THÖRESS
Dual Function Amplifier
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“DFAmp”
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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 Dual Function Amplifier (DFAmp)!
The DFAmp represents an ultimate implementation of a line control amplifier and a
headphone driving amplifier. Both functions are performed by the same minimalist
vacuum tube circuit with very low output impedance. The amplifier is built with
meticulous hand construction using our proven point-to-point hard 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. Please read the following explanations and
instructions carefully to get the most out of your amplifier.
GT SELECTOR
The DFAmp allows for subtle tonal manipulations via four on-the-fly selectable tone
control presets (timbre registers) on two different gain levels implemented by means
of a 6-position rotary switch which we call GT Selector (EMPFINDLICHKEIT & KLANG,
G/AIN and T/ONE). Position 3 and 6 of the GT selector are assigned with neutral
tonality (flat frequency response). The mapping between selector positions, gain and
sound effects is described by the chart below.
pos1: (-)6dB gain, bass boost style-3 and treble boost > B(+++)/TR(++).
pos2: (-)6dB gain, treble boost > B0/TR(+).
pos3: (-)6dB gain, NEUTRAL > B0/TR0.
pos4: full gain, bass boost style-2 > B(++)TR0.
pos5: full gain, bass boost style-1 > B(+)/TR0.
pos6: full gain, NEUTRAL > B0/TR0.
Notably, the timbre registers act in a much more subtle way than common bass-and-
treble tone control facilities and do not rely on clumsy and sound degrading
conventional tone control circuitry. Each register is realized by interposing solely one
additional capacitor (per register and channel) to the neutral mode circuit!The timbre registers of the DFAmp are implemented without the aid of conventional clumsy and
sound degrading tone control circuitry!
The timbre registers are useful for restoring tonal imperfections of the listening
program (often given by a lack of extension on one or both ends of the audio band)
and for equalizing the response of individual headphones by adding bass and/or
treble extension to a given component. The bass + treble boost register assigned
with pos1 of the TG selector can also be used for counteracting the so called
loudness effect (weaker perception of bass and treble frequencies at lower
loudness). In practice, a combination of all three equalizing purposes will likely be
simultaneously applicable.
Use the 4 timbre registers (GT selector pos1/2/4/5) for counteracting tonal imperfections of the
listening program and for equalizing the response of headphones!
The boosting introduced by the timbre registers is obtained by attenuating the mid
band gain of the amplifier with respect to the gain at upper or lower frequencies of
the audio band. Thus, the volume needs to get (slightly) adapted after the GT
selector has been moved in between pos1/2/3 or pos4/5/6 in order to preserve the
effective listening loudness of the foregoing sound image.
The impact of the timbre registers is to a certain degree dependent on the volume
control setting: the higher the angle of rotation the more pronounced the sound
effect (whereas the effect declines towards the end of the rotational range). Hence
the user can tune the impact of the timbre registers to his requirements by
connecting the program source to inputs with higher or lower gain characteristic
(see below) and/or by choosing a higher order lower gain on the power amplifier (in
case this component allows for gain adjustment).
INPUTS
The DFAmp comprises 6 line level inputs (2×6 RCA jacks) divided in 3 groups with
different gain and input impedance characteristics as described below.
High Gain on Inputs 1/2/3
The gain on inputs 1, 2 and 3 is 26dB (20-times) and 20dB (10-times) with GT
selector in pos4/5/6 and pos1/2/3 respectively. These inputs offer a comparatively
high input impedance of 80.000 ohms and are suitable for classic analogue program
sources such as phono preamplifiers, tuners or tape machines.
Medium Gain on Inputs 4/5
Inputs 4 and 5 are appropriate for medium output program sources such as CD/DVD
players, streamers or DACs, offering 18dB gain (8-times) 12dB (4-times) with GT
selector in pos4/5/6 and pos1/2/3 respectively. The input impedance on these
inputs is 30.000 ohms.
