Unison Research P70 amplifier

Fully balanced dual mono valves amplifier in Push-Pull

Designing the P70 has required about one year of work. The very first prototype has been developed in 2006, and it immediately showed all the critical elements related with this kind of design. It took time to find all the electronic solutions that have lead to the current circuitry.

The P70 is now an amplifier capable of delivering more than 70 W per channel into a 6 Ω  load, with Total Harmonic Distortion lower than 0,2% over the whole audio band. Its performances are comparable to those of a good single ended amplifier.

 

Structure of P70

The amplifier is laid out in dual mono configuration. Both the amplifier stages and the power supply circuits are completely independent. The signal path in the amplifier is fully balanced from the input through the output. This means that the signal at the output terminals is balanced with respect to the amplifier ground.

The P70 has four line inputs. All of them can be balanced or unbalanced, an external switch allows the selection. The volume potentiometer is a four sections motorised Alps blue series potentiometer. The selection of the channel is performed by four high quality relè.

All the operations of the amplifier, included the safety functions, are controlled by a microprocessor to ensure maximum reliability and intuitive user interface.

The amplifier itself is constituted by an input stage featuring two double triodes ECC83 and one double triode ECC82, and a power stage with two KT88 per channel.

The output transformer has been custom designed by Unison Research and ensure a bandwidth of more than 30 kHz at full power.

 

The preamplifier is constituted by a double differential pair in an original configuration. The two differential stages are DC coupled and allow to reach the needed gain. They are followed by a couple of cathode followers, again DC coupled, which guarantee the low output impedance required. The power supply for the whole preamplifier stage has a very high voltage, around 600 V.

The input stage has a local feedback, characterised by different feedback factors for the bias component and the signal. The two different values are set keeping into account the different need for precision on the value of the bias and of the signal.

The importance of a stable controlled bias in the amplifier is due first of all to the choice of the DC coupling between the stages and also to the need to allow the same signal excursion along the paths of the balanced signal.

The circuit we have designed amplifiers signals up to 200 V p-p. conversely, the feedback factor affecting the signal has been kept to the lowest possible value.

 

Specifications

Power Output:  70 W +70 W RMS

Output Impedance:  6 Ω  (4 - 8 ohms)

Input Sensitivity:  500 mV

Input Impedance:  47 k Ω

Frequency Response:  10 Hz to 40,000 Hz (0,5 dB, 1 W)

Signal-to-Noise Ratio:  83 dB A

Total Harmonic Distortion :  0,3% (10 W)

Negative Feedback:  12 dB

Damping Factor:  8

CMRR:  59 dB

Power Requirements:  105 - 120 / 210 - 240 V , 50/60 Hz at rest 360 W

Dimensions (W x H x D):  460 x 450 x 200 mm

Weight:  35 kg

 

Carver SD/A-490t CD player

Our ultra-advanced new SD/A-490t includes two vacuum tubes whose classic design has remained unchanged for over 50 years. We and many other critical listeners believe that this anachronistic addition to an already excellent CD player design significantly enhances its sound.

 

The amplifier that doesn't amplify - Between a CD player's D/A converter and external outputs is circuitry called a buffer amplifier which actually doesn't boost the signal strength at all. Instead, the buffer amp is a unity gain device which increases output current, and acts as a sort of electronic shock absorber, isolating the relatively fragile D/A chip set from the nasty outside world of demanding analog components.

 

Tubes versus Solid State -  More than 98% of all CD players use solid state deivces for buffer amplifiers. A handfull of hard-to-find, esoteric designs in the $1200to2500 range employ one or more tubes instead.  In ultra-expensive preamplifiers and power amplifiers, tube sound is subjectively described as "mellower", "warmer", "more open and natural" or simply "less harsh than solid state". Objectively, it's safe to say that tubes; - produce even-order distortion versus transistors odd-order distortion, particularly 3rd harmonics which are especially unpleasant to the ear; - act as a pure Class A device when used in a buffer stage (Class A outputs is considered the optimal amplifier configuration); - "Round off" the waveform when they clip, while over-driven solid state devices cut off sharply, causing audible distortion.

