User Manual for
GROOVE SLEUTH MK.II
NON-EQUALISING
PHONO PREAMPLIFIER
(for needle-drop* recordings with Stereo Lab Software which is supplied
free with this product)
* A needle-drop is a term which means a version of a music album that has been transferred from a vinyl
record to a digital audio medium. Needle-drops are also sometimes called vinyl rips.
Version 5.1 (February 2018 – new universal Groove Sleuth Mk.II)
Chapter 1 - Introduction
Phædrus Audio's Groove
Sleuth Mk.II preamplifier
is designed to be used in
conjunction with Pspatial
Audio’s Stereo Lab
(Phonograph or
Audiophile) app which
runs under OS X on the
Apple Mac. Stereo Lab has
a wide feature set but it devotes a large part of its
functionality to software equalisation and
decoding of analogue records.
This isn't just technology for technology's sake.
There are real, audible reasons for doing this:
phase-linear warp and rumble filtering is only
possible in the digital domain and reveals a bottom
octave with unprecedented clarity and realism.
The accuracy of RIAA equalisation and perfect
channel balance ensures an uncoloured sound
with superb stereo sound staging. And the
flexibility in recording characteristics will bring to
life LPs you thought mediocre. Moreover, Stereo
Lab also includes software decoders for QS and SQ
quadraphonic and Ambisonic LPs; thereby bringing
life to forgotten, analogue, multichannel gems.
For Stereo Lab to process needle-drop captures
and equalise them, it needs recorded files of the
"raw" signal, direct from the groove, unfettered by
analogue equalisation. And that is where the
Groove Sleuth Mk.II preamplifier comes in. It is a
phono preamplifier of the very highest quality but
without equalisation, so that the signal fed to the
computer is the closest version of the signal direct
from the groove, but at a suitable amplitude for
digitisation. The Groove Sleuth Mk.II preamplifier
has various options to augment this basic task to
aid with monitoring and to ease integrating these
units into a high-quality audio system. These are
described in the pages that follow.
Chapter 2 - Safety
General
Before using any piece of equipment
manufactured by Phædrus Audio, be sure carefully
to read the applicable items of these operating
instructions and the safety suggestions. Keep them
for future reference. Follow the warnings indicated
on the unit, as well as in these operating
instructions.
THE USER SHOULD NOT ATTEMPT TO SERVICE THE
UNIT. ALL SERVICING SHOULD BE REFERRED TO
QUALIFIED SERVICE PERSONNEL OR FACTORY
ONLY.
Phædrus Audio products should NEVER be
connected to the external power supply or in any
other way energised when the case is opened
and/or the circuit boards are accessible.
General Safety Instructions
Do not operate this equipment near any
source of water or in excessively moist
environments.
Keep this equipment away from babies,
children and pets.
Do not let objects do not fall, or liquids be
spilled, onto the enclosure.
Situate this equipment away from heat
sources or other equipment that produce
heat.
Ensure this equipment has adequate
ventilation. Improper ventilation will
cause overheating, and can damage the
equipment.
When cleaning this equipment, remove
all connections to the unit; including
power and gently wipe with a clean lintfree cloth; if necessary, gently moistened
with lukewarm or distilled water. Use a
dry lint-free cloth to remove any
remaining moisture. NEVER use aerosol
sprays, solvents, or abrasives on this
equipment.
This equipment should be serviced by
qualified service personnel or returned to
Phædrus Audio when: an object (or
objects) have fallen into the enclosure; or
liquid has fallen into, or been spilled into
the unit; or the unit has been exposed to
rain or high humidity; or the unit does not
operate normally or exhibits a marked
change in performance; or the unit has
been dropped, or the enclosure has been
damaged.
Chapter 3 - Gramophone record
equalisation in software
The signal recovered from a gramophone
(phonograph) record via an electrodynamic pickup
(moving-coil or moving-magnet type) has the bass
drastically attenuated and the treble boosted.
Replay processing is therefore required to present
a complimentary characteristic to restore the
original audio balance. The electronic amplifier
which corrects for the equalisation applied during
recording is today universally called an RIAA
preamplifier. The design of good, accurate RIAA
equalisation has taxed the ingenuity of audio
hardware engineers for sixty years.
Pspatial Audio believe that, after 60 years,
hardware RIAA equalisation has just about reached
the end of the developmental road and that
equalisation is nowadays better performed in
software for the following reasons:
REASON 1: Greatly increased digital
resolution
Stereo Lab has internal processing in software
which uses double-precision floating-point math.
