THÖRESS FFPre MKII Manual de usuario

THÖRESS

Full Function . Preamplifier

==========================

"FFPre MKII"

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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 ha e acquired a ersatile acuum 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 pro en 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 ser ice

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 acti e 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. Alternati ely, the FFPre is

a ailable 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

respecti ely.

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 comparati ely high

input impedance of 80.000 ohm to the connected program source and is suitable for

classic line le el 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. The input impedance on these inputs is 30.000 ohms.

Summarizing, the gain pattern on the inputs of the FFPre are

(MC, MC, MC; 18, 18; 26) dB and (MM, MM, MM; 18, 18; 26) dB

on 3xMC and 3xMM units respecti ely. Other gain patterns can be easily

implemented on demand, for example,

(MC, MC, MC; 10, 10; 18) dB or (MM, MM, MM; 18; 26, 26) dB.

OUTPUTS

The output impedance of the line section is sufficiently low (around 300 ohms) to

simultaneously dri e long cable lines and power amplifiers with an input impedance

as low as 10.000 ohms without compromising sound quality. The 3dB-down

frequency under 10.000 ohm loading is still well below the audio band (lower than

5Hz, line output coupling capacitor 3.3MFD).

The output of the line section is lead out through 2x2 RCA jack’s channel wise

connected in parallel (twin output). Thanks to the twin output it is possible to

simultaneously dri e a power amplifier and an acti e sub-woofer without further

adaptation in which case the effecti e load impedance (input loads of power

amplifier and subwoofer dri ing module in parallel) should preferably not come

significantly under 10.000 ohms. The twin output of the FFPre is also helpful for

proper dual-channel mono installation with SINGLE-COIL cartridges as described in a

dedicated paragraph of this manual.

Furthermore, the FFPre comprises a pass-through output (QUELLE) for the acti ated

input. This design choice ob iously allows to combine the internal phono section of

the FFPpre with an external line de ice.

The FFPre phono section can be tapped via the pass-through output!

In case of such an installation it is ad isable to connect the pass-through output to a

line input with high input impedance (equal or higher than 30.000 ohms) in order to

ensure a sufficiently low 3dB-down frequency of the low end response. The phono

output coupling capacitor (0.33MFD) has been chosen to gi e a 3dB-down frequency

of 5Hz when no additional external loading is imposed on the phono circuit ia the

pass-through output. In cases where line inputs with sufficiently high impedance are

not at disposal it is ad isable to install output coupling capacitors with higher

capacitance alues than 0.33MFD in the output of the phono circuit. For example, a

critically low effecti e load alue 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 gi e a still acceptable extension of the bass

response down to 15Hz.

Line amplification is performed by a unique single-stage, zero-feedback circuit

employing one 12J5GT acuum tube per channel (12SN7GT tubes in MKI units)

operated at high idle current. As a result of this purist concept the output signal is

phase-in erted (shifted by 180 degrees) relati e to the line and phono input signal.

Users who make a point of a formally correct o er-all signal phase can apply a simple

correcti e (in case it is known that all other components of the system offer phase

neutral operation).

To ensure a formall correct over-all phase of the signal in a setup including the FFPre the

loudspeakers must be connected to the power amplifier with reversed polarit (red

binding post of the amplifier connected to the black speaker terminal)!

PHONO EQUALIZATION

The gain of a phono pre-amplifier has to ary with frequency in order to restore the

pre-emphasis introduced to the signal during the record cutting process. Therefor a

phono pre-amplifier is sometimes called PHONO EQUALIZER (Phono Entzerrer). A

pre/de-emphasis characteristic is completely and unambiguously determined by a

set of edge frequencies (equi alent to so called time constants)

f1 > bass roll-off, f2 > bass turnover, f3 > treble roll-off.

The gain rises below f2 (bass boost) and falls off abo e f3 (treble attenuation/roll-

off) with a slope approaching 6dB/octa e. f2 determines the end point of the bass

boost. The difference between the arious pre/de-emphasis prescriptions

established by prominent record companies in the inception of high-fidelity audio is

rather small, often negligible, whereas in the most cases the crucial bass-turno er

frequency f2 equals 500 Hz. A few examples of prominent de-emphasis prescriptions

are gi en at the end of this manual.

