It often happens that old things gathering dust in the attic or bought for pennies on the secondary market bring the most pleasant surprises. My story is about just that. It's about a seemingly unremarkable pair: a Soviet amplifier and Soviet speakers, which together formed a system whose sound made me look at listening to music at home in a new way.
The heroes of this story are the PAS-240 amplifier, model 6, and the ASP Optimus Classic SB II speakers. These are not the top models of their time, but rather mass-produced, affordable equipment from the late 80s and early 90s. Our parents often assembled them into systems, and many people associate them simply with “cassette players.” But, as it turned out, their potential was much higher.
In this article, I simply want to share my personal impressions of how this pair sounded in my living room. Without complicated technical terms and nostalgic sighs, but only about what the ears hear and the soul feels when you encounter unexpectedly lively and warm sound from what seems to be the most ordinary set.
ASP Optimus Classic SB II
The speakers are well-made and very attractive in appearance. If you didn't know that this was an original design, you might think that it was a well-known brand. However, you can still feel the handiwork. In the veneer joints, for example. But this only emphasizes the individuality of each product.
The warm-up lasted one month, 2-3 hours a day. After a month, I stopped hearing changes in the tonal balance of the sound.
The PAS-240 model 6 amplifier and ASP Optimus Classic SB II speakers are perhaps one of my most successful audio experiments. The amplifier with a tube-transistor circuit produces a warm, detailed sound that lacks only excessive harshness — everything sounds natural and voluminous. The speakers fit perfectly into this sound image: they are honest, musical, with good bass and lively highs. Together, they create a real sense of presence — you're not just listening to music, it's as if you're in the same room with the performer. It's not the loudest or most dynamic set, but it knows how to draw you in. You sit there for a long time, close your eyes, and lose track of time.
PAS-240 amplifier
The PAS-240 model 6 amplifier arrived on June 2. Thus, the manufacturing time was four months. I think the delay in manufacturing was due to the COVID-19 pandemic.
According to the manufacturer, the amplifier is designed as a “dual mono” circuit based on field-effect transistors with separate transformer power supplies for each channel. The manufacturer does not provide any information about the operating mode of the amplifier.
The amplifier was packed in foam and a branded box. No issues were found when inspecting the amplifier's appearance.
The amplifier has a minimalist design. On the left is the input selector knob, on the right is the volume control, and in the center is a dim blue power indicator. The photos do not reflect the full brutality of the design.
The amplifier's microprocessor has its own control logic. When voltage is applied, the volume control is set to the minimum volume position, then the motor drive sets the volume control to the 9 o'clock position.
If you use the remote control to turn the amplifier on/off in the future, the volume control will remain in the position it was in when it was turned off. The volume control works smoothly, and the volume can be adjusted very comfortably — both with the remote control and by turning the knob.
The listening room is 25 square meters (~4.5 x 5.5 m). (~4.5×5.5 m), the speakers are installed on the short side of the room, the distance between the centers of the speakers is 225 cm (further increasing the distance leads to a “break” in the sound stage), the speakers are slightly turned inward at an angle of 15°. The listening position is in the center between the speakers at a distance of two meters.
Each speaker is mounted on a concrete base measuring 50x50x5 cm and weighing 25 kg (standard paving slabs). The spikes are firmly embedded in the concrete. I should mention that the concrete base slightly raised the low frequencies. Tapping the speakers with your palm allows you to judge the good soundproofing of the enclosures.
The highlight of the PAS-240 amplifier is its patented ZDS technology. The speakers are connected to the amplifier using three wires: two as usual, and the third, made of the same material and of the same length, is connected to a special ZDS terminal (separate terminals for the left and right channels) and to the negative (black) terminal of the speaker. I tried listening to the system for a sufficient amount of time without using ZDS technology, i.e., connected with two wires.
Summary: with the ZDS system, the accuracy of the sound increases. This is expressed both in a slightly different timbre (or rather, in its complete absence) and in the clarity of the sound. With ZDS, any material sounded significantly more accurate. In general, the word “accuracy” is key to describing the resulting system. But that's getting a little ahead of ourselves.
Currently, the speakers are connected to the amplifier with three two-meter-long Onetech JET 40 wires (each with a cross-section of 4 mm², multi-strand copper with a purity of 99.96% at a price of 399 rubles per running meter — here and further, prices are as of the time of writing this article, August 17, 2020).
Let's move from description to practice.
Power
The apartment building where I live is relatively new, built in 1999. The power supply is good. All the wiring in the apartment has been replaced with 2.5 mm² copper. A separate wire from the switchboard goes to the sockets to which the amplifier and other audio equipment are connected. The amplifier is connected with a standard 0.75 mm² power cable from a Hewlett-Packard laser printer. An attempt to replace this power cable with a thick Chinese one (16 mm thick, with a cross-section of 4 mm²) costing 2,000 rubles ended in failure — the sound quality deteriorated. Detail and volume were lost.
Listening 1
Source — Marantz CD-48 CD player, coaxial output used, connected with a coaxial cable (ordinary Chinese cord, costing 1,400 rubles per pair) to the S.M.S.L M400 DAC (uses the latest AK4499 microchip), which is connected to the balanced input of the PAS-240 amplifier via a Chinese balanced cable, 50 cm long and costing 2,200 rubles per pair. For listening, I chose a fairly rare edition (2,000 copies) of the BG and Aquarium CD released by OCS in 2003.