CD audio represents the audio signal with a
dynamic range of 96dB, smaller then than the
capacity of the human hearing system, which has a
dynamic range of about 120dB. The very best
analogue circuits can just about match this
dynamic range. But, by contrast, double precision
floating-point math is a binary format which has a
precision of 53 bits or 320dB. That's a dynamic
range which is ten billion (1010) times greater than
the hearing system.
REASON 2: Filter accuracy and stability and
perfect left-right channel matching
Even the very best electronic components can only
be manufactured with a certain degree of accuracy
which is rarely better than 1%. Physical
components are also subject to ageing such that
they go "off value". Digital processing ensures
perfect channel balance and frequency response
for ever, which guarantees an uncoloured sound
with superb stereo sound staging.
REASON 3: Better warp and rumble handling
- with phase-linear filtering in software
In a perfect world, all gramophone records would
be perfectly flat, there would exist no inevitable
resonance of the arm-mass and the stylus
mounting compliance and the mechanical
vibrations from the driving motor would be
eliminated. But LPs do not exist in a perfect world
so, when warp or rumble (as these imperfections
are named) are present, they are better
eliminated. The technique always employed to
remove these effects is high-pass filtering and that
is the approach taken in Stereo Lab too: a slightly
under-damped fourth-order filter may be
employed as a rumble filter so that the response
falls sharply below the audio passband. However,
very differently, the rumble filter is a phase-linear,
non-causal design which means there is no phase
distortion introduced. Phase distortion is
inevitable, real and audible in causal, filters and
can never be eliminated in analogue designs]. But
it is entirely eliminated in software processing. The
result is a bottom octave which will sound like
you've never heard it before.
REASON 4: Flexibility of equalisation
characteristics - to cope with records not
equalised with RIAA curve
Conventional wisdom has it that, by the mid-fifties
in a belle époque of international cooperation,
most American labels and most major European
labels had adopted the new RIAA standard and
had brought to an end a very chaotic situation
which had existed since the dawn of electric
recording in which the record companies all
specified different equalisation for their discs.
However, the truth is that many labels were much
slower to adopt the RIAA curve and disc recording
characteristics were not effectively standardised
until the late 1960s, or possibly even later. It is
therefore a great boon to the vinyl enthusiast to
have flexible equalisation characteristics. But such
flexibility, combined with perfect mathematical
precision is very complicated and expensive to
implement in hardware.
In providing digital equalisation as part of Stereo
Lab, Pspatial Audio wished to offer a
comprehensive range of these non-RIAA
equalisation options for gramophone disc
collectors whilst avoiding a complex and over
technical user-interface. So, Stereo Lab features
equalisation options to cover any disc (or indeed
cylinder) recording from the 1880s to the present
day.
Chapter 4 – The Groove Sleuth
Mk.II Preamplifier
The signal from a gramophone pickup is too small to
apply to the line input of most sound-cards or audio
interfaces. What is required is a dedicated phono
preamplifier to bring the small signal from the cartridge
up to a healthy level for input to the computer soundcard.
Many phono preamplifiers exist at all price levels
from a host of manufacturers. But, the vast
majority of the phono preamplifiers apply RIAA
equalisation in the hardware of the unit and that is
not what is required here. We need a preamplifier
which provides gain and impedance conversion,
without applying the equalisation. These are
unfortunately very rare, especially models which
guarantee extremely low-noise, exemplary
headroom, excellent linearity, and an accurate and
extended frequency-response. It is to fill this need
that the Groove Sleuth preamplifiers were
developed.
The Groove Sleuth Mk.II
The Groove Sleuth Mk.II is a second generation
product which replaces all the models in the
original Groove Sleuth range. Please refer to this
block diagram of the Groove Sleuth Mk.II
preamplifier in the following description.
The Groove Sleuth Mk.II preamplifier is suitable
for high-output moving-coil (HMC) and movingmagnet (MM) cartridges, and optional
transformers may be fitted for low-output movingcoil (MC) cartridges. The Groove Sleuth Mk.II is
also suitable for Phaedrus Audio PHLUX (PHLUX II)
active moving-magnet cartridges. (See Chapter 5
for more information about PHLUX active
cartridges.)
Each base unit is equipped with a high-quality
looping path called iLOOP, and the Groove Sleuth
Mk.II preamplifier has an option for RIAA and
limited alternative equalisations.
In the base options, the unit simply presents the
cartridge with the correct impedance at the IN
phonos and amplifies the signal. The output is
presented on the phonos marked OUTPUT on the
rear of the Groove Sleuth Mk.II unit.
