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THÖRESS
Full Function . Preamplifier
==========================
"FFPre MKII"
................................................................
I N S T R U C T I O N
M A N U A L
Thank you for purchasing the THÖRESS Full Function Preamplifier (FFPre)!
You have acquired a versatile vacuum tube preamplifier incorporating a state-of-the-
art line control amplifier (2x12J5GT tubes) and a ground-breaking tube phono
equalizer (2x12JGT+2xPC86 tubes) in one chassis. 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 highest reliability, low noise performance and ease of service
for many years to come. Please read the following explanations and instructions
carefully to get the most out of your FFPre.
INPUTS
The FFPre is equipped with a MC gain phono section with excellent signal-to-noise
performance implemented in purely active operation mode (no built-in step-up
transformers!) and three on-the-fly selectable phono inputs P1, P2, P3 with equal
gain status (65dB at 1kHz) yet different cartridge loading. Alternatively, the FFPre is
available with MM gain phono section (45dB at 1kHz) on demand. The standard
cartridge load pattern on the phono inputs of 3XMC and 3xMM units is
(P1, P2, P3)=(100, 200, 500) ohms and (P1, P2, P3)=(47, 47, 47)K
respectively.
The cartridge load values installed on the inputs of 3xMC units are printed on the rim of
the rear panel (under the lid) !
The phono inputs are complemented by three-line inputs with different gain and
input impedance characteristics as described below.
Normal Line Gain
The gain on input #6 is 26dB (20-times). This input presents a comparatively high
input impedance of 80.000 ohm to the connected program source and is suitable for
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Summary of Contents for THÖRESS FFPre MKII
- Page 1 THÖRESS Full Function . Preamplifier ========================== "FFPre MKII" ..............I N S T R U C T I O N M A N U A L Thank you for purchasing the THÖRESS Full Function Preamplifier (FFPre)! You have acquired a versatile vacuum tube preamplifier incorporating a state-of-the- art line control amplifier (2x12J5GT tubes) and a ground-breaking tube phono equalizer (2x12JGT+2xPC86 tubes) in one chassis.
- Page 2 classic line level program sources such as phono preamplifiers, tape machines and tuners. Low Line Gain Inputs #4 and #5 offer 18dB gain (8-times, 8dB lower gain compared to input #6) and are meant for modern high-output digital sources such as CD/DVD players, streamers or DAC-s.
- Page 3 not at disposal it is advisable to install output coupling capacitors with higher capacitance values than 0.33MFD in the output of the phono circuit. For example, a critically low effective load value of 10.000 ohm would require a coupling capacitance of 3.3MFD in order to maintain the original no-load 5Hz 3-dB-down frequency, whereas 1MFD would give a still acceptable extension of the bass response down to 15Hz.
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Page 4: Phono Cartridges
PHONO CARTRIDGES Early microgroove records carry a monophonic signal written into a LATERALLY excited triangular spiral groove of constant depth. Such FIRST-GENERATION microgrooves were originally meant to get tracked by a spherical 25-micron stylus mounted to a MONO-FLEXIBLE cantilever (25-micron refers to the spike radius of the diamond/sapphire tip). - Page 5 grooves whereas the fairly well separated R and L signals are converted back into a consistent mono signal. In this case the signal generator of the cartridge transforms only the lateral excitations into signal. While vertical stylus movements do not contribute to signal conversion.
- Page 6 SINGLE-COIL MONO A monophonic cartridge with DUAL-COIL generator outputs two copies of the monophonic signal and therefor allows for dual-channel mono playback within the regular stereophonic wiring scheme. However, if the 4 input terminals of a stereophonic phono preamplifier (hotL, groundL, hotR, groundR) with single-ended (non-balanced) circuit topology are wired to a SINGLE-COIL cartridge through a stereophonic tonearm cable, in an attempt to distribute the monophonic signal over the stereo channels for dual-channel mono playback, groundL and groundR will...
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Page 7: Noise Performance
channel mono playback in the above manner! Some phono devices with non-balanced circuit topology feature a so called MONO SWITCH. Here the monophonic signal is distributed over the channels at the input (hence ground loop noise is induced), processed in the initial L and R amplifier stages (distorted in each branch!), mixed together somewhere in the middle of the circuit and then re-distributed over both channels of the following circuitry, whereas the ground loop noise introduced to the wanted signal in the initial amplifier stages... - Page 8 Idle noise emitted by the FFPre line section may become audible in the system when the gain of the power amplifier is rather high and not adjustable (as it is sometimes the case with solid state devices) or the loudspeaker is exceptionally efficient (horn system), whereas a worst-case mismatch scenario will obviously arise when both conditions meet.
- Page 9 The FFPre is equipped with six tubes (4x12J5GT+2xPC86 on MKII units and 4x12SN7GT+1xPCC88 on MKI units respectively). These tubes are unarguably among the most linear amplification devices ever developed in the history of electronic technology. The amplifier comes with a set of new-old-stock tubes which have been hand-picked to meet tight specifications.
- Page 10 Place the FFPre on the RIGHT side of the rack to avoid/minimize electromagnetic interference with other components of the system! 6. Connect phono cartridges to suitable phono inputs (P1, P2 or P3). Do not forget to connect the ground wire of the tonearm cables to the ground terminal adjacent to the phono inputs.
- Page 11 in the power inlet module. On rare occasions, the fuse may blow at the switching-on moment due to the current spike drawn by the mains transformer in this instant. Should this condition arise more regularly it is advisable to use a fuse with slightly higher current rating.
- Page 12 • 2x line outputs with low output impedance. • Pass-through output for the active input. • Ultra low noise and leakage mains transformer produced in-house for 230Vac (115Vac via jumper setting), 100Vac (Japan), 120Vac (USA, Canada), 220Vac (South Korea, China, Thailand, Indonesia), 240Vac (UK) or 245 Vac (Australia). •...
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