PRS 1.5  reference preamplifier

MODELS

SPECIFICATIONS

TESTIMONIALS

REVISIONS

The preamplifier, key element in the system, is mandatory to take advantage of analog sources like vinyl discs and to use the digital to analog converters at full resolution. 

The impossible had to be made possible: to insert an element and not to lose any detail of sound. 

The research and the development of the PRS1.5 actually took us many years… 

JMF Audio had designed excellent preamplifiers in the past. One of them has even become legendary in Asia. However the new challenges for the ultimate reference JMF Audio preamplifier were extremely severe:

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 massive tooled block of aluminum with the JMF Audio logo engraved on.

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

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

After selection on technical aspects, refined selection on measurement, the final decision on absolutely all the audio components that the PRS1.5 contains has been taken after long listening tests in the newly built JMF Audio's studio. The audio boards were designed in the great JMF Audio's tradition (PGP gold) and have benefited of the results of the now JMF Audio's 30 year experience in audio. They are mounted on a suspension system that makes them quasi acoustically floating and immune to vibrations. 
The PRS1.5 features JMF Audio's direct coupling design (no capacitors on the audio path).
Each input selector is shielded for the best signal integrity and lowest cross talk.
Absolutely all analog parts are drastically selected and hand mounted.

The integrated power supply, free of radiation, is double shielded and located next to the audio circuits for an instantaneous energy delivery following JMF Audio's proprietary DUAL-STAR-POWER concept. Before delivery every PRS1.5 undergoes a burn-in phase and a listening test with comparison to our reference.

Beside being the most transparent preamplifier,
the PRS1.5 is the ultimate JMF Audio HQS power amplifiers' driver !

 

 

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
Massive anodized 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)

Clients' comments:

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

"Saturday I plugged the (PRS1.5) preamp in my Mark Levinson 436. Right from the first notes: clearly superior to my ML32, 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 amps. Congratulations on this success!"  Mr. C.M. soon after purchased HQS7001 power amplifiers, and later upgraded to HQS9001.

 

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

"We were shocked (when we first listened with the PRS1.5 and CM4B 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. Moreover, [...] I am experiencing what you meant by *wider sound stage, 3D rendering, air* ; which you used to explain the HQS9001 performance at the beginning of the communications with you. [...] My friend (who owns the) Accuphase C-2810 prefers the PRS1.5 [...]. Thank you for providing jewelry products."

 

Mr. R.Y. (HQS6002, PRS1.5, SR8, CM4), Singapore, formerly Wavac mono amps and preamp. 

"I’ve been using a Japanese brand (tube amp) called Wavac and cables were either Argento Audio (Denmark) or Crystal Cable (Netherland). The most notable difference was the liveliness of the music, the soundstage and details. Your amp is also quieter." via email (2011)

 

Mr. J.P. (HPM500, HQS9001, PRS1.5, SR8, CM4, DXC6.10) formerly Lamm preamplifier and amplifiers.

"I admitted that with your DAC [version 1] the sound was excellent without a preamp." [...] When the PRS1.5 came out: "I have had very good feedback from my trusted friend. Please reserve one for me." After reception: "It is true that with the addition of the PRS1.5 and the DAC running at full resolution, the result is sensibly better on every aspects. Your next clients will be very surprised." 

 

Mr. A.M. (HQS9001, PRS1.5, DXC2.2 MKII, SR8, CM4) formerly Spectral preamplifier and amplifiers.

"I first tried the [JMF Audio] DXC2.2 [version 1] with and without my [former] preamplifier. I didn't find an improvement with the preamplifier. So I sold it and I was confident using the JMF Audio DAC directly, given that I have digital sources only." After demo of the PRS1.5 prototype: "It is shocking. The sound is greater. I must plan this purchase. Please keep me posted with the first clients' comments."  After delivery: "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 other clients are amazed..." Mr. A.M later upgraded to DXC2.2 MKII.

 

Mr. J.M.B. (PRS1.5, PC3) 

"Owner of a high quality Linn system (Komri Aktiv (8 Klimax solo…) linked to a Lenco 75 JTN (I am a vinyl addict), I had been looking at replacing my Klimax Kontrol preamp for years.
After analyzing the market and a few tests (Audio Research, Mark Levinson…), I was not satisfied about the results, especially for the price, a friend suggested me JMF Audio that offered to test at home their PSR1.5 model. 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…" (2014)

 

Revisions:
PRS 1.5 -C Major upgrade. Power supplies and shieldings. Superb sound result. (2016)
PRS 1.5 -B Improved power supply (AC side)
Series models Rear panel with one additional balanced input 
 

The device revision (B, C, D...) is indicated by a silver badge located on the rear panel. Please contact JMF Audio for the upgrade of your product. 

 

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