INT-25 is the entry-level integrated power amplifier for Pass in the United States. It has an output power of only 25 watts. Many people may have lost interest in integrated power amplifiers with such a small power. However, the low-power crystal amplifier is the basis for Pass’s reputation. At that time, the Aleph series entered the world with pure Class A amplification circuits, starting from low power, and the INT-25, a pure Class A 25 watt, seems to pay tribute to the Aleph of more than 20 years ago.
seems to pay tribute to Aleph
Back then, Aleph had a nickname, called Teppanyaki, which meant that the working temperature was so high that it could fry poached eggs on the surface of the case. What about INT-25? Almost, when it warms up and exerts its musical charm, it is so hot, very much like the Aleph of the past, but the INT-25 wears a modern Pass chassis and looks much more elegant, unlike the industrial style of the Aleph of the past. .
At present, the main equipment of Pass is still the power amplifier, especially the mono power amplifier. There are a total of six Class A mono power amplifiers and two Class AB mono power amplifiers. There are fewer stereo power amplifiers. Class A has XA30 .8 and XA25. Class AB has three models: X350.8, X250.8 and 60 vs. INT-25 for this audition. The most closely related amplifier between
and IMD-25 is the XA25. What these two devices have in common is that they are the only Pass devices that do not have a round blue meter head. The reasons are not difficult to consider. One is to save costs. The blue Although the power meter looks good, it has nothing to do with the sound performance after all, so it can be omitted. Another reason is that the chassis size of INT-25 and The cost is reflected in the selling price, making the INT-25 and XA25 relatively affordable.
One of the only remaining American audio masters
Nelson Pass can be said to be one of the few remaining masters who has experienced the budding and prosperous era of Hi End in the United States. His famous work is the Threshold 800A power amplifier, and he was the first to propose dynamic class A amplification, and then in 1991 Pass Labs was established in 2006 and is still on the front line. Like Nelson Pass, the only remaining master who is still working hard in his own company is Jeff Rowland. The other remaining master, Dan D'Agostino, left Krell, which he founded, and started a new D'Agostino stove to bring the United States to the United States. Hi End The fire burns brighter.
Pass The current product line is roughly divided into three lines. One is the Xs series with separated power supply, then the XA series with Class A amplification, and then the high-power Class AB X series. The three integrated amplifiers are post-amplifiers. An extension of the preamp circuit, X250.8 derives INT-250, XA60.8 derives INT-60, and INT-25 is based on XA25, plus the simplification of INT-250 and INT-60 preamp circuits. Version. Where is the simplification? There are fewer input terminals, XLR is cancelled, and there are only 3 sets of RCA.
The philosophy of subtractive design
This philosophy of subtractive design can be seen everywhere on INT-25. Simplicity is beauty. Using a simpler gain amplifier stage can improve the response speed and working stability of the line, and at a lower For voltage amplification, a higher bias voltage can be set to allow the amplification circuit to operate in a pure Class A state. Of course, this simple pure Class A amplifier circuit sacrifices output power. If you need greater output power, Pass has many power stages for you to choose from, but you have to pay several times the price to get one.
Don’t underestimate the INT-25’s 25-watt output power. Although the output is only 25 watts, Pass uses a pair of industrial-grade MOSFET power crystals with a peak output of 700 watts and a maximum current output of up to 40 amps, but it only extracts With a power output of 25 watts, it can be seen that even if the INT-25 outputs full power, the MOSFET crystal is basically in a relaxed working state. The use of a pair of power crystals instead of multiple low-power crystals reduces the problem of parts matching errors.The subtractive design of
INT-25 also includes canceling the resistance between the amplification circuit and the speaker terminal, which is equivalent to letting the power crystal directly push the speaker. This not only removes the staining of the resistor itself, lowers the distortion, but also increases the damping factor, allowing INT -25 has better control over the speakers. This design is the same as the XA25 power amplifier, except that the INT-25 has an additional preamplifier circuit.
NOS FET Exclusive Collection Parts
The preamp of INT-25 inherits INT-250 and INT-60, but the input terminals are slightly simplified. The preamplifier adopts Current Feedback Amplification (CFA) and is set in common source mode. The amplification component only uses two pairs of FETs, and they are NOS FETs collected by Pass. Well, this is another great trick of the original manufacturer. Even if you can copy the model number of the FET parts, you cannot buy the same batch number. It is definitely a unique formula.
