PRS 1.5 line stage and pre-amplifier
Selecting the source, controlling the volume... Caring for the music...
The power amplifiers had made JMF Audio’s knowhow in analog recognized from world-class recording studios in Nashville, USA, to audio connoisseurs in Japan. Although capitalizing on decades of experience in analog designs for demanding professionals and music lovers, the research and development for the reference pre-amplifier required some additional years of dedication…
Absence of insertion loss and faithfulness to the music being major challenges to achieve.
The PRS 1.5 was eventually unveiled. And the performances were beyond the initial expectations…
—-
The JMF Audio PRS 1.5 reference pre-amplifier features a dual mono design, fully balanced circuitry, short signal path, and relies on the innovative CSV volume control (Intellectual Property registration).
> CSV is a purely passive volume control based on digitally driven and galvanically isolated stepped attenuators.
> CSV features zero noise, zero distortion, zero phase shift, infinite headroom, by design.
> CSV is sealed and shielded under a machined block of aluminum, now of Orose® grade.
> CSV features a quadruple redundancy for a far superior to potentiometers expected life time.
> CSV is buffered by JMF Audio's SSA Super Symmetrical Analog technology involving hand calibrated input and output stages.
In addition to the main aspects, the details are of significant importance regarding the musical result:
PRS 1.5’s dual mono design with JMF Audio’s proprietary PGP 24 carat gold analog printed circuit boards embedding the exclusive CSV precision volume control. The components are populated on both sides for compactness and a short signal path.
Each printed circuit board is made up of more than 700 parts.
For improved immunity to vibrations, each channel’s assembly is mounted on its own sub-chassis and benefits from dedicated suspensions.
The PRS 1.5 pre-amplifier has taken advantage of the result of JMF Audio’s long researches on the sound neutrality of passive components, semiconductors and materials, as described in the pages related to the HQS power amplifiers. The JMF Audio PRS 1.5 pre-amplifier utilizes selected and uncommon components for audio applications: instrumentation metal-case semiconductors, proprietary printed circuits boards substrates...
Due to the requirements for specific components from the aeronautic, aerospace and fast-train industries located in France, some companies have specialized in manufacturing custom parts. Thanks to our initial activities in high-frequency electronics, as told in the History of the Brand, we have collaborated with such specialists for over 30 years, which has allowed JMF Audio to obtain made to measure components and parts, especially passive, that best suited our criteria, for the music.
The PRS 1.5 takes advantage of JMF Audio’s innovative and still unrivaled hand calibrated precision balanced input stage, enabling 100dB of typical interference rejection. This means 30 to 100 times better than professional balanced circuitry. This parameter has been enhanced based on psychoacoustic criteria.
The proprietary DCS coupling allows a direct signal path, free of link capacitor.
Un-balanced incoming signals are automatically balanced at the input and take advantage of the symmetrical amplification structure.
The JMF Audio’s proprietary PGP 24 carat gold printed circuit board substrate is incompatible with the automated processes. The hundreds of components populating both sides of the boards are hand mounted and soldered one by one by our specialized technicians using JMF Audio's specific solder, under a magnifying glass. A process that requires skills and patience and results in the application of jewels manufacturing methods.
A total of 8 adjustment points are hand calibrated on each pre-amplifier after 100 hours of operation at the manufacture.
—-
The PLS linear power supply technology from JMF Audio is now part of the PRS 1.5. It is the result of over a decade of research and development on the mains current (PCD 302 and PCD 102). It is based on a dedicated and made to measure low-noise and low-vibration toroidal transformer of the same technology as the large transformers that have equipped the JMF Audio power amplifiers for long.
The JMF Audio Instruments for the music® are entirely hand crafted in our workshops and pass stringent tests. Every manufactured pre-amplifier has been verified by listening in our studios after an operating period of over 100 hours and placed in comparison with our references.
The dual chassis design, with the Orose® enclosure made of 10 to 16mm thick anodized and brushed aluminum parts, lays on JMF Audio’s proprietary decoupling feet. Whichever the chosen anodizing color Silver or Black, the engravings are filled with rose-gold and the controls, inserted in guided cylinders for smooth operation, are precisely machined in solid blocks of steel.
The volume knob is hold in a dual bearing compartment, designed for the rotation to provide the desired smoothness and feel of power control.
Each PRS 1.5 pre-amplifier is delivered with an Owner’s Manual containing the warranty terms and registration information.
