Amp/Preamp Asylum: REVIEW: Jeff Rowland Coherence II Preamplifier (SS) by Stitch

Model:	Coherence II
Category:	Preamplifier (SS)
Suggested Retail Price:	$14500,--
Description:	Solid State Balanced Preamplifier
Manufacturer URL:	Jeff Rowland
Model Picture:	View

Review by Stitch on December 30, 2012 at 06:58:17
IP Address: 84.152.224.128 Add Your Review
for the Coherence II

The internal Design from Rowland got my attention long ago, it is rare, and very expensive when done right (the main reason why most ,Designers‘ avoid it, it kills Profit, and others simply have not the knowledge to do every step right) ...

Excellent line-level transformers have long been available to professionals in the recording studio world but they have always been vastly too expensive for mainstream high-fi gear. They remain too expensive for any but the finest high-end audio components to this day.
Even among modern line-level transformers, the Jensen models chosen for Jeff Rowland Design Group’s new products are stand-outs. Here’s are some of the reasons they are so close to perfect: Very expensive high-percentage-Nickel alloy cores. Virtually all commercial grade transformers use low-carbon steel or silicon steel. Though affordable, or even cheap by comparison, they have a lot of hysteresis as demonstrated by their fat BH loops. Nickel, on the other hand has a desirably narrow BH loop.
(,B‘ is the notation for magnetic flux density and ,H‘ is magnetic force. Plotted together, they graphically illustrate hysteresis. A large separation between the magnetizing and demagnetizing curves (a "fat" loop) shows much hysteresis and a small separation (a "narrow" loop) approaches the ideal of no hysteresis.

Huge core size compared to the power handling needed. The microwatt to milliwatt power levels seen at line-level would normally require only a tiny core. However, very low frequencies at high levels demand big cores to avoid the response roll-off and distortion of saturation. In order to handle deep sub-bass at outrageously high levels without complaint, these transformers are massively bigger than would otherwise be indicated.
Super-wide passband. Like most any high-end audio amplifying stages, these transformers have a few extra octaves of frequency response at each end. That’s 0.5Hz to 180KHz!
 Nearly perfect group delay and hence excellent phase response in the audio band. Before his death in 1989, Deane Jensen pioneered the use of a Bessel lowpass function to define the shape and characteristics of the transformer’s upper frequency limit.

Very good line level transformers aren’t damaging to the sound. How do they manage the miracle of subjectively improving the sound so dramatically? That is harder to explain definitively – and possibly not fully understood.
Let’s start with why recording studios love them so much:
- Transformers break ground loops. Since the transformer’s primary and secondary aren’t electrically connected, no ground loop currents can flow. Hair- pulling, aggravating ground loop related hum and noise problems disappear.
Transformers have ultra-high common mode input impedances (inputs-to-ground), unrivaled by active differential circuits. This is also a result of the galvanic isolation provided by the insulated, shielded primary windings. Direct connection to a differential (balanced) amplifier’s inputs doesn’t guarantee perfectly balanced operation – transformers do. 
It should be noted that many studios have been seduced by the low cost and great looking specifications of the solid-state "diff-amps" sold as transformer replacements over the years. The harsh reality is that there is a huge gap between laboratory measurements and real-world performance.

Most studios can’t afford the extravagance of transformers over diff-amps. Nevertheless, there is a rapidly growing cadre of perfectionists in professional audio who are returning to transformers as the ultimate signal interface.
 These usability issues should be important to we audiophiles as well, but our list pretty much starts and ends with sonics. Ease-of-use is important to a manufacturer supporting a product, but some of the more radical "tweaks" consider dealing with difficult hook-ups a red badge of courage. They wouldn’t dream of compromising the sound for convenience. Fortunately, line-level input transformers improve the sound as well.
Jeff Rowland Design Group’s Coherence Preamplifier II, Model 2 and Model 6 power amplifiers employ Jensen line-level input transformers. The Coherence II also uses Jensen line-level output transformers.

