Amp/Preamp Asylum: REVIEW: Jeff Rowland Model 2 & BPS-2 Amplifier (SS) by Stitch

Model:	Model 2 & BPS-2
Category:	Amplifier (SS)
Suggested Retail Price:	$9000,--
Description:	Stereo Power Amplifier & Battery Power Source
Manufacturer URL:	Jeff Rowland
Model Picture:	View

Review by Stitch on December 26, 2012 at 05:11:36
IP Address: 84.156.35.121 Add Your Review
for the Model 2 & BPS-2

Ok, let‘s face it: The finish from these units whisper to you „touch me baby....and press the button....yes....maybe I sound even better than I look ...“

A fully balanced design like Rowland's requires essentially double the components of an unbalanced design; this is undoubtedly part of the reason for the Model 2's cost. The circuit topology is of the current-feedback rather than the more common voltage-feedback type—an approach that, according to Rowland, offers wider bandwidth, very fast settling time, and low distortion at all frequencies.

What is „magic“?
Hm, maybe the absence of mechanical artefacts, the absence of anything which remembers you that you listen to something unreal...The dynamics and placement of images are just amazing. As I broke-in the amplifier, these details grew even stronger. With better recorded CDs, the Model 2 envelops you in the sound, making you an integral part of it, another instrument, albeit a passive one. It is strange, in a gratifying way, that with the Model 2 & BPS-2, I look forward to each listening session, waiting with growing anticipation what new discoveries I could make with my music. I never forgot the musical experience with Model 8 many years ago, it was so damn‘ good, but later Rowland went out of my focus when Switch Mode Power Supplies were used. I was impressed from their power but sonically they didn‘t move me at all. Years later I had the chance to listen to an „old“ Rowland System and it was like a wake up call...long story short, I bought such an amp, it was simply much better sounding than spectral 360 monos for example I listened to 2 moths earlier. Sonically simply a total different chapter....Bass is tight, tight, shows absolutely no mercy and it is really quick. Not fat and bloated, nor thin and and fast, just right with a full body. The high frequencies are 2die4. Violins have such enormous details and speed in the air, very, very hard to find in solid state design. For me it is one of the very few best overall amps JR has ever designed, and I write that in the year 2012.
In combination with the matching BPS a class on its own, when you use normal Speakers which doesn‘t need 120W to wake up. Ever listened very loud with transistor amps, normally somewhere they start to go on - my / your - nerves. Music no longer screams at you when played loud but just sings. Tone of string and brass instruments must be heard to be appreciated. You can actually hear the different tones of violins used within the ensemble. And what I really like, I can listen with very low volume and I can hear all details in the right timing, with the right body and the right dynamic. I don‘t need a kind of minimum volume to get all the tiny details. When you ask me for the „character“ of that Amp (you know, we all like this, warm/cold/fast/black/analytic/ attributes) I have to dissapoint you. None. What you feed you get.

The Divinity

Decca SXL 2136 La Boite a Jou Joux 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.