Features:
Balanced inputs
3 (IN0, IN1, IN2)
Unbalanced inputs
3 (IN3, IN4, IN5)
Balanced outputs
2 (OUT1, OUT2) allowing bi-amplification
Unbalanced outputs
1 (OUT3) modular, fixed or variable
Volume display
[30] to [99]
Relative volume setting between sources
[-9] to [ 6] display for -9 to +6dB
Source display
[i0] to [i5]
OUT3 set as fixed line level output (direct)
For a tape loop (reel-to-reel or recorder) or a headphone amplifier, upon pressing Direct button. [di] displayed on selection, recalled by a dot light during normal use
Bypass for surround sound AV processor
from IN5 (unbalanced) upon configuration or IN2 (balanced) in option
For active sub-woofers or a headphone amplifier
OUT3 set as variable output (default)
dia. 4mm type
Ground connection (earth)
JMF Audio MBR1, user selectable code-set to prevent from interference
Remote control
Technical specifications:
Maximum input level at up to unity gain
9V (+20dBu, XLR bal) / 4V (+14dBu, RCA)
Total harmonic distortion plus noise
0.0002% typ. (+22dBu 1kHz in / bw. 22..22k Hz)
Interferences rejection (balanced input)
100dB typ.
> 10k ohm (XLR and RCA inputs)
Input impedance
3V (+11dBu, XLR bal) / 1.4V (+5dBu, RCA), version F
Maximum input level at max volume
10V (+22dBu) into 10k ohms load
Maximum output level
1Hz..150kHz (intentionally limited for RF immunity)
20Hz ..20kHz (+0.0 / –0.0dB)
Global signal bandwidth
120dBA typ. (+22dBu), version F
Signal to noise ratio (SNR)
>100dB (10V output 1kHz, gain min)
Channel separation
50 ohms
Output impedance
12dB (XLR bal in) +18dB (RCA in), version F
0dB (XLR bal in) +6dB (RCA in), prior to version F
Maximum gain output/input
70 steps of 1dB
Volume control range
better than 0.05dB above volume [40]
Volume control step precision
< 0.1dB above volume [40]
Volume control left/right level mismatch
Specific to modular output OUT3:
Maximum gain in variable mode
Output impedance in variable mode
Gain in direct mode
0dB (RCA in/RCA out) -6dB (XLR in/RCA out)
12dB (RCA in / RCA out), version F
50 ohms
Output impedance in direct mode
600 ohms
100, 120, 220-240 V AC - 50/60Hz (according to country of destination), version G
AC mains power supply
< 30W in operation (< 2W in standby), version G
Power consumption
Orose® up to 16mm thick machined anodized aluminum, machined steel buttons and rose-gold
Enclosure
482 wide (front panel) x 320 deep x 106 high mm including feet (19” x 12.6” x 4.2” high)
Dimensions
14 kg (31 lbs), version G
Net weight
Silver or Black anodizing
Finishes
Measurements with Audio Precision APX555 equipment. Voltage values are RMS. Specifications are based on the manufactured products at date of writing and may change with product evolution.
Reviews and literature:
Links to the articles will be found on a dedicated page. > Reviews page
Awards and books are listed on another page. > References
Comments:
The JMF Audio PRS 1.5 has seduced music lovers from all areas for more than a decade. Experienced audio enthusiasts and sound engineers have found in the PRS 1.5 pre-amplifier the precision, timbres rightness, amplitude, greatness in the presentation of music as well as the ideal companion for the JMF Audio power amplifiers.
We are thankful to the enthusiastic JMF Audio Instruments for the music® owners for their feedbacks, comments and the wish for some of them to get the information published.
However it has been decided to limit the comments on this page to a few from recording studio professionals. Music enthusiasts are invited to discover and experience for themselves. JMF Audio would be pleased to guide and advise a representative.
---
Mr. Mic A. sound engineer and producer, New York (PRS 1.5 version D), after a 30 year quest, 2017:
"The sound character, tone, detail, musicality, timing, placement of the instruments was like nothing I ever experienced. Thank you for your dedication."
> Read full article
References to albums produced with JMF Audio’s instruments as well as links to reviews and books will be found on a dedicated page.
> References
Versions history:
The PLS linear power supply technology from JMF Audio is now part of the PRS 1.5. It is the result of over a decade of research and development on the mains current (PCD 302 and PCD 102). It is based on a dedicated and made to measure low-noise and low-vibration toroidal transformer of the same technology as the large transformers that have equipped the JMF Audio power amplifiers for long.
G
New volume knob’s dual bearing compartment for enhanced feel. SSA’s new output stage for a total amplification of +12dB (previously 0dB). New internal cabling design. Evolution of the power supplies management.
F
New Orose® enclosure
E
Major evolution, 2017. While the original PRS 1.5 outperformed a passive attenuator in terms of sonic transparency, its version D now equals a direct link made of the JMF Audio CM8-C cable.
> Read the first impressions in New York studios
> Article on the test conditions and truth demonstrations (coming soon)
D
Major evolution. Finalization and homogenization of the global isolation and shielding concept initiated in 1985. Applies to all JMF Audio products.
C
Minor change.
B
Addition of a third pair of balanced inputs
First series
Two pairs of balanced inputs available
Pre-series
Upgrades:
JMF Audio products are designed to be references and to last. The base of these instruments is safe and modular. Upgrades are proposed for the original owner to take advantage of the results of our continuous research and development efforts, without the need for product change. More information can be found on our policy page. > Policy and Warranty