The Line Stage that isn‘t there

So how does the Coherence II Series 2 handle the audiophile standards? Superbly. Their astonishing clarity and transparency allow the subtlest of details from the farthest corners of the stage to appear in the listening room unimpeded. The completeness of the sound, the natural separateness of image boundaries and the lack of electromechanical colorations lifted the recording into transcendence. It is this ability that makes the Coherence II so extraordinary. They materialize musicians in the listening room. There is a gravitas, a ,grounding‘, a sheer centered and weighted density to each image, that makes recorded music astonishingly convincing. The three-dimensional quality is so great, you feel you can walk into the soundstage and stroll among the musicians. Each player and singer has enough “elbow room” to blossom separately into the recording acoustic, but the clarity of the individual parts never muddy or obscure the gestalt. The Preamps’ ability to individualize details makes ordinary recordings compelling, and compelling recordings utterly enthralling. In parallel with this is the Preamplifiers’ breathtaking transparency, which is particularly audible on ensembles. Specially in combination with good Phonostages you can hear easily, that this unit is able „to do things“ which are very remarkable. It simply has no ,sonic fingerprint‘.

This is a Preamplifier for those who love the ,inner voices of music‘’, you will always detect new details from the same Record. A primary reason for this is the Preamplifiers’ almost freakish inter-transient silence. That unit is, subjectively, the quietest Preamplifier I have heard. A lowering of the noise floor that profoundly affects an audio system's transparency, resolution, clarity and intranote silence. What is transparency? I think, it is a subjective measurement of the background noise floor of an audio system. Noise you don't realize is present until it's absent. Noise emanating from AC lines, EMI and even the parts and circuit boards themselves (that was the reason why some use Teflon, or swear on ultra clean ground --> John Curl, CTC Blowtorch). Noise obscuring the spaces between the notes. An AC power line conditioner is one way to lower your audio system's noise floor (but normally they kill the high frequencies and the sound becomes sooner or later MP-3 Standard) or a Battery Power Supply (BPS) such as the Rowland Coherence II Preamplifier).

The Divinity

Decca SXL 2136 La Boite a JouJoux Printemps
Not the typical sonic blockbuster but it is the type of subtle and delicate music that is perfect for a quiet night. The subtle details have their own, unique kind of magic. Ultra-Transparent. One of the great recordings.

London CS 6006 Espana
From the very first moment you can hear a Performance which is spectacular with the Cadence, with stunning mid and low bass. There is a clarity and impact which is outstanding. Imaging is unusually good, the soundstage is wide linked with appropriate depth.

London CS 6046 Nights in the Garden of Spain
The better the units are the more you can hear the subtle interplay between guitar and orchestra. The Solist is not wrapped into the orchestra, his playing has its own volume and strength.
Clarity, warmth, dynamics are keywords for these records

London CS 6205
short description: SOUNDSTAGE / AMBIENCE / PRESENCE

Lyrita SRCS 109 Arnold - English Dances
Very problematic record, with Phono- / Linestages which miss the sonic target by a mile it is simply awful, really horrible, when the System is really done right, it is a killer Performance. The first time when my cup of tea went cold while listening was with a Lamm chain (LL2.1, LP2, M1.2R) and the Cadence / Coherence II pass with flying colors...

RCA LSC 2400 - Ballet Music from the Opera
The Verdi selections continue with the Triumphal March, also from Aida. It receives a spectacular performance that almost convinces me of its musical worth. The antiphonal trumpets are recorded very well, especially their boulevard-wide vibrato. Its flavour is magnificent in its gaudiness and emphasizes the grand nature of the opera. The string tone is vibrant, the tactile sense of bow on string sounding rich and very sensual. Macro and micro dynamics are represented truthfully, with percussion instruments adding to the wonderful overall effect. Placement of instruments is pinpoint within the large soundstage, and unison woodwinds and upper strings are separated easily by space and timbre.

Mercury SR 90212 Chabrier Espana
That was the first session in their new recording hall in Detroit. The abilities from Paray shine here at his best. There is an „easy going“ through the complex Performance which is very hard to find. The first notes of Espana, the opening, is among the most impressive moments you can get from a record. When we talk about the Golden Era of Analog, that one is a part of it.

