SPL Passeq User manual

PASSEQ
Passive Mastering Equalizer
• Test Report
• Manual / Handbuch

PASSEQ
Passive Mastering Equalizer
Manual

Content
PASSEQ
Version 1.2 – 12/2017 2
Package Contents 2
Introduction 3
King of the passive equalizers 3
Technical Aspects 4
120 Volt Technology 4
120 Volt Technology - Diagrams 5
The Basics of Frequency Filtering 6
Filter Types 6
Shelf Filters 6
Peak Filters 6
Bandwidth 6
Passive EQs 7
Installation 8
Voltage Selection 8
First Steps 8
Cabling: Rear Side 9
XLR inputs and outputs 9
Control Elements 11
Layout of Control Elements 12
Frequency 12
LF+ and LF- 12
MF+ and MF- 13
HF+ and HF- 13
Q (HF+ Band) 13
Gain 14
Output 14
Channel Switch 14
Auto Bypass 14
Recommendations on using Equalizers 15
Basic Approaches and Working Techniques 15
EQ Yin & Yang 15
First cut, then boost 15
Specications 16
Measurements 16
Security Advices 17
Contact 19

2
Version 1.2 – 12 / 2017
Developer: Wolfgang Neumann
This manual includes a description of the product but no guarantee as for specific charac-
teristics or successful results.
Unless stated otherwise, everything herein corresponds to the technical status at the
time of delivery of the product and user manual by SPL electronics GmbH.
The design and circuitry are under continuous development and improvement.
Technical specifications are subject to change.
Package Contents
PASSEQ Passive Mastering Equalizer
Power cord
Manual
The PASSEQ Equalizer is available in different colors.
Black: Modell 1650
Red: Modell 1654
Do consider keeping the original packaging. It can come in very useful whenever you need
to transport your gear. If there is ever the need to send it in for repair, the original packag-
ing guarantees a safe shipment.
The SPL PASSEQ Mastering Equalizer was designed, developed and manufactured in
Germany.

3
Introduction
King of the passive equalizers
The PASSEQ Mastering Equalizer is a dual-channel, passive equalizer.
The PASSEQ Mastering Equalizer – Model 1650/1654 is a new revised edition of the well-
known SPL Passeq – Model 2595.
Both units are based on our 120V Rail Technology. The new PASSEQ Mastering Equalizer
features the same high-quality characteristics as the previous model, though it was
revised and optimized to fulfill all requirements of a Mastering Equalizer.
The Passeq of the first generation was the first passive equalizer which provides three
separate frequency ranges for the boost and the cut stages. With 12 switchable frequen-
cies per band, totaling 36 boost and 36 cut frequencies, the Passeq was the most power-
ful passive EQ system ever made. The new PASSEQ Mastering Equalizer features the same
amount of cut and boost frequencies, though the choice of frequencies was changed and
the Q-factor was individually newly adjusted for every selectable frequency with an opti-
mal coil, condenser, resistor combination. Each boost and cut frequency now got an indi-
vidual optimized Q factor. Especially the mid bands are much more harmonious for work-
ing on program material than they were on the previous model. When we were fine-tun-
ing, through component selection, within countless listening sessions, the focus was on
receiving musically sounding curves, which are clearly on par with legendary devices like
the Pulteq EQ from the decades of the 1950’s and 60’s, but without all disadvantages
of a 60-year-old original, like a high noise level and most of all a very limited choice of
frequencies.
All passive filter components (variable resistor, capacitor and coil) deliver excellent sonic
characteristics. An important part of this process is played by coil and condenser loading
and saturation characteristics. The resulting inertia in contrast to the characteristically
extremely fast reaction of active filters is the reason for pleasant, beneficial sonic char-
acteristics. We tend to perceive these attributes in terms of an increased suppleness and
transparency, with perceptibly improved, silky highs and warm and punchy basses.
Another highlight of the new PASSEQ is the HF+ Band, which was expanded with the fre-
quencies 25kHz and 35kHz, sounding so incredibly good, that you don‘t want to turn it off
anymore.
Thanks to the big detented output control, you can increase or attenuate the output level
by 10dB, to reach following devices with the perfect desired level. This is important, espe-
cially when it comes to mastering. A fader ranging from 0dB to limitless, like the previous
model provided, would not be helpful in this case. With the PASSEQ you can also adjust
the parameters Gain, Q (HF +) and Output in 41 steps with the detented potentiometers.
All other parameters can be adjusted with 12-position switches. Thanks to these switches
and detented potentiometers, a precise recall is very easy to realize.
In addition to that, the handling of the PASSEQ Mastering Equalizer was improved through
small corrections of the positioning and naming of the control elements. Like all new
SPL Mastering devices, the new SPL PASSEQ provides an Auto Bypass. Of course each
of the two channels can also be manually activated or deactivated with the big illumi-
nated pushbuttons. Thanks to the Auto Bypass, this can also be realized automatically in
a freely selectable time frame.

