SPL 9738 User manual

Model 9738
Manual
Dual Channel Parametric Tube/LC Equalizer

By Hermann Gier and Paul White
Version 2.2 - 1/1999
The information in this document has been
carefully verified and is assumed to be correct.
However Sound Performance Lab (SPL)
reserves the right to modify the product
described in this manual at any time. Changes
without notice.This document is the property
of SPL and may not be copied or reproduced
in any manner, in part or full without the
authorisation of SPL.
Limitations of Liability:
In no event will SPL be liable for any
damages, including loss of data, lost profits,
cost of cover or other special, incidental,
consequential or indirect damages arising
from the use of the unit, however caused and
on any theory of liability. This limitation will
apply even if SPL or an authorised dealer has
been advised of the possibility of such
damage.
SPL electronics GmbH
P.O.Box 12 27
D- 41368 Niederkruechten,Germany
Phone +49 - 21 63 / 98 34-0
Fax +49 - 21 63 / 98 34-20
eMail: [e-mail]
© 1999 SPL electronics GmbH. All rights reserved. QURE® is a registered trademark of SPL electronics GmbH.
Qure
Model 9738
Manual

3
Contents
Dear customer,
Thank you for the confidence you have shown towards SPL
electronics GmbH by purchasing the SPL QURE.You have decided to
use a tool of high performance which sets you in the position to
have faster success and a better sound quality in your music
productions and pre-masterings. As a typical SPL unit the QURE
combines exemplary specifications and high manufacturing stan-
dard with excellent sound quality to provide you a precious
component for recording purposes. Please read this manual
carefully to ensure you have all the information you need to use
the QURE. We wish you every success with it.
Your Sound Performance Lab-Team
I would like to start with my thanks to all our staff, who created
what is to be described here.The importance of their exceptional
qualification and talents cannot be overestimated.Special thanks
to Wolfgang Neumann for his exceptional creativity in EQ and
filter design.
Our products are often tested and compared in many publica-
tions and by our customers themselfs and constantly valued with
best results. I would like to pass on this broad appreciation to
those,who deserve it – my excellent colleagues.
Hermann Gier
Foreword
Thanks
Foreword............................................................................................... 3
Thanks.................................................................................................... 3
Introduction......................................................................................... 4
Operation Safety................................................................................. 7
Connections.......................................................................................... 8
Applications......................................................................................... 9
CONTROL ELEMENTS
WARM UP & READY .......................................................................... 10
MASTER ............................................................................................... 10
IN ........................................................................................................... 11
HF/LF CUT ON .................................................................................... 11
HF CUT.................................................................................................. 11
LF CUT .................................................................................................. 11
LF ........................................................................................................... 12
MF .......................................................................................................... 12
HF........................................................................................................... 13
BW.......................................................................................................... 13
B/C ......................................................................................................... 15
LF/MF/HF ON ..................................................................................... 17
QURE ON ............................................................................................. 17
QURE ..................................................................................................... 18
SHIFT QURE ......................................................................................... 20
OUT........................................................................................................ 20
Power supply........................................................................................ 21
Specifications....................................................................................... 22
Warranty................................................................................................ 23

