amplifiers
ART27A and ART108A Class A Triode Amplifiers
The ART27A and ART108A are very special amplifiers designed for reference quality use by a limited number of discerning audiophiles - no more than 250 of the stereo ART27A and 125 pairs of the mono-block ART108A will be produced.
Speaker systems vary in sensitivity with some highly regarded speakers measuring an output of 86 dB or less from one Watt at one meter to other high-efficiency systems producing as much as 104 dB. Further, room dimensions, speaker placement, and listening placement vary widely – also significantly impacting power demands. Accordingly, the power demands of different high-end audio installations vary widely. To address a range of these needs, conrad-johnson offer these two amplifiers utilizing the same basic circuits and built to identical standards, differing only in the number of output tubes, size of the output and power supply transformers, and scale of the power supply required to achieve their different output power levels.
The circuit for these amplifiers is designed for Class A operation of KT88 output tubes configured as triode devices – a single pair for each channel achieves 36 Watts per channel in the stereo ART27A suitable for highly efficient systems, while the mono ART108A employs four pair to produce 160 Watts – ample power for the vast majority of applications.
The amplifiers boast independent discrete regulated power supplies for the output stage in addition to separate regulated supplies for both input and inverter stages (with separate regulators for each channel in the ART27A).
The conrad-johnson design team has long appreciated the critical importance of parts quality in achieving top performance.
conrad-johnson’s commitment to executing their reference level products with only the highest quality parts is unmatched in the industry. Precision laser-trimmed bulk metal foil Vishay resistors are used throughout the voltage gain stages and related power supplies. CJD Teflon dielectric capacitors are used for coupling the inverter stage to the output stage, and to bypass the large value polypropylene capacitors in the regulated power supplies for the voltage gain and inverter stages. Amplifier output is coupled to speakers through proprietary wide-bandwidth Translinear output transformers optimized for Class A operation of triode connected KT88s. Even the machined OFC connectors and the internal wiring have been carefully selected for optimal sonic performance. Attention to every detail enable them to extract the full potential from their circuit designs and ensures that their products will perform to this potential for years to come. The ART27A and ART108A amplifiers are built without compromise to achieve a new standard in musical performance, and they are built to last.
ART150 and ART300 Amplifiers
In celebration of their 40th anniversary, conrad-johnson has introduced two new ART amplifiers: the ART150 stereo amplifier and ART300 mono-block amplifier.
These amplifiers are designed for conrad-johnson’s own reference use as well as for industry professionals and dedicated audiophiles. As with previous anniversary products, these amplifiers will be offered as limited editions, with just 250 units of the ART150 and 125 pairs of the ART300 to be sold through selected conrad-johnson dealers and distributors.
The ART150 and ART300 amplifiers embrace conrad-johnson’s firm belief that the surest path to both state-of-the-art musicality and exceptional reliability is to keep the circuits simple and build them with the finest available parts.
The audio circuit of these amplifiers has just three elements, each as simple as possible, and each essential to the operation of the amplifier. A voltage gain amplifier (a single triode) is direct-coupled to a cathode coupled phase inverter (each phase handled by a single triode), which in turn drives the output stage. Power is developed by KT150 output tubes, chosen for their musical accuracy, high power, and reliability. A single pair is used for each channel to comfortably and reliably achieve the 150 Watts per channel power rating of the ART150, while two pairs are used to produce 300 Watts in the mono ART300. A small amount (about 12 dB) of loop negative feedback reduces distortion and achieves a sufficiently high damping factor to control reactive loudspeaker systems. To assure continued peak performance, the owner need only make a simple bias adjustment when new tubes are installed. Built in LED bias indicators allow the user to make this adjustment using only the supplied adjustment tool.
Separate, low impedance, discrete dc power supply regulators are provided for the input and phase-inverter stages, thoroughly isolating these stages from the power demands of the output stage. These power supplies are designed to maintain a rock solid supply at all audio frequencies.
The ART150 and ART300 amplifiers maintain the exacting quality standards for which conrad-johnson is internationally known.
Resistors are precision laser-trimmed metal foil types. CJD Teflon dielectric capacitors are used for coupling the inverter stage to the output stage, and to bypass the large value polypropylene capacitors in the regulated power supplies. Proprietary wide-bandwidth output transformers contribute to excellent high frequency performance. Even the machined gold plated OFC connectors and the internal wiring have been carefully selected for optimal sonic performance. Attention to every detail enable them to extract the full potential from their circuit designs and ensures that their products will perform to this potential for years to come. The ART150 and ART300 are built without compromise to achieve a new standard in musical performance, and they are built to last.