In fact, Nelson Pass is not afraid of you copying at all, and even encourages DIY. He established FirstWatt in 1998, generously disclosed various design lines, and even provided DIY kits. This is to tell you that the manufacturer not only develops lines, but also produces quality products. The key, from the procurement, matching, selection and production of parts, are all the details that create good sound. What Pass sells is not just electronic parts, but the organism that combines these parts.
Mute mute function that is convenient for vinyl players
If your impression of Pass amplifiers is that they are big and heavy, it means that you are an audio expert and know the way of Pass. Every time the editorial department mentions that you want to audition the Pass amplifier, you must first Ask who can help move the machine, not what model it is, but the INT-25 is fine. It weighs 51 pounds, which is neither heavy nor light, but it is not difficult for one person to move it. The design of the machine is very simple. The panel only has a volume knob and five function buttons. From left to right are the power switch, three-stage input and mute. For vinyl players, the simple mute function is convenient to eliminate the popping sound of the stylus when changing discs. The digital screen displays the volume, 00 represents silence, and each step increases or decreases by 1 dB, with a maximum of 63 dB. The back panel of
is also simple, with three-stage input RCA gold-plated terminals, no XLR, and no Pre Out, which means you can only use the INT-25 as a comprehensive power amplifier and cannot do a preamp output. The speaker terminals are large-sized Furutech, and the locking Y plug can be easily tightened. There is a physical power switch on the rear, but there is no 12V Trigger, which means that the automatic control system must be set from the infrared receiver on the panel. As for the remote control, Pass has been an aluminum alloy public version design for many years. It is used on INT-25. Some functions are ineffective, such as left and right channel balance, Pass Thru, ext amp on, Tape, etc. It only has volume control and screen display ( Display), power and mute are useful.
The volume number should be turned up relatively high
If you think that 25 watts is not powerful enough, INT-25 will definitely surprise you. At first, I also thought that 25 watts should be limited, so I first used Dynaudio Coontour 60 to match it. After a while, the INT-25 didn't feel like a 25-watt amplifier at all, it felt more like a 100-watt amplifier, only the volume setting was a bit mysterious. The maximum volume display number of
INT-25 is 63. If we imagine it based on the traditional knob volume control, 12 o'clock will fall in the middle of 31~32, but in fact the volume sounds very quiet, at least above 45. The sound will be full and rich. Most of the time I listen to it at a volume of 50. Sometimes when I encounter a CD with a lower level, I can push it to 60, almost full power output.
Although the volume should be turned up relatively high, it feels a bit like stepping on the accelerator to drive, but the 25 watts of thrust of the INT-25 is stable. Even if I use close to full power output, drive the Contour 60 and listen to the rhythm. Intense Michael Jackson, played to a blast volume (almost to the point of damaging my hearing, I only dared to try it for a few seconds), the 25-watt INT-25 was not overloaded, the volume was very loud, but there was no sound breaking. I think the key lies in the over-provisioned power crystal. A MOSFET that can withstand 700 watts/40 amps can only produce 25 watts. Even if it is full power output, for a power crystal with a voltage of 700 watts, it is just a matter of wiggling your little finger. Properly.
can actually push Alexia 2
Since pushing Contour 60 is not a problem, I looked at the Wilson Audio Alexia 2 on the side and was eager to try it, so I switched to it. How does the INT-25 perform? It completely exceeded my expectations. If U-Audio's listening room was not so big, it would not be easy to hear flaws when using INT-25 with Alexia 2 in a smaller space. The overall sound purity is very high, the timbre is warm, and the sound field is clear. Translucent and open.
However, the listening room of U-Audio is relatively large (about 20 square meters). If you encounter the orchestral strong section, the low frequency section is a little bit difficult to grasp, but this has exceeded my expectations for INT-25. After listening to the two pairs of speakers alternately several times, I decided to use the Alexia 2 pairing to write down the listening experience. The INT-25 was up to par.
The real strength is when the machine is hot enough.