4
Congratulations on purchasing the QURE, one of the most
advanced and musical sounding parametric equalizer currently
available.
The QURE is a fully parametric equalizer, specially designed to
meet the most demanding studio applications.It is designed as 3-
band, two-channel system with input and output gain controls,
high-cut and low-cut filters as well as the new QURE-circuitry for
the creative and corrective sound shaping of vocals, instruments
and complex stereo material. Both balanced XLR and balanced
stereo jacks are provided for signal connections to and from the
QURE.
Its musically optimized parametric filters, based on a sophisti-
cated refinement of state-variable-filter technology (SVF),include
proportional bandwidth, tube technology for a warm and fat
sounding mid-range, LC filtering for clear and transparent upper
frequencies,transistor and semi-conductor technology for a volu-
mious low end.
The proportional-Q principle provides precise control over a
frequency range,from 15Hz to 21kHz, while the low noise level of
-99dB (A-weightened), and the enormous dynamic range of
113dB,make the QURE ideally suited for mastering and cutting.By
employing circuitry designed around the principles of perceived
sound, rather than simply designing by numbers, the QURE over-
comes the limitations of conventional parametric equalizers.
The QURE circuitry
The QURE circuitry is a new SPL development which gives the
name for the unit and also represents a new technology, which
uses coils to increase the presence of vocals and the depth of the
music.At the same time it is ideally suited to cure recordings from
digital harshness. The name is derived from ‘cure’ in combination
with Q from EQ.
The signal runs through a tube circuitry featuring a Sovtek
12AX7 double triode tube in a mixed current/voltage coupling
mode. This stage is extremely clip-resistant and produces a plea-
sant and musical sounding tube-THD spectrum.
The QURE ON switch puts a coil/condenser/resistor filternet-
work (LCR) into the tube output stage.This network is integrated
into the coupling path of the tube and reacts on the dynamic
reponse of the input signal by influencing THD spectra and phase
response. The QURE potentiometer changes the frequency
response and produces a fresh and silky top-end and a mid-range
free of sharpness and harshness.The presence and‘aura’ of vocals
is largely improved.
The QURE is a parametric
equalizer for creative
sound design
The QURE combines a
technology-mix of five
decades of audio engineering
Exemplary specification
contribute to the excellency of
this EQ
The QURE circuitry improves
presence,clarity and depth.
It can also be used to cure
recordings from digital
harshness.
A new LCR network combined
with a 12AX7 tube reacts on
the dynamic response of the
audio and altersTHD and
phase response.
Introduction

5
Proportional Q
Unlike most other equalizers which use constant-Q filters, the
QURE adopts the proportional-Q principle to realize maximum
musicality. Conventional constant-Q designs keep the amplitude
constant,regardless of the adjusted bandwidth (Q).The disadvan-
tage of this is, when it comes to sound creation, frequencies
above and below the center frequency are often boosted so
intensely that they lose their musicality. With proportional-Q it is
quite different; the amplitude of the processed frequency band is
reduced as the bandwidth broadens. Adjusting the bandwidth
back to a narrow bandwidth (high Q), will increase the amplitude
of the center frequency to its former level. Furthermore, with
proportional-Q, there is no need to constantly readjust the
boost/cut control when varying the bandwidth – as is usually
necessary with constant-Q equalizers. It is generally perceived
that equalizers based upon constant-Q designs produce acousti-
cally comparable results, and suffer from limitations in the areas
of sound flexibility and musicality. Often there is only one truly
usable position on the Q-control.
The proportional-Q principle offers a wide range of possible
potentiometer settings and makes it easier to identify the desired
frequencies within the sound spectrum – even subtle nuances
become clearly audible.Equalizing with proportional-Q is therefore
more intuitive and subjectively musical than with constant-Q
equalizers. The QURE forms its response curve around the center
frequency with a bell-like response, so that frequencies closer to
the center frequency are emphasized slightly more; frequencies
further from the center are less affected. The development of
these filter curves was the result of extensive listening tests, and
the result is an equalizer that combines technical excellence and
precision with unsurpassed musicality.
The Frequency Bands
The QURE is configured as a two-channel, 3-band equalizer with
a separate hard-bypass switch for each band. The filters are
connected in series. The three filters bands cover a frequency
range from 15Hz to 21kHz. In addition each channel is equipped
with high- and low-cut filters.
Tuning the equalizer is very intuitive because the frequency
control law has been designed to match the characteristics of the
human hearing system.The perfectly linear phase response of the
QURE circuitry, combined with its wide bandwidth, contributes to
the sonic excellence of this esoteric equalizer.
The mid-band features the ‘non-reciprocal response’ of the
BOOST/CUT control which qualifies this band to operate as a
notch filter, too. Cutting is allowed to -36dB at high Q (Q5)
whereas the low and high band offer cutting of -15dB. The sonic
advantage of the ‘non-reciprocal response’ design is the vast
dynamic response making the filter sound very open and clear.
With the musical
proportional-Q principle the
amplitude of the processed
frequency band is reduced
as the bandwidth broadens.
Equalizing with
proportional-Q is more
intuitive and subjectively
musical than with
constant-Q equalizers.
The QURE is a two-channel,
3-band equalizer with the
filter bands connected
in series
The mid-band features
a‘non-reciprocal response’
of the BOOST/CUT control

