ModelModelModelModel C-120C-120C-120C-120 StereoStereoStereoStereo PreamplifierPreamplifierPreamplifierPreamplifier (with(with(with(with PS-120PS-120PS-120PS-120 PowerPowerPowerPower SupplySupplySupplySupply Unit)Unit)Unit)Unit)

ModelModelModelModel P-1120P-1120P-1120P-1120 MonoMonoMonoMono BlockBlockBlockBlock PowerPowerPowerPower AmplifierAmplifierAmplifierAmplifier

We were unaware of behaviors of modulated high audio frequency that resulted inuncomfortable transient distortion before we became acquainted with Tetsuo Kawanishi,former associate professor of the University of Electro-Communications Tokyo, and thedesigner of the Shuhgetsu NRF solid-state amplification technology. After exhaustiveauditioning and investigation of Prof. Kawanishiʼs prototype amplifiers with different speakers,we asked him to design a combination of commercial equipment, preamplifier and poweramplifier, as we were converted by his patented circuit design.

◎ Sonic Characteristics of Shuhgetsu Amplifiers

○ High-level of information density: Enables you to catch subtle point of sounds.

○ No coloration: Assures you an experience of the original sound from musical instrument.

○ Highly accurate timbral portrayal: The piano, horn, or soprano vocalization likely coming

"Shuhgetsu"NRF Solid StateStereo System

up at specific musical scales that does not irritate ears.

○ No annoying peaks at high output level: No looming aggressive sound and distortions.

○ Precise spatiality: You can see instrument placement quite clearly, and hear eachinstrument reproduced independently.

○ Accurate phase: Produces wide listening area so you can well enjoy music at any positionoff the speakerʼs front.

○ Full stages driven by stabilized power supply: Exceptionally stable reproduction of lowfrequency range that allows you to appreciate tonal scales of low-pitch instruments.

○ Quite distinct airiness and perspective of acoustic field: Reproduces the atmosphere of liveperformance in your listening room.

○ Sound unworldly like a limpid stream, and powerful like the ocean wave.

○ Depth of character: A Shuhgetsu Amplifier can as a matter of course reproduce acousticinstruments and any category of music.

◎ Genuine sound of musical instrument with no electronic distortions,employing patent applied circuit that deletes Transient Distortion caused byNegative Resistance.

● Transient Distortion caused by Negative Resistance

What is 'negative resistance' and how harmfully is it to reproduced sounds?Solid-state amplifiers generally adopt 'feedback' circuitry to minimize high-frequencydistortion, but it usually does not work perfectly resulting in possible degradation of real part(pure resistance excluding inductance and capacitance) of each input and output impedance(usually complex number) into negative behavior, or negative resistance. Such deficit ispresent in emitter-follower and cathode-follower (as used in Marantz type equalizer) circuits.

Transient distortion may arise once Negative Resistance is generated.:Negative resistance tends to oscillate a circuit which destabilizes an amplifier's operatingpoint, causing music signal to be improperly amplified with transient distortion, whichmuddies the reproduced sound.

Infections of external noise:When the circuit containing this negative resistance is exposed to external high frequencynoise, its operation is increasingly destabilized with all the more transient distortion. In theold days of vacuum tube, such high frequency noises seldom existed in audio reproduction.But since the invention of semiconductors, the negative resistance issue is exacerbated withthe transistorʼs mass application in audio designs, and further compounded with digitaltechnologies development. Infections of high frequency noises generated by electronicequipment has incomparably increased more than ever. (In a feedback type amplifier, highfrequency noise may also be modulated by audio signals.)

● What measures are taken in the Shuhgetsu amplifiers to cope with negativeresistance? (2 patents applied)

In order to remove negative resistance generated in input impedance, the designer added apatented circuit with carefully calculated constant value in the input stage. Furthermore, inthe feedback line which returns to the first stage of the amplifier, another patented circuit isinserted with differently calculated constant value to infinitely remove negative resistanceborn in output impedance.

Herewith, NRF (negative resistance free) circuit is accomplished wherein the operating pointis stabilized. Shuhgetsu amplifiers employ NRF circuit in voltage amplification, poweramplification and stabilized power supply circuits to dramatically decrease transient distortion.

◎ Super High Fidelity music reproduction by use of carefully selected circuitcomponents which are graded as close as possible to ideal elements.