Suddenly, spaces between instruments open up. Instruments in the rear of the soundstage (or hall) appear from behind a curtain. Subtler musical details such as one instrument playing softly in the presence of a louder instrument, pop out. Low frequencies are quicker and more detailed. Many of todays audio components (and systems) exhibit good transparency. Clarity on the other hand (and the accompanying sense of spaciousness surrounding the instruments), seems to have eluded many top flight audio components. A clarity defines as the removal of a veil or curtain immediately in front of a musician. An increase in the openness, spaciousness and ,airiness‘ surrounding the musician.
Nothing is ever smeared or obscured with the Coherence II Series 2; the listener can choose to focus on one instrument or voice and effortlessly follow it throughout a piece, but can just as easily relax and let the whole of the event wash over the room. Pitch definition and differentiation are superb. Bass guitars and kick drums are singularly distinct from one another, in this respect rivaling the very best solid-state amps. But authority lives in the mid-bass. Many components, not just electronics, make the mid-bass lean to increase perceived detail in the lower midrange. This is common enough, in part because it is difficult to get the mid-bass correct, and because its opposite, a slight rise in this part of the spectrum, is grossly audible. The Coherence II neither add nor subtract energy in this crucial band. The result is an especially carefully controlled power and force-fulness that make other Preamplifiers sound washed out and wimpy by comparison. Anyway, when you want the full monty, here it is.

The Sound of Battery Power Supply

You can hear immediately a much deeper Soundstage, a better detail separation and something really amazing: to colors of tones get more real, the instruments simply sound more lifelike. The ,cleanness‘ of signals are responsible for these abilities. The music grabs your attention in a way you don‘t notice in the first seconds, you automatically sit straight and your brain focus on it. In a way, like listening to a CD versus LP... For me, there is no way back, the whole Rowland System runs in Battery Mode and it is a - unique - sonic step ahead.
I listened to a lot of Transistor Preamps in the last 10 years, but none was able to get these tonal colors right. The Brain normally cheats the majority of Listeners, because he knows from reading the info that there is a „trumpet“, there is a „Violin“ ... but between hearing and „hearing“ can be a huge difference. I wanted units with exactly these kind of Power Supplies, not Switch Mode units, they sound different, not so dead and cold ...
Starting with the battery chemistry, a proven and much more manageable type called absorbed-electrolyte Sealed Lead Calcium (SLC) was chosen for the DCPS. Unlike NiCad, which gives no reliable indication of its charge needs, the terminal voltage of an SLC battery will rise significantly, repeatedly and dependably as full charge is approached. Better still, SLC "first cousin," the flood-electrolyte Lead-Acid (LA) battery, enjoys a reputation of lasting up to several years in the brutal environment of an automobile engine compartment. In the more civilized indoor world of a home audio system, SLC has the potential to last even longer than LA. There is not a risk with SLC batteries, since there is slightly less electrolyte present than is necessary to totally deplete the plates of lead-sulfate. From the plate’s point of view, the battery is never quite fully discharged. Cell reversal is as important a concern for SLC as it is with NiCad, but is much more manageable. SLC offers about 67% higher cell voltage at 2.0 volts per cell versus NiCad’s 1.2 volts. This means that an SLC battery’s voltage can drop substantially lower before the first cell reverses, making low-battery detection easier and more accurate. There are also 40% fewer cells to seal and interconnect for a given battery voltage. Utilizing a battery chemistry ideally suited to its task would not be of much benefit if it was abused by the charger. Jeff Rowland Design Group’s charge management method includes voltage regulation, current limiting and ripple filtration designed and built with the same care as if it was the amplifier’s main power supply.Voltage regulation ensures that the battery is maintained at precisely a full charge when the amplifier is in standby mode.
Re-charge is about 16h continuous playing in Battery mode..

Probably one of the most significant Preamps of all time?

Definetly one with VERY expensive Parts ... and a lot of Brain inside.

Good Audio Design is timeless.

