so the silver color is no big deal.
Figure 8. Initial power-up and function checkout.
Figure 9. Those handles really helped out with pulling the amps out of their boxes and with maneuvering the
amps into the equipment cabinet.
Figure 10. The obligatory peek under the hood.
As I noted in my XP-25 phono preamp review, the XP-25 is more affected by magnetic fields than my previous Xono phono preamp. Putting four large sheets of cold rolled steel under the XP-25's control module cabinet shelf and four smaller steel sheets under the left side of the control module's chassis (where the input circuitry is located) significantly reduced the hum to a faint level. Adding more steel sheets did not reduce the hum further. I thought I would have more hum issues with the more powerful X600.5, but I actually needed less shielding. I achieved the same level of hum reduction using only the four small sheets under the XP-25's input circuitry. Apparently, the X600.5s use a better shielded transformer.
Pass Labs X600.5 - One Year Follow Up
One year out I am still thrilled with my investment in the X600.5s, which were installed on 4/10/13. The amp's sound significantly improved during the first 8 days of use, then reached a performance plateau, then after a month of being on 24/7, there was a further increase in image weight and bass weight. No further improvements or changes were observed until vibration abatement was applied in October of 2013 and no improvements or changes were observed thereafter. The amps have been left on continuously since installation and have only been turned off for very brief periods of time when switching components or cables during equipment measurements or trials.
Pass Labs introduced a ".8" series of amps in January of 2014 that has higher class A output. In the case of the X600.8, it offers 100 watts of class A operation compared to the X600.5's 80 watts of class A operation. The X600.8 costs 18% more than the X600.5. Since I am still on a "honeymoon" with the X600.5s, it will be a while before I consider upgrading.
Those of you who are not Pass amplifier owners may want to skip this section since "meter movement" is somewhat of an inside joke.:twisted: The meter movement of a Pass Labs power amplifier indicates the state of bias current at a particular time. When the needle is stationary, the amplifier is operating in pure class A mode. When the needle moves, it indicates class AB operation.
I only see my meters move under two conditions: (1) Heavy bass content during at normal listening levels. (2) Heavy bass content during higher than normal listening levels. Here are two example videos. The videos were taken with the following equipment and were posted to YouTube straight out of the camera with no video or audio post processing:
Camera: Nikon D800 (Set at ISO 2200, 30 fps, f/3.5, 1080p)
Lens: Nikon Nikkor AF-S f/2.8 24-70mm Zoom
Microphone: Nikon ME-1 Stereo Microphone (70-16,000 Hz FR) mounted on a tripod.
The music in the first video is "Isunova Pi" by E. S. Posthumous ("Cartographer" CD). The needle moved during the heaviest bass notes, most notably during the first 20 seconds. The average sound pressure level was 90 dB-C. The XP-30 preamp volume was set at 64.
Video 1. Meter movement at normal listening levels.
The music in the second video is "Your Love Is My Love" by Whitney Houston ("Whitney's Greatest Hits" CD). The needle moved constantly during the driving bass beats. The sound level was turned up to 72 to get an average sound pressure level of 104 dB-C. This resulted in easily noticeable meter movement (and the need to wear ear plugs). At normal listening levels the meter barely moved during the bass beats.
Video 2. Meter movement at high listening levels.
I was surprised the audio came out as well as it did considering the D800's relatively "noisy" audio circuits (which are optimized for voice) and the limited frequency response of the "cheap" ME-1 microphone.
Increased Electricity Usage
As previously mentioned, I prefer to keep my power amps on continuously. The X600.5s draw 25% more current and consume 25% more power at idle than my previous power amps, Parasound Halo JC 1s. Table 1 shows the differences in idle current draw and idle power consumption between the two amplifiers.
Table 2 shows my electricity bills before and after (in red) the X600.5s were in stalled on 4/10/13. The June 2013 bill, which covered the period from April 23, 2013 to May 22, 2013 was the first full month of X600.5 use.
At $0.09 per kilowatt hour, the JC 1s cost $41.60 per month to run continuously. The X600.5s cost $55.66 per month to run continuously, which was an increase of 33.8% ($14.06) over the JC 1s...and it was/is worth it!:biggrin: All the amounts in red in table 2 would be $14.06 less if I still had the JC 1s.
Audio System Upgrades After The X600.5s
I've done a tweak hear or there during the preceding 12 months. Nothing major, just some further efforts in electrical and mechanical noise abatement. It's nice to be able to sit and listen without thinking about a bucket list of audio projects.
1. Black Hole 5 vibration damping material for SDA SRS 1.2TL loudspeakers. (4/26/13)
2. Dynamat Xtreme vibration damping material for XP-30 and XP-25 preamps and X600.5 power amps. (10/11/13)
3. Dynamat Xtreme vibration damping material for Cary CD 306 PV SACD/CD player. (10/12/13)
4. PS Audio AC 12 power cords for preamplifiers and source components. (11/09/13)
5. AudioQuest Perfect Surface Silver jumpers for SDA SRS 1.2TL loudspeakers. (4/09/14)