My experience with the INT-25 is that it feels like a vacuum tube machine. It is a slow-heating machine. When it is first turned on, the sound is clear and slightly boney, but when the machine is hot enough , the warm, smooth, soft tone is really charming, and the reason why INT-25 reminds me of the Aleph in the early years is that the machine is very hot, and it will be hot to touch the heat sink with your hands, and the entire case is evenly heated The heat, even the handle on the back panel will be hot, is the suitable working temperature of INT-25. That's why I would like to remind you that it is best not to stuff the INT-25 into a cabinet, for fear of insufficient heat dissipation. I placed it on the top shelf of the audio rack and turned on the air conditioner. The heat sink of the INT-25 will still be hot to your hands. You know how much space it needs to release heat.
Therefore, when listening to the INT-25, I always turn it on as soon as I get to work and let the INT-25 warm up for an hour before listening. The original manufacturer's manual recommends not to shut down the machine as much as possible, hoping to keep the INT-25 at the optimal operating temperature at all times. However, it is a bit worrying to keep the pure Class A machine shut down for a long time. It may cause the electronic parts to age prematurely. You might as well turn off the INT-25. To play as a vacuum tube machine, after turning it on every day, do not turn it off until you are ready to take a rest and stop listening to music, then turn it off again, maintaining a cycle of turning it on and off once a day.
A crystal machine with a vacuum tube flavor
In terms of timbre performance, although the INT-25 is a crystal machine, the warm tones in the mid- and high-frequency bands are soft and mellow, and have the taste of vacuum tube chicken. The mid- and low-frequency has a strong sense of volume, but it is not explosive. , but with a soft texture, presenting a sense of ease in listening. For example, "The Stockfisch DMM-CD/SACD Vol.1" by German Tiger Fish, and "No Sanctuary Here" by Chris Jones, the opening is deep low frequency, INT-25 can easily lay out the electric bass , and the volume is sufficient. , but it is not an explosive type, but has a rich and mellow appearance. The mid- and high-frequency bands have enough power to support the momentum of the music. The audio and video are condensed and huge, with the analytical power of a crystal machine, and at the same time, it is like an vacuum tube . warm colors.
Switching to the sixth song, Sara K.’s live recording “Stop Those Bells”, the crisp sound of the Slide guitar and the bright and bright tone contrast present a bright and hearty crystal tone. I would say that INT-25 is a crystal integrated power amplifier with the warmth of a vacuum tube. Its tone has a soft texture in the mid-low frequency band, similar to the Q-bomb of a vacuum tube, but its resolution and audio-visual line drawing in the mid-high frequency band are also outstanding. It has the clarity and transparency of a crystal machine.
is like listening to Eva Cassidy's "Live At Blues Alley" or "Bridge Over Troubled Water". The INT-25's transparent analysis of mid-to-high frequencies, in the prelude of the electric guitar Solo, is mixed with the subtle sound of the collision of wine glasses, and Eva Cassidy's singing voice echoed sweetly in the center of the sound field. After the electric bass joined in, the entire stage was laid out. The electric bass's voice was clear and full of grainy notes. It was impossible to imagine that this was actually a 25-year-old movie. A comprehensive power amplifier with a watt output power, the fingering changes of the electric bass are clear and grainy, contrasting with Eva Cassidy's bright voice.
The timbre is attractive and focused.
I quickly forgot about the existence of the amplifier and focused on the music. Eva Cassidy’s focused and emotional singing voice, and the appearance of the band struggling to respond to the lead singer. The jazz drums became more and more intense. The chords of the piano and electric guitar are padded thicker and thicker, until they fall at the top, and Eva Cassidy's soft singing makes the music bottom until applause breaks out. What fascinates people about INT-25 is the infectious power of conveying the emotions of music.
Do you still care that the INT-25 only has 25 watts of output, maybe it is not powerful enough? Using INT-25 to push Alexia 2 does have some concerns about a small engine towing a big truck, but this is the data on the books. In actual combination, INT-25 can maintain the balance of Alexia 2 in most cases. The sound is very smooth, even if the music develops into explosive passages, I thought that the INT-25 would give in, but in fact it always rides through smoothly, and the driving force far exceeds my imagination for 25 watts. I think that in a space of less than ten square meters, if you listen to music at a moderate volume, the INT-25 should not be insufficient when pushing any speakers.
Naturally presents Bach's dignified and pure musical beauty
I would like to take the "Bachian Keyboard Concerto" performed by pianist Plea and the St. Martin's Orchestra as an example. Listen to the first movement of BWV1052. I don't often use this CD to test the sound. , the dignity and rigor of Bach, the lack of dramatic contrast, and more of the pure beauty of the music's depth, are so fascinating when listened to with the INT-25 and Alexia 2.
