At that point, it transitions into class AB operation like a normal amplifier and keeps going to over 100W per channel before it reaches 1% distortion. As such the 30W power spec is a massive underestimate of what the amplifier is capable of. Even at that 100W per channel level, the clarity, ease, control and smoothness of the Pass amplifier was second to none in my listening room.
Pass Labs XA30.8 Class A Stereo Power Amplifier
- The Pass XA30.8 is the best built amplifier I have ever tested.
- It weighs 93 lbs, with the power supply, output devices and heat sinking most manufacturers would use for amps with many times the power output level.
- The soundstage size and depth, midrange liquidity and lack of glare was the best ever in my listening room.
- The amp had plenty of power to drive my Gallo Reference 3.5s. I only ever wanted for more power in rare circumstances.
- The measured performance on the bench was without fault.
Several years ago, I tested Pass Labs new XA30.5 30W stereo class A power amplifier and declared it the best amplifier I had ever tested personally. Since then, Pass Labs has upped their game and released a new revision of their class A and Class AB amplifiers, the .8 series. These new amplifiers are not revolutionary new designs, rather careful evolutions of the previous .5 series. Pass sent me their new “low power” XA30.8 to see how much better things could get.
Full power input level:
1.5 Hz-100 kHz
Power output per channel into 8 ohms:
Power output per channel into 4 ohms:
Distortion (1 kHz at maximum power output):
Maximum voltage and current swing:
40V / 20A
50 kOhm single ended 100 kOhm Balanced
Leaves class A:
Current draw at idle:
Power consumption at idle:
19 x 21.5 x 7.5
Pass Labs, Pass Labs XA30.8, ss Labs Stereo Power Amplifier, Power Amplifier, Power Amplifier Reviews 2016
Most all of the new .8 series amplifiers are bigger and heavier than their predecessors (only the largest of the amps are the same weight, they were already big enough to handle the .8 treatment). The XA30.8 weighs 93 lbs. as compared to the 76 lbs. of the previous model. The heat sinks are significantly larger to allow increased bias current compared to the .5 models. Class A amplifiers dissipate a significant amount of power even at idle. In the case of the XA30.8, the heat sinks have to get rid of 375W of heat the entire time the amplifier is on. The old XA30.8 needed to dissipate only 200W. This shows the bias current has been increased by 40% in the new model. In addition, the case is larger to accommodate an even larger power supply.
There have been several smaller refinements in circuit layout, input impedance and the turn-on circuit, amongst others. The basic specs of the new amp are about the same as the previous model: the amp leaves class A and transitions into class AB at 61 W per channel into 4 ohms. The measured 1% THD point, where most manufacturers define their power output level as the amp begins to clip, is in excess of 100 W per channel, as confirmed by our measurements of the previous version of this amp, the XA30.5, and measurements of this amp. The Pass Labs specifications they publish are exceptionally conservative. They claim 1% distortion at the maximum rated class A output power, but our measurements show the real distortion numbers to be at least 10 times better than this claim.
The main difference with the new amp, with more output devices running at even less of their rated output power, is the region of single ended class A bias. With the previous amp, this region was about the first 1 W of output power. With the new model, this region has been increased, again by increasing the bias current of the single-ended class A constant current source by 40%.
Normally, you’d need to choose between single ended and push-pull in an amp design, but the clever circuit of the XA30.8 allows the amp to operate like a single ended class A amp at low power output levels. Speaking of circuits, this, and all Pass amps, are monuments to old-school analog circuit design. The entire amp is based entirely on bare transistors. There isn’t an integrated circuit to be found anywhere. In fact, other than in the power supply and in the bias regulation circuit, there aren’t even capacitors in the circuit. Nelson Pass has forgotten more than most people will ever know about analog audio circuit design. You can read even more about the Pass amplifier circuit design and the clever trick they do to allow single ended class A operation at low power.
If it turns out you do actually need more power, Pass makes matching class AB amplifiers. In the case of the XA30.8, the class AB counterpart is the X150.8. It is very similar internally, but biased to leave class A at 12W rather than 30W into 8 ohms, but is capable of larger voltage and current swings so it finally runs out of steam at 150W rather than ~100W. It’s just a question of what you’d prefer: more class A power and less maximum output power, or more maximum output power at the expense of less class A power.
The rear panel is very similar to the earlier XA30.5, but has one nice new addition. The large, wingnut style binding posts with built in tightening clutches now can accommodate banana plugs in addition to spades. Nice, sturdy handles help you heave this massive amp into the rack Anything bigger than this (or the similarly sized XA60.8 monoblock) and you’ll need help. The quality of the case, front panel and blue lit meter are as good as it gets, as it should be for an amp priced like this one.
The XA30.8 certainly did not disappoint. As with the previous iteration, the soundstage with my Gallo Reference 3.5 was jaw dropping. And this was with an improvement in my reference amp since the last test. I had replaced my Emotiva XPA-1s with a NewClear NC1000L amp a while back. The soundstage of the Pass amp was wider, taller and more well defined than the digital amp. And not by a little bit, either. I would estimate 50% more soundstage height and depth, and an increase in width of a foot or so past the speakers on either side.
Of course, this was most obvious on well recorded material with the spatial cues to tell. Two good (and very different) examples were Jon Faddis’ “Rememberances” in 24-96, and the 24-88.2 recording of Daft Punk’s “Random Access Memories.” In both cases, the soundstages were huge. In addition, the size, shape and presence of each image, whether it was Faddis’ flugelhorn or Giorgio Moroder’s voice, were as about as realistic as I’ve ever heard in my room with my system.