The gain of this preamplifier is a little lower than
the typical mid-band gain of an RIAA preamplifier
because, without RIAA equalisation, the crestfactor of the signal is somewhat greater than
with a typical music signal (by about 4dB). The
signal amplification is designed for the lowest
possible distortion and noise-floor; a discrete
transistor stage with multiple, paralleled
transistors being necessary for the latter. This
amplified signal is sent to an external audio
interface for digitisation and subsequent recording
equalisation in Stereo Lab.
Transformer option
When ordered with the MC option (GS-MC), the
Groove Sleuth Mk.II preamplifier includes a step-
up transformer stage. Transformers are heavy and
expensive, but they sound great! And they do offer
the lowest possible noise-floor. The transformers
selected for the Groove Sleuth Mk.II preamplifier
are of the highest quality: they possess high
primary inductance, very low leakage and are fully
mu-metal screened.
Signal loop (iLOOP)
The Groove Sleuth Mk.II preamplifier features the
iLOOP; a wide-bandwidth, low-noise and distortion
buffered loop-through. This is especially
convenient for enthusiasts who already have an
excellent LP replay solution but who want to
introduce computer audio into their system. This is
because the Groove Sleuth Mk.II integrates
transparently into a pre-existing setup and
provides new functionality without upsetting
what's there already.
iLOOP always outputs the phono signal at highoutput HMC (or MM) signal levels. In fact, if
moving-coil cartridge transformers are fitted and
the iLOOP output is fed to a moving-magnet input,
the Groove Sleuth will function as a first-rate,
wide-bandwidth, low-noise MC preamplifier.
RIAA+
The Groove Sleuth Mk.II preamplifier may include
a high-quality equalisation stage (GS-RIAA+) so
that the "loop" signal is equalised and emerges at
line level on the phonos marked iLOOP/RIAA. The
equalisation filter is a high-precision, passive
network. Previously, we have only offered optional
RIAA equalisation for monitoring. However,
because Pspatial Audio's Stereo Lab software has
its greatest application in equalising the many
recording characteristics of historical recordings, it
was felt helpful to incorporate limited, variable
equalisation in the hardware preamplifier to make
record monitoring less fatiguing (it's hard work
listening to a 78RPM equalised with the RIAA
curve). Three carefully judged, generalised settings
are included:
RIAA, labelled RIAA
pre-RIAA (for late 78s and early LPs),
labelled LP; and
Early (which is for all records made up
until the late 1940s) labelled 78.
In this way record-monitoring may always be
comfortable and accurate. This is followed by
slightly more make-up gain (+24dB) than the midband loss in the RIAA network because the signal
now has the crest-factor of the original music
signal.
Power supply and warm up
The Groove Sleuth Mk.II preamplifier is designed
so that the analogue sections remain energised all
the time since this is consistent with the best
audio practice
The Groove Sleuth Mk.II incorporates the very
low-noise battery supply which was previously
only in the Groove Sleuth MINI. This means the
preamplifier can be powered from a conventional,
international-style power supply but be switched
to battery supply during needle-drops to ensure
the very best possible noise and aliasing
performance. This delivers first-rate quality at a
very reasonable price. A switch on the front-panel
allows the battery supply to be selected and a LED
indicates battery health and charge.
The Groove Sleuth Mk.II has well over 24 hours’
operational charge, but we recommend battery
play be limited to approximately 12 hours. The
unit may be kept in charge mode when listening
with only a minute loss of quality. By means of an
advanced power-supply design, this condition is
achieved whilst remaining compatible with
European Eco-Consumption directives.
If the unit is unplugged or the power is removed or
interrupted, the analogue circuitry is held in a
muted state for about 5 seconds until the various
bias voltages are stabilised. Therefore, do not be
alarmed if the unit does not produce an audio
output immediately after connecting power.
Connecting the Groove Sleuth to your
sound card
The
Groove Sleuth Mk.II is connected to your soundcard's line inputs (as shown above). Levels should
be set on the interface in the normal way and you
will find that the preamplifier delivers audio at a
sufficiently high level for all commercial soundcards, both internal and external.
Chapter 5 – Phaedrus Audio
PHLUX II - Active Phono
Cartridge
The Phaedrus Audio PHLUX II active phono
cartridge a new development in phono cartridge
technology in which a moving-magnet motor
system is buffered by a miniature amplifier
thereby securing the performance of a moving-coil
cartridge with the superior tracking and general
convenience of the moving-magnet type. Using a
combination of the PHLUX II cartridge, the Groove
Sleuth Mk.II and Pspatial Audio’s Stereo Lab
software, first-rate needle-drops may be obtained.