6
Stepped potentiometers for
easy recall;individual bypass
for each filter band
Central grounded shield
layout,single op-amps,
Sovtek tubes,custom
made condensers
and potentiometers
General Features
To allow easy recall of all control settings the QURE is equipped
with stepped potentiometers throughout. The number of steps is
optimized to the control function: 11 steps for bandwidth, 31
steps for frequency and boost/cut, and 41 steps for input gain,
HF/LF Cut filters, and QURE control. Each band can individually be
switched in and out of the signal path making comparison easy
and avoiding the need to nullify the boost/cut control.
Each filter is mounted on a separate printboard featuring a
‘central grounded shield layout’ (CGSL) for maximum rejection of
interfering frequencies. Single op-amps are used throughout to
minimize noise and THD.The tubes in use are the well-acclaimed
Sovtek 12 AX 7. Furthermore selected custom made condensers
are used to produce harmonical and pleasant sounding THD
spectra.The frequency controls are also custom made featuring a
control characteristic that is designed to realize a gentle
frequency sweep with a musically optimized control range.
Overview
• 2x 3-band EQ with variable HF and LF cut filters
• QURE circuitry (Tube + LCR)
• Variable input gain (-12 dB to + 18 dB)
• Variable output gain (-7dB to + 4 dB)
• Hard-bypass for each filter band and both cut filters
• Master relay hard-bypass for entire unit
• Central Grounded Shield Layout
• SPL super-balancing hybrids (CCMR -90 dB)
• Tube warm up circuitry for prolonged tube-life
• Overrated internal toroidal power supply
• PREMIUM-Version (recommended):
LUNDAHL in- & output transformers (LL1539 & LL1540)

7
Important security advices
Operation Safety
The housing of the QURE has the standard 19"-EIA format and
occupies 2U (88.9 mm) in your rack. When installing the unit in a
19"-rack, the rear side of the unit needs some support, especially
in a touring case.
Choose the installation location of your unit carefully:
The QURE should not be installed near units which produce
strong magnetic fields or extreme heat. Avoid placing it in direct
sunlight.
Also avoid locations subject to vibration and excessive dust,
heat,cold,or moisture.
Keep it away from sources of hum such as transformers or
motors.
Do not install the QURE directly above or below power ampli-
fiers.
Check that the voltage details quoted on the back panel are the
same as your local mains electricity supply. Use a minus (-)
screwdriver to set the voltage selector to the voltage for the area
in which the unit will be used.
Never cover up the ventilation slots on the top of the unit. If,
during operation,the sound is interrupted or indicators no longer
illuminate, or if abnormal odor or smoke is detected, or if liquids
are spilled on the unit, immediately disconnect the power cord
plug and contact your dealer.
WARNING: Do not open the cabinet of this unit, because to do
so might result in damage to the unit,or injury by electric shock.If
any foreign object or substance enters the unit, contact your
dealer for assistance.To reduce the risk of electric shock, do not
expose this appliance to rain or moisture.
To prevent damage by lightning, disconnect the power cord
from the household AC outlet during an electrical storm. When
disconnecting the power cord from the household AC outlet,
grasp the plug; do not pull the cord. Refer servicing to qualified
personnel only!
Do not apply excessive force when using switches and controls.
When moving the unit, be sure to first disconnect the power cord
from the household AC outlet, and disconnect cords connected
to other equipment.
Do not attempt to clean the unit with chemical solvent as this
might damage the finish. Only clean the QURE with a clean, soft,
lint-free cloth.