 

The SD/A-490t's output section - Our new CD player uses two 6DJ8 dual triodes placed between the digital-to-analog converter and a motorized volume control. Operated at less than 30% of their maximum capacity, the tubes achieve a highly linear output voltage with very low static and transient distortion while providing very high dynamic headroom. And because they're "loafing" at ⅓ their rated current capability, the SD/A-490t's tubes are designed to last the life of the CD player without replacement or need for adjustment.

 

An array of features as rich as its sound - We've designed the SD/A-490t to be both useful and easy to use. 21-key front panel or remote programming. Fixed and variable output. Programming grid display. Random "shuffle" play. Variable length fade. Automatic song selection to fit any length of tape. Even index programming for classical CD's. plus our proprietery Soft EQ circuitry which compensates for variables in special (L-R) information and midrange equalization found in many CD's mastered from analog tapes.

 

Specifications

Decoding:  1-bit linear, two channels

Frequency Response :  8 Hz - 20 kHz (+0,2 dB -1,0 dB  nominal)

De-emphasis Error:  +0,5 -1,0 dB Nominal

Output Level at 0 dB :  2,5 volts +_0,5V

Harmonic Distortion:  0,25% Nominal

Signal-to-Noise Ratio  104 dB Nominal

Channel Separation(EQ Off / On):  88 dB / 17 ±1,5 dB Nominal

Channel Balance at 1 kHz , 0 dB:  ±0,5 dB Nominal

Wow and Flutter:  Unmeasurable (quartz crystal accuracy)

Power Requirements:  120 V or 220 V 50/60 Hz

Power Consumption:  30 W

Dimensions (W x H x D):  483 x 96 x 311 mm (19 " x 3,8" x 12,25")

Net Weight:  4,5 kg (9,941 lbs)

 

Audio Research D-70 power amplifier

If a preamplifier is viewed as the control center of a music system, then an amplifier can be regarded as the "engine" which power the system.. There is a misnomer among the audio community that amplifiers have no distinct "sonic signature" of their own, and that amplifiers varying widely in design and construction exhibit only minimal sound differences. Whit thirty years of design experience Audio Research has discovered this is not the case.

Claims for amplifier similarity have been strictly based on static performance measurements made into purely resistive loads. This is a poor test basis, similar to comparing a racing engine to a road model at identical idling speeds and concluding that they are equal in performance. In fact, amplifiers vary widely in their sonic character and recent advances in amplifier technology make this easily demonstrable .

From a performance standpoint, amplifiers must meet the same criteria for preamplifiers including clarity. High Definition , harmonic accuracy and dynamic range. Perfect linearity under difficult load coditions is impossible to achieve. However, Audio Research has been responsible in extending amplifier performance to new limits for nearly two decades.

 

Design Criteria

When designing a high performance power amplifier, the engineer is faced with four primary considerations:

• Audio quality
• Construction quality
• Power
• Costs.

So successfully blended are these criteria that Audio Research amplifiers now extend state-of-the-art. Performance without sacrifice in power, construction quality or at unreasonable cost.

Because Audio Research has given continuous attention to improving all aspects of amplifier design for many years. Audio Research now manufactures amplifiers which appear modest in price compared to state-of-the-art. Models of just a few years ago. Yet the performance capabilities of these amplifiers are so great that they overwhelm recent state-of-the-art. Amplifieres built without cost constraints.