More information is available from
www.phaedrus-audio.com/PHLUX.htm
The power to the PHLUX/ PHLUX II active cartridge
is supplied via the signal cable: rather as phantom
power is delivered to modern microphones. In this
way, the PHLUX may be fitted to any standard
turntable without any rewiring. All that is required
is that the phono preamplifier supplies the
appropriate current and voltage to the turntable
leads. This circuitry is provided within the Groove
Sleuth Mk.II.
PHLUX-II digital correction
The PHLUX-II cartridge has a very level frequency
response. Variation is confined to ±1dB. This is a
very good result and is illustrated in the graph
above by the red trace.
Nevertheless, ±1dB is just perceptible; especially
when it is a monotonic 2dB drop as shown in the
graph. The result is a very slightly "warm" tonal
balance. So, before applying recordingcharacteristic equalisation, it is possible to correct
this very slight response anomaly in Stereo Lab
software. The black trace indicates the corrected
response which brings the variation of the PHLUXII frequency-response to less than ½dB; a result
below accepted levels of perceptibility.
The combination of PHLUX-II, Groove Sleuth Mk.II
and Stereo Lab offers a solution with which to
extract the information captured on the original
record with forensic accuracy.
Chapter 6 - Recording "Needledrops"
To record a needledrop, you will first need
a program which
records audio. Pspatial
Audio can recommend
Audacity, a free, easyto-use, audio editor and
recorder which runs on
the Mac platform (and, in fact, on Windows and
GNU/Linux too). Audacity is free software,
developed by a group of volunteers and
distributed under the GNU General Public License
(GPL). Audacity features, not only the recording
tools you need, but other tools which you can use
to enhance your needle-drops like click and noise
filtering and speed change. You can read about
and download Audacity on their website
(http://audacity.sourceforge.net/).
Setting parameters
You will also need to configure Audacity so that it
matches the settings you have made in the Audio
MIDI Setup utility. The selections are made in the
Preferences/Devices and Preferences/Quality
dialogues as illustrated above. You may also need
to adjust buffer depths in the software
(Preferences/Recording) for the higher sampling
rates. We’d recommend you adjust the Audio to
buffer parameter to 50 milliseconds as a good
starting point.
Recording levels
Set recording level so that peak music levels reach
between-12dBFS and -6dBFS. Do not be tempted
to over-record because this will cause distortion
which Stereo Lab cannot rectify. It is
recommended that loudness processing is also
applied during the Stereo Lab software
equalisation process. In this way you can be
assured of the best dynamic range from your
music and of good matching between needle-
drops and other audio files (for example CD rips).
There is no need to anticipate the effect of the
RIAA filtering in Stereo Lab because the software
will automatically adjust the level of the input file
for best resolution of the processed file.
Remember to depress the front-panel switch of
the Groove Sleuth Mk.II to switch to battery
supply (green LED) before making a needle-drop:
this will ensure that the needle-drop recording is
of the highest quality. Reselect external supply
when the recording is made to preserve battery
charge.
Chapter 7 – Decoding
Quadraphonic and Ambisonics
discs
There were many interesting and important
recordings made in Quadraphonic sound and
versions of many classic recordings were mixed in
Quad'. Many still only available as vinyl records,
recording these LPs and decoding these recordings
in software allows us to revisit, and indeed
rediscover old friends.
Many beautiful and important recordings were
made in Quadraphonic
Stereo Lab allows decoding of SQ and QS
Quadraphonic and Ambisonics recordings to
multichannel audio files so that they can be played
over a square of four loudspeakers (as was the
intention in the 1970s) or over a modern 5.1
system. No special precautions need to be made in
recording needle-drops of quadraphonic or
Ambisonics discs. It is recommended that
equalisation is applied to the needle-drop in
Stereo Lab before decoding.
Chapter 8 - Specifications
Size: Groove Sleuth Mk.II: 112 × 50 × 225 mm (W-H-L)
Preamplifier Supply: DC input on screw locking connector.
Power: Groove Sleuth preamplifiers are designed to be compatible with European Eco-Consumption directives.
Consumption is less than 4 Watts in all configurations and active. The unit is intended to remain energised all the time.
Groove Sleuth Mk.II Preamplifier
Sensitivity @ 5cm/s recorded velocity: Nominal 5mV RMS (-44dBu); or 500µV RMS (-64dBu) when GS-MC option fitted.
