PRS 1.5  line stage and pre-amplifier

MODELS

SPECIFICATIONS

TESTIMONIALS

REVISIONS

Selecting the source, controlling the volume...    Caring for the music...

The quality of the power amplifiers propelled JMF Audio to the reference recording studios of Nashville, USA, in 1989, as reported in the History of the brand. Although capitalizing on more than 30 years of experience in analog designs for music lovers, the research and development for the PRS 1.5 pre-amplifier took many years, as the first owners who followed the genesis can attest...  

The impossible had to be made possible: to insert an element without loosing any detail of music. 

The JMF Audio power amplifiers owners had dreamed of the matching control unit. It had to be up to our expectations. We think it was also worth the wait. 

JMF Audio had designed excellent preamplifiers in the past. However the new challenges for the reference JMF Audio preamplifier were extremely high:

1. For sound quality the goal was to equal a fixed passive attenuator carefully designed by JMF Audio.
2. For precision, left/right perfect symmetry, low glitch on changes, precisely defined steps had to be assured.
3. For ease of use, remote control operation had to be possible as with our DXC D/A converters.

Point 1. was a test that none of the preamplifiers we tested passed successfully. (obviously, we thought)
Point 2. was easy to fulfill for integrated circuits based preamplifiers but rarely possible on the best sounding ones which volume control were based on resistor ladders or potentiometers. Resistor ladder units featured large glitches.
Point 3. was not a problem for many preamplifiers but the best sounding ones were passive and not remote controllable though.

The PRS1.5 eventually saw the light. Not only it is the only preamplifier to successfully fulfill point 1, but it also surpasses by far this target ; mostly thanks to the hand calibrated input/output stages and impedance matching provided by JMF Audio's SSA Super Symmetrical Analog technology.

 

The PRS1.5 is a dual mono, fully balanced design that embeds the innovative CSV volume control.

CSV is a fully passive volume control system based on a digitally controlled switches network.

CSV by concept features zero noise, zero distortion, zero phase shift, infinite headroom!

CSV is sealed and shielded in a machined block of aluminum, JMF Audio engraved.

CSV features a quadruple redundancy for an expected life time far superior to the best potentiometers.

CSV is input and output buffered in the PRS1.5 by JMF Audio's SSA Super Symmetrical Analog technology.

Complementing the major aspects, the details are of significant importance regarding the musical result: 

The PRS 1.5 has taken advantage of the result of the long researches of JMF Audio on the sound neutrality of passive components, semiconductors and materials, as described in the section about the power amplifiers. The PRS 1.5 pre-amplifier utilizes selected and uncommon components for audio applications: instrumentation semiconductors, bespoke passive components, selected and noble materials... 

After selection on technical aspects, refined selection on measurement, the final decision on absolutely all the audio components that the PRS 1.5 contains has been taken after long listening tests in the newly built JMF Audio's studio.

 

Engraved walnut front panel finish (option)

The PRS 1.5 inherits of the JMF Audio' power amplifiers innovative and still unrivaled hand calibrated precision input stage technology, enabling 100dB of common mode rejection of interferences carried by the input cables, this means more than 30 times better than found in professional balanced circuitry. This parameter having been enhanced by integrating psychoustic criteria. 

The proprietary DC coupling circuit allows a direct signal path (enhanced and improved with revision D). 

Un-balanced incoming signals automatically take advantage of the symetrical structure right from the input. 

The same care has been taken for the output section for enhanced balancing precision.  

This defined JMF Audio's SSA Super Symmetrical Analog technology, possibly unique... 

A total of 8 adjustment points require manual calibration after a 100 hour burn-in period on each preamplifier.

The preamplifier's mono audio boards feature metal case ulta low noise discrete components (military grade) and bespoke capacitors on the power supplies (starting from revision D). Every components and connectors on the audio path have been selected for their reliability and on listening for their natural sound characteristics. 

The JMF Audio proprietary PGP pure gold finish of the printed circuit board is incompatible with the automated processes. The hundreds of components populating both sides of the boards and in the CSV volume section are hand mounted and soldered one by one by our specialized technicians with JMF Audio's bespoke solder, using a magnifying glass. A work that recalls jewels manufacturing.

 

Certainly the most transparent line stage, the PRS 1.5 is also the matching driver for the JMF Audio HQS power amplifiers.

The JMF Audio elements are entirely hand crafted in our workshops and pass severe tests. Since revision B, every pre-amplifier has even been verified by listening in our studios after an operational period of over 100 hours, so as to ensure its future owner will receive the best.

 

 

 