 

Features

Patented Audio research cross-coupled and fully balanced circuitry

Front panel power switch relay coupled for smooth and reliable turn-on

Front panel LED indicators for line and screen

Front panel fusing for line and screen

Sonically selected components for optimum sound performance

Near military grade construction used hroughout

 

Specifications

Power Output:  65 watts per channel minimum continuous at 16 ohms from 20 Hz - 20 kHz with less than 1% Total Harmonic Distortion

Power Bandwidth:  10 Hz to 60 kHz (-3 dB points)

Input Sensitivity:  95 V RMS for rated output

Input impedance:  75 k Ω nominal

Noise:  greater than 90 dB below rated power, broadband unweighted

Dimensions (W x H x D):  19" x 7" x 16,5"

 

Dynaco Dynatuner FM-3

The Dynatuner is the culmination of more than threee years intensive research on a new concept of FM tuner design. Both the tuner and the stereomatic multiplex integrator represent a totally new design so inherently non-critical, so completely stable, so accurately reproducible, and so easily aligned that the average kit builder will have no difficulty in meeting its specifications in full, without the use of any test instruments whatsoever. The Dynatuner will be most recognized for its low distortion, but it has achieved the most successful blend of sensitivity, stability and linearity yet realized.

The Dynatuner is a kit in every sense; no sections are pre-built or pre-aligned - but Dyna's proven engineering has made it the easiest of all FM tuner kits to build,, and simpler than most competitive amplifiers. The use of heavy duty XXXP and fiberglas pre-punched circuit boards assures exact placement of all components - an essential factor in critical tuner circuits. The excellent specifications of the Dynatuner are possible, and guaranteeable, unit to unit, lab model to production kit, because of the extraordinary uniformity which etched circuits provide, and the inherent stability of the Dynatuner circuit configuration.

 

The design of the Dynatuner evidences several engineering innovations. A cathode coupled RF stage, rather than a cascode input, has been refined to provide equivalent sensitivity without the disadvantages of cross-modulation (images) generally associated with the cascode design. Outstanding AM supression has been achieved,, with noticeable improvement in difficult urban reception areas, and reduced interference from multipath dispersion. Four stages of IF amplification, furnishing four stages of progressive limiting, plus careful attention to limiter design, result in superior suppression of impulse noise such as auto interference, and yield more usable low level signals than other tuners of equivalent sensitivity. We have expended some gain (sensitivity) to achieve better low level limiting, where it counts the most. The Dynatuner limits on noise alone - contributing to its low interstation noise level.

 

The Dynatuner's combination of performance 9high sensitivity, lack of drift, low noise, high selectivity, and lowest distortion) reliability (top-grade etched circuit construction, highest quality parts, conservative operation of components, ease of alignment) and simplicity of construction and operation, plus unsurpassed flexibility (with the FMA-2 and the FMX-3) make it an outstanding example of the Dynakit reputation for obsolescence-proof design.

 

Specifications

Based on IHF standard T-100

Useable Sensitivity:  4 mV for total noise and distortion 30 dB below 100% modulation

Signal-to-Noise Ratio:  70 dB at 100% modulation

Total Harmonic Distortion:  less than 0,25% at 100 % modulation

IM Distortion:  less than 0,5% from 10 mV - 100,000 mV at 100% modulation

Drift:  less than 0,03%

Frequency Response:  10 Hz - 15 kHz ±0,5 dB

Audio Output:  2 volts at 100% modulation

Output Impedance:  less than 5000 ohms

Discriminator peak to peak Separation:  greater than 900 kHz

Antenna Input:  300 Ω (balanced), 75 Ω (unbalanced)

Dial calibration Accuracy:  0,2%

Useable Sensitivity Stereo:  3 dB less than mono mode

IM or T.H.D. :  less than 1% ( including 19 kHz and 38 kHz residual)

Stereo Separation :  30 dB

Capture ratio:  5 dB

Selectivity:  54 dB

Audio Hum:  73 dB below 1 V output

AM Suppression:  greater than 63 dB

Power Consumption:  55 watts

Audio Note P2 SE power amplifier

The P2 SE is a pure Class A, single-ended amplifier. Its development is the result of Audio Notes ongoing research to find ways to make better audio products. A side from the six key features on which the design is based, atechnique called "Comparison by Contrast" is used to ensure that the product is developed with the most important specification of sound quality as the overriding factor.

