Esoteric S-05 stereo power amplifier (Ex-demonstration)

£12,750.00 £9,450.00

Esoteric S-05 stereo Class A power amplifier

What we Say:

The Esoteric S-05 is a pure Class A power delivering 30W per channel into 8 ohms. This doubles into 4 ohms. The S-05 is a stereo power amplifier built in a large chassis.

The Esoteric S-02 is a substantial design weighing in at 30Kg. The amp is dual mono in construction with identical amplifier stages on either side  of the chassis. The large power supply sits between them. The power supply is split into two sections. A large toroidal transformer and Power supply board is used for the voltage gain stage of the amplifier. Then a much larger 940VI EI core transformer feeds a large bank of smoothing caps for the output stage. Each channel has a dedicated set of windings from the transformer.

The amplifier case has large ventilation grills on the top so will run relatively cool during use.

The S-05 is best paired with a pre-amplifier of similar quality and similarly specified source components.

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What they say:

The S-05 is a Class A stereo power amplifier that is thoroughly focused on the unique tone that can only be expressed by this model. It incorporates many of the development results of the flagship model “Grandioso M1X” to refine its overflowing driving power and pure performance.


Class A amplifiers are dense with little distortion. This general Class A characteristic alone does not begin to describe the S-05’s appeal. Passionate and vivid colors, like a direct-heating tri-tube amplifier. The overwhelmingly high speed sound start-up, backed up by the abundant idling current. Powerful drive capability and open-ended dynamism…. Regardless of the amplification method, the S-05 is a new milestone in Class A amplifiers, a sincere pursuit of what an amplifier should be, and the culmination of ESOTERIC’s commitment.


With the flagship Grandioso C1X/M1X, ESOTERIC has challenged the limits of fidelity in pre-power transmission and opened up new horizons. ESOTERIC’s unique current transmission “ES-LINK Analog” is the ideal method for pre-power transmission, where signal levels are extremely low in actual use.
This Grandioso technology has been carried over to the S-05. Compared to conventional voltage transmission, ES-LINK Analog transmits approximately 100 times more current. Therefore, it is less susceptible to noise, and all the energy of the music is transmitted from the preamplifier to the power supply.
In addition, in principle, the output signal from the preamplifier and the input signal to the power amplifier are not affected by the impedance of the connecting cables, so the output signal from the preamplifier and the input signal to the power amplifier can be kept identical to each other to an extremely high degree.

ES-LINK Analog – ESOTERIC’s unique current transmission
Esoteric’s unique current transmission system “ES-Link Analog” is the ideal method for preamp to amplifier transmission where the signal level is extremely low. Compared to the conventional voltage transmission, it transmits approximately 100 times more current, making it less susceptible to noise and sending the full energy of the music to the amplifier.
Also, it is not affected by the impedance of the interconnects running between the preamp and amplifier, so it maintains a perfect integrity between the output signal of the preamp and the input signal to the amplifier.


In conventional voltage transmission, the output impedance of the source device is low, and the input impedance of the target device is high. In other words, the current required for signal transmission tends to be kept low.
Also, due to the resistance component (impedance) of the transmission path (interconnect cable), the voltage of the transmitted signal is attenuated by the level calculated by Ohm’s law (voltage = current × resistance) when delivered to the target device. Therefore, a longer the cable causes increased resistance which has significant affects on that signal.

In contrast, in current transmission, the output impedance of the source device is high and the input impedance of the input device is low, resulting in a “High out, Low in” circuit, and the current level is maintained higher during signal transmission than in voltage transmission, allowing a powerful audio signal delivery.
Also, in current transmission, the current level output from the source device always matches the one on the target device. Imagine using a hose to send water from a faucet to a bucket. As long as there are no holes in the hose, the same amount of water from the faucet will always flow to the bucket, regardless of the length of the hose.
Similarly, if the cable that serves as the transmission path is not divided into multiple paths, all current from the source device will be delivered to the target device, and the current values flowing will always be the same, even if the transmission path is longer.
This advantage of accurate transmission of even the smallest signals is evident from the fact that current transmission is widely used in measuring instruments that measure precise signals.
Conventional voltage transmission impedance of the ESOTERIC products is designed several tens of ohms on out-going circuits and around 100k ohms on in-coming circuits. In contrast, the ES-LINK Analog out-going/in-coming circuits are designed approximately 1kΩ on the out-going circuit, and 0Ω on the in-coming circuit.
If we focus on the current value that flows when transmitting audio signals, the current level of ES-LINK Analog transmission when transmitting audio signals at the same level as normal voltage transmission is approximately 100 times higher than the current level flowing in voltage transmission. Consequently, the high current level allows for the full energy of the music to be delivered.

–Dynamics –

The power is so overwhelming that its size is unimaginable. The source of this power is ESOTERIC’s carefully designed power supply. The power supply is the most important component in realizing a powerful and rich sound stage for the amplifier block, which always requires a large current for Class A operation.
Thanks to ESOTERIC’s unique power supply design, the S-05 boasts dynamic musical expression that transcends its size.



Bare mount over-sized power transformer
The S-05 uses the maximum capacity that can be installed (940VA EI core transformer). By using a transformer with a much larger capacity than the original product performance, the S-05 is able to follow dynamic changes in current supply extremely well, resulting in a dynamic and open sound. The suppression of transformer vibration also results in the suppression of current flow. For this reason, the transformer is bare-mounted without a case.


