THÖRESS PHONO ENHANCER MKIII Manuel utilisateur

THÖRESS

Parametric . Phono Equalizer . Series

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"PHONO ENHANCER MKIII"

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I N S R U C I O N M A N U A L….........

Thank you for purchasing the THÖRESS Parametric Phono Equalizer!

You have acquire a highly versatile vacuum tube phono preamplifier offering MM

an MC amplification with excellent signal-to-noise performance in purely active

operation mo e (without the ai of built-in step-up transformers) an unique on-

the-fly tone a justments by means of three 6-position rotary switches TCSW1,

TCSW2, TCSW3, which we call tone selectors. The tone selectors give rise to subtle

bass, mi le tone an treble control functions which are highly effective tools for

restoring tonal imperfections of the replaye vinyl program (eventually intro uce

uring the recor ing or cutting process), implemente without involving clumsy an

soun estructive conventional tone control circuitry!

The amplifier is built with meticulous han 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 an

ease of service for many years to come. Please rea the following explanations an

instructions carefully to get the most out of your phono preamplifier.

INPUTS

The amplifier comprises 6 phono inputs with gain pattern (5xMC+1xMM), five inputs

with 65 B MC gain an one input with 45 B MM gain (presenting a stan ar 47K

loa to the cartri ge). Alternatively, a gain pattern (1xMC+5xMM) can be

implemente on request. However, it is not possible to install an arbitrary MC+MM

gain pattern on the amplifier for technical reasons. The cartri ge loa ing is

(100, 200, 300, 500, 1000 / 47.000) ohms an (500 ohm/47K, 47K, 47K, 47K, 47K).

on (5xMC+1xMC) an (1xMC+5xMM) stan ar units respectively. Other loa values

can be easily installe on eman .

The MC load values installed on each individual MC gain input are printed on the rim of

the rear panel for reference!

It is not possible to install arbitrary MC+MM gain patterns on the Phono Enhancer for

technical reasons!

OUTPUTS

The output impe ance of the amplifier is sufficiently low (aroun 300 ohms) to

simultaneously rive (up to 3) long cable runs an line inputs with an input

impe ance as low as 10.000 ohms without compromising soun quality. The 3 B-

own frequency un er 10.000 ohm loa ing is still well below the au io ban (lower

than 5Hz, output coupling capacitance 3.3MFD). The circuit outputs terminate in 2x3

RCA jacks connecte in parallel. This esign choice is useful for proper (hum-free)

ual-channel mono installation with single-coil cartri ges, without inconvenient

a aptions, as escribe in a e icate paragraph of this manual.

Connect the Phono Enhancer to input 1, or 3 in case our Dual Function Amplifier is used

for line amplification!

PHONO EQUALIZATION AND TONE CONTROL

The gain of a phono amplifier varies with frequency in or er to restore the pre-

emphasis intro uce to the signal uring the recor cutting process. Therefor a

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

pre/ e-emphasis characteristic is completely an unambiguously etermine by a

set of e ge frequencies (equivalent to so calle time constants)

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

The phono gain rises below f2 (bass boost) an falls off above f3 (treble

attenuation/roll-off) with a slope approaching 6 B/octave. The ifferences between

the various pre/ e-emphasis prescriptions establishe by prominent recor

companies in the inception of high fi elity au io are rather small, often negligible,

whereas in the most cases the crucial bass-turnover frequency f2 equals 500Hz. A

few examples of prominent e-emphasis prescriptions are given in terms of e ge

frequencies an time constants at the en of this manual.

The Phono Enhancer performs highly accurate RIAA de-emphasis when the tone selectors

rest in default position,

(TCSW1, TCSW , TCSW3) = pos(6, 6, 1) > (f1, f , f3) = (50, 500, 1 4) Hz.

RIAA is the most wi ely use equalization characteristic given by the NEW

ORTHOPHONIC prescription establishe by RCA along with vinyl MICROGROOVE isc

in the late 1940s, which later on was appointe as phono playback stan ar .

Notably, the tonal footprints of in ivi ual recor s (even between those issue by the

same recor company in the same perio of time) vary much more wi ely than the

tonal ifferentiation even between the most istinctive e-emphasis prescriptions,

hence

Humble de-emphasis curve selectors are not suitable for restoring optimal tonal balance

of analogue disc records. They are useless, misleading and puzzling to the user!