8
THE QURE is fitted with both XLR connectors and TRS stereo jacks
for balanced operation,though the jacks may be used with unba-
lanced connections simply by plugging in mono jack-plugs. The
level difference that normally occurs when a balanced input or
output is used unbalanced is automatically compensated for.
Should the need arise to use the XLR connectors in an unba-
lanced system, pin 3 of the XLRs should be grounded. Inserting a
mono jack also unbalances the XLRs.
Both output stages operate in parallel, so it is possible to
connect two different destination units simultaneously, for
example to record to two different media at the same time or split
the output between a mixer and effects processor. However, only
one type of input (jack or XLR) should be connected at a time –
the QURE is not intended to be used as a mixer!
To ensure optimal signal quality, SPL has developed a super-
balancing hybrid input/output stage using all laser-trimmed resi-
stors with a tolerance of 0.01%.This approach has resulted in high
CCMR (common mode rejection) values better than -90 dB at
1 kHz.
As a precaution, before connecting the QURE switch off the
power to the unit and to all connected units.
Connections
12
3
Pin wiring: XLR connectors
1=GND 2=Hot(+) 3=Cold(-)
Pin wiring: Stereo Jack plug
Tip=Hot(+) Ring=Cold(-) Sleeve=GND

9
Application 1:
The QURE inserted into two
individual tracks
Application 2:
The QURE between playback
and recording unit
to treat a final mix
Applications
1.Processing single instruments or vocals
To process single instruments or vocals insert the two separate
QURE channels into the specific inserts of your console to process
two signals independently.
Note that the MASTER switch will bypass both channels
together. Use the bypass switch of each filter band when proces-
sing two independent sources.
You can also insert the unit into the master breaks during
mixdown or into the sub-groups, when specific elements of the
mix are being treated selectively.
When patching the QURE into the sub-groups or master-breaks
of the console, note if they are switched ‘pre’ or ‘post’ fader. They
should best be switched ‘pre’ fader, so that a variation of the
master fader does not affect the input level of the QURE.The effect
level and the treated sound will then remain unchanged.
2.Processing final mixes
To process a final mix, either while mixing or during post-
production prior to cutting insert the QURE into the master
inserts of your console or right in between a playback and a
recording unit.
The special characteristics of the QURE allow you to add weight
and punch to the bass end of a mix or to lift harmonic detail out
of the top end of a mix, without inadvertently adding harshness
or muddiness to the sound. In this respect, the QURE can produce
results every bit as dramatic as those achieved using sub-bass
synthesizers or harmonic generators, but without adding distor-
tion to the original signal.
Right channel into Qure input 2
Left channel into
Qure Input1
Output 2 into recorder in R
PLAYBACK
Insert send channel Y into Qure input 2
Insert return channel Y
Insert return ch. X
MULTI-TRACK
MISCHPULT
Insert send channel X
into Qure input 1
RECORDER Outp. 1 into recorder in L

10
Control Elements
The QURE features a special relay circuitry that slowly builds up
the 275 volts over a period of 45 sec. Thereby the lifetime of the
tubes is increased by up to four times. In pre-mastering this
circuitry garantees a reproducable sound for a long time. The
tubes in use are Sovtek 12 AX 7s.
The WARM UP-LED (red) illuminates after the main power has
been switched on.After 45 seconds it switches to READY (orange-
LED). The in- and outputs of the tubes are de-coupled at 10Hz
with condensers of high voltage and capacity (1 microFarad/
400 V/5%) to minimize offset and humming noise.
If the unit is already switched to active with the MASTER switch
during the warm up period you will not hear any processing until
the QURE switches to READY. Then the processed signal is swit-
ched to the outputs. Although you may not have done any equa-
lization to the signal you will hear a little difference between the
processed and the unprocessed signal because the tubes already
produce a portion of their typical sound.
MASTER switches the QURE´s entire sound processing on or off.
The illuminated switch indicates that the QURE has been activated.
The MASTER function is a relay-hard-bypass function which
links the input socket directly with the output socket to bypass all
filters by pressing just one button.
To increase operation reliability the QURE monitors the power
supply´s primary and secondary voltages and switches automati-
cally to hard bypass once certain tolerances have been exceeded
(power failure safety).
WARM UP &
READY
2
1
MASTER
2
1
3
4
5
6
7
11 1312
9
16
15 81410