The song “Kostroma Mon Amour” (gain control at 11 o'clock) sounds piercing. Grebenshchikov's voice is recognizably languid, with characteristic intonations, but thanks to the crystal-clear sound, it is perceived not as showing off, but as a restrained confession. The bass guitar part is well-defined, precise, and magnificent.
The accompaniment is unobtrusive. The soundstage is wide, with the voice slightly forward. Good work by the sound engineer. I really enjoyed it. And then I tried an experiment: I connected the DAC to the amplifier's unbalanced input. Not bad. But it lacked the highest level of detail and transparency.
Listening 2
The source is a Cayin i5 portable player (using AK4490), whose line output is connected to the amplifier's unbalanced input with a Supra BiLine-MP cable (3.5 mm mini-jack to 2xRCA, priced at 4,740 rubles).
“Dance of the Skomorokhs” (from the opera “The Snow Maiden” by N.A. Rimsky-Korsakov) performed by the Minnesota Orchestra (conductor Eiji Oue, disc Tutti, reference recording, FLAC). Volume control at 11 o'clock. Complete presence in front of the orchestra. From the barely audible piano to the thunderous, chest-thumping fortissimo of the kettledrums and cymbals! Delightful!
And all this sounds clear and detailed, without blending into a muddy mess. The amplifier and speakers cope perfectly with the explosive nature of the piece. Wonderful performance, excellent recording, superb reproduction!
Listening 3
The source and connection are the same as for Listening 2. The Lebek sisters' album Amoria is a masterpiece. Admittedly, I have it in FLAC format. The first track, Con Amores, La Mi Madre, begins with a cappella. The magnificent mezzo-soprano carries us forward and upward. And from there, a 14th-century song pours down on us. An extraordinarily beautiful voice. Modest piano accompaniment. Precise and soulful to the point of tears. A wide, deep soundstage. It feels as if we are in a cathedral. The volume control is set to 11 o'clock.
Listening 4
The source is a Pro-Ject X1 vinyl player, an Ortofon 2M Blue cartridge, and a PS Audio PS-II Mk5 phono preamplifier from Konstantin Babin. The turntable is connected to the standard phono preamplifier (which came with the set) with a Pro-Ject Connect it E cable, and the phono preamplifier is connected to the unbalanced input of the amplifier using two ordinary Chinese RCA-RCA cables costing 1,400 rubles per pair. I should note right away that the signal level from the phono preamplifier is slightly too high. Therefore, we set the volume control between 10 and 11 o'clock.
The Balkanton record “Organist Lionel Roge performs works by J.S. Bach on the Grossmünster organ in Zurich.” The very first piece, “Passacaglia and Fugue in C minor” BWV-582, is shocking. You can hear the organ breathing. I often go to the St. Petersburg Philharmonic, but I've never heard anything like this. And when the lower register of the organ sounded, it reminded me of infrasound. Powerful and at the same time detailed and well-defined. There's bass! Deep and just right.
Listening 5
Source and connection — same as Listening 4. The album “Lyrics” by Muslim Magomayev. 1974, Melodiya, USSR. A powerful baritone with a recognizable timbre. The lyrical introduction to the first song on the album, “Thank You,” is followed by a powerful chorus. Very balanced sound of the soloist and orchestra. Aesthetic pleasure. Who said that they wrote badly in the Soviet Union?! Just kidding. Of course, they wrote badly. There aren't many good records. But they do exist.
I also listened to a lot of typical material, such as Deep Purple (Machine Head, Fireball, In Rock), Pink Floyd (Dark Side…, The Wall, Wish You Were Here), The Beatles, Eagles, Doors, Dire Straits, etc. Mostly vinyl, but sometimes FLAC. This did not add anything significant to the description of the sound of the set.
About the sound of the system at low volume. The system sounds decent, i.e., with normal bass and good detail, starting from the volume control position at 9.5 o'clock. I usually listen to music with the volume control at 11 o'clock.
About the wiring. The gestalt is complete. See above for what's there now.
I listened to the set intensively (2-3 hours daily) for three months. I formed the following impressions of the sound of the PAS-240 model 6 amplifier and ASP Optimus Classic SB II speakers.
So, this duo of the PAS-240 amplifier and Optimus Classic speakers was a pleasant discovery for me. I did not expect that a set of relatively inexpensive and not the newest components could produce such a coherent and pleasant sound.
The sound turned out to be lively and warm, especially good for vocals and acoustic instruments. The amplifier does not strive for dry analyticality, and the speakers actively help it in this, smoothing out any rough edges and adding their own softness. Together, they work as a single unit.
This system is a great example of how you don't always need the latest models and big budgets to enjoy music. It reminded me of the simple joy of listening to my favorite tracks without getting into the details of the specs. The music flows easily and unobtrusively, filling the room with a cozy sound.
If you are looking for an inexpensive, reliable, and soulful option for your first or second system, this pair is definitely worth considering. It can become that “cozy corner” where you want to return after work to simply relax to good music.