Low Gain on Input 6Input 6 (input impedance 30.000 ohms) is assigned with an exceptionally low gain of
10dB (3-times) and 4dB (1.5-times) with GT selector in pos4/5/6 and pos1/2/3
respectively. This input is reserved for sources with exceptionally high output
characteristic as they are found on some CD players and DAC-s with vacuum tube
output circuitry. This input can also be used for enhancing the impact of the timbre
registers as described in the section GT SELECTOR.
Summarizing, the gain pattern on the inputs is
(20, 20, 20; 12, 12; 4)dB and (26, 26, 26; 18, 18; 10)dB
with GT selector in pos1/2/3 and pos4/5/6 respectively.
OUTPUTS
The outputs of the circuit simultaneously terminate in triple main output ( 3x2RCA
jacks on the rear panel) and a frontal 3-step toggle switch which feeds the two
adjacent headphone outputs KH1 and KH2 (2×6.35mm jack sockets). The line
outputs are connected to the circuit permanently whereas the headphone outputs
can be disengaged by setting the toggle switch to the middle position. Thanks to the
triple master output it is possible to simultaneously drive up to two pairs of power
amplifiers and an active sub-woofer without further adaptation.
Use the toggle selector to activate or disengage the headphone outputs,
(left, middle, right) —> (KH1 on, KH2 off . KH1+KH2 off . KH1 off , KH2 on)!
Do not activate a headphone output/headphone during the warming-up phase of the amplifier!
Do not switch the DFAmp on or off while a headphone is connected, and the respective output is
switched active!
Always disengage the headphone outputs (toggle selector in middle position) before connecting
or disconnecting a headphone unit!
Do not forget to switch off the power amplifier (active loudspeaker, sub-woofer) before using
the DFAmp in headphone driving mode!
Always make sure that the headphone outputs are disengaged (toggle selector in middle
position) before using the DFAmp in line mode (loudspeaker playback), even when no
headphone unit is connected!
The circuit of the DFAmp consists of a (phase-inverting) triode gain stage (12J5GT or
6J5GT tube) followed by a (phase-neutral) unity-gain current buffer (12GN7 power
tube operated at high idle current). As a result of this purist concept the output
signal is phase-inverted (shifted by 180 degrees) relative to input signal. Users who
make a point of a formally correct over-all signal phase in their system can apply a
simple corrective (in case it is known that all other components of the system offer
phase neutral operation).
To ensure a formally correct over-all absolute phase of the signal in a setup including the DFAmpthe loudspeakers ought to be connected to the power amplifier with reversed polarity (red
binding post of the amplifier connected to the black speaker terminal)!
HEADPHONES
Listening to recorded music through headphones is not merely an emergency
substitute for loudspeaker playback but can be a thrilling and enjoyable listening
experience in its own right. There are remarkable differences between the two
listening scenarios worth a closer consideration…
At first, in case of loudspeaker playback the acoustical property of the listening
environment characterized by the trinity of reverberation behavior, room mode
patterns (both of which phenomena are related to sound REFLECTIONS at the room
boundaries) and grade of diffusion has a strong influence on the over-all sonic
outcome. Room mode patterns are specific areas in the auditory, where the sound
power distribution peaks or dips thanks to standing waves between pairs of room
boundaries, particularly opposite walls (one distinguishes between axial, tangential
and oblique modes). Room modes are strongly frequency dependent and especially
relevant and critical at low audio frequencies where the wavelength of the sound
waves approach the magnitude of the room dimensions (below 330Hz,
corresponding to a wavelength of about 1m). Some rooms have less critical mode
patterns than others but the occurrence of room modes as such cannot be avoided
or overcome (unless the room is an acoustically dead so called anechoic chamber).
Consequently, the placement of the loudspeakers and the listening position
(stereophonic triangle) are critical setup parameters which need to be carefully
chosen and finely tuned in order to obtain optimal sonic results in a given auditory.