The Model 2 has XLR balanced inputs only, but Rowland provides a neat pair of XLR-to-RCA adaptors; the Model 2 can be driven balanced or unbalanced(Rowland follows the convention of having pin 3 on the XLR connector as positive so that comparisons with equipment having the more common, ANSI-standard, pin-2-positive assignment involved reversing the absolute phase to compensate). One toggle switch at the rear allows for selection of low-impedance (600 ohm) or high-impedance (36k ohm) operation; another the choice of 26dB or 32dB gain. It is your choice what you will finally choose, it depends on your System in general...The Model 2 stereo amplifier is designed with two power supply options. The power supply for the standard AC mains-powered version consists of a conventional power supply comprised of two isolated toroidal transformers, one each for positive and negative DC voltage respectively.  A second option is an isolated DC power supply, in a separate companion chassis, which provides pure DC power through a one-half meter DC power cable. This power supply incorporates sealed, lead calcium batteries with built-in charge management circuitry. When this power supply option is used, the conventional power supply located within the power amplifier becomes the unregulated DC power source for the battery charging circuitry.
The technological features of the Model 2 amplifier are the result of many years of investigation into the relationship between an amplifier’s performance and changes caused by mechanical movement, unstable temperature and environmental conditions and undesirable electromagnetic/electric field interactions. These factors become increasingly interrelated and important as the dimensions become smaller and, as a result, impact the more delicate and emotionally involving musical expressions. By establishing an exceptionally stable foundation and controlling the aforementioned changes, the musical signal is more accurately amplified and transferred throughout the unit.
Structure
All chassis components of the Model 2 are precision machined from 6061-T6 aluminum alloy in specific dimensions. Dimensional accuracies are held within 0.005 in. tolerance throughout the entire structure. By selecting "golden mean" non-divisible dimensional ratios throughout, a non-resonant stable structure is created. For instance, each cooling fin of the amplifier heatsink is non- harmonically related to the adjacent cooling fin. The increased physical mass of this heatsink design also increases the "thermal mass" which, in turn, extends the thermal time constant, thereby reducing short-term temperature variations of the power semiconductors.
A machined aluminum tube, physically isolated via large neopreme "O" rings, contains two toroidal power transformers. This component is sandwiched between two machined subchassis structures spanning the entire length of the amplifier. This subchassis assembly also rigidly clamps the two large power supply capacitors thus creating a non-resonant power supply subassembly and adding structural integrity to the entire amplifier.
Easily accessed plug-in modules containing critical audio circuitry enhance mechanical stability and thermally stabilize the circuitry. These plug-in modules also protect the internal components against adverse environmental conditions and allow for easy product update or service. These modules are held in place by captive aluminum bars.
Power Supply
The power supply toroidal transformers have been specifically designed to improve operating performance under all AC mains conditions. The toroidal transformer cores are individually machined before winding to remove sharp edges around the inner and outer perimeters to allow a smoother and more accurate copper wire lay and decreased electrical resistance. The transformers operate at a much lower flux density than conventional designs. A lower flux density (approximately 1.5 Tesla at 50 Hz) reduces the possibility of magnetic saturation under all operating conditions. Each transformer has its own full-wave bridge rectifier for each positive and negative voltage. This eliminates the common transformer center tap ground return for capacitor charging surge currents and eliminates transformer secondary voltage imbalances.
Two large electrolytic capacitors totalling 260 000 uF provide low ripple and high transient current capabilities. These capacitors have been specifically designed for low ESR, ESL and long operating life. All DC voltages are supplied by means of stranded copper wire instead of printed circuit board traces or metal power busses to provide wide bandwidth power transfer. All electrical circuits are protected against overload with fast-blow fuses mounted directly onto the circuit board of each heatsink. The main power supply delivers positive and negative 24 V for the output sections. Local bypassing near the output transistors with large film capacitors provide high frequency energy storage. Separate regulators provide positive and negative 15 V to the input amplifier sections. Positive 12 V is derived for all other amplifier housekeeping functions. The entire amplifier circuit topology was designed to operate on lower voltages which permits very reliable high-speed operation. Since all of the circuits operate in a differential balanced mode, the power supply voltages required are reduced by fifty percent. Also, both polarities of power supply currents are symmetrically utilized by the amplifier at all times. This configuration also allows the amplifier circuits to reject power supply errors since the power supply is common to both phases of the signal in real time.
Signal Circuitry
An important aspect of the Model 2 design is in the implementation of transimpedance amplifier technology. Although originally developed for video amplifiers, this particular circuit topology is well suited for use in audio power amplifiers. Unlike the conventional voltage feedback circuit topologies used in virtually all other audio amplifiers, the transimpedance or current feedback circuit topology has numerous performance advantages such as wider bandwidth, very fast settling time and extremely low distortion at all frequencies. Above all, the inherent simplicity of this topology can be implemented with very few active and passive components.
The input signal enters the amplifier in either single-ended or balanced modes. This signal is developed across the primary windings of a specially designed input transformer. This transformer provides total isolation of ground currents which can circulate between source components and the power amplifier. Additional benefits include the effective filtering of high-frequency signals not related to the musical signal. The input transformer has been recently developed using extensive computer aided design (CAD) programs, precision proprietary winding techniques and high-percentage nickel core materials. These transformers achieve performance that has not been previously obtainable with input transformer technology. Noteworthy performance parameters are flat response bandwidth to 200 KHz, less than 1% overshoot, pure resistive loading without the need of RC filtering, common mode rejection ratio (CMRR) greater than 60 dB at 20 KHz, constant group delay throughout the entire bandwidth, 12 dB per octave Bessel filter alignment, extremely low distortion of less than 0.01% at 20 Hz and insensitivity to a wide range of source impedances from 0 to 1 Kohm.
The transformer secondary voltage is amplified by a small-signal Class A all JFET amplifier. This amplifier is powered by the aforementioned bipolar 15 V power supply. Each of the output phases (0 deg and 180 deg) from this amplifier drive a balanced transimpedance output amplifier section with gains of five on each phase. These output sections are powered by the aforementioned bipolar 30 V power supply. Since the input and output sections are totally independent, there is no overall loop negative feedback. The output section for each phase incorporates eight individually tested and matched 150 watt bipolar output transistors, totalling sixteen output transistors per channel. All components in the output stage were strategically chosen and placed for minimum length and electrical inductance thereby optimizing the damping factor throughout the audio frequency range.
The transimpedance amplifier topology is accomplished with two buffers and two bipolar current mirrors. Conceptually, the operation is simple. The midpoint of two resistances are connected to the output of an input buffer amplifier. The input of the input buffer amplifier is connected to ground potential. The open end of one resistance is connected to the overall amplifier input. The open end of the other resistance is connected to the output of the overall amplifier. The ratio of these two resistances determines the overall gain of the overall amplifier. Since the overall amplifier is inverting, the midpoint of the two resistances will always be at zero volts. The input buffer amplifier maintains the midpoint of the two resistances at ground or zero potential. Any deviation from ground or zero potential at this low impedance point is reflected as an error current in the input buffer amplifier and mirrored by the two bipolar current mirrors across a high impedance point. This high impedance point is then buffered and current amplified by the driver and output stages. The error signal current is not limited by some finite value which is the case in all conventional voltage feedback amplifier topologies. Also noteworthy is the absence of capacitors or storage elements in the current feedback section which is comprised solely of two resistances. The amplifier receives as much error current as is necessary, irrespective of frequency to virtually eliminate slew rate limiting. The overall result is extremely good damping and linearity over large amplitude and frequency ranges.
Another less apparent but very important feature of the above mentioned topology is that the overall amplifier quiescent and bias currents can be accurately and independently controlled away from the critical signal circuitry. The conventional bias control circuitry, which must be thermally coupled to the heatsink and is located at a very high impedance and "vulnerable" point in the amplifier circuit in a conventional design, is eliminated and replaced by a simple resistor closely coupled to the actual signal circuitry. The temperature of each heatsink is accurately monitored by precision temperature sensing servo circuitry. This circuitry supplies the necessary bias current to external ports in the transimpedance output section. Thereby, the bias and signal circuits remain independent of each other, and strict control of temperature is thus maintained. When the amplifier is switched into standby mode, via the front panel push button, the bias current of the output stage is dropped to a very low level. The input signal is muted during this state as well. This feature allows the entire amplifier to achieve an authentic standby or "sleep" mode with all voltages present, thus assuring a dramatically reduced warm-up time and elimination of turn-on/turn-off transients appearing at the speaker outputs during on/off transitions.
DC offsets are maintained below 1 mV at both speaker outputs by DC servo circuitry. Abnormally high offset voltages will cause the amplifier to revert to standby mode. Due to excellent thermal stability throughout the entire amplifier, the DC servo circuitry only operates during long-term circuit drifts and permits the low frequency response of the amplifier to extend close to DC.
Switches located on the backpanel allow the user to control operational parameters of overall gain and input impedance. These switches operate small-signal relays located adjacent to their respective circuit functions.