The P2 SE design is derived from the Audi Note 's key technological features originally embraced by the On Gaku and kegon amplifiers.

These features include:

Pure Class A operation

Zero negative feedback

Single-ended output stage

Valve rectification

Directly heated, triode output stage.

Pure Single-ended operation.

The P2 SE is a single ended amplifier. This means that the complete music wave form reproduced by the amplifier is preserved as one "whole". Consequently, a true single-ended amplifier must be pure class A and operates in a coherent and natural way.

This produces significant sonic advantage compared to convetional push-pull amplifers since push-pull amplifers demand that a new "mirror" image wave form be created for the topology to work. Creating this perfect mirror image of the original wave form is rather a tall order and far from the only problem associated with push-pull amplifiers.

The stage uses one 6SL7 dual triode per channel. These tubes are connected in a SRPP method and this stage generates most of the required gain.

Since the amplifier is single-ended, no complex phase splitting circuitry is required and the signal from the 6SL7 tubes can be coupled to the output stage. Here, Audio Note aluminium foil, paper in oil capacitors are used instead of the inferior quality film types used so commonly in the audio industry.

The final output trasformers (one of the most critical components in a vacum tube amplifer) are of custom Audio Note design and provide previously unavailable performance characteristics. These transformers use massive cores to reduce saturation effects. This allows the P2 SE to produce impressively extended and controlled bass performance.

Specifications:

Maximum Output:  18 Watts RMS per channel into 4 or 8 Ω loads

Tube Compliment:  4 x 6L6 / 5881;  2 x 6SL7

Input Impedance:  100 k Ω

Power Consumption:  165 VA

Fuse Ratings:  2 A anti-surge (110 to 120 V supply);  1,2 A anti-surge (220 - 240 V supply)

Dimensions (W x H x D):  300 x 140 x 410 mm

Weight:  19 kg

Copland CSA-14 amplifier

The Integrated Amplifier CSA 14, combines the benefits of both valve and transitor amplification, in a way unheard of before, usually hybrid Amplifiers dedicate one section of the amplifier to valve in isolation from the rest beacuse, the virtues of solid state and valve design are not the same, a synergy between them can be created, offering an alternative to either.

The Copland CSA 14 uses two valves in the input pre-differential driver stage of the amplifier allowing the notably smooth and transparent properties of the valves to blend with the power and dynamics of transitor electronics.

The synergy achieved surpasses, the found in other Hybrid Amplifier, in its relability while combining only the positive attributes from each element. 

The CSA 14 is build into a slim compact chassis. With the same build and sonic qualities, that have always formed the cornerstone of Copland's philosophy, offering exeptional valvue, whist the design allows the listener to relax and enjoy the astronnishing sound quality.

Due to popular demand, Copland have simplified one of their high-end amplifiers, in this case the CSA 14, to provide a solid state produkt of real quality, at a point within reach of the aspiring audiophile.

Specifications:

Output Power:  2 x 60W

Phono Input Impedance:  47 k Ω

Phono Sensitivity:  3 mV

Line Input Impedance:  33 k Ω

Line Sensitivity:  130 mV

Power Bandwidth:  5 Hz -30 kHz ±3 dB

Frequency Response:  5 Hz - 120 kHz ±3 dB

Total Harmonic Distortion:  better than 0,09%

Hum and Noise

Line :  better than 90 dB

Phono :  better than 76 dB

Phase:  non inverting

Vacuum Tubes:  2 x 6922 All valves are hand selected and identically matched.

Grounding:  Separated grounding on power supply. Signal/chassis connected to signal ground

Power Consumption:  250 watts

Dimensions (W x H x D):  430 x 125 x 375 mm

Weight (shipping):  13 kg

Synthesis Soprano amplifier

Soprano - 12W A-Class Integrated stereo tube amplifier

Following the success of the much-celebrated NIMIS, Synthesis took on the challenge of recreating a 12W A-Class integrated stereo tube amplifier. Using a new technologies a new business development and Luigi Lorenzon’s constant pursuit of perfection, he succeded in creating an entry level amplifier that is able to satisfy even the most dedicated audiophile.