By contrast, the Phono Enhancer allows for highly impactful yet subtle tone control

via e ge frequency shift! Tonal manipulations of this kin have a much stronger

impact in restoring a satisfactory tonal balance of a given recor when a juste

intuitively by ear

rather choosing the e ge frequencies to formally suit the e-emphasis prescription

associate with the recor company an the vintage of the recor . In or er to

etermine selector settings which gives the most satisfactory tonal balance for a

given recor procee as follows.

STEP 1

Adjust the SONIC PRESENCE with TCSW .

Edge frequency f ===> middle-tone (MITTELTON).

Listen carefully to the recor with tone selectors in efault position pos(6, 6, 1). Turn

mi le-tone switch TCSW2 counter-clockwise to a lower position if you observe a

isturbing sharpness in the sonic presentation. This manipulation increases the bass-

turnover frequency f2 an such gives rise to a smoother (warmer) sonic

presentation. Conversely, turning TCSW2 clockwise upwar s lifts the presence of the

soun image whereas the most vivi presentation is reache in pos6 (RIAA,

f2=500Hz).

Determining the optimal position of TCSW is a crucial part of the sound enhancing

procedure!

STEP

Determine the optimal

DISTANCE AND EXTENT OF THE SOUNDSTAGE

by adjusting TCSW1.

Edge frequency f1 ===> bass (BASS).

Lowering the position of TCSW1 lifts the low frequency response of the amplifier

(relative bass boost below 100 Hz) in a subtle way an such lea s to a presentation

with more punch an bo y. Also, the soun stage will appear eeper, wi er an

more istant.

Weak low end extension of the program can be compensated by lowering the position of

TCSW1!

The boosting effect is obtaine by attenuating the mi ban gain of the amplifier

with respect to the low frequency en . Consequently, in or er to maintain the

listening lou ness of the previous soun image, the volume nee s to get a apte on

the line evice after moving TCSW1.

Adapt the listening volume in order to maintain the listening loudness after moving

TCSW1:

TCSW1 moved counter-clockwise > volume(+),

TCSW1 moved clockwise > volume(-).

Moving TCSW1 counter clockwise to a lower position will also smooth out any

sharpness possibly left in the soun image after step 1 has been taken. This effect is

the more pronounce the lower a position has been previously chosen for TCSW2.

Thus a recor which is exceptionally thin an sharp soun ing with RIAA settings

(6/6/*) will soun more full bo ie when both selectors TCSW1 an TCSW2 rest

below the RIAA efault positions. Since recor s from the early times of high fi elity

au io were often cut at the low en of the au io ban , the bass boost facility

associate with TCSW1 (an in irectly with TCSW2) is a impactful tool for restoring

the original soun image of an ol recor ing session.

STEP 3

Tune the BRIGHTNESS and TREBLE RESOLUTION with TCSW3.

Edge frequency f3 ===> treble (HÖHEN).

Finally, attention shoul be given to TCSW3. The function associate with this switch

is very similar to the treble function of a conventional tone control facility, although

its effect is much more subtle. Turning this knob clockwise upwar s to a higher

position lifts f3, hence re uces the amount of treble attenuation in the e-emphasis

an thus lea s to a brighter sonic presentation. When TCSW3 rests in position 6 the

frequency response of the amplifier is flat above the bass-turnover frequency f2 (no

treble attenuation).

Many early microgroove recor s soun more appealing when the treble switch

TCSW3 is set to an elevate position in or er to brighten-up the sonic presentation.

However, as an unwante si e effect of treble boosting, groove noise may become

more clearly au ible. So treble resolution must occasionally be sacrifice to a certain

egree in or er to keep the groove noise floor at an acceptable level (especially

when the recor in question happens to be in poor con ition). The most effective

metho for cleaning recor s is escribe at the en of this manual.

Record cleaning is a crucial activity for all vinyl lovers who wish to fully exploit the sonic

capabilities of the Phono Enhancer!

STEP 4

Verify the determined selector settings and

RECORD THE OPTIMAL CONTROL PATERN FOR LATER REFERENCE.

Recor the positions of TCSW1, TCSW2 an TCSW3 establishe so far as a temporary

result. Then critically check an re-consi er the settings by comparing an re-

evaluating the soun images while switching the selectors one or two steps upwar s

an ownwar s from the previous optimum. Once a final ecision upon the optimal

selector settings for the given recor has been ma e the result might be written on

the recor sleeve for later reference.