The phono section of the FFPre performs highl accurate RIAA de-emphasis, (f1, f2, f3) =

(50, 500, 2124) Hz!

This most widely used equalization characteristic is gi en by the NEW

ORTHOPHONIC prescription established by RCA along with the microgroo e inyl

disc in the late 1940s, which later was appointed as phono playback standard.

PHONO CARTRIDGES

Early microgroo e records carry a monophonic signal written into a LATERALLY

excited triangular spiral groo e of constant depth. Such FIRST-GENERATION

microgroo es were originally meant to get tracked by a spherical 25-micron stylus

mounted to a MONO-FLEXIBLE cantile er (25-micron refers to the spike radius of the

diamond/sapphire tip). A mono-flexible cantile er is one which does not comply in

ertical direction.

By contrast, the groo e of a stereophonic record carries two signals (more or less

sharply separated from each other) coded LATERALLY AND VERTICALLY into the

groo e by also arying the depth of the groo e relati e to the record surface

(concomitant with the lateral groo e modulation). Consequently, stereophonic

cartridges are obligatorily fitted with an OMNI-FLEXIBLE cantile er, that is one which

complies in all degrees of freedom.

A phono cartridge with mono-flexible cantilever will seriousl and irrecoverabl damage

the groove when it is (accidentall ) used for tracking a stereophonic record!

A stereophonic cutting head produces a monophonic groo e when it is fed with

identical signals on both channels. A groo e obtained in this manner is significantly

narrower than a first-generation monophonic microgroo e, due to the new groo e

standards introduced for stereophony, whereas a 17-micron stylus was specified for

tracking such SECOND-GENERATION microgroo es. During the stereophonic era

more sophisticated stylus profiles (Shibata, Micro Ridge, Paratrace, Gyger, an-den-

Hull etc) ha e been de eloped from the humble spherical 17-micron stylus in order

to reduce tracking distortion and to enhance tracking ability of phono cartridges.

These modern stylus profiles pro ide the further ad antage of reduced record and

stylus wear on account of an increased contact area (line contact) between the

stylus tip and the groo e walls.

Phono cartridges with a sophisticated st lus profile tend to (drasticall ) outperform

humble cartridges fitted with a simple spherical st lus!

A phono cartridge with omni-flexible cantilever and a spherical 25-micron st lus can

faithfull track (NARROW) second-generation microgrooves, likel with reduced tracking

abilit , although this t pe of st lus was originall intended for tracking (WIDE) first-

generation microgrooves!

Conversel , ever phono cartridge with a spherical 17-micron st lus (or one of its modern

derivatives) can faithfull track (WIDE) first-generation microgrooves although this t pe

of st lus was originall intended for tracking (NAROW) second-generation microgrooves!

Stereophonic groo es are mono-compatible in a two-fold sense...

At first, e ery monophonic cartridge with omni-flexible cantile er (and a stylus

profile suitable for microgroo e reading) is able to faithfully track stereophonic

groo es whereas the fairly well separated R and L signals are con erted back into a

consistent mono signal. In this case the signal generator of the cartridge transforms

only the lateral excitations into signal. While ertical stylus mo ements do not

contribute to signal con ersion. Thus, monophonic cartridges ignore ertical stylus

mo ements e en when they are fitted with an omni-flexible cantile er. Secondly,

e ery stereophonic cartridge is able to read both, early and second-generation

monophonic microgroo es faithfully, whereas identical signals are de eloped in the

R and L channel generator coils. Hereby, the omni-flexible stylus, theoretically, is

exposed to lateral excitation only. Howe er, in reality ertical mo ements of the

stylus due to groo e imperfections (warp, dirt, scratches) are con erted into signal

and such add noise artifacts to the wanted cartridge output.

Ever stereophonic cartridge is capable of faithfull tracking both earl and second-

generation monophonic microgrooves, et it tends to produce more tracking noise than

dedicated mono cartridges!

Stereophonic cartridges with a sophisticated st lus are not onl suitable for faithfull

tracking (earl and second-generation) monophonic microgrooves but tend to

(drasticall ) outperform dedicated mono cartridges fitted with a humble spherical st lus!

