JMF AUDIO PRS 1.5

Select the source, control the volume... Take care of the music...

The quality of the power amplifiers propelled JMF Audio to the reference recording studios in Nashville (USA) in 1989, as recorded in the Brand History. Although drawing on over 30 years of experience in analog designs for music lovers, the research and development of the PRS 1.5 preamplifier took many years, as early owners following the genesis can attest...  

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

Owners of JMF Audio power amplifiers had dreamed of the matching control unit. It had to live up to our expectations. We believe that the wait has also been worth it.

JMF Audio had designed excellent preamps in the past. However, the new challenges for JMF Audio's reference preamplifier were extremely high:

1. For sound quality the goal was to match a carefully designed fixed passive attenuator by JMF Audio.

2. For precision, you had to ensure perfect left/right symmetry, low shifting glitch, precisely defined pitches.

3. 3. For ease of use, remote control operation had to be possible.

Item 1. was a test that none of the preamps we tested passed with flying colors, unsurprisingly.

Item 2. was easy to accomplish for IC-based preamps, but rarely possible on better-sounding ones whose volume control relied on resistor ladders or potentiometers. The resistor ladder units had large glitches.

Point 3 wasn't a problem for many preamps, but the best sounding ones were passive and not remote controllable.

The PRS 1.5 ended up seeing the light. Not only is it the only preamp to successfully meet point 1, but it far exceeds this goal; especially 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 fully balanced dual mono design incorporating the innovative CSV volume control.

> CSV is a fully passive volume control system based on digitally controlled step faders.

> CSV by concept presents zero noise, zero distortion, zero phase shift, infinite headroom.

> CSV is sealed and shielded in a machined block of aluminum.

> CSV features quadruple redundancy for an expected life span far exceeding that of the best potentiometers.

> CSV is input and output buffered on the PRS 1.5 by JMF Audio's SSA Super Symmetrical Analog technology.

As a complement to the main aspects, the details have a significant importance in the musical result: 

The PRS 1.5 has taken advantage of the result of JMF Audio's long investigations into the sound neutrality of passive components, semiconductors and materials, as described in the section on power amplifiers. The PRS 1.5 preamplifier uses selected and rare components for audio applications: instrumentation semiconductors, custom passive components, selected and noble materials... 

After the selection in technical aspects, the refined selection in measurement, the final decision on absolutely all audio components contained in the PRS 1.5 has been made after lengthy listening tests in the newly built JMF Audio studio.

The PRS 1.5 inherits from JMF Audio's power amplifiers the innovative and still unmatched precision hand calibrated input stage technology, which allows 100dB of common mode rejection of interference carried by the input cables, this means more than 30 times better than what is found in professional balanced circuits. This parameter has been improved by integrating psychoacoustic criteria. 

Proprietary DC coupling circuitry allows for a direct signal path (improved and perfected with revision D). 

Unbalanced incoming signals automatically take advantage of the balanced structure from the input. 

The same care has been taken in the output section to improve the precision of the balance.  

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

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

The preamplifier's mono audio cards incorporate ultra-low noise (military grade) metal case discrete components and custom capacitors in the power supplies (starting with revision D). All audio path components and connectors have been selected for their reliability and natural sonic characteristics. 

The PGP pure gold finish on the printed circuit board, owned by JMF Audio, is incompatible with automated processes. The hundreds of components that populate both sides of the plates and the CSV volume section are assembled by hand and soldered one by one by our specialized technicians with JMF Audio custom soldering, using a magnifying glass. A job reminiscent of jewelry making.

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

JMF Audio elements are manufactured entirely by hand in our workshops and pass rigorous tests. Since revision B, each preamp has even been audition-verified in our studios after an operating period of over 100 hours, to ensure that its future owner receives the very best.

Characteristics:

Type: Stereo Symmetrical Line Preamplifier

Revision: Version “E”

Frequency response: 1 Hz – 100 KHz (+0.0 / -0.1 dB)

Inputs: 3 x XLR + 3 x RCA

Outputs: 2 x XLR + 1 x RCA (configurable)

Gain between sources: (-9 dB) – (+6 dB)

Maximum input level: +22 dB – XLR / +16 dB – RCA

Input impedance: > 5 KΩ / XLR and RCA

Output 1 and 2 (XLR) impedance: 50 Ω

Output 3 (RCA) impedance: 50 Ω – 600 Ω

Maximum input level: +22 dB XLR / +16 dB RCA

Harmonic Distortion (THD): 0.0005%

Signal-to-noise ratio: > 130 dB

Crosstalk between channels: < -120 dBA

CMRR (Common Mode Rejection): 100 dB

Remote control: MBR1 (included)

Volume: 70 1 dB steps – Step accuracy better than 0.05 dB above volume [40] – Left/Right volume asymmetry < 0.1 dB above volume [40]

Measures:

Unit weight: 12 kg net

Finishes: New brushed aluminum “orose black” – “orose silver”

Measurements with Audio Precision APX555 equipment. Voltage values ​​are RMS. Specifications are based on products manufactured on the date of writing and may change with product development.