11
IN
3
HF/LF CUT ON
4
HF CUT
5
LF CUT
6
The QURE features an IN control that enables you to set the level
at which the QURE filters operate. The level can be changed
between -12dB and +18dB.
To run the unit hotter set the level between the 0dB-position
and the clockwise position (up to +18dB).This will result in a more
intensely processed sound. Conversely, in order to achieve milder
processing, set the level between the 0dB-position and the
counter clockwise position (up to -12dB).
The IN control is followed by high (HF) and a low frequency (LF)
cut filters with individual frequency controls.The HF/LF CUT ON is
the hard-bypass switch for both filters. If the cut filters are not
needed the HF/LF CUT ON switch routes the audio around this
section to provide maximum audio quality when in bypass (LED is
not illuminated).
The HF CUT and LF CUT are usually used as a pair to provide
control over the extremes of the audio spectrum.
The HF CUT filter is a 2nd order Butterworth filter defining the
upper roll-off frequency the audio is to have.
Fully counter clockwise the control is set to its starting position of
20kHz. Even if the HF/LF CUT filters are activated there is hardly
any audible frequency limitation to the spectrum. All frequencies
below 20kHz are passing through.Turning clockwise reduces the
upper roll-off frequency until fully clockwise the minimum roll-off
frequency of 2.5kHz is reached.
Diagram 3 illustrates the frequency response curves for the
highest roll-off (20kHz) and the lowest roll-off frequency (2.5kHz).
The LF CUT filter is also a 2nd order Butterworth filter defining the
lower roll-off frequency the audio is to have.
Fully counter clockwise the control is set to its starting position of
40Hz. All frequencies above 40Hz are passing through. Turning
clockwise increases the lower roll-off frequency until fully clock-
wise the maximum roll-off frequency of 200Hz is reached.
Diagram 3 (page 12) illustrates the frequency response curves
for the lowest roll-off (40Hz) and the highest roll-off frequency
(200Hz).

12
The low frequency control (LF) operates over more than four
octaves. The center frequency can be varied between 15Hz and
365Hz.
Diagram 3:
Frequency responses for the
lowest (40Hz) and highest
roll-off (200Hz).
HF CUT:20kHz to2.5kHz
LF CUT:40Hz to 200Hz
Diagram 4:
Frequency responses for the
lowest (15Hz) and highest
(365Hz) LF control setting
at max.B/C and Q5
LF (Low Freq.) 7

13
Diagram 5:
Frequency responses for the
lowest (200Hz) and highest
(5kHz) MF control value at
max.B/C and Q5
Diagram 6:
Frequency responses for the
lowest (1kHz) and highest
(21kHz) HF control setting at
max:B/C and Q5
The mid frequency control (MF) also covers more than four
octaves.The center frequency can be varied between 200 Hz and
5 kHz.
The high frequency control (HF) covers more than four octaves.
The center frequency can be varied between 1kHz and 21kHz.
MF (Mid Freq.)
8
9HF (High Freq.)

14
The bandwidth (BW) control is identical for all three frequency
bands. The BW control determines the width (or the Q) the
frequency curve around the selected center frequency is to have.
The parameter is measured as a quotient Q of the following
formula: Q = (fofu)/ (fo-fu)
fois the upper corner frequency and futhe lower corner
frequency measured at the -3 dB point of the frequency curves.
Narrow bandwidth corresponds with a high Q and vice versa.
The BW is set to ‘high Q’ (Q5) when turned fully counter clock-
wise. The influenced range covers approximately 0.2 octaves.
Turning the BW control fully clockwise selects ‘low Q’ values
(Q0.5) covering approximately 2.5 octaves.
The QURE utilizes the proportional-Q principle, also known as
‘variable Q’. The amplitude varies depending on the Q setting.
Diagram 7:
All 11 steps of the BW control
from smallest Q (Q5) to broa-
dest Q (Q0,5) are shown.
The center frequency is1kHz.
The diagram is valid for both
LF and HF band.
Diagram 8:
As diagram 7,but for the
non-reciprocal response
of the MF band.
BW (Bandwidth) 10