Detecting an optimal stereophonic triangle is a matter of playing out one acoustical
detriment for another and always comes down to a compromise between ground
tone and sub-bass response at the listening spot. Fortunately, at least the
reverberation and diffusion properties of the auditory can be controlled to any
desired degree by installing appropriate absorber and diffusor elements (the larger
the auditory the more elaborate provisions are needed for impactful acoustical
tuning). Proper acoustical tuning inevitably goes along with a sacrifice of space and
more or less invasive interventions in the interior of the auditory (a suspended
acoustical ceiling being the least obtrusive yet still highly effective tuning option).
By contrast, the transducer capsules of headphones couple directly to the ear drum
of the listener. So the signal does not suffer any haze induced by the acoustical
imperfections of an auditory, in this case. As a result, high grade closed back
headphones are capable of phenomenal bass performance which can hardly ever
attained with loudspeaker playback even under the most fortunate conditions
(ultimate components, favorable room geometry, ambitious acoustical tuning,optimal stereophonic triangle).
Secondly, the vast majority of loudspeakers employ directly radiating cone
transducers and as such are highly inefficient power transformers (less than 2% of
the electrical power is converted into acoustical power). Therefor large cone
excursions and comparatively high electrical power levels are required in order to set
free even a modest level of acoustical power with ordinary loudspeakers. Moreover,
since the sound power density (acoustical power with respect to surface area)
discharged by a (omni-directional) sound source is a quadratic function of the
distance, a loudspeaker positioned say D=3m away from the listener has to radiate
about 6000 times higher an acoustical power than the transducer capsule of an
over-ear headphone (d=0.039m) in order to evoke the same loudness at the
eardrum of the listener, 6000=square(D/d)=3m/0.039mx3m/0.039m. So very low
(acoustical and electrical) power levels are typically involved with headphone
listening, which obviously benefits transducer accuracy (midget cone excursion) and
fidelity of the driving amplifier (very low non-linear distortion). For example, a 60
ohm headphone with ordinary efficiency can be easily driven to a saturated loudness
level with a voltage swing well below 5Vpp (Vpp denotes voltage measured peak-to-
peak), corresponding to a maximal impulse power of about 0.05 watts,
0.05W=(5Vppx5Vpp)/(8x60ohm).
So obviously there are good reasons in favor for headphone listening!
As in case of loudspeakers, headphones should sound as neutral as possible. Neutral
in the sense that the timbre of musical instruments is replayed with utmost
accuracy. In order to meet the neutrality demand a headphone capsule obviously is
required to evoke an in-ear presentation which is tonally equivalent to the
presentation of a calibrated high grade monitor loudspeaker in a favorable acoustical
environment at the designated sweet spot. A requirement which is as easy to
formulate as it is hard to translate into a framework of measurable targets. In fact
this coherence relation is still under research and a point of discussion among
experts until the present day.
The first attempt to determine practical criteria for neutrality with regard to
headphone capsule design was based on the analysis of the response measured at
the alleged eardrum position of a dummy head (supposed to mirror the
physiognomy of the average human) evoked by a loudspeaker calibrated for even
response in the acoustically standardized environment of a reverberatory chamber
(total reverberation, zero absorption, so called DIFFUSE FIELD CONDITIONS). This
procedure has obvious shortcomings: heads, auricles and ear canals of humans differ
considerably and a reverberatory chamber is by no means comparable with an
acoustically tuned monitor room of a sound studio. Moreover, this analysis does not
take into account the ability of humans to perceive structural- borne sound (via boneconduction) which, as psycho-acoustics has revealed, is an inseparable and non-
negligible element of our sense of hearing.