The majority of currently produced high-grade monophonic MC cartridges are

deri ati es of stereophonic models and as such employ a dual-coil signal generator

(two separate generator coils terminating in 4=2x2 output terminals) with an omni-

flexible stylus. The only difference to the corresponding stereophonic ariants is that

the generator coils are not arranged at a 45-degree angle to the tracking plane, as it

is needed for stereophonic reading. Examples of omni-flexible dual-coil mono

cartridges are the AUDIO TECHNICA AT33-Mono, the LYRA mono cartridges and the

DYNAVECTOR DV-X1s-Mono.

Use a DYNAVECTOR DV-X1s-Mono for ultimate pla back of mono records with

microgroove coding!

Mono-flexible single-coil MC cartridges are currently produced by MIYAJIMA LAB in

Japan, all of which models (unfortunately) come with simple spherical stylus profiles.

The highly outstanding TEDESKA mono cartridges made in Berlin by Hyun Lee are

other examples of mono-flexible single-coil MC cartridges from current production.

Whereas the ORTOFON Mono CG-25 and the EMT OMD-25 are widely known classic

single-coil MC cartridges (pick-up heads). These old-timers offer an astonishingly

good sonic presentation e en when judged by today’s standards. Howe er, they

cause excessi e record and stylus wear due to their spherical diamond profiles and

tracking weights in excess of 4 grams, especially when combined with intage

tonearms without anti-skating facility. Their use is therefore questionable when

maximum sound quality and preser ation of aluable records is the main goal.

Ne ertheless, they will be an ob ious choice when it is aimed to compose a setup for

authentic monaural playback.

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. Howe er, 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 o er

the stereo channels for dual-channel mono playback, groundL and groundR will

una oidably meet at the cartridge terminals (2 contact pins) or within the cartridge

body (2x2 contact pins pairwise connected in parallel inside the cartridge body). This

unwanted conducti e connection will e oke residual hum in the amplifier due to the

so-called GROUND LOOP EFFECT. This is not a peculiarity of the FFPre but holds

generally for phono amplifiers with single-ended (non-balanced) circuit topology.

Single-coil phono cartridges cause residual hum when the are wired to both inputs of a

stereophonic phono preamplifier with non-balanced circuit topolog !

The FFPre allows for hum-free dual-channel mono playback with single-coil

cartridges on each indi idual phono input!

The key to hum-free dual-channel mono installation with single-coil cartridges in the

context of phono equipment with single-ended (non-balanced) circuitry is to

distribute the monophonic signal o er the R+L channels at the OUTPUT of the phono

preamplifier rather than at the cartridge terminals, in the manner described below.

Connect the L-plug of the (stereophonic) tonearm cable with the L-jack of the

chosen phono input, while the R-plug is let to hang freely, such a oiding a critical

conducti e connection between groundL and groundR. Isolate the armature of the

R-plug with the aid of a small glass test tube (or similar accessory) in order to

pre ent unwanted contacts. This installation permits hum-free amplification of the

monophonic signal in the L-section of the FFPre , while the R-section of the amplifier

runs at idle (is not fed with signal). Connect the ground wire of the tonearm cable to

the ground terminal of the chassis in the usual manner! Connect both plugs of the

interconnect cable (L+R power amplifier > FFPre) into the L-channel output jacks of

the FFPre (possible in iew of the twin output terminals of the FFPre). Now both

power amplifiers are dri en by the L-output signal of the FFPre (Y-connection). The

system is now ready for replaying mono records with single-coil cartridge in dual-

channel mono playback mode. Do not forget to restore the regular stereophonic

wiring scheme when the single-coil listening session is o er!

The s stem repla s the L-signal on both loudspeakers (rather than a consistent

stereophonic signal) when the s stem if fed with a stereophonic signal (from a

stereophonic cartridge or line level program source) while the s stem is wired for dual-

channel mono pla back in the above manner!

Some phono de ices with non-balanced circuit topology feature a so called MONO

SWITCH. Here the monophonic signal is distributed o er 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 o er both channels of the following circuitry, whereas the

ground loop noise introduced to the wanted signal in the initial amplifier stages

cancels away during the mixing process. Ob iously a clumsy and sound destructi e

concept!