Input load: 47kohms // 220pF (MM); 100R (GS-MC option); 150kohms, 9V dc phantom supply (PHLUX)
Gain (to computer output): 33dB (× 45)
Frequency response: ±0.1dB from 20Hz to 50kHz
Distortion: 0.005% THD at maximum output level
Equivalent input noise (EIN): <500nV RMS (-124dBu), A-weighted. Input shorted.
Signal to noise (wrt nominal sensitivity and un-weighted): 80dB
Maximum input signal (prior to clipping at full charge): 75mV RMS
Maximum input signal (prior to clipping after 6 hours on battery): 60mV RMS
Headroom (wrt nominal sensitivity at full charge): 23dB
Headroom (wrt nominal sensitivity after 12 hours on battery): 20dB
Battery: 9V Ni-MH (nickel–metal hydride) E-block type.
iLOOP (Intelligent Loop)
Function: Wideband, buffered loop-thru
Frequency response: ±0.1dB from 20Hz to 50 kHz
Output load: 47kohms (non-critical). Suitable for feeding any MM input
RIAA+ correction circuit option
Gain (to RIAA output): 37db/58dB (MM /MC); RIAA curve; pre-RIAA curve: Blumlein curve
RIAA response accuracy: ±0.2dB from 40Hz to 20kHz (RIAA)
RIAA IEC amendment: Not implemented; rumble roll-off performed in software
RIAA Neumann Pole or eRIAA: Not implemented 1
Phædrus Audio reserves the right to change specifications without notice.
Chapter 9 - Warranty and service
Service
If you experience a problem with a Phædrus Audio product, contact support@phaedrus-audio.com. We will diagnose the
problem remotely and advise you of the warranty status. If a repair or replacement is required, we will issue a Return
Merchandise Authorization (RMA) number and tell you where to send the unit to be repaired. You MUST have an RMA
number before you return the equipment to Phædrus Audio's support service. Phædrus Audio will not accept responsibility
for loss or damage in shipping or for equipment returned without valid paperwork and/or a valid RMA number. Remember,
warranty is void if product serial numbers have been removed or altered, or if the product has been damaged by abuse,
accident or unauthorized modification and/or repair (see Phædrus Audio Limited Warranty for details). There are no user
serviceable parts inside.
PLEASE RETAIN YOUR SALES RECEIPT. IT IS YOUR PROOF OF PURCHASE COVERING YOUR LIMITED WARRANTY. LIMITED
WARRANTY IS VOID WITHOUT SUCH PROOF OF PURCHASE.
Phædrus Audio's Limited Warranty
Warranty service conditions are subject to change without notice. For the latest warranty terms and conditions and
additional information regarding Phædrus Audio limited warranty, please see complete details online at www.phaedrusaudio.com.
1
The Groove Sleuth preamplifier's RIAA equalisation does not include the Neumann pole in the transfer-function of the equaliser. The truth is that the
inclusion of a zero in the playback RIAA de-emphasis at 3.18µS compensates for pole whi ch never existed in the record equaliser (see
http://www.pspatialaudio.com/neumann_pole.htm
Appendices
Appendix 1 - Model Codes
The model/order codes for Groove Sleuth Mk.II preamplifier are:
GS-II- Cost-effective, battery-assisted preamplifier with iLOOP and support for MM (MC options) and Phaedrus
Audio PHLUX/ PHLUX II active phono cartridge. Optionally equalising. Supplied with basic external, highquality, universal power-supply unit.
Options
GS-RIAA+ - EQ option including: RIAA; pre-RIAA (for late 78s and early LPs); and Early (which is for all records
made up until the late 1940s). (Note that RIAA+ options replace iLOOP)
MC-INPUT – Addition of transformer input stage for all MC cartridges.
Appendix 2 - Declaration of Conformity
The Manufacturer of the Products covered by this Declaration is
Phædrus Audio
Maidstone
Kent
UK
The directives covered by this declaration are:
89/336/EEC Electromagnetic Compatibility directive
73/23/EEC Low Voltage Equipment directive
The products covered by this declaration are:
Groove Sleuth Mk.II non-equalising phono preamplifier
The basis on which conformity is being declared: The manufacturer hereby declares that the products identified above
comply with the protection requirements of the EMC directive and with the principal elements of the safety objectives of
the Low Voltage Equipment directive, and that the following standards have been applied:
IEC INTERNATIONAL STANDARD 60065 - Audio, video and similar electronic apparatus – Safety requirements
The technical documentation required to demonstrate that the products meet the requirements of the Low Voltage
Equipment directive has been compiled and is available for inspection by the relevant enforcement authorities. The CE
mark was first applied in 2015.
Signed:
Richard Brice, Technical Director
Date: October 2017
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