Another welcome trait that was preserved from the previous version is the ease and complete lack of glare in the midrange and treble that the XA30.8 delivers. It sounds almost tube-ish in its smoothness and liquidity, but with a complete lack of tonal coloration. For the tube-o-philes among you, give this amp a listen. You might find everything you love about tubes with none of the drawbacks.
Since I didn’t have a XA30.5 around to directly compare, I’m not sure how much better the 30.8 is than the 30.5 in the soundstaging and tonal character department, but I can be pretty sure it’s not any worse. One place where the amp did improve is the bass. It was clear that with the 30.5, there was a bit of an impact with the lower power output. Bass transients were rounded off a bit. I could tell at high listening levels the amp was running out of steam on bass heavy electronica (as I like to listen to) because I could start to see the current meter wagging a bit.
The new higher biased 30.8 has mostly fixed this issue. Bass performance is much better, with transients plenty sharp and impactful. I still could detect a bit of a lack of energy on some albums. Royksopp’s “Melody A.M.” was just a touch less exciting through the Pass amp than with the NC1000L, but that was more than made up for by the improved soundstage, smoothness and detail. This time, I never saw the current meter move, so that says the amp never left class A while I noticed. Still, if I was a rich man, I’d probably go for the XA60.8 monoblocks, which I bet would give me back that little bit of excitement I missed with the XA30.8. With my speakers, anything more would be useless. In any case, I can’t afford either the $6,800 XA30.8 or the $12,800 a pair XA60.8s. But if I could, I would buy them.
Measurements were performed with a M-Audio Profire 610 Firewire sound interface and Spectra Plus FFT analysis software. The XA30.8 was measured using an 8 ohm 300W power resistor as the load. I measured at 1W, 15W and 30W into the 8 ohm load. I was unable to measure the 1% THD power level this time because my new sound card’s inputs reach their maximum input level before the Pass amp does. In fact, testing the XA30.5 a few years ago, I blew up my old sound interface and had to get this new one. As an aside, I had to measure the output of the amp with the positive terminal of the sound interface on one of the amplifier’s outputs and the negative attached to chassis ground, since my sound interface is not floating. The XA30.8 is a differential amp, so the negative terminal of the amp cannot be connected to ground. This means I am giving up some of the distortion cancellation from the balanced output stages when making the measurements, so the measurements presented below are pessimistic.
I measured THD+N with a 1 kHz input signal at 1W, 15W and 30W output power into 8 ohms. As expected the distortion is lower at the lower power levels, but is still an excellent 0.11% even at the maximum power level of 30W. As expected, the frequency spectrum of the distortion is biased towards low order harmonics, another reason why the XA30.8 sounds so good. This is particularly true at 1W power level, where the only distortion products visible are the second harmonic, a little bit of the third and maybe a little of the fourth poking through the noise in the trace. This shows how overbuilt the XA30.8 is and how conservative the 30W output power rating is. The distortion measurements are improved by a factor of a few from the XA30.5 I tested a few years ago. I maxed out my sound card input level at about 50W power level and the XA30.8 was still well below 1% THD, but since I was reaching the sound card’s limit, even some of that distortion was from the sound interface, not the amp. It’s clear the real 1% THD point is well north of 100 W per channel, but I’d need better test equipment to find it. Note that the plots show THD and THD+N. Since I had some 60 Hz pickup I couldn’t get rid of (likely from the trick I needed to do to measure the balanced amp), this polluted the THD+N measurement and made it worse than it actually is.
Intermodulation distortion, measured with 60 Hz + 1 kHz tones was also measured at 1W, 15W and 30W. At 1W, it’s a spectacularly low 0.01%, increasing gradually with power output.
Frequency response is flat as a board as expected all the way to the limit of the sound interface. The small slope you see is the response of the sound interface, not the amp itself. This measurement was done at 15W output power.
The Pass Labs XA30.8 is a very expensive amplifier. It does not have a lot of power output, although it does have a lot more power on tap than the 30 W per channel specification would suggest. But it’s one of the best amplifiers I have ever heard. Certainly the best amplifier I have tested in my listening room. If you have even moderately sensitive speakers, and especially if your system has powered subwoofers, the XA30.8 might just be the perfect amplifier. It has everything you could ever want, with the exception of massive power output. Most people do not need massive power output. If your ego can allow it, this Pass amp could give you world class sound. And I really mean world class in the sense that no amount of money spent could do any better. In my own personal case, I found only one small drawback with the XA30.8 with my speakers and musical taste that would push me to the next larger amp in the Pass lineup. But that comes at almost double the price. I think for a lot of listeners, the XA30.8 could be the holy grail. Yes, it’s expensive. But it’s worth it. If I had the money I would have already placed the order.
$6,800 is a Lot Of Money. But THE XA30.8 is Actually Worth Every Penny of That. Given the Build Quality, Both Inside and Out, The Sound Quality Delivered and the Measured Performance, I Can’t Imagine A Customer Not Thinking They Got Their Money’s Worth. If I Had The Money, I Would Most Definitely Buy a PASS LABS XA30.8 CLASS A AMP.
- Spectacular build quality.
- Engineering is second to none.
- Soundstaging, image quality, timbre and smoothness are world class.
- Plenty of power for almost all applications.
- Over delivers on almost every specification of consequence.
- I wish I could afford it.
- A little more power to match my musical taste (but Pass has the XA60.8 for that).