15
Proportional-Q automatically
readjusts the amount of
boost or cut to keep the
subjectively perceived
loudness constant
Diagram 9:
Symmetrical frequency
responses at maximum boost
and cut and high Q (+/- 15dB,
Q5) for LF and HF bands.
Using low-Q values, automatically readjusts the amount of boost
or cut selected to keep the subjectively perceived loudness
constant.With constant-Q equalizers there is often only a limited
range of useable settings. Sometimes this is so narrow, you may
wonder why the Q control was not permanently fixed at the point
it sounded really good. Above that position it often starts to
sound harsh and peaky,and below with the broad bandwidth,the
sound is colored so you need to constantly re-set the boost/cut
control. Not so with proportional-Q. The Q control provides
useable settings over the entire range – giving you more versati-
lity to be creative. EQ adjustments with proportional-Q sound a
lot more musically related and offer a greater range of possible Q-
choices that really sound good and appropriate.Diagram 7 and 8
show frequency responses with varying Q and maximum B/C.
Tips on adjusting the bandwidth
Q adjustments are largely depending on the character of the
source material and whether processing single instruments or
vocals or final mixes.
Q values between 1 and 2 are useful to equalize vocals, guitars,
keyboard sounds and suchlike. When the bandwidth is broader
than half an octave it is easy to find and to manipulate the charac-
teristic elements.Very narrow Q values (Q3 to Q5) are often used
with high frequencies to eliminate disturbing frequencies within
cymbal sounds or to precisely emphasize the kick frequency of
the bass-drum or snare. Broader Qs are selected when boosting
dull source material which has lost high frequency content due to
de-noising,de-clicking and/or de-essing.To process bass frequen-
cies Q values are chosen between Q0.5 and Q0.8. Q values
between Q0,8 and Q1.2 are recommendable for frequencies
between 100Hz and ca.700Hz.
The BOOST/CUT control (B/C) of the LF and the HF frequency
band provides control ranges of +/- 15dB.
B/C (Boost/Cut)
11

16
The BOOST/CUT control of the MF band realizes maximum
boost of 15dB and maximum cut of -36dB.This response is called
‘non-reciprocal response’. Due to the enormous headroom of this
filter design the sound of the MF band is even more open and
transparent and almost unlimited in dynamic response.
All B/C controls feature stepped potentiometers with 31
detends which allow adjustments in steps of 0.5dB. Due to the
non-reciprocal response of the MF band the cut values are adju-
stable in 1dB steps.
Setting up procedure: When trying to locate the precise
frequency range requiring adjustment, set the B/C control fully
clockwise to provide maximum boost. By sweeping through the
frequency ranges, it should be easy to locate the precise
frequency range that needs cutting or boosting.
Diagram 10:
Frequency responses for max.
BOOST/CUT and low
Q adjustments (+/- 15dB,
Q0.5) for the LF and HF bands
Diagram 11:
Non-reciprocal responses of
the MF band (+/-15dB,Q5)
Stepped potentiometers for
easy recall and precision
adjustments of 0.5dB

17
Diagram 12:
Non-reciprocal responses of
the MF band (+/-15dB,Q0.5)
Once found, the B/C control can be backed off to provide the
desired degree of cut or boost and the Q setting adjusted by ear.
Initially, it helps to bypass the other equalizer sections so that you
can work on each equalizer independently.
When the equalizer sections have been set independently, they
can be switched in simultaneously with the MASTER switch and
further adjustments made if required. The OUT control can be
used to restore any level change caused by intensive EQ cutting
or boosting. Where more subtle treatments are required, the
QURE’s exploitation of psychoacoustic principles enables it to
significantly improve the focus, tonal balance and general clarity
of detail within a mix, with the bare minimum of processing.This
is particularly important when a client wants to improve the
sound of a mix but doesn’t want to make any significant change
to the overall tonal balance.Even filter boost/cut settings of half a
dB can bring about significant changes in the perceived quality of
the mix being treated.
Each filter band has an individual hard-bypass switch. It makes
comparison between processed and unprocessed signal easy
without having to reset the B/C control as with conventional EQ
designs.
The QURE ON switch activates the new QURE tube and coil
circuitry which is especially designed to clarify vocals and
increase their presence while at the same time the dimensionality
of the mix is improved.
Another interesting application is to combat digital harshness.
The QURE circuitry creates a ‘sonic blur’ which softens harsh and
edgy sounds and reduces ear fatigue.
12 LF/MF/HF ON
13 QURE ON