● Theoretical values of high grade resistors and capacitors used in Shuhgetsu areabout the same value in high frequency reproduction as in the following:

○ Resistors with minimum value variation regardless of frequency change.○ Select electrolytic capacitors and low-capacitance capacitors for free of coloration inreproduced sound.○ Block type electrolytic capacitors and film capacitors strictly selected for smoothing ofripple current and absorption of rectifying pulses in the power rectification circuit.○ Adoption of EMe (epitaxial mesa) power transistors and low noise type SiE (SiEP) smallsignal transistors.○ TO-3 metal package power transistors for their minimal mechanical vibration andelectromagnetic wave generation properties, which reduces cross-modulation distortion.(Generally, a power transistor generates imperceptible mechanical vibration by music signals,while also generating electromagnetic waves in parallel with the signals. This often impactsinput stage and causes cross-modulation distortion.)

◎ Balanced Connection adopted in both preamplifier C-120 and power amplifierP-1120 with positively deleted in-phase common mode noise and hum noise, forstabilized reproduced sound with drastic improvement in dynamic scaling, localization,airiness, and spatial perspective.

● Cable Matching:Because the wavelength of audio frequency is sufficiently long compared to the length ofwiring used in audio equipment, less attention has been paid to wiring affecting sound quality.However, it is quite important to emphasize cable matching in high frequency reproductionbetween an amplifierʼs internal wiring and speaker cables when we consider the influence ofhigh frequency noise to an amplifier. When matching is not properly taken, reflections atcable ends will occur to cause possible increase of a particular bit of high frequency noise.

Shuhgetsu amplifiers are devised with countermeasures that assumed a characteristicimpedance of 75 ohms for line cables and 120 ohms for speaker cable respectively. Werecommend use of cables specified by the Shuhgetsu designer.

● Balanced Connection:In order to clear up these problems once for all, Shuhgetsu amplifiers employed Differential

Input Balanced Transmission Scheme, wherein 3-line information transmission (phasebetween hot and cold differs by 180 degrees) with a cold line added to ordinary two-lineunbalanced transmission (hot and ground). This method enables cancellation of highfrequency noise riding on a signal line as in-phase element and delete to the utmost limit inorder to depress transient distortion as much as possible. This is an effect impossible withunbalanced system. Further merit is in heat-up time of the amplifier. The designerKawanishi's unbalanced type amplifiers used to require at least 15 minutes in heating up, butbalanced type enables quick music-listening right after the power is switched on with idealsound quality.

● Does balanced connection produce bad sound?:This balanced connection method produces dramatic improvements but may require morespace and make the equipment bulky due to the need to process two independent signals inone chassis. So some other miniature balanced type amplifiers with perfect specificationshave adopted IC operational amplifiers for amplification stage to save space. Generally, an ICoperational amplifier is of high feedback nature and generates negative resistance that maymuddy the sound, thus leading listeners to conclude that an unbalanced type is actuallybetter in sound. On the other hand, unbalanced amplification fosters listeners' delusions thatthe sound is better because it becomes only partially aggressive when it comes under theinfluence of high frequency noise. Therefore, Shuhgetsu balanced system without the use ofsuch IC operational amplifiers is both theoretically and realistically superior in reproduction ofnatural sound by common mode noise removal.

◎ Powerful and Sharp Bass in the P-1120 power amplifier, thanks to use ofstabilized power supplies placed in all power amplification stages to prevent voltagedrop at significant power output

● Whereas a power amplifier generally employs a stabilized power supply only in the frontpower amplification stage, Shuhgetsu P-1120 has stabilized power supplies throughout – upto the power stage, unlike others. This full-stage stabilization is costly but enriches bassreproduction by depressing voltage drop at high output.

● An ideal power supply has zero source impedance to prevent voltage drop from DC to highfrequency area, and does not have high frequency noise. Source impedance of Shuhgetsuamplifier P-1120 is in the order of 0.01 ohm up to around 10KHz, and stays within 0.1 ohmeven in higher (than 10KHz) frequency area due to special decoupling capacitors circuit inthe power supply.

● If the source impedance is high in a preamplifier, overall sound becomes less powerful andsharp. An ideal power supply should be a stabilized type having low impedance. So,Shuhgetsu preamplifier C-120 is also designed with this type of supply unit PS-120, which ishoused in a separate chassis.

● P-1120 is built with a large capacity EI core transformer with excellent electromagneticand electrostatic shielding to secure stable and clean power supply.