Coherence II Specs

 Specs refer to the latest iteration of the product. 
OVERALL GAIN  Adjustable for each input +/-20 dB relative to unity gain (0 dB)
in 0.5 dB increments
INPUT IMPEDANCE Adjustable for each input 18k or 600 ohms
OUTPUT IMPEDANCE 50 ohms
MAXIMUM INPUT LEVEL 13 volts RMS at 0 dB gain
MAXIMUM OUTPUT LEVEL 13 volts RMS (24 dBm)
OUTPUT NOISE LEVEL 12 microvolts, 20-20 kHz bandwidth, 0 dB gain
SIGNAL TO NOISE RATIO Greater than 96 dB
CHANNEL SEPARATION Greater than 110 dB, @ 20-20 kHz bandwidth
FREQUENCY RESPONSE 5 Hz-160 kHz, -3 dB
THD + NOISE 0.0016% 10 volt output, 600 ohm load
GAIN RANGE 63.5 dB, 127 equal increments
 GAIN RESOLUTION 0.5 dB +/- 0.03 dB over entire range
CHANNEL BALANCE +/- 0.03 dB throughout entire range
INPUTS 7 per channel (XLR) 
1 per channel, home theater bypass mode (XLR)
1 pair XLR to RCA adapters included
OUTPUTS 2 main outputs per channel (XLR) 
2 record outputs per channel (XLR)
  1 pair XLR to RCA adapters included

DIMENSIONS 17.5 in (W) x 12.0 in (D) x 3.7 in (H) 
44.5 cm (W) x 30.9 cm (D) x 9.40 cm (H)
WEIGHT 40 lbs. (18 kg)

POWER SUPPLY 
POWER CONSUMPTION 40 watts maximum, 10 watts nominal
MAINS VOLTAGE 100V, 120V, 220V, 240V, 50/60 Hz
BATTERY COMPLEMENT 2 each 12 volt, 7.2 amp/hour user replaceable
sealed, lead calcium, maintenance-free batteries

BATTERY SERVICE LIFE 5-8 years 
AC UNASSISTED RUN TIME 14-18 hours based upon initial battery full charge
DIMENSIONS 17.5 in (W) x 12.0 in (D) x 3.7 in (H) 
44.5 cm (W) x 30.9 cm (D) x 9.40 cm (H)
WEIGHT 43 lbs. (19.5 kg)

The difference between Coherence II and Coherence II Series 2

 The Coherence II Series 2 was released April 1997. The Coherence Series 2 upgrade involves the redesign of the attenuator amp circuitry. The actual circuit topology is similar; however, all of the circuit components were improved, taking advantage of recently available modern surface mount technology. The output amplifier is a newly developed, dual high-current transimpedance amplifier which handles both phases of the output circuit on one isothermic, copper lead frame power device. This output amplifier and all associated surface mount circuitry allow significant reductions in circuit loop area and path length yielding wider bandwidth, faster setting time, reduced dielectric absorption and greater thermal tracking stability. The overall sonic result is greater clarity during complex music passages and increased resolution of inter-transient silence.

Product Weakness:	XLR cable needs different termination when you use it with different amplifier
Product Strengths:	The total lack of any mechanical artifact present in almost every other Transistor Preamplifier

Associated Equipment for this Review:

Amplifier: Lamm M1.2Reference
Preamplifier (or None if Integrated): Lamm L2R
Sources (CDP/Turntable): EMMLabs CDSA-SE / Basis Debut vac.
Speakers: Reference 3A
Cables/Interconnects: SignalCable 'Silver Resolution'
Music Used (Genre/Selections): RCA LSC/Decca SXL // XRCD
Room Comments/Treatments: done
Time Period/Length of Audition: 2 years
Type of Audition/Review: Product Owner

Amplifier:	Lamm M1.2Reference
Preamplifier (or None if Integrated):	Lamm L2R
Sources (CDP/Turntable):	EMMLabs CDSA-SE / Basis Debut vac.
Speakers:	Reference 3A
Cables/Interconnects:	SignalCable 'Silver Resolution'
Music Used (Genre/Selections):	RCA LSC/Decca SXL // XRCD
Room Comments/Treatments:	done
Time Period/Length of Audition:	2 years
Type of Audition/Review:	Product Owner