Pass Labs XA25 vs First Watt F7- The two newest Nelson Pass amplifiers go head-to-head

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Nelson Pass releases two low-powered amps, and jelt2359 is ready with his trusty Hifiman HE6

 

On Top: First Watt F7 Power Amp

Output: 20W into 8 Ohms, 30W into 4 Ohms

Damage: $3000 USD

Inputs: Single-ended only

Gain: 14.5dB

Damping Factor: 100

Below: Pass Labs XA25 Power Amp

Output: 25W into 8 Ohms, 50W into 4 Ohms

Damage: $4900 USD

Inputs: Single-ended only

Gain: 20dB

Damping Factor: 500

I own multiple speaker amps and do not have a single pair of speakers to my name. Instead, I use them solely to drive my headphones. After doing this for many years (I use a banana taps to XLR adaptor for this purpose), I’ve learnt that good amp is a good amp, whether it’s meant to be driving speakers or headphones. Make sure the gain and output power isn’t too much; look for quiet amps with low noise floors (a pitch black preamp helps a lot as well), and you’re in business.

In this context, the newest two amps from the legendary Nelson Pass seem tailor-made for me. Both are low-powered amps meant for high efficiency speakers, and are perfect for headphones. First Watt had in the past been Nelson’s ‘personal test-kitchen’ of sorts, with every amp hand-built by him, with limited runs, until he moved on to his next crazy invention. This has changed in recent times, with his other company Pass Labs now taking over distribution, manufacturing and support for all First Watt amps as well. First Watt has always had a philosophy of ‘less is more’, and the First Watt F7 is a refinement- a further simplification- of arguably Nelson Pass’s most popular amp, the First Watt F5. On top of having only four transistors and four resistors in the circuit- the bare minimum for a circuit of this type- it also employs a rare combination of both negative and positive feedback, working in combination. Nelson Pass akins this to a Tango dance.

On the other hand the Pass Labs XA25 adopts the ‘more is more’ philosophy of Pass Labs, but with some caveats. Taking on the immensely popular XA series design, the XA25 limits it to single-ended only. Instead of using multitudes of output devices under-driven in parallel ala the Point 8 architecture, the XA25 also uses only a single new-style output device per channel. The XA25 is stiff (it is stable up to ½ ohms!), it is powerful (it peaks at 200W), and Nelson Pass writes that this was an amp that was simple in its design but surprising in its performance. It is currently the only in-production amp of the “XA series” of amps from Pass Labs that’s not a Point 8 design, and speaking to the good folks over there they’re simply not sure if this new-style output device (affectionately named ‘Hockey Pucks’) can scale upwards towards more power. In short, this amp may only be possible as a low-powered design! Lucky me.

 

Page 2: The Sound

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When jelt2359's Shure earphones stopped working ten years ago he was forced, kicking and screaming, to replace them. He ended up with more than 20 new IEMs. Oops! jelt2359 flies to a different city almost every week for work, and is always looking for the perfect audio setup to bring along.

6 Comments

  1. Alessandro on

    Thank you for the Reply! I pair the XA 30.8 with an XP 20 preamp so I guess it is not a preamp issue – which btw has a fine level adjustments very handy with the headphones – but as you are interestingly pointing out it is probabky an issue of the output noise of the XA 30.8 and I understand the better we are below 100 UV the better it is. I was just looking at some FirstWatt incanations which have 30 UV output maybe they sound fantastic with headphones….
    If I may and if you can, which amps are you currently rolling in your full headphones set up?
    Again thanks and take care
    Alessandro

    • jelt2359 on

      Yes, those other amps may be good options as well (F1J/F2J), although I have personally not tried them. Another thing to bear in mind would be the gain, the less the preamp has to attenuate the better. To this end the F7 has 14dB, the XA25 20dB, the XA30.8 has 26dB.

      I you’re really going to go down this route it’s probably worth picking up a Hifiman HE6. The Audezes are great options, very different presentation (more intimate, warm), but the HE6 really takes well to additional power, and is very insensitive so has less hiss on speaker amps than any of my other headphones. In this regard it’s simply the best headphone out there for speaker amp use. Unfortunately it’s been discontinued so you’ll need to look for a used unit.

      Apart from my First Watt F7, Pass Labs XA25, and Hegel H20, I also have two tube speaker amps- an Ear Yoshino V12, and an Almarro A318B.

      • Alessandro on

        That is super helpful! Many many thanks….

        EAR V12, great choice, I love EAR and it Jaguar engine like design:)

        All the best
        Alessandro

        • jelt2359 on

          Yes, I must admit that with the EAR V12 amp, I admire it as much for its looks; as its sound! It is absolutely a work of art!

  2. Alessandro on

    Hi, thanks first of all. I found your review very interesting. I do have an XA 30.8 and since my time to use it with speakers is diminishing (as I listen at late night hours) and I’m a big heandphones fan, I’m trying too to use my XA 30.8 as the the main amp to power up my headphones. I paired it directly via its speaker binding posts to the headphone cable using a tail adaptor (banana to XLR four pin female) to Audeze LCD 2 (pre fazor) and LCD 3 Fazor, which are quite power hungry, and though the sound/scale/dynamics were excellent the level of noise floor is simply to much. How di you made the trick? Aren’t the Audeze a good match?
    Thanks for your comments
    Alessandro

    • jelt2359 on

      Thanks for the kind words! The XA30.8 has more than four times the noise floor of the XA25 (200uV for the former, less than 50uV for the latter), and more than twice vs the F7 (100uV for the First Watt), so it’s not surprising you’re hearing more noise than I did. In general, headphones are much more sensitive to noise, and some amps end up sounding really noisy on my setup even though reviews of the same component say the opposite. There’s no way around this, unfortunately. One thing I have found helped, though- the quality of the preamp. On my Hegel H20, for example, with some preamps I hear it as really noisy, whereas with my Chord Dave’s digital pre I find it pitch black.

      I don’t think the problem is your choice of headphones. I own the LCD2 and LCD3 as well, and have used them with speaker amps to great effect as well. In conclusion: at this point, I own five speaker amps, and have nary a pair of speakers to my name. Some are noisier, some are not; and the preamp matters.

      Hope this helps!

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