New model of stereo tube amplifiers with DAC's on board, guaranteeing exceptional sonic performance from any digital source.

Made with the finest materials & advanced technology, this series is a sophisticated blend of research & experience.

Designed without compromise far a rich sound & faithful music reproduction.

The SOPRANO provides a minimum of 12 Watts per channel, power output from a pair of EL84's in Ultra-Linear (UL) - push/pull operation.

The SOPRANO features a newly designed custom output transformer resulting in a rich sound stage but with an authority that belies its 12Wpc

FEATURES

- USB -

DAC on board 24bit for a extraordinary listening experience from computer’s file.

- Phono Stage -

Hi quality Phono stage for MM cartridges.

-SPDIF inputs (Coax and Optical) Built around a AKM chip. 24 Bit 192KHz Hi Quality DAC for an extraordinary sound result.

- Output Transformer -

The Output transformer uses a Hi-Grade iron-Silicon for superb frequency reproduction & width. With this newly designed custom output transformer unique to the Soprano we are able to achieving a highly delicate & precise sound reproduction faithful to the original recording.

- Mechanical Chassis Construction -

The power supply & output transformers are held by an extremely rigid structure that keeps the unit free from unwanted vibrations which further helps reduce unwanted noise to the tubes.

- Binding Posts -

Gold plated professional binding posts for a continued oxidization free connection further improve sound refinement.

- Sockets -

Ceramic sockets for a continued oxidization free connection further improve sound refinement.

- Components -

Components for the amplifier have been selected with great care throughout. Only the best available components are considered & all must undergo an exhaustive analysis of their sonic influence prior to final selection.

- Selected Tubes -

All tubes used are selected after 2 stage warm up. A fully computer monitored machine controls the process & at the end of this, selects the perfect tubes which are then matched for a perfect balance.

Technical Specifications:

Power Stage (1 ch.):  Matched pair EL84/6BQ5

Input Stage (1 ch.):  Hi Performance audio OP-AMP JRC4580

Driver (1 ch.):  Matched pair MJD340 (Designed for audio amplifier)

Input Impedance:  100 k Ω  

Input Sensitivity:  100 mV RMS for rated power

Output Tap:  6 Ω  

Power Stage Config.:  Push-Pull Ultra Linear 43% tap

Power Output:  12 W RMS into 6 Ω  A-Class

Power Bandwidth:  15 Hz to 50 kHz  -3,0 dB

Frequency Response:  20 Hz to 20 kHz  -0,5 dB

Distortion:  1% at 1 kHz max power (12W)

Signal-to-Noise ratio:  90 dB A weighted

Analogue Inputs:

1 Line,

1 Phono MM (47 k Ω) 40 dB gain

Digital Inputs:

1 SPDIF coax, 1 SPDIF optical 1 USB “B” type Windows/Mac/iOs/Android compatible

Max Resolution:  1 SPDIF coax, 1 SPDIF optical 1 USB “B” type Windows/Mac/iOs/Android compatible 24 Bit 192KHz

Remote Control:  Volume and Sources control

Power Requirements:  230 V AC 50 Hz (120 V AC 60 Hz) - 80W maximum

Dimensions (W x H x D) :  310 x 150 x 295 mm (12,2” x 5,9" x 11,6”)

Weight:  10,0 Kg (22.0 lbs)

I like

Audio Innovations - The First Audio Amplifier

The Audio Amplifier Series from Audio Innovations challenges a number of traditionally held beliefs, the most fundamental of which is the insistance that inn order for an amplifier to have a sufficient dynamic range, it must have a very high static power output. The second main misconception is that the amplifier must have low distortion; the third being the bandwidth nevessary to reproduce the audio apectrum.

