Further explorations on the differences between the Pass Labs INT25 and INT60.
Disclaimer: all ‘statements’ written in this post are my subjective findings, based on my system and my room. I ran both amps on my horn loaded loudspeakers, with a fairly high sensitivity of 96dB. Both amps never ran out of breath, heck the needle of the INT60 barely moved at (earthquake) high volume levels. In other words: depending on your loudspeakers, your miles may vary :-)
Another note: I have zero affiliation with Pass Labs.
As mentioned in my previous post, both amps have a surprisingly similar sound signature. Even though this post is aimed at the differences….. let’s start with the similarities.
The 25 and 60 are potential lifelong soulmates to music lovers. They are very capable of reproducing ‘music’, instead of ‘sound’. Both machines bring contradicting sound properties at the same time, such as:
Elegant and exciting.
Coherent and transparent.
Lush and decisive.
These qualities are what many audiophiles crave, but are seldom seen together.
Now…. The differences.
The magical INT25: The advantages of this amplifier is that it it has fewer gain stages. The strength of this simpler design is that it enables to “see” deeply into the recording. The 60 is also good at this, but less than the 25. Also, the 25 sounds slightly more lush and nimble. More playful.
The mighty INT60: Compared to the 25 with a single pair of FET’s, the 60 has banks of smaller transistors. The sound is more rich and resolute compared to the 25. Both amps sound slightly left of neutral, and the 60 has more ‘meat on the bone’. She is also able to take an “ordinary” recording and make it listenable.
Both amps sound incredibly right and will probably satisfy many music-first audiophiles. One of the important factors in this hobby is system matching. It will depend on the other links in your chain as to which amp you prefer. In my system and room, and to my taste, I give the nod to the 60.
Final thoughts on the design of the INT25: I’ve built a few early First Watt designs in the past and I find a resemblance in the INT25. The simple, yet elegant set-up is still intriguing. The dual FET’s connected directly to the loudspeaker without ballast resistors result in low distortion and Class A operation into low impedance and reactive loads. I will not be surprised when Nelson Pass is going full circle to further development on this path for his next (final?) generation of amplifiers. Maybe a similar design with larger heat sinks for dissipation? Bigger, faster power supply? Balanced? A more tuned pre-stage? A recipe for a killer future reference amp.
Cheers, Markuzz.
