THÖRESS F2a11 Integrated Amplifier Single-Ended Triode
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“F2a11 Integrated”
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P R O D U C T D E S C R I P T I O N
The F2a11 Integrated Amplifier utilizes the famous F2a11 vacuum tube in single-
ended triode operation mode for an output power of 2×6 watts into a 4, 8 or 16 ohm
load. The F2a11 is a power pentode of matchless built quality exclusively
manufactured by SIEMENS in the 1950s and early 1960s which has been specifically
designed for the most demanding industrial applications. When operated in triode
mode this extraordinary tube offers excellent sonics on par with the finest classic
filamentary triodes such as 300B, 2A3, AD1 or PX25. A 12SN7GT double-triode is
employed in the driver stages. The triode sections of the 12SN7GT tube are
equivalent to a 6J5GT single-triode, a highly regarded classic medium-gain octal base
triode with fairly low transconductance from the early times of tube electronics,
unarguably one of the most linear amplification devices ever developed in the
history of electronic technology.
The amplifier can be employed as a stereophonic power amplifier (in combination
with a line or full function preamplifier), in which case the volume controls of the
amplifier serve as input attenuators to match the gain of the line device to the
efficiency of the loudspeaker.
Our All-Tube Integrated entirely relies on minimalist single-ended zero-feedback
schematics. Deliberately ignoring the fact that many music lovers persistently believe
in the myth that balanced technology (and the associated cable configuration with
XLR connectors) is generally superior to single-ended concepts. Readers who want to
learn more about our view on balanced techniques and our general design approach
and are encouraged to read the article (THÖRESS – Behind the Curtain) available on
request.
The amplifier is built with meticulous hand construction using our proven point-to-
point wiring techniques, whereas much care has been taken in arranging each aspect
of the internal construction to ensure low noise performance, ease of service and
the highest reliability for many years to come. Although reasonably priced, the
F2a11 Integrated shares the non-compromise approach with our larger mono
amplifier models. It is by no means an entry-level component, but a state-of-the artdevice which is likely to be sonically superior to any competitive product regardless
of price. The sound of our F2a11 amplifier is powerful, warm, clear and natural.
Particularly when combined with our highly efficient 2CD12 highly efficient
loudspeaker the sonic presentation is of utmost refinement and will easily meet the
expectations of even the most critical and experienced music lover.
INPUTS AND VOLUME CONTROL
The amplifier comprises 3 line level inputs (2×3 RCA jacks) with equal gain status
selectable via rotary dial located on the rear panel. High-grade continuously variable
single-potentiometers are employed for separate (manual) volume control of the
channels. These parts are made to our specifications by ALPS in Japan to allow for
conveniently fine volume adjustment (taper with low angle sensitivity). Each pair of
potentiometer is hand-picked from a larger production batch by careful
measurement to ensure equal attenuation characteristics with respect to rotational
angle (hence the slots surrounding the volume knobs are reliable scales for balance
adjustment). Notably, it is not possible to install remote volume control on the F2a11
Integrated. Music lovers who consider remote volume control as an indispensable
feature are encouraged to take a closer look at our EHT Integrated Amplifier!
TRANSFORMERS
The F2a11 Integrated Amplifier is equipped with proprietary output transformers
(OPT) of ultimate quality made in-house. These parts allow for precise matching of a
4, 8 or 16 ohm loudspeaker load to the power tube by way of jumpers soldered to
the secondary terminals. Furthermore, the mains transformer is also produced in-
house to the highest possible standards. Thus, we can easily built transformers for all
kinds of mains voltages, for example for 100Vac (Japan), 120Vac (USA, Canada),
220Vac (South Korea, China, Thailand, Indonesia), 240Vac (UK) or 245 Vac (Australia).
Although the mains transformer has been optimized for low leakage and ultra low
body noise emission it is mounted to the amplifier chassis via isolation elements in
order to eliminate even the slightest interference of residual transformer vibrations
with the circuit.
F E A T U R E O V E R V I E W
• All-Tube Integrated Amplifier with 2×6 watts of output power utilizing the famous
Siemens F2a11 Power Pentode in single-ended triode mode and a highly linear
12SN7GT double-triode in the driver stages.
• Minimalist zero-feedback schematic.
• 3 line level inputs (2×3 RCA jacks) selectable via rotary dial on the rear panel.
• High-grade continuously variable potentiometers for separate (manual) volumecontrol of the channels.
• Ultimate C-Core output transformers (OPT) produced in-house. Precise 4, 8, and
16 ohm loudspeaker load matching via jumpers soldered to the secondary
terminals of the OPT.
• High-grade electrolytic capacitors (made in Germany) in the power supply.
• Ultra low noise mains transformer made in-house for 230Vac (115Vac via jumper
setting), 100Vac (Japan), 220Vac (South-Korea, China, Thailand, Indonesia) or
245Vac (Australia).
• Full hand construction, point-to-point wiring throughout.
• Nonmagnetic aluminum casework, anodized printing on front and rear panel,
powder-coated chassis, and lids.
• Dimensions: 150x595xH330 mm,
330=20 (case feet) +210+100 (power tube over case),
595=575+20 (binding posts).
• Weight 18 Kg.
• Dimensions of the shipping crate 400x950xH460 mm.
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THÖRESS…
A Tribute to Professional Audio Components
from the Golden Age of the Electronic Tube !
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