Features:
Balanced inputs 3  (IN0, IN1, IN2)
Unbalanced inputs 3  (IN3, IN4, IN5)
Balanced outputs 2  (OUT1, OUT2)
Unbalanced outputs 1  (OUT3*)
Volume display [30] to [99]
Relative gain setting between sources [-9] to [ 6] display for -9 to +6dB gains
Source display [i0] to [i5]
*Out3 can be set to follow the volume control
or set as direct (DI) for a tape loop 
or to drive a headphone amplifier
[di] display on selection, 
recalled by a dot light on normal use
Ground connection (earth) dia. 4mm banana type
Remote control IR, all functions using MBR-1
Massive aluminum volume control button /  double bearing / massive aluminum compartment / smooth rotation.
Machined 10mm thick anodized and brushed aluminum chassis, mounted on special damped and anti skidding JMF Audio feet.
Gold plated analog mono boards embedding CSV and mounted on suspensions for acoustical isolation.
Specifications:
Input impedance > 5k ohm / XLR and RCA inputs
Maximum input level +22dBu XLR bal / +16dBu RCA
On normal output OUT1 (OUT2), at volume max:
Bandwidth 1Hz .. 100kHz  (+0.0 / –0.1dB)
20Hz ..20kHz   (+0.0 / –0.0dB)
Signal to noise ratio > 130dB        (+22dBu 1kHz narrow band)
128dBA typ.   (+22dBu 1kHz in / bw. 22..22k Hz)
THD+N 0.0005% typ. (+22dBu 1kHz in / bw. 22..22k Hz)
Crosstalk left/right < -120dBA
Output impedance 50 ohms
Maximum gain output/input 0dB (XLR bal in)   +6dB (RCA in)
Volume control range 70 steps of 1dB
Volume control step precision better than 0.05dB above volume [40]
Volume control left/right level mismatch  < 0.1dB above volume [40]
Specific to modular output OUT3: 
Maximum gain in variable mode (at volume max) 0dB (RCA in)   - 6dB (XLR bal in)
Output impedance in variable mode 50 ohms
Gain in direct mode (DI) 0dB (RCA in)   - 6dB (XLR bal in)
Output impedance in direct mode (DI) 600 ohms
Power consumption < 25W in operation   (< 1W in standby)

Owners' comments:

The JMF Audio PRS 1.5 has seduced music lovers from all areas. Whether these experienced audiophiles and sound engineers used to defend fully passive designs, tube based designs or whether they used to trust famed brands in solid-state technology, they have found in the JMF Audio PRS 1.5 the precision, timbres rightness, amplitude, greatness in the presentation of music.

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 just a few. Music enthusiasts are invited to discover and experience for themselves. JMF Audio would be pleased to guide and advise a representative.

Please refer to the Contact page and our Policy.

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Mr. C.M. (HQS9001, PRS1.5, CM4)

"Saturday I plugged the [PRS 1.5] preamp in my Mark Levinson 436. Right from the first notes: clearly superior [...], better hold low frequencies and more dynamic, unique JMF Audio mids for musicality, wider and nearer sound stage. In summary: more music and less hifi. A reference preamp to be associated to all power amplifiers. Congratulations on this success!"   (via e-mail) Mr. C.M. soon after purchased HQS7001 power amplifiers, and later upgraded to HQS9001.

 

Mr. M.I. (HQS7001, PRS1.5, CM4, SR8, PC2), Asia, on JBL speakers:

"We were shocked [when we first listened with the PRS1.5 and CM4 cables]. What I can say is that the sound is very flat over the frequencies and the sound has become soft. At the same time, it sounds as if it is with very very very high resolution. [...] I am experiencing what you meant by 'wider sound stage, three dimentional rendering, air' [...]. Thank you for providing jewelry products." (via e-mail)

 

Mr. R.Y. (HQS6002, PRS1.5, SR8, CM4), Singapore. 

"I’ve been using a Japanese brand (tube preamplifier and amplifiers) and cables were either [from Denmark] or [from Netherlands]. The most notable difference was the liveliness of the music, the soundstage and details. Your electronics is also quieter." via e-mail (2011)

 

Mr. A.M. (HQS9001, PRS1.5, DXC2.2 MKII, SR8, CM4)

"I can listen louder, the sound is clearer, wider, more lively; there is so much more information... Congratulations for having taken up this challenge. I can believe that the previous clients were amazed..."

 

Mr. J.M.B. (PRS1.5, PC3) France

"Owner of a high quality [English made] system linked to a Lenco 75 JTN (I am a vinyl addict), I had been looking at replacing my preamp for years. After analyzing the market and a few tests [...], I was not satisfied about the results, especially for the price. A friend suggested me JMF Audio [...]. After one week of direct comparison, I concluded: what a superb transparency! More details. Simply Music. The three dimensional rendering is gigantic. Loudspeakers and walls just disappeared… It confirmed me that even if the source quality is very important, the preamp quality shall not be neglected. For myself, I have found my happiness [EDIT] the last preamp of my life...  My system is now musical… Before acquiring a new high price preamp, I strongly advise to evaluate JMF Audio…"  (via e-mail, 2014)

 

 

Mr. Mic A. multiplatinum records sound engineer and producer, New York  (PRS1.5 revision D), after a 30 year quest for the ultimate preamplifier.

"I was blown away... The sound character, tone, detail, musicality, timing was like nothing I ever experienced . It was shocking! You created a monster! I heard so much detail on the disc I never heard before.. and the way I heard it is really impressive. And placement of instruments....wow is all I can say!!!!! really... you did it! Congratulations !!" (e-mail)

> Read full article 

 

Revisions history:
PRS 1.5 -D Major upgrade, 2017. The original PRS1.5 outperformed a passive attenuator. The PRS1.5-D equals a direct link made of the JMF Audio CM8-C cable, a feat.

> Read the first impressions in New York studios

> Article on the test conditions and truth demonstrations (coming soon)

PRS 1.5 -C Major upgrade. Finalization and homogenization of the global isolation and shielding concept initiated in 1985. Applies to all JMF Audio products.
PRS 1.5 -B Minor change.
Series models Rear panel with one additional balanced input 
 

JMF Audio products are designed to be references and to last. The base of these instruments is safe and modular. Upgrades are proposed for clients to take advantage of the results of our continuous research and development efforts, without the need for product change. It means "details", but details make the differences and can lead to the exceptional. The device revision (B, C, D...) is indicated by a silver badge located on the rear panel and is linked to the product serial number in JMF Audio's tracking files. 

> More information about our upgrade policy.

 

 

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