THÖRESS 845 Single-Ended Triode Mono Power Amplifier

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Our SE845 Mono Amplifier, the flagship of our all-tube power amplifier line, employs
the famous 845 power triode in single-ended (Class-A) operation mode for an output
power of up to 20 watts into a 4, 8 or 16 ohm loudspeaker load. The 845 is a brightly
glowing filamentary tube which requires a voltage swing of around 300V peak-topeak at the control grid for full excitation and concomittantly presents a critically
high internal impedance of about 2000 ohms to the associated output transformer
(OPT). Designing a driver stage and an OPT which allow to fully exploit the enormous
sonic capabilities of the 845 tube are therefor highly challenging tasks.
Our Monoblocks feature an exceptionally linear single-stage driver taylored around a
pair of 2xEL822/CV2382 power tubes operated in triode mode with high idle
current. Furthermore, the OPT is made in-house to perfectly suit the circuit context.
Using a highly elaborated dual-coil winding over an exceptionally large proprietary
tape wound cut core (C-core), such ensuring very low transformer distortion and
excellent frequency response. These crucial design choices are to a large extent
responsible for the richly textured, clear, warm and dynamic sonic presentation of
our amplifier. Making it an ultimate component and a perfect complement to our
DFAmp or FFPre, which easily measures up to the highest expectations of even the
most critical and experienced music lover. And easily outperforms competitive
products, regardless of price.
BUILT
The amplifier is built with meticulous hand construction using our proven point-topoint wiring techniques. 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.

TOPOLOGY
The amplifier is entirely based on SINGLE-ENDED ZERO-FEEDBACK schematics.
Decidedly ignoring the fact that many music lovers still 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
are encouraged to read the paper (THÖRESS - Behind the Curtain) downloadable on
the ABOUT button of our website.

LOW NOISE OPERATION
Specific design choices guarantee low noise operation of the amplifier, even when it
is combined with a highly efficient loudspeaker. At first, the 845 triode is DC heated
whereas the cathode point of the output circuit can be balanced with respect to the
filament of each individual 845 power tube by means of a rotary potentiometer.
Once the catode point balance adjustment has been made, the signal current is
distributed evenly over both ends of the filament and residual hum due to heater
voltage ripple vanishes! Secondly, the amplifier has been specifically designed to
have a moderate gain (low input sensitivity). This design choice helps to avoid idle
noise issues (and ensures conveniently fine volume adjustment) in a wide variety of
setup scenarios.
MAINS TRANSFORMER
The SE845 mono amplifier is equipped with a mains transformer produced in-house
to ensure the highest possible quality and reliability. This part has been optimized
for low body noise emission and low leakage. Nevertheless, it is mounted to the
chassis via isolation elements in order to eliminate even the slightest interference of
residual transformer vibrations with the circuit. Since the mains transformer is
produced in-house we can readily customize the amplifier for all kinds of mains
voltages, such as 230Vac, 100Vac (Japan), 120Vac (USA, Canada), 220Vac (South
Korea, China, Thailand, Indonesia), 240Vac (UK) or 245 Vac (Australia).

F E A T U R E O V E R V I E W
• All-Tube Mono Power Amplifier utilizing the famous filamentary 845 power
triode in single-ended operation mode.
• 2x20 watts of output power.
• Minimalist (pure class-A) zero-feedback schematic.
• Powerful single-stage driver utilizing EL822/CV2382 power pentodes operated in
triode mode at high idle current.
• High grade electrolytic capacitors made in Germany in the power supply.
• C-core filter choke made in-house.
• Ultimate tape wound cut core (C-core) output transformer with dual-coil winding
manufactured in-house.
• Precise 4, 8 and 16 ohm loudspeaker load matching via jumpers soldered setting
to the secondary terminals of output transformer.
• Low noise low leakage mains transformer produced in-house for 230Vac, 100Vac
(Japan), 120Vac (USA, Canada), 220Vac (South Korea, China, Thailand, Indonesia),
240Vac (UK) or 245 Vac (Australia).

• Full hand construction, point-to-point wiring throughout.
• Non-magnetic case (aluminium throughout), anodized printing on front and rear
panel, powder-coated chassis and lids.
• Dimensions: 150x595xH330 mm,
330=20/feet+210+150/tube over case,
595=575+20/speaker terminals, weight 18 Kg (each monoblock).
• Dimensions of the shipping crate: 950x400xH460 mm.