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 continous playing from Model 2 Amp with the BPS-2, really amazing Design.

Description: Solid-state stereo power amplifier.
Power output: 75W into 8 ohms (18.75dBW), 150W into 4 ohms (18.75dBW).
Power bandwidth: 0.5Hz-160kHz -3dB. THD +noise: <0.05% at rated power.
Damping factor: > 100, 20Hz-20kHz, 8 ohms, equivalent to an output impedance of less than 0.08 ohms.
Output current: 20A continuous, 35A peak.
Overall gain and sensitivity: 26dB or 32dB; 141mV or 72mV (1W, 8 ohms).
Input impedance: 36k ohms or 600 ohms.
Common-mode rejection ratio: > 60dB, 20Hz-20kHz.
Power consumption: 25W standby; 225W idle; 400W maximum. 
Dimensions: 17.5" W by 14.25" D by 5.25" H.
Weight: 47 lbs.
Price: $5800.

Description: Battery Power Source BPS-2
Battery quantity and type: six 6V, 12 ampere-hour Sealed Lead Calcium; Panasonic LCR6V12P or equivalent.
Charging type: microprocessor-controlled 4A maximum current, float level constant voltage. 
Dimensions: 15.5" W by 5.25" H by 14.25" D.
Weight: 52 lbs.
Price: $3200.

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

Associated Equipment for this Review:

Amplifier: Lamm M1.2Reference
Preamplifier (or None if Integrated): Rowland Coherence II Series 2
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):	Rowland Coherence II Series 2
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