The First Audio Amplifier is the first amplifier to significantly deviate from these design criteria. It is also first commercially available amplifier using the Direct Heated Triode, this being the most linear and load tolerant amplifying device available.

Special Features and Facilities

7,5 watt Pure Class A

Direct Heated Triodes type 684G or 2A3

No overall or local feedback employed

Fully hardwired circuit. No Printed Circuit Board

Handmade paper in oil capacitors for best possible signal transfer.

Non-magnetic resistors

Signal input wired with Audio Note 99,99% pure silver cable type AN-S

Cathode biased output stage

4 Ω , 8 Ω , 16 Ω output impedances, switchable on the back fascia

I like

McIntosh MC-60

The Mcintosh Model MC-60 is a 60 watt high fidelity power amplifier designed for home entertainment systems and professional applications where high power and distortion free performance is required. The Model MC-60, like all other McIntosh power amplifiers. Uses the exclusive McIntosh high efficiency output circuit and bifilar output transformer to obtain the high standard of performance found in this amplifier.

Some of the more important characteristics of the amplifier are less than 1/3% harmonic distortion at any power output up to 60 watts and at any frequency in the audio spectrum, 20 to 20,000 cps; less than 1/2% intermodulation distortion for all power levels up to 120 instantaneous peak watts; and noise and hum level 90 dB or more below the rated output level.

The MC-60 has two high impedance inputs and many be operated from any signal source deliviring 0,5 volts or more, or directly from a McIntosh Audio Compensator or pre-Amplifier such as the  Models C-4, C-8, C-104 or C-108.

Output impedances of 4, 8 and 16 ohms are provided for direct connection to loudsapeakers. An additional 600 Ω output is present for use with lines.

Specifications

Power Output:  60 watts continuous

Input Level:

Input 1 :  0,5 volts to 30 volts, with gain control

Input 2 :  2,5 volts (for use with McIntosh Audio Compensators and pre-Amp)

Frequency Range: 

20 to 30,000 Hz ±0,1 dB at 60 watts output

16 to 60,000 Hz ±0,5 dB at 60 watts output

10 to 1000,000 Hz ±1,0 dB at 30 watts output

Total Harmonic Distortion:  less than 1/3% at 60 watts output or less, 20 to 20,000 Hz

Intermodulation Distortion:  less than 1.2% if instentaneous peak power is below 120 watts

Impulse Distortion:  Negligible

Noise and Hum level:  90 dB or more below rated output

Damping Factor:  15 or better for 4, 8 and 16 Ω output, 20 for 600 Ω

Input Impedance:

0,5 meg for 0,5 volt input

0,13 meg for 2,5 volt input

20 cycles to 40,000 cycles

Output Impedance:

4, 8, 16 and 600 ohms (600 ohmis balanced to ground)

Phase Shift:  ±8° 20- 20,000 Hz

Tube Complement:

Rectifier :  2-5U4GA

Pre-Amp :  12 AX7

Phase Inverter : 12AU7

Voltage Amp : 12BH7

Driver : 12AX7

Output : 2-6550

Dimensions (W x H x D):  14" x 10" x 8"

Weight:  41 pounds net

Finish :  chrome and black

I like

Quad II Integrated Amplifier

The Quad II-Classic Integrated

The rekindled interest in 2 channel analogue hi-fi been remarkable to witness. The popularity of vinyl has grown steadily over the last years and now represents a significant proportion amongst real music enthusiasts. Quad has been at the forefront of this trend with its development of some of the world's most stunning amplifiers  loudspeakers and phono stages. Creating a compact audiophile integrated solution for LP and Vintage Hi-End Audio lovers while working in collaboration with one of the industry's edteemed legendry figures, Tim DeParavicini.

Through his contemporary designs based on Qad's novel amplifier technology developed over half a century ago for his invention of the first Quad II Mono Amplifier introduced in 1953, our classic range of amplifier and speaker componenets represent far more than a nostalgic trip down memory lane. Each product represents as significant a design statement as their original counterparts.