18
The QURE ON switch puts a coil/condenser/resistor filternet-
work (LCR) into the tube output stage.This network is integrated
into the coupling path of the tubes and reacts on the dynamic
reponse of the input signal changing THD spectra and phase
responses. It sounds similar to a ‘closed shelving bandpass’
frequency response, but with a time frame in which harmonics
are newly created or become more present in close relation to the
dynamic response of the source material.
Diagrams 13 and 14 show how the harmonic content is altered
of a period of 30 seconds. Diagram 13 shows a standard sweep
from 1kHz to 4kHz within that time frame and the corresponding
harmonical spectrum. Diagram 14 shows the treated signal with
the QURE circuitry. The comparison shows, although both
diagrams represent a linear frequency response, that the harmo-
nical structure after the QURE treatment is enhanced,new harmo-
nics have been created and existing harmonics show a more
stable response. Also, so-called ‘cross-harmonics’ (between the
main harmonics) are more intense. What cannot be seen are the
effects on phase response.
How to use the QURE circuitry
By activating the QURE circuitry the overall output level raises
inevitable by +2 dB. There are two ways to compensate for this
effect.
1. Activate the QURE circuitry (Press QURE ON) which lets the
output level raise by about 2 dB. Use the mid-range filter (MF) to
cut harsh or annoying frequencies with a medium or broader
bandwidth to achieve a linear frequency response. Use the QURE
control to select the frequency range.With the SHIFT QURE switch
you can jump from a high frequency range (2 kHz-6 kHz) to a
lower frequency range (400 Hz-2 kHz).
2. Activate the QURE circuitry (Press QURE ON) which lets the
output level raise by about 2 dB. Turn the OUT control counter
clockwise and compensate for the level increase.
The QURE potentiometer changes the frequency response and
produces a fresh and silky top-end and a mid-range free of shar-
pness and harshness.
Especially vocals gain clarity and presence. They seem to step
right in your face while at the same time the dimensionality of the
music is getting bigger.This sound pattern is achieved by simulta-
neously influencing THD spectra and phase responses.
The QURE potentiometer changes the center frequency of
processing from 2kHz (counter clockwise) to 6kHz (clockwise).To
process a deeper frequency spectrum use the SHIFT QURE switch
(see 15).
Integrating a coil/condenser/
resistor filternetwork (LCR)
into the signal path
Tips on using the
QURE circuitry
14
QURE

19
Diagram 13:
The diagram shows a
frequency sweep from 1kHz
to 4 kHz with the correspon-
ding harmonical structure
over a period of about
30 seconds.
The frequency response is
linear.
The MF band is active with
B/C set to zero.
Diagram 14:
By activating the QURE-
circuitry the harmonical
content is changed.
The MF-Band was used to
create a linear frequency
response.
Now the harmonics are
much more regular,almost
equalized.The density is
increased and also new
harmonics which are missing
in the upper diagram are
now present.

20
The SHIFT QURE switch changes the controllable frequency
range of the QURE control from 2kHz-6kHz (SHIFT QURE not
active) to 400 Hz-2 kHz when the SHIFT QURE is active and the
status-LED illuminates.
The signal runs through a tube circuitry featuring a Sovtek
12AX7 double triode tube in a mixed current/voltage coupling
mode.The output stage is extremely clip-resistant and produces a
pleasant and musical sounding tube-THD spectrum.
The OUT-control can attentuate up to -7dB in case that extense
equalization has been used or to compensate for the 2dB level
increase when the QURE circuitry is active. Cut values are
provided up to +4dB which may be used when intensive cutting
has led to a lower signal level.
15
SHIFT QURE
16
OUT