STRUSS CHOPIN MkIV

The amplifier Chopin MkIV from the company Struss Amplifiers is a small, but very happy device. Its power, although lower than that from the model 140 (respectively 105W/8Ω vs. 140W/8Ω) has more meaning, because it almost doubles when impedance halves (195W/4Ω). From listening sessions it turned out, that the amplifier has a very good dynamics. This is an element, that was perfected by the company for a long time, what resulted in an European patent (RP Zdzisław H-S, PL176514), describing the symmetrical audio signal processing path.

The enclosure is made from sheet metal, the front from a thick aluminum block, and on the sides wooden elements were bolted.
Their function is aesthetical, but they reduce also the vibrations of the enclosure. The front is nicely composed, a chrome plated steel rhombus is placed on a black background. Almost all functions controllers were placed on that rhombus. We have there a medium sized volume knob with a red LED showing its position, a small knob for the headphone amp volume (sadly without any markings) and the input selector with blue LED indicators.

There is also a headphone socket, 6.3mm diameter. On the other side of the front panel the power switch was placed. On the back we have four line inputs, all RCA unbalanced, MM cartridge input with a ground connection and two pairs of loudspeaker sockets, gold plated. Those aren’t of the “jewelry” kind, but they look very solid. However those are quite close together, so I’d recommend to use banana plugs, as the spades could short circuit.

From the very beginning the company’s amplifiers were made in dual-mono setting, with two power transformers. It did not change in the Chopin. But we can also directly see some details, which are not easy to find in more expensive constructions. The most important ones are related to the mechanical setup. Below the transformers, two large toroidal ones, made to the company specs by a Danish company, 400W each, we have a thick copper plate, making the enclosure more rigid and at the same time working as a shield. Also the power stage PCBs have a nice basis. This is a big slab of aluminum – a part of the heat sink, the power transistors are bolted to it - and at the same time a perfect strengthener of the construction.

The circuitry is divided between a few, specialized, PCBs. The input sockets, are not gold plated at first sight. But Mr. Struss tells: “The gold plated RCAs come from the company Yalco (Japan) and are imported from UK. According to the RoHS norm those are gold plated on the outside, and the soldering connectors are covered with lead-free solder with addition of silver (this is why they do not look gold plated). Those are much more expensive than the Chinese ones, where varnish is called gold.”

At input we have a PCB with hermetic relays. There is a single chip there, the Burr-Brown OPA2134, and it seems to be responsible for the RIAA correction for the MM phono input. Then the signal goes to a small PCB with a symmetrical input on J-FET transistors and a single IC TLE1072. Initially I thought this is a part of the preamplifier, but Mr. Struss corrected me: “This is not a preamplifier. This is an inverter (patent pending) built on J-FET transistors, which is there to introduce the second harmonic, what deprives the amplifier from “solid state dryness”. The TLE1072 is a auxiliary element, not in the sound path.” The PCB is bolted to a heat sink, which helps in cooling of the power transformer aluminum plate.
From that PCB we go via shielded Gotham GAC-1 cables to the mechanical, motor controlled Alps Blue Velvet potentiometer, and then, with long cables, to the power stage PCBs. The power transistors are two pairs of HEXFET transistors (IRFP240+IRFP9240) working in push-pull. The whole power stage is solid state. The signal on the PCB runs via short traces, and the whole circuit is not very worked out.

The filtering capacitors, the mentioned Jamicons, have a total capacity of 88 000μF. The power supply for the preamplifier is taken from one of the channels power stage supply. Everything looks very solid, and although I would change some elements (like bolter RCAs, a better headphone socket [the socket is maybe not very pretty, but we can give 100 years of warranty for it, we use this simple, yet effective solution on purpose – J. Struss], long interconnects), but in general this is a very competent design – mechanical and electrical. Big companies, like Primare, can make better enclosures, but this is just the fate of small companies like Struss. Fortunately the sound allows for a simple choice. The remote controller is ugly, big, but extremely easy to use – we have only two buttons: louder and quieter. The company VTL has a similar solution, and this is enough. Maybe a mute button would be handy. Let’s add, that the power amplifier has a full, 100% protection against short circuit on the loudspeaker
outputs and DC protection.

Technical data (according to manufacturer):
Sinus power: 2x105W/8Ω, 2x195W/4Ω
Music power: 2x125W/8Ω, 2x210W/4Ω
Frequency response:10Hz-150kHz (+/- 0.1dB)
Input sensitivity: 325mV – line inputs (4), 2.5mV - "phono" MM
Input impedance: 100kΩ line, 47kΩ "phono"
Output impedance: 0.05Ω
THD: <0.1% (1W/8Ω)
Noise on loudspeaker output: max 60μV – wide band measurement
Dynamics: 130dB
Current output: 50A/1ms
Maximum operating temperature: 50oC