More recent research carried out by HARMAN International Industries have put
forward elaborated variants of the diffuse field target response curve (Harman target
response curves for over-ear/on-ear/in-ear headphones) by also taking into account
subjective ratings of a group of (trained and non-trained) test persons in order to
narrow down the notion of neutrality in the context of headphones. Latest AKG
(nowadays a brand of Harman International) headphone models, K371 for example,
are claimed to meet a Harman target response curve, whereas the equally highly
acclaimed Beyerdynamic DT-770 PRO series of headphones (described below)
follows the original diffuse field target response specifications.
As if the conditions were not difficult enough to analyze, there are other effects
related to the headphone apparatus themselves which make things even more
complicated at the design stage. The tonality of the presentation is namely also
dependent on the distance of the diaphragm to the eardrum, the clamping force and
ear cup seal. (The first dependency of which is more pronounced with headphones
employing a dome diaphragm, while it is fairly negligible with components
employing planar transducers.) Therefore, the perceived tonality is to some degree
related to the physiognomy of the listener. Moreover, the concrete form of the
dummy head used for evaluation at the design stage inevitably leaves its mark on
the response characteristic of the headphone component under creation.
The foregoing remarks may be taken for an explanation why the majority of
headphone products deviate to such a high degree from neutrality, and as a matter
of consequence, why advanced music lovers tend to dismiss headphone listening.
Neutrality is especially critical with open-back headphones, which typically suffer
from a more or less severe lack of bass extension and therefor tend to sound
incomplete and dissatisfying. Planar magnetic components with full size transducers
are an exception to this rule. However, here an impeccable bass response is achieved
at the expenses of weak treble extension and inaccurate sound color rendering,
hence some other form of haze/coloration. Headphone manufacturers do their best
to mask these tonal issues by all kinds of gimmicks and artifices in order to endow
their open-back headphone models with a still fairly consistent over-all tonality and
idiosyncratic presentation, which at last prove to be efforts with questionable
success.
Use professional grade circumaural CLOSED BACK headphones whenever it is possible. It is a
widespread missapprehension that open-back headphones are generally superior to closed back
models. The contrary is the case!
In the following four HONEST sounding closed back headphone models are
described in detail. Each of which model has proven to offer a high degree of tonalneutrality combined wide band response and great clarity of presentation, and
therefor to measure up to the expectations of a discerning music lover. Only one of
the four models obligatorily needs mild equalization support via the timbre registers
of the DFAmp in order to procure impeccable tonal balance. These assessments are
based on extensive long term listening tests of the designer of the DFAmp himself.
Audio Technica ATH-M70x
Over-ear, closed back, dynamic driver capsules, 35 ohms, detachable straight and
coiled cables.
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The M70x is the flagship of the highly regarded Audio Technica Monitor Series of
professional grade headphones. A working horse intended for demanding sound
studio applications. Not as widely known as the classic Sony MDR-7506 cans
described below. But certainly, superior to the Sony old-timers in many respects. The
honest presentation delivered by these cans is exemplary. They offer full and well
extended yet tight bass response, uncolored mids and crisp high frequency
performance in beautiful balance. It cannot be denied that the M70x are slightly too
bright sounding but by no means are they aggressive or piercing. Which make these
headphones perfectly suitable for the reproduction of program with a dull tonality (a
characteristic often found on (non-remastered) monophonic and early stereophonic
recordings of classical music). The M70x does sound most convincing with all kinds
of musical genres, just as one would expect from a component optimized for
accurate and neutral sound reinforcement.
In view of their well extended and highly resolvent treble performance the M70x is
particularly suitable to replay music with highly complex sound texture, for example
cantatas or oratorios of classical music. All in all the flagship model of the Audio
Technica M-Series of headphones are amazingly consistent sounding headphones
(without equalization in the electronic domain!) and are, in our estimation, among
the best headphones available on the market. The M70x readily debunks open-back
legends like the Sennheiser HD600, HD800 or the Audeze LCD3 as useless costly toys
when it comes to uncolored and honest playback.
Fostex T40RP
Over-ear, closed back, planar-magnetic, 50 ohm, detachable straight long and short
cable.