PHONO CARTRIDGES

Early microgroove recor s carry a monophonic signal written into a LATERALLY

excite triangular spiral groove of constant epth. Such FIRST-GENERATION

microgrooves were originally meant to get tracke by a spherical 25-micron stylus

mounte to a MONO-FLEXIBLE cantilever (25-micron refers to the spike ra ius of the

iamon /sapphire tracking tip). A mono-flexible cantilever is one which oes not

comply in vertical irection.

By contrast, the groove of a stereophonic recor carries two signals (more or less

sharply separate from each other) co e LATERALLY AND VERTICALLY into the

groove by also varying the epth of the groove relative to the recor surface

(concomitant with the lateral groove mo ulation). Consequently, stereophonic

cartri ges have to be fitte with an OMNI-FLEXIBLE cantilever, one which complies in

all egrees of free om.

A phono cartridge with mono-flexible cantilever will seriously and irrecoverably damage

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

A stereophonic cutting hea pro uces a monophonic groove when it is fe with

i entical signals on both channels. A groove obtaine in this manner is significantly

narrower than a first-generation monophonic microgroove, ue to the new groove

stan ar s intro uce for stereophony, whereas a 17-micron stylus (instea of 25-

micron) was specifie for tracking such SECOND-GENERATION microgrooves. During

the stereophonic era more sophisticate stylus profiles (Shibata, Micro Ri ge,

Paratrace, Gyger, van- en-Hull...) have been evelope from the humble spherical

17-micron stylus in or er to re uce tracking istortion an to enhance tracking

ability of phono cartri ges. These mo ern stylus profiles provi e the further

a vantage of re uce recor an stylus wear on account of an increase contact

area (line contact) between the stylus tip an the groove walls.

Phono cartridges with a sophisticated stylus profile tend to (drastically) outperform

cartridges fitted with a humble spherical stylus tip!

A phono cartridge with omni-flexible cantilever and a spherical 5-micron stylus can

faithfully track (NARROW) second-generation microgrooves, likely with reduced tracking

ability, although this type of stylus was originally intended for tracking (WIDE) first-

generation microgrooves!

Conversely, every phono cartridge with a spherical 17-micron stylus (or one of its modern

derivatives) can faithfully track (WIDE) first-generation microgrooves although this type

of stylus was originally intended for tracking (NARROW) second-generation

microgrooves!

Stereophonic grooves are mono-compatible in a two-fol sense...

At first, every monophonic cartri ge with omni-flexible cantilever (an a stylus

profile suitable for early or secon -generation microgroove rea ing) is able to

faithfully track stereophonic grooves whereas the fairly well separate R an L

signals are converte back into a consistent mono signal. Hereby the signal

generator of the monophonic cartri ge transforms only the lateral excitations of the

stylus into signal while vertical stylus movements o not contribute to signal

conversion. Cartri ges with a monophonic generator ignore vertical stylus

movements even when they are fitte with an omni flexible cantilever! Secon ly,

every stereophonic cartri ge is able to rea both, early an secon -generation

monophonic microgrooves faithfully, whereas i entical signals are evelope in the

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

expose to lateral excitation only. In reality vertical movements of the stylus ue to

groove imperfections (warp, irt, scratches) are converte into signal an such a

noise artifacts to the wante cartri ge output.

Every stereophonic cartridge is capable of faithfully track both early and second-

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

dedicated mono cartridges!

Stereophonic cartridges with a sophisticated stylus are not only suitable for faithful

tracking of (early and second-generation) monophonic microgrooves, but tend to

(drastically) outperform dedicated mono cartridges fitted with a humble spherical stylus

tip!

The majority of currently pro uce high-gra e monophonic MC cartri ges are

erivatives of stereophonic mo els an as such employ a ual-coil signal generator

(two separate generator coils terminating in 4=2x2 output terminals) an are fitte

with an omni-flexible stylus. The only ifference to the correspon ing stereophonic

variants is that the generator coils are not arrange at a 45- egree angle to the

tracking plane, as it is nee e for stereophonic groove rea ing. Examples of omni-

flexible ual-coil mono cartri ges are the AUDIO TECHNICA AT33-Mono, the LYRA

mono cartri ges an the DYNAVECTOR DV-X1s-Mono.

Use a DYNAVECTOR DV-X1s-Mono for ultimate playback of monophonic microgroove

recor s!

Mono-flexible single-coil MC cartri ges are currently pro uce by MIYAJIMA LAB in

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

The highly outstan ing TEDESKA mono cartri ges ma e in Berlin by Hyun Lee are

other examples of mono-flexible single-coil MC cartri ges of current pro uction.