Mono switches are sound destructive and go along with clums circuitr and are

therefore not helpful when ultimate sound qualit is the aim!

SUBSONIC ARTIFACTS

Coupling capacitor alues in the phono section of the FFPre ha e been carefully

chosen to ensure a low 3db down edge frequency at the low end while pro iding a

certain amount of attenuation of subsonic frequencies. Howe er, notably the phono

section of the FFPre does not incorporate dedicated subsonic filtering! The amplifier

will therefore pitilessly re eal subsonic artifacts which may ha e creeped in the

signal due to improper phono installation (turntable poorly isolated against structure

borne noise, too low resonant frequency of the tonearm-cartridge combination, or

comparable shortcomings).

The FFPre does not emplo high-slope subsonic filters!

High-slope subsonic filters do not solve but mask phono installation problems while

seriousl compromising sound qualit !

NOISE PERFORMANCE

Much care has been taken in arranging each aspect of the internal construction of

the FFPre so as to achie e an extraordinary signal-to-noise performance e en

though the phono amplifier operates in purely acti e manner (without the aid of

step-up transformers!). Howe er, electromagnetic stray fields emitted by mains

transformers or switching mode power supplies of other electronic de ices

positioned near the FFPre may, under unfortunate circumstances induce hum in the

amplifier ia electromagnetic interference. The phono section of the FFPre is

particularly susceptible to this kind of noise induction for ob ious reasons.

The FFPre requires considered placement for optimal signal-to-noise performance!

Place the FFPre on the right hand side of the rack in order to avoid/minimize

electromagnetic interference with other components of the setup!

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 de ices) or the loudspeaker is exceptionally efficient (horn

system), whereas a worst-case mismatch scenario will ob iously arise when both

conditions meet. In order to a oid idle noise issues and to ensure con eniently fine

olume adjustment, the gain of the power amplifier needs to be properly matched

to the line gain of the FFPre with respect to the efficiency of the loudspeaker. Proper

matching can be easily achie ed in case the power amplifier allows for gain

adjustment. In a matched scenario the olume controls rest near the middle position

for a saturated listening loudness (assuming that the program sources are connected

to line inputs with suitable gain figures).

Idle noise ma become audible in the s stem when the gain of the power amplifier is not

properl matched to the gain of the FFpre line section with respect to the efficienc of

the loudspeaker!

The input selector of the FFPre produces moderate switching noise when it is mo ed

in between the phono positions (P1, P2, P3) or from posP3 to pos4 or backwards,

particularly on (3xMC) units. This effect is not a peculiarity of our preamplifier and

would arise in the same manner with any kind of phono amplifier with on-the-fly

selectable inputs due to the extreme input sensiti ity of such de ices. The

magnitude of the noise emission is dependent on the gradation of the effecti e

impedances (internal impedance of the cartridge in parallel with the associated load

resistor) presented to the phono circuit on adjoining phono inputs. The noise

disturbances will ob iously remain inaudible and without impact when the olume

control is set to a low angle of rotation before mo ing the input selector.

Alwa s turn the volume controls to zero or at least to a ver low angle of rotation before

moving the input selector!

The FFPre outputs hiss when an open input (no cartridge connected) is switched

acti e, because in this case the thermal noise produced by the cartridge load resistor

Rmc is not shunted with the low impedance generator coils of a cartridge. The

magnitude of the hiss noise is proportional to the resistance alue of Rmc.

The FFPre is grounded in the sense that there is a conducti e connection between

the central zero point of the circuit and the ground terminal of the power inlet

module (and thus a conducti e connection between circuit zero potential and

earth/ground by means of the respecti e lead of the power chord). On rare

occasions, residual hum may arise in a setup with the FFPre due to the so called

ground loop effect, which typically comes into play when more than one component

of a system is grounded in the abo e sense.

Multiple grounding in a s stem can be resolved b interrupting abundant earth

connections either b adjusting ground lift switches or, in case ground lift switches are

not in place, b substituting 3-core power chords b 2-core parts!