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The Fostex T40RP is the closed-back model of the famous Fostex RP series of
headphones. A truly classic headphone component (in production since the 1970s)
featuring small size planar magnetic transducers with a diaphragm surface area
comparable to the effective cone area of a typical dynamic capsule! These cans have
a beautiful tone and offer a very uncolored refined midrange performance (although
admittedly the upper bass noticeably bleeds into the mids) yet suffer from weak androlled-off treble response. Fortunately, the lack of treble definition is not as
pronounced as with most planar magnetic components employing full size
transducers (Audeze, for example). The user can make a virtue out of necessity and
activate the T40RP for playback of too bright and thin sounding program. Or when
he is in the mood for enjoying music in a very smooth, laid-back manner.
Alternatively, he can equalize the T40 by activating one of the timber registers with
treble boost (pos1/2 of the GT selector) in order to transform these cans into a truly
world class component capable of reproducing music in a highly convincing way
irrespective of genre.
Sony MRD-7506
cable.
Over-ear, closed back, dynamic driver capsules, 63 ohm, non-detachable coiled
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These headphones, in production since more than 40 years, are generally considered
as sound studio standard for recording, monitor and mixing applications. This
reputation is well justified. In the low end they are full-bodied but very tight
sounding, with remarkable extension in the sub-bass. The mid-range presentation is
highly resolved and is complemented with a crisp and amazingly coherent treble
response, though not quite as well extended as in case of the M70x described
above. Over all these headphones deliver a tight, articulate and highly involving if
not explosive “”close to the ear”” performance which is very satisfying with all kinds
of musical genres. The only notable deviation from neutrality occurs in the presence
region (1-3kHz) where the Sony cans are slightly too forward sounding. Which, on
the one hand, make them ideal for playback of program which tends to lack
presence articulation and bite yet, on the other hand, less suitable for playback of
sensible classical music where highly precise sound color rendering is crucial
(classical chamber music, for example). The sonic presentation of the MDR-7506
profits from mild treble boost (GT selector, pos2) when a well extended slightly
pronounced treble response suits the program.
Beyerdynamic DT 770 PRO 80 ohm
Over-ear, closed back, dynamic, 80 ohm, non-detachable cable.
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Beyerdynamic is a famous german company (with very long history) which
specializes in headphones and microphones for professional use. Beyerdynamic
headphones enjoy a high reputation among musicians, sound engineers and
audiophiles worldwide. This holds particularly for the DT-770 PRO family of closed
back headphones (available with 16, 35, 80 and 250 ohm capsule impedance) which
have been specifically designed for demanding sound studios application where
neutrality and high resolution are crucial features. These headphones, constructed
to follow the classic diffuse field target response, combine elaborate design (allessential parts are replaceable), excellent built quality and favorable sonic
capabilities at a ridiculously low price point. In our experience the 80 ohm model is
the most neutral sounding variant of the 770 family, so it is no wonder that the “”DT-
770 PRO 80 ohm”” described and recommended here is by far the most widely used
headphone from the Beyerdynamic product line.
As for the sound characteristic, first of all, it should be noted that the 770/80 excels
with an exceptionally firm and well extended bass response (due to a unique bass
reflex design). Which makes the 770/80 a joy to listen to when bass lines are an
impellent force of the musical program. The midrange performance is impeccable
yet slightly recessed with respect to the bass (this characteristic is definitely
overdone in the DT-1770 TESLA derivate, a model not described and not
recommended here). The treble response of the 770/80 is quite in balance with the
bass, which gives the over-all-response a mild V-shaped characteristic.