◎ Sturdy Housing and Provisions for Electromagnetic Wave

● Power Amplifier P-1120:

1) 5.6mm thick steel sheet for chassis to secure internal components and suppressmechanical vibration at all points.2) Hospital-grade shielding for power transformer winding gaps, as used in medicalequipment against electromagnetic wave and static electricity to block off common modenoise in the power supply.3) Appropriately isolated stage placement to prevent interference between flux leaked fromthe power supply and electromagnetic wave generated in the amplification circuit.● Preamplifier C-120 and Power Supply PS-120:1) 3mm thick steel sheet as strong support structure for PC board unit, with vibrationabsorption rubber float system.2) Separate power supply unit to suppress magnetic flux leakage to the preamplifier circuit.3) Hospital-grade shielding for power transformer winding gaps, as used in medicalequipment against electromagnetic wave and static electricity to block off common modenoise in the power supply.

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Additional Technical Description

1. Circuit constant of the Shuhgetsu amplifier was determined not through monitoringscound quality, but by numeric calculation using a computer of a condition whereinnegative resistance does no exist after having analyzed input and output impedancesmodelling on a single stage differential amplification with emitter-follower circuit.Then the circuit constant is as straightly as possible applied in an actual circuit todetermine a final circuit design. Thus, the Shuhgetsu circuitry was determined not bycut and try method but by using the values logically calculated as are. On the otherhand, the elements chosen and used by monitoring sound are such parts as resistorsand capacitors which are of high grade required to realize the determined circuitdesign as ideally as possible.

2. Key components used for the Shuhgetsu amplifier are as below:A) EMe power transistorsB) SE capacitors for compensationC) RIFA film capacitors as used for coupling or bypassingD) RIFA Type 02 electrolytic capacitorsE) NIKKOHM plate type resistorsNONE of OFC parts including wires are being used.

3. Points taken care through sound monitoring to select required parts:A) Much care was taken to enable to hear every note of the piano sound in any scale

without deforming the sound image as well as the sound of collision occurring when thepiano hammer is percussed. For example, there should not occur abnormal sound of asingle note that suddenly brings pressure on the eardrums, and each note in tremolosshould be clearly recognized.B) Lift of soprano or alike vocal in a cetain interval should not abnormally give

pressure on the eardrums.C) Sound image of horn(s) should not deform otherwise distance perspective

becomes hard to recognize.D) The violins in a string concert should not be tightened or get clogged so that sound

softness peculiar to strings as often heard in a concert house can be sensed.E) A single note in piccicato part for contrabass should not unusually hollow in a room,

and descending intervals can be clearly caught. (Such low pitched tone instruments ascontrabass, bassdrum, timpani, or organ when simultaneously played can be cleanlyheard.)F) Finally, the Shuhgetsu should reproduce a concert hall presence in an audio

listening room.

4. Shuhgetsu amplifier does not need a special listening room.Conventional amplifiers had a problem in transient characteristics, so is much affected bya listening room, where listeners have to care much for curtains, rug or carpet, or othersound absorption material, but Shuhgetsu with super transient characteristics sets youfree from sound absorption cares. In any type of room, Shuhgetsu sounds in its own way.You also do not have to worry about the position to place a speaker system. Even if thespeakers are roughly placed, more than a certain level of presence can be obtained. Itspractical service area is quite wide allowing a listener with less knowledge about theacoustic field to command the Shuhgetsu. Ideally, the best is to place the speakers facingthe front and listen at the vertex of an isosceles triangle. Further, it is suggested to giveminimum 1 meter gap between the speakers and the wall behind.

Designer Tetsuo KawanishiJan. 19, 2009

His following patents are employed in the Shuhgetsu:No. 2118015 Collector type 2 stage feedback amplification (Dec. 6, 1996)No. 2794667 Negative feedback amplification (June 26, 1998)

About the Output Circuit of P-1120 Power Amplifier

P-1120 output stage is ended with Complementary Parallel Push-Pull circuit. DesignerTetsuo Kawanishi explains why he adopted this circuitry as follows.

“As known widely, a transistor amplifier was born with semi-complementary push-pullcircuit. Later a complementary circuit designs were developed little by little, and amplifiermanufacturers began employing the complementary circuit except for a part of power IC,and majority of the manufacturers have followed one after another up to the presentdate.

Recently, production of power transistors suitable for audio use tend to be discontinued,so there are some manufacturers who went back to semi-complementary design. I amusing complementary circuit for high end and semi- for less expensive products.

Parallel connection is adopted for the Shuhgetsu P-1120 to achieve high power outputsuccessfully without sacrificing audio quality as long as maximum two parallel stages.This is the best choice to satisfy both of power output and sound quality. Many othermanufacturers employ more than four parallels knowing that sound suffer demerits suchas blur and lack in delicacy. Therefore, P-1120 can outstrip other higher output poweramplifiers with 4 parallels. An example of the reports from my client is that Telos-200sounds generally inferior to P-1120.”

April 4, 2009

Translation: M. Shibazaki, SIBATECH, Inc.