Whereas the ORTOFON Mono CG-25 an the EMT OMD-25 are wi ely known classic

single-coil MC cartri ges (pick-up hea s). These ol -timers offer an astonishingly

goo sonic presentation even when ju ge by to ay-s stan ar s. However, they

cause excessive recor an stylus wear ue to their spherical iamon profiles an

tracking weights in excess of 4 grams, especially when combine with vintage

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

maximum soun quality an preservation of valuable recor s is the main goal.

Nevertheless, they will be an obvious choice when it is aime to compose a setup for

authentic monaural playback.

SINGLE-COIL MONO

A monophonic cartri ge with DUAL-COIL generator outputs two copies of the

monophonic signal an therefor allows for ual-channel mono playback within the

regular stereophonic wiring scheme. However, if the 4 input terminals of a

stereophonic phono preamplifier (hotL, groun L, hotR, groun R) with single-en e

(non-balance ) circuit topology are wire to a SINGLE-COIL cartri ge via a

stereophonic tonearm cable, in an attempt to distribute the monophonic signal

over the stereo channels for dual-channel mono playback, groun L an groun R

will unavoi ably meet at the cartri ge terminals (2 contact pins) or within the

cartri ge bo y (2x2 contact pins pairwise internally connecte in parallel). An

unwante con uctive connection is forme which will evoke resi ual hum in the

amplifier ue to the so calle GROUND LOOP EFFECT. This is not a peculiarity of the

Phono Enhancer but hol s generally for phono amplifiers with a single-en e (non-

balance ) circuit topology!

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

stereophonic phono preamplifier with non-balanced circuit topology!

The Phono Enhancer allows for hum-free dual-channel mono installation with single-coil

phono cartridges on each individual input!

Monophonic MC cartridges with DUAL-COIL generator (two separate generator coils

terminating in x contact pins) can be used on any MC input of the Phono Enhancer

without adaptation!

The key to hum-free ual channel mono installation with single-coil cartri ges in the

context of with single-en e (non-balance ) phono equipment is to istribute the

monophonic signal over the channels at the OUTPUT of the phono preamplifier

rather than at the cartri ge terminals, in the manner exemplarily escribe below.

SINGLE-COIL MONO INSTALLATION (with MKII and MKIII units)

Precautions at the Input

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

esire phono input. Insert the R-plug of the tonearm cable in one of the RCA jacks

(labelle SINGLE-COIL MONO) below the phono inputs. These jacks are not

connecte to the circuit an solely serve as ummy terminations to receive i le RCA

plugs of stereophonic tonearm cables. Connect the groun wire of the tonearm

cable to one of the groun terminals as usual. This installation obviously avoi s the

critical con uctive connection between groun L an groun R an such permits

hum-free amplification of the monophonic signal in the L-section of the phono

preamplifier, while the R-section of the amplifier runs at i le (is not fe with signal).

This wiring scheme is obviously also applicable an meaningful with ual-coil mono

cartri ges, although it is not obligatory for noise suppression in this case.

SINGLE-COIL MONO INSTALLATION (with MKI units)

Precautions at the Input

Insert the R-plug of the (stereophonic) tonearm cable into the R-jack of the esire

phono input. Let the L-plug of the cable hang freely an isolate the armature of this

plug with the ai of a small test glass (or similar accessory) in or er to prevent

unwante contacts. This installation avoi s the critical con uctive connection

between L-groun an R-groun an ensures hum-free amplification of the

monophonic signal trough the R-section of the phono equalizer, whereas the L-

section runs at i le (is not fe with signal). This wiring scheme is also applicable an

meaningful with ual-coil mono cartri ges, although it is not obligatory for noise

suppression in this case.

SINGLE-COIL MONO INSTALLATION

Precautions at the Output

Switch the esire single-coil cartri ge active on the Phono Enhancer. Choose an

unassigne input of the line amplifier. This input, in the following enote by MON

for the sake of convenient explanation, is exclusively reserve for ual-channel

mono playback. STER be the line input employe for regular stereophonic phono

playback fe by the Enhancer through an interconnect cable IC1 in the usual manner.

Prepare an i le (or inary stereophonic) interconnect cable IC2 in or er to establish a

secon connection (Phono Enhancer > line amplifier), in a ition to the existing

cable connection IC1. On the receiver si e (line amplifier) the plugs of IC2 go into the

jacks of MO in the usual manner. However, on the Phono Enhancer insert BOTH

plugs (R+L) of IC2 into unemploye L-channel output jacks (possible since the Phono

Enhancer features 3 pairs of output jacks). This installation obviously istributes the

mono signal appearing at the L-signal output of the phono amplifier over the L+R

channels of the line evice (Y-connection). The system is will be rea y for replaying

mono recor s in ual channel mo e with the chosen single-coil cartri ge once input

MO has been switche active on the line evice.