Another peculiarity of the 770/80 (applicable to all Beyerdynamic headphone
models) is the comparatively large air chamber between the driver capsules and the
ear drum which promotes a certain airiness of the sound image (wide sound stage),
an effect which is further yielded and supported by the recessed midrange response,
by the way. In this respect the 770/80 differs from the characteristic of the other
headphones models described above, which subjectively tend to place the musical
movement closer to the ear. The designer of the DFAmp generally prefers a more
immediate presentation but readily admits that the more distant and spacious
presentation of the 770 has its own appeal. Nevertheless, the 770/80 is capable of
reproducing all kinds of musical genres in a convincing manner and there is no doubt
that this headphone model belongs to the exquisite guild of honest sounding
headphones (without support of equalization in the electronic domain!).
The ATH-M70x, T40RP (equalized in the described manner), MDR7506 and DT770/80
represent the “”holy quartet”” of neutral headphones. Every music lover who is
interested in headphone playback should own these components for reference!
NOISE PERFORMANCE
Much care has been taken in arranging each aspect of the internal construction of
the DFAmp so as to achieve an extraordinarily good noise performance. However,
electromagnetic leakage fields emitted by mains transformers or switching mode
power supplies of other electronic devices positioned in the vicinity of the DFAmp
may under unfortunate circumstance induce hum into the signal lines of the
amplifier via electromagnetic interference. Thus:
The DFAmp requires considered placement for optimal performance!
Idle noise 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 occur when both conditions arise simultaneously.
In order to avoid idle noise issues and to ensure conveniently fine volume
adjustment the gain of the power amplifier needs to be properly matched to gain of
the DFAmp with respect to the efficiency of the loudspeaker. Proper matching can be
easily achieved in case the power amplifier allows for gain adjustment. In a matched
scenario the volume 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 may become audible in the system when the gain of the power amplifier is not
properly matched to the gain of the DFAmp with respect to the efficiency of the loudspeaker!
The DFPre outputs slight hiss noise after the moment of powering on. The noise
fades away after the warming-up process of the amplifier has come to an end. When
a headphone is (accidentally) switched active during the warming-up phase a
pronounced switching transient and voltage surge (limited to +/-15V) will be passed
on to its transducer capsules. Therefor it is advisable to observe a delay of at least
one minute after the moment of switching on before activating a headphone. The
switching transient is of negligible magnitude when the amplifier has reached a
stable operation mode (a few minutes after the moment of switching on).
Do not activate the headphone outputs during the warming-up phase of the amplifier!
Never switch the DFAmp on or off while a headphone is connected and switched active!
Always make sure that the headphone outputs are disengaged (toggle selector in the middle
position) before connecting or disconnecting headphones to the DFAmp!
TUBES
The DFAmp is equipped with four vacuum tubes, 2x12J5GT+2x12GN7 (or
2x6J5GT+2x12GN7). The 6J5GZ/12J5GT is a medium-gain octal-base single-triode
with fairly low transconductance from the early times of the tube era, whereas the
12GN7 is a late all-glass high transconductance power tube with high gain
capabilities, making it an ideal choice for buffer applications. Both tubes are
unarguably among the most linear amplification devices ever developed in the
history of electronic technology. The amplifier comes with a set of NOS tubes which
have been hand-picked to meet tight specifications.
The use of tubes with questionable characteristics may lead to a degraded performance of the
amplifier. Even serious damage may occur in worst case scenarios!
SETUP
To setup the Dual Function Amplifier power off all devices of the system and proceedas follows.
Do NOT connect the amplifier to the mains until steps 1 to 10 have been taken.
1. Make sure that the frontal power switch is in OFF (AUS) position.
2. Bring the master power switch on the power inlet module into the ON position.
It is advisable to switch off the DFAmp at the power inlet when the unit will not be used for a
longer period of time!
3. Move the GT selector to pos6 (full gain, neutral tonality).
4. Bring the ground switch (GSW) on the rear panel into position ERDE
(earth/ground). With this GSW setting the amplifier is grounded in the sense that
there is a conductive connection between the central zero point of the circuit and
the ground terminal of the power inlet module (thus a conductive connection
between circuit zero and earth/ground potential by means of the respective lead of
a (3-core) power chord). This connection can be interrupted by bringing the GSW
into the LIFT position in order to overcome multiple grounding in the setup, which
typically results in hum issues due to the so called ground loop effect.