The new Quad II Classic Integrated  Amplifier is perfectly balanced and completely integrated amplifier system to resolve system matching and offer exceptional performance nd value within a relatively compact and classically styled chassis.

Performance as you would expect from one of the most famous names in hi-fi, is nothing short of breattaking. The 25 watt per channel specified, belies their power and ability to drive even the most difficult loads. The remarkable output transformer design is characterized through its speed, agility and ability to convey the genuine passion of live performnce.

Design and Engineering

The KT-66 output valves, in push-pull configuration are visually stunning, even when safely secured within the cage tht protects them. Each valve produces around 25 watts per channel output in "Pure ClassA" which allows a suebrbly refined sound that appropriately matches modern as well as contemporary loudspeakers.

The package had to retainn the retro look of it famous preamplifier predecessor with th epower amplifier and transformers blended into a modern compact look. It has an understated elegance which lies beneath its smooth curves and lustrous finish because it uses a circuit dating back over fifty years to the time when vacumm tubes ruled the electronics industry and peter Walker was considered by many to be the master of audiophile design.

All Quad products are expected to last a lifetime - even longer. Many Quad customers still derive immense pleasure listening to products built over fifty years ago. The new Quad II Classic Integrated Amplifier is no exception, and with periodic servicing and a caring hand, you can expect its performance to continue for decades to come.

The Quad II Classic Integrated Amplifier operates in Pure Pentode (Beam Tetrode) output with partial cathode loading, this being more linear than so called ultralinear. It is a pure Class A operation, whereas its push pull operation's efficiency can only rach 50% max and its power supply is the usual capacitor filter with diode bridge rectifier, AC 6,3 volts heaters to the valves that is shared between both channels.

Equipped with a bi polar transistor phono amplifier that uses 4 transistors per channel with low feedback to provide correct RIAA equalisation. Also has a gain switch for moving coil caartridges, 0,25 mV at 1 kHz , a circuit which operates from a regulated 36 V derived directly from th emain HT valve. It ensures a very high overload performance from rcords.

The phono circuit is housed in a shielded compartment providing low noise RF proofing within th emain package.

Amplification Process

The Quad II Classic Integrated Amplifier output is 25 watt per channel  Integrated Amplifier had to obey Peter Walker's Philosophy  of cathode loading of the output stage and simplicity of design.

Upon Input, a selector switch routes the required signal to the volume control then on the first of 3 small driver valves. This first valve is an ECC83 acting as a differential balance circuit that is a phase slitter.

The output going into a pair of ECC88 valves that both operate as a cascode circuit for high gain and wide bandwidth directly drives the output valves (KT 66) via capacitors.

The circuit had to have high gain than a normal power amplifier to offer a nominal 250 mV input sensitivity on the various inputs.

Push pull feedback is arranged from the cathodes of the output back to the ECC88 valves to provide low distortion and noise with consistent performance.

Specificastions

Stereo Power Output:  25 W per channel into 8 Ω

Total Harmonic Distortion:  0,06% (at 15W &700 kHz )

Signal-to-Noise ratio:  better than -95 dB (ref 25 W into 8 Ω)

Frequency Response:  20 Hz - 20 kHz +0 dB -0,5 dB

Crosstalk: better than 75 dB

Gain :  34 dB

Noise:  -98 dB (275 mV input)

Valve Type:  4 x KT66; 4 x ECC88; 2 x ECC83

Input Channel:  3 x Line Level; 1 x MM/MC Phono and Tape monitor

Dimensions (W x H x D):  200 x 310 x 380 mm

I like

Luxman D-103u CD Player

High-Quality Vacuum Tube Analog Output Stage

The D-103u was designed to make the unique design of the D-105u available to more conservative budgets - without compromising on sound quality. That means using the same basic components in the analog signal path: two triode vacuum tubes in the output stage to recreate the delicate, transparent tones of the original performance.