The orchestra opens the first movement, and the unison of the theme in minor is laid out together with the piano. The staccato adds tension to the music, and then the piano unfolds the theme, and the INT-25 integrates beautiful counterpoint interweaving of voices, and It sounds like the distance between the piano and the orchestra is relatively close, and the sound field is shallow, but the tone is richer. However, this richness is not due to lack of analytical power. On the contrary, Praia's nails are sliding over the keys. The INT-25 did not let go of the sound at all. When the music turned into a major key, the INT-25 brought out a brighter luster, and the music atmosphere became a little more lively, but it was still a steady and dignified Bach.
Chamber music can be called a masterpiece
If you are a lover of chamber music, the INT-25 must be full of charm. I would like to cite "Schumann, Bach and Bram", a collaboration between Argerich and Perlman. "Collection of His Works", this is one of the rare recordings of the two of them collaborating. Argerich with a sharp and explosive piano sound, paired with the gentle and kind-hearted Perlman, inspired the bright colors of the violin , which is incomparable with the usually heard Perlman. Mann is very different. The violin is a little less rounded and has more momentum. The high-spirited expression of the INT-25 brings out a moderate amount of tension to compete with the decisive notes of the piano.
The first movement of Schumann's Violin Sonata No. 1 has an uneasy restlessness. The rhythm of the piano dominates the floating of the music, while the violin seems to be fighting for the dominant melody in the undulating waves of the piano. The passionate theme leads to more For passionate piano, INT-25 presents a more powerful Perlman, and also gives Argerich's piano a majestic thickness. The two instruments either compete for dominance, or express their feelings to each other, in conflict and harmony. , showing the romantic restlessness in Schumann's heart.
Brahms 's music contrasts even more
Chamber music can show romantic beauty and interpret inner emotional impact. What about orchestral music? Switch to "Brahms' Symphony No. 2" conducted by Bernstein with the Vienna Philharmonic. The first movement starts from the triplet in the bass of the string group, and the thick and solid brass emerges romantically from the depths of the sound field. theme, INT-25 lays out the string group and brass group with a thick texture, and tilts the sound field slightly forward to create an intimate tone. The woodwind group and string group gradually join in, stacking up Brahms's heavy feeling. , INT-25 uses dense timbre and rich layers to show natural and rich orchestral colors.
The warm color at the beginning of the first movement will soon enter Brahms' powerful and rich jump style. At 1 minute and 42 seconds, the gentle melody guided by the string group suddenly enters a phrase with big jumps of notes. The orchestra collided sharply, and the brass danced with it. The INT-25 did not collapse, stretching out Brahms' tension. Then the string group and the woodwind group murmured a dialogue, and the music then eased into the romantic second theme. The dense layering of string groups looks beautiful and romantic on the INT-25. At 3 minutes and 24 seconds, the heavy melody of Brahms' dance reappears, even more arrogant, and the passionate voice of the violin part unfolds an intense musical scene on the INT-25. I can almost imagine Bernstein looking at the violin Part, the left hand urges the musician to play hard.
Music partners who can stay together forever
INT-25 Is it so powerful? Yes, I underestimated it at first because of its 25 watt power. It wasn’t until I mastered the performance of INT-25 that it only sounds good when it’s hot enough. I gradually tested it with more difficult music, and then I discovered the charm of INT-25. . Its power is still limited, but its tone quality is full of aesthetic and romantic luster. If your listening space is not too large and the speakers have medium to high efficiency (not necessarily high efficiency), INT-25 can be used as a long-term companion. Shou's music partner, or you have heard of Aleph's legend but have never had the opportunity to see it. INT-25 can be said to be a classic reappearance of Pass's return to its original aspirations. It is worth seeking out and listening to in person.
Pass INT-25
Type: Class A crystal amplifier integrated power amplifier
Output power: 25 watts/8Ω, 50 watts/4Ω
Input: RCA × 3
Gain: 26 dB
Input impedance: 48
Frequency response : DC - 100kHz / -2dB
total harmonic Wave distortion: 0.1%@25w/8Ω/1 kHz
Damping factor: 500
Peak current output: 10A
Size: 17 × 6 × 17.9 inch (W × H × D)
Weight: 51
Reference price: 48,000 yuan
Author: Guo Han Cheng