Note that the system will replay the L-signal on both loudspeakers (rather than a

consistent stereophonic signal) when you (accidentally) play a stereophonic cartridge

through MO!

When you play a single-coil cartridge trough STE the mono signal is replayed on the L-

loudspeakers only (while the R-Loudspeaker runs at idle)!

Some phono evices with non-balance circuit topology feature a so calle MONO

SWITCH. Here the monophonic signal is istribute over the channels at the input

(hence groun loop noise is in uce ), processe in the initial L an R amplifier stages

( istorte in each branch), MIXED together somewhere in the mi le of the circuit

an then re- istribute over both channels of the following circuitry, whereas the

groun loop noise intro uce to the wante signal in the initial amplifier stages

cancels away uring the mixing process. Obviously a clumsy an soun estructive

concept!

Mono switches rely on clumsy, sound destructive circuitry and therefor are not suitable

when ultimate sonics are the aim!

LATERALY ENCODED 78RPM RECORDS

The groove co ing on lateral mono 78rpm recor s is similar to the co ing of

microgroove recor s (laterally excite triangular spiral grooves of constant epth).

However, the ancient grooves are consi erably wi er (an eeper) than early or

secon -generation microgrooves an are meant to get tracke by a spherical 65-

micron stylus. Stereophonic MM (moving magnet) cartri ges with a 65-micron stylus

tips are rea ily available an the performance offere by these humble pick-up

evices is more than sufficiently goo for a equate 78rpm playback.

78 rpm records can be adequately tracked and reproduced with a humble stereophonic

MM cartridge of current production with a spherical 65-micron stylus!

Since 78rpm recor s were cut without treble pre-emphasis an often lack bass

extension, they will likely soun best when equalize with zero treble attenuation

(infinite f3), maximal low frequency extension (f1 as low as possible) an regular

bass-turnover frequency (f2=500Hz), even when the formal bass turnover-frequency

associate with the recor company an the vintage of the recor happens to be

lower than 500Hz.

78rpm records with standard grooves are likely to sound best with selector settings

(TCSW1, TCSW , TCSW3) = pos(1, 6, 6)!

Nevertheless, lower bass-turnover frequencies than 500Hz can be easily

implemente on some positions of TSCW2 on eman , for those users who

specialize in 78rpm playback an place importance on more finely gra uate bass-

turnover frequency selection.

SUBSONIC ARTIFACTS

Coupling capacitor values between the amplifier stages of the Enhancer have been

carefully chosen so as to give a very low cut-off frequency while provi ing a certain

amount of attenuation of subsonic frequencies (unwante but not always avoi able

artefacts). However, notably the FFPre oes not incorporate e icate subsonic

filtering. The amplifier will therefore pitilessly reveal subsonic artefacts which may

have creepe in the signal ue to improper phono installation (turntable poorly

isolate against structure borne noise, too low resonant frequency of the tonearm-

cartri ge combination, or comparable shortcomings).

The Phono Enhancer does not employ high-slope subsonic filters!

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

seriously compromising soun quality!

NOISE PERFORMANCE

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

ensure low noise performance of the amplifier in spite of a purely active operation

mo e (without the ai of passive step-up transformer gain). However,

electromagnetic stray fiel s emitte by mains transformers or switching mo e

power supplies of other electronic evices positione in the vicinity of the Phono

Enhancer may un er unfortunate circumstances in uce hum in the amplifier via

electromagnetic interference.

The Phono Enhancer requires considered placement for optimal signal-to-noise

performance!

Place the Phono Enhancer on the right-hand side of the rack in order to avoid/minimize

electromagnetic interference with other components of the setup!

The Enhancer outputs a pronounce switching transient (bump noise) when the

input selector is move from pos5 (MC gain) to pos6 (MM gain) or backwar s. This

effect is unavoi able for technical reasons. If the switching transient acci entally

reaches the power amplifiers (an thus the lou speakers), no harm will occur within

a setup consisting of THÖRESS components, even when our higher power amplifiers

(SE845 or EHT mono blocks) are part of the setup. However, there might be worst

case scenarios beyon our imagination (soli state amplifiers with huge power

output an too inertial protection circuitry, exceptionally fragile lou speakers etc.)

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