Use the GSW to overcome hum issues caused by multiple grounding in the setup!
5. Make sure that the headphone output selector rests in the middle position (AUS,
both headphone outputs KH1 and KH2 disengaged).
6. Turn the volume control knob (manually) to a very low angle of rotation.
7. Remove 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 conductive connection between the lid
and the chassis. Make sure that the lid sitts on the chassis with correct orientation (5
slot stars head-on, 4 stars on the rear side).
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!
Always 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 inlays and the tube protection case) for later
use. It has been specifically designed for safe transport under rough conditions !
8. Bring the amplifier into its final position.
9. Connect the program sources to suitable inputs. Make sure that these
components are powered off before setting up these connections.
10. Connect the DFAmp with the power amplifier (active speakers, subwoofer).
Choose a reasonably low gain on the power amplifier in case this device allows for
gain adjustment. If our EHT mono blocks are used for power amplification, set the
gain selector to pos1 (low gain). Re-consider the gain setting on the power amplifier
after the setup has been completed until optimal gain matching with the DFAmp isattained with respect to the efficiency of the loudspeaker. This is the case when the
volume control knob of the DFAmp rests near the middle position for convenient
listening loudness.
11. Connect the DFAmp to the mains with a 3-core power chord.
LINE OPERATION
12. Power on the program sources (while the DFAmp is still powered off).
13. Switch on the DFAmp while the power amplifier is still powered off. Wait for at
least 30 seconds until the warm-up process on the amplifier has come to an end.
14. Switch on the power amplifier.
When powering off the system, always switch off the power amplifier first and then power off
the DFAmp and the program sources, observing a delay of at least 30 seconds!
Always make sure that the headphone outputs are disengaged (toggle selector in middle
position) before using the DFAmp in line mode (even when no headphone is connected)!
15. Listen to music through the loudspeakers. Adjust the listening volume manually
or via remote control. Use the timbre registers (GT selector pos3/4 and pos 5/6) to
enhance the presentation if necessary. The minimalist control module features only
two pushbuttons (volume up, Lauter and volume down, Leiser) and is powered by
2pcsxAA batteries (not delivered with the unit). The batterie compartment is locked
with a metric size 2.5 Allan screw.
Do not forget to switch off the power amplifiers (active speakers, sub-woofer) before employing
the DFAmp in headphone driving mode!
Never switch the DFAmp on or off while the power amplifiers OR a headphone is connected and
switched active!
HEADPHONE DRIVING MODE
16. Make sure that the power amplifiers are switched off and that the headphone
outputs KH1 and KH2 are disengaged (toggle selector in middle position).
Do not forget to switch off the power amplifiers (active loudspeakers, sub-woofer) before
employing the DFAmp in headphone driving mode!
17. Activate the desired headphone output with the toggle selector.
18. Listen to music. Adjust the listening volume manually or via remote control. Use
the timbre registers (GT selector pos3/4 and pos 5/6) to enhance the presentation if
necessary. The minimalist control module features only two pushbuttons (volume
up, Lauter and volume down, Leiser) and is powered by 2pcsxAA batteries (not
delivered with the unit). The batterie compartment is locked with a metric size 2.5
Allan screw.
Always disengage the headphone outputs (toggle selector in middle position) before
disconnecting/de-installing a headphone!Never switch the DFAmp on or off while a headphone is connected and switched active!
Do not activate the headphone outputs during the warming-up phase of the amplifier!
Always disengage the headphone outputs (toggle selector in middle position) before using the
DFAmp for loudspeaker playback (even when no headphones are connected)!
Always disengage the headphone outputs (toggle selector in middle position) before powering
off the DFAmp, even when no headphones are connected!
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THÖRESS…
A Tribute to Professional Audio Components
from the Golden Age of the Vacuum Tube !
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