The FFPre is equipped with six tubes (4x12J5GT+2xPC86 on MKII units and

4x12SN7GT+1xPCC88 on MKI units respecti ely). These tubes are unarguably among

the most linear amplification de ices e er de eloped in the history of electronic

technology. The amplifier comes with a set of new-old-stock tubes which ha e been

hand-picked to meet tight specifications.

The use of tubes with questionable characteristics ma lead to degraded noise and sonic

performance of the amplifier. Even serious damage ma occur in worst case scenarios!

Never switch on the amplifier unless ALL tubes have been installed!

Never pull a tube out of the socket while the amplifier is powered on!

Alwa s deinstall the tubes and wrap them up in the original protection case before

transporting or shipping the amplifier!

SETUP

To setup the FFPre power off all de ices of the system and proceed as follows.

0. Do not connect the amplifier to the mains until steps 1 to 8 ha e been taken.

1. Make sure that the frontal power switch (NETZ) rests in OFF (AUS) position.

2. Bring the master power switch on the power inlet module into the ON position.

Switch off the amplifier at the power inlet when the unit will not be used for a longer

period of time!

3. Ascertain that both olume control knobs rest in zero position or at least at a ery

low angle of rotation.

4. Remo e the top lid of the amplifier (eight metric 2.5 Allen-screws to release) and

install the tubes carefully. Ascertain that the guide pin of the octal base tubes is

properly aligned with the socket opening! Tighten the screws properly when

reinstalling the lid so as to ensure a proper conducti e connection between the lid

and the chassis. Take care to place the lid on the chassis with correct orientation (5

slot stars head-on, 4 stars on the rear side).

Never power on the FFPre unless ALL tubes have been installed!

Never pull a tube out of the socket while the amplifier is powered on!

Alwa s deinstall the tubes and wrap them up in the original protection case before

transporting or shipping the amplifier!

Keep the original crate (including the four soft foam inla s and the tube protection case)

for later use. It has been specificall designed for safe transport under rough conditions!

5. Bring the FFPre into its final position. Obser e the remarks made on optimal

positioning in the paragraph NOISE PERFORMANCE.

The FFPre requires considered placement for noise-free operation!

Place the FFPre on the RIGHT side of the rack to avoid/minimize electromagnetic

interference with other components of the s stem!

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. If one or more single-coil cartridges is to be used in dual-channel

mono playback mode, follow the instructions gi en in the respecti e section of this

manual to ensure a proper installation. Note that the amplifier is internally grounded

in the sense that there is a conducti e connection between the central zero point of

the circuit and the ground terminal of the power inlet module (and thus a

conducti e connection between circuit zero and earth/ground by means of the

respecti e lead of the power chord).

7. Connect line le el program sources to suitable line le el inputs (4/5/6).

8. Connect the FFPre to the power amplifier (acti e loudspeaker, subwoofer).

Choose a reasonably low gain on the power amplifier in case this de ice allows for

gain adjustment. If our EHT mono block is used for power amplification, set the gain

selector to position 1 (lowest possible gain). Re-consider/adjust the gain setting on

the power amplifier after the setup has been completed until optimal gain matching

between the FFPre and the power amplifier is attained with respect to the efficiency

of the loudspeaker. This is the case when the olume controls of the FFPre rest close

to the middle position for con enient listening loudness.

9. Connect the FFPre to the mains with a 3-core power chord.

10. Power on the program sources.

11. Select the desired program source with the input selector.

12. Power on the program sources (while the FFPre is still powered off).

13. Switch on the FFPre while the power amplifier remains powered off. Wait for at

least 1 minute until the warm-up process on the amplifier has come to an end.

When powering on the s stem, alwa s switch on the program sources and the FFPre

before the power amplifier, observing a dela of at least 1 minute!

14. Complete the setup procedure by switching on the power amplifiers (acti e

speakers, subwoofer).

Never switch the FFPre on or off while the power amplifier is on!

When powering off the s stem, alwa s switch the FFPre and the program sources AFTER

the power amplifier, observing a dela of at least 30 seconds!

FUSE

The FFPre draws a current of 0.3A/0.6A from the 230Vac/115Vac mains

corresponding to a power consumption of 70 watts. It is protected with a

1A slow-blow 5x25mm fuse

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