Advanced Digital Output Stage

The D-103u also offers 18-bit , 8-times oversampling digital filters, and independent dual D/A converters. The STAR Circuit helps preserve signal purity at all stages.

"Mid-Ship" Mechanism

The ideally balanced, central position of the disc tray combines with Luxman's High-Rigid Lock mechanism to enhance the anti-resonance of the D-103u

Features Emphasize Ease of Use

Convenient D-103u features include: remote volume control, switchable front panel display dimmer, vacuum-tube warm-up switch, and 32-track random access and track programming.  In sum, the D-103u offers everything that a music lover could ask for  - and more.

Direct link to the LV-103u

The D-103u is the mainn playback source in serial remote control with the Luxman LV-103u Ultimate Fidelity integrated amplifier.other D-103u features include:

Memory Auto Check;  Automatic Scan/Pause; Fade-In/Out; Emphasis Display; CD Single Compatibility

Specifications:

Frequency Response:  5 Hz - 20 kHz (±1,0 dB)

Total Harmonic Distortion:  0,05% (at 1 kHz)

Signal-to-Noise Ratio:  105 dB

Dynamic Range:  89 dB

Channel Separation:  89 dB

Analog Output

Fixed :  2,0 V/ 47 k Ω

Variable :  0 -  2,0 V / 47 k Ω

Digital Outputs:

Coaxial :  0,5Vp-p / 75 Ω

Optical :  -21 to -15 dBm / 660 nm Wavelength

Dimensions (W x H x D):  438 x 145 x 320 mm

Weight:  6,5 kg

I like

Audio Research Dual-100

Audio Research Dual-100 Features:

Exclusive New Circuitry (Patented and Patent Pending)

Quality Construction

1/8" anodized aluminum chassis;

Silicon power supply;

Choke filtering;

Heavy duty epoxy-glass circuit board;

Conservative design;

Many precision parts;

Extra quality components;

Thermistor controlled warmup.

Conservative Specifications

Unique Guarantee (Investment protected; 5 years, part and workmanship; 2 years, vacuum tubes/home use; registered warranty transferable)

Ultra Stable Performance: Ideally suited for complex loads such as electrostatic speakers (may be operated into open circuit or any combination of reactive and/or resistive load)

 Unique Circuitry - Delivers superior performance under dynamics of music

 Overload Stability - and lack of crossover distortion provides clean effective loudness of much larger amplifier.

In the evolvement of the Dual 100 design, foremost consideration has been placed on listening quality. Needless to say, there was no place for the "but we've always done it this way" philosophy in its design. Certain well-known principles (but seldom used) are obviously  retained, such as quality of construction, an an adequate power supply. From a circuit standpoint, however, little of it resembles convention.

 One patent has been issued, another is pending, and even beyond thgis, the circuitry is unique. Interestingly enough, it is also very straight-forward and remarkably long-term stable.

 The output stage is one of these unique circuits, and needless to say, it does main fixed regardless of amplitude or complexity of signal.

Specifications:

Frequency Response:

30 Hz to 15 kHz at 1 watt ±1 dB

30 Hz to 15 kHz at 75 watts ±1 dB

Sine Wave Power:  at least 75 watts RMS 30 Hz to 15 kHz

Harmonic Distortion:  less than 0,15% at 1 kHz at 75 watts

Hum and Noise:  at least 80 dB below rated output

Input Sensitivity:  1,0 V RMS for rated output

Impulse Distortion:  essentially none 30 Hz to 15 kHz

Permissible Loads:  Open circuit, resistive, capactive, inductive, or any combination, series or parallel

Output Impedance:  4, 8, 16 ohms

Load Regulation:  from 16 Ω resistive load to open circuit less than 1 dB change 1 kHz

Dimensions  (whd):

Power Supply :  17" x 13" x 10-1/2"

Amplifier :  17" x 13" x 8"

Weight

Power Supply :  88 lbs

Amplifier :  45 lbs