Power rectification circuit with dual mono configuration
Unless the sound source is monaural, the left and right music signals are different. The power rectification circuits are not shared by the left and right channels, but are dual mono circuits, which avoid mutual interference between the left and right channels, resulting in clear channel separation and resolution.


Multiple block capacitors in parallel
In the S-05, the rectification system also incorporates the special attention that is unique to this model. The block capacitors are Grandioso grade high quality custom capacitors. Dual mono and parallel configuration of four 10,000μF capacitors per channel is used. The rectification operation is time-delayed in parallel to stabilize charge and release, thereby ensuring a large current supply required for Class A operation at all times. Therefore, it can faithfully and agilely follow the dramatic changes in the music signal and fully express its dynamism.



Low impedance design
Critical wiring from the primary side to the power supply section, drive stage, etc., is bolted with extra thick cables. The response of the power supply is maximized by ensuring a low impedance.。

– Circuit Design –

Less is More

This may seem a bit surprising considering the weighty appearance of the S-05. However, the signal paths are connected in the shortest possible time, and the circuitry is surprisingly simple. The clear sound quality is supported by the “subtractive aesthetics,” so to speak, created by the crystallization of advanced engineering. Class A amplifiers generate a lot of heat, so internal temperature stability is extremely important.
For this reason, we optimized the position and circuitry of the temperature compensation circuit to stabilize the temperature of the entire amplifier block. This contributes to high sound quality because it speeds up the stabilization of the idling current after power-on and allows the amplifier elements to operate at their best characteristics.
The phase compensation circuit is a simple one-pole configuration and the final stage is coil-less, minimizing negative feedback (NFB) and enhancing the dynamism of the music. The minimalist circuit philosophy allows the harmonics (overtones), which are the most important but easily lost in music, to be preserved and rendered in an expressive manner.


While the circuitry is simple, the S-05 has been thoroughly implemented in a dual monaural configuration from the input stage to the final stage through the use of material resources, eliminating any compromise in the qualitative quality of reproduction.
The components are of the highest class, with a board pattern using 105 µm thick copper foil, and ultra-thick gauge cables with connector connections eliminated as much as possible, all with the boldness and power that is typical of power amplifiers. The eight bass bars in the drive stage are made of luxurious 1.0mm thick high-purity OFC material, and MOS FET switches without mechanical contacts are used in the speaker output section.
With reduced internal impedance, even woofers with large diameters are powerfully gripped, and the drive power effortlessly reaches the limit point of the low frequency range.


The S-05 is not only powerful, but also delicately renders the gradations that connect climax and silence. The signal is received by a newly designed balanced amplifier independent of each input system and transmitted in a balanced manner up to the amplification stage to ensure noiselessness and a high degree of amplification stability.
FET switches with minimal tonal coloration are used for all switching switches in the audio signal path, including input switching. Selected high-quality components accentuate the tonal texture.

– Minimal, Versatile –


The S-05 offers luxurious functionality befitting a high-end system and can be used in a variety of ways. When paired with the N-05XD network DAC/pre, the S-05 completes a high-end system with only two components in a minimalist style. The ES LINK Analog connection allows you to enjoy a simpler, more refined musical experience without being overwhelmed by the presence of other components. The S-05 can also be linked to the N-05XD for power on/off.
The S-05 can be system-up to a mono-block amplifier using two units. Mode switching supports BTL drive for powerful high output, and bi-amp drive for high-quality sound of multi-way speakers with separate HF/LF inputs. Build your dream Class-A amplifier system according to the sound quality and characteristics you seek.
The 3.5mm mono mini plug cable for connection is sold separately. Please prepare a separate cable of the length appropriate for your environment.

S-05BTL mode
When more driving power is required, such as when the efficiency of the speakers to be driven is low, the “BTL mode” deploying two S-05s is recommended. The two built-in amplifier circuits can be bridged to form a high-power 120 W (into 8 ohms) monaural amplifier system, while the balanced drive provides a powerful grip and firm drive for the speaker units.
S-05Biamp mode
When two S-05 units are deployed and set to “bi-amp mode,” the same audio signal is delivered from the output terminals that were L/R in stereo mode. This means that a single unit can be used as a monaural power amplifier with two speaker outputs. The output power is the same as when one S-05 is deployed in normal stereo mode (30W/8Ω), but as shown in the figure, the HF/LF units of the speaker can be driven by separate power amplifier circuits, enabling a more pure sound of a multi-way system speaker. This mode is effective when resolution is more important than driving power.

Mechanical Perfection

To achieve the one and only design goal of “reproducing the master sound,” the S-05 chassis optimally controls all vibrations that affect the sound quality. The S-05’s mechanical engineering is like that of a sports car, with the balance between rigidity and flexibility pushed to the limit. The sleek and clean form of the chassis is a testament to its high degree of perfection. For example, the enclosure, which requires rigidity, makes extensive use of aluminum blocks and is thoroughly non-resonant.
On the other hand, the top panel, which needs to be free of vibration for an open sound, has a semi-floating structure, and the isolation feet have a special structure that reduces mechanical stress and enhances sound quality. In addition, the large heat sink of the amplifier block has a special wave shape that disperses the peak resonance of the fins and suppresses resonance.