4
Technical Aspects
120 Volt Technology
SPL‘s goal was to push analog signal processing to the limits. That‘s why we combined the
best possible components with a high-grade optimized circuit design.
We have been using the in-house developed 120-volt technology - the highest-ever oper-
ating voltage used for audio applications - in all our products from the Mastering series
for years. Some of the most highly respected Mastering studios today revolve around
SPL consoles and signal processors from our Mastering series (Bob Ludwigs Gateway
Mastering & DVD in the USA, Simon Heyworth‘s Super Audio Mastering in the UK, Galaxy
Studios in Belgium, and the legendary Wisseloord in the Netherlands, for instance).
The 120-volt technology is based on op-amps developed internally by SPL‘s co-founder
and Chief Developer Wolfgang Neumann. The PASSEQ features the most advanced gen-
eration of these op-amps. They boast with even better tech specs thanks to the thermal
behavior optimization they underwent under the hands of Bastian Neu.
Ultimately, the supply voltage is key for the overall dynamic response of a processor.
Voltage is to an electrical circuit what cylinder capacity is to an internal combustion
engine:
You can‘t replace cylinder capacity with anything else, except more cylinder capacity.

5
Technical Aspects
120 Volt Technology - Diagrams
These diagrams clearly show the advantages of our 120-volt technology in comparison to
other circuits with a lower operating voltage. The direct relation between operating level
and maximum level is fundamental for the classification: the higher the operating level,
the higher the maximum level a circuit can handle. And since virtually all essential acous-
tic and musical parameters depend on this relation, a higher operating voltage also
has a positive impact on the dynamic range, distortion limit and signal-to-noise ratio. The
result is a clearly more laid-back and natural sound with less unpleasant coloring.
Do bear in mind that dB scales do not represent linear but rather exponential increases. A
3 dB increase corresponds to doubling the acoustic power, +6 dB correspond to twice the
sound pressure level, and +10 dB correspond to twice the perceived loudness.
When it comes to volume, the 120-volt technology exhibits a performance that is twice
that of common components and circuits, in regard to maximum level and dynamic range,
with values that are approximately 10 dB higher. THD measurements of the SPL op-amps
show a difference of more than 3 dB compared to the OPA134 at 36V — in terms of sound
pressure level, that corresponds to an improvement of more than 50%.
The operating level most commonly used for audio equipment is 30 volts.
120
125
130
135
140
145
dBu Dynamic Range
OPA 134@30 VOPA 134@36 VSPL-OP@120 V
124,2
129,1
141,4
0
5
10
15
20
25
30
35
dBu
OPA 134@30 VOPA 134@36 VSPL-OP@120 V
21,5 22,5
33,2
Maximum Levels
0
20
40
60
80
100
120
Volt
+/- 15 Volt +/- 18 Volt +/- 60 Volt
30 V
36 V
120 V
Operational Voltages
-115
-113
-111
-109
-107
-105
dBu TL 071@30 VOPA 134@36 VSPL-OP@120 V
106
111,7
114,2
THD&N

6
The Basics of Frequency Filtering
Filter Types
There is basically only one type of filter used in the PASSEQ: The bell-filter or peak-filter.
But since the center frequency of the peak-filter, concerning the HF and LF bands, is only
marginally within the perceptible hearing range, these filters auditorily and visually rather
correspond to shelf-filters.
Shelf Filters
A shelf filter increases or decreases the energy of all frequencies above or below a chosen
frequency. Depending upon the direction of processing one refers to high frequency (HF)
or low frequency (LF) shelf filters. Beginning with the threshold frequency, the frequency
band is boosted or cut much like a shelf. The maximum boost or cut achieved at the point
furthest from the threshold frequency. The threshold frequency is usually about 3 dB less
(with the overall increase set to maximum). This gives the typical rising form of the shelf
filter’s response curve.
Peak Filters
A peak filter boosts or cuts a chosen frequency‘s energy with a maximum amplitude and a
definable frequency range around this frequency with a fall off of up to 3dB to both sides.
The chosen frequency with the maximum amplitude is called center frequency—it takes
place in the middle at the peak of the response curve. The response curve forms a bell,
thus peak filters are also often referred to as bell filters
Bandwidth
The width of a frequency range or band is musically defined in octaves. The technical
counterpart to this is the “Quality” of a filter, and the abbreviated “Q” is the most com-
mon value for the bandwidth of a filter.
A high Q value means a narrow bandwidth while a smaller Q factor corresponds to a wider
one:
Bandwidth 2 Octave: 0.7 Q
Bandwidth 1 1/3 Octave: 1 Q
Bandwidth 1 Octave: 1.4 Q
Bandwidth 1/2 Octave: 2.8 Q.