ART300 Power Amplifier of the Year Award:
ART300 Amplifier Reviews:
Classic 62 and CLASSIC 120 Vacuum-Tube Stereo Power Amplifiers
The conrad-johnson design team is committed to adapting the advances from their state-of-the-art pursuits to more affordable offerings accessible to a wider range of music lovers.
This resolve is clearly evident in their new range of Classic amplifiers. Borrowing heavily on the technology of their flagship ART amplifier, the Classic amplifiers preserve the distinctive tonal character of individual instruments and voices, with each clearly located within the overall acoustical environment of the original recording. Musical transients are reproduced with realistic impact, but without artificial enhancement. Like their more costly siblings, the Classic amplifiers capture the emotional impact of the live event, never getting between the listener and the musical performance.
There really is no mystery to their chosen path to outstanding musical performance: best results come from simple circuits executed with quality parts.
The circuit design for the Classic amplifiers is about as simple as possible, employing just seven vacuum tubes in the Classic Sixty-Two. Single-ended triode voltage gain and inverter stages are coupled to an output stage comprised of a single pair of ultra-linear operated EL34 tubes for each channel. The Classic One-Twenty adds a second pair of output tubes to each channel to achieve twice the output power. Simple but highly effective discrete voltage regulators supply rock-solid stable DC voltage to the critical voltage gain and inverter stages. And speaking of simple, maintenance of the Classic amplifiers could hardly be easier: the owner need only make a simple bias adjustment using the built in bias indicators when installing fresh output tubes.
The use of premium quality component parts is the other half of the conrad-johnson recipe for superior musicality.
In this area as well, the Classic amplifiers are leaders in their class. Precision, metal-film resistors yield low noise performance for greatest clarity. Polypropylene and polystyrene capacitors, chosen to achieve a high degree of temporal accuracy, are specified for both the audio cir¬cuits and the regulated plate voltage supplies for the input and inverter stages. The result is an exceptional range of dynamics – reproducing both subtle variations in level as well as dramatic loud crescendos. Their proprietary trans-spectral wide-bandwidth output transformers contribute importantly to the extended, “airy” highs that help distinguish the Classic amplifiers from ordinary tube amplifiers.
The base model Classic amplifiers offer an ideal introduction to the joys of modern tube amplifiers, while the ease of use, low maintenance costs, and reliability will be a revelation for those who have only experienced “entry-level” tube gear.
Those who wish to take the experience a step further will want to investigate the upgraded Classic Sixty-Two SE and Classic One-Twenty SE amplifiers. These special edition versions upgrade the output tubes to KT120s and incorporate CJD Teflon Capacitors and ultra high-performance metal foil resistors in strategic applications in the circuit. Any of the Classic amplifier models are sure to rekindle your passion for enjoying great music in your home.
CAV45-S2 Stereo Control Amplifier
The control amplifier represents a distinctly different approach to high-performance home audio. In many ways it is the ultimate embodiment of conrad-johnson’s design philosophy that simple circuits yield best results.
Similar in function to an integrated amplifier, a control amplifier offers the significant potential improvement of eliminating extra connections, external cabling, and inter-device connection considerations that limit conventional audio systems. But the control amplifier also eliminates an entire stage of audio circuitry (the line stage) and its inherent colorations.
The CAV45-S2 is a vacuum-tube control amplifier. Its audio circuit is similar to conrad-johnson’s highly regarded Classic Sixty power amplifier, with triode voltage gain and phase inverter stages and an output stage comprised of a pair of EL34s per channel operated in ultralinear mode to produce 60 watts per channel.
The use of carefully selected, high-quality parts enables the CAV45-S2 to properly exploit the dramatic potential of a control amplifier to enhance the immediacy of musical experience afforded by fine recordings. All resistors in the audio circuits and related power supplies are precision metal film types. With the exception of the large power supply reservoir capacitors (which are specially chosen electrolytic capacitors bypassed by polypropylenes), all capacitors in these circuits use polystyrene and polypropylene dielectrics.
This execution of minimalist circuitry with quality parts result in a control amplifier that is notable for its resolution of subtle dynamic shadings and palpable imaging, for a natural harmonic tonality, and extraordinary resolution.
The CAV45-S2 features larger value electrolytic capacitors in the unregulated power supply, yielding improved bass response and lower noise floor. The binding posts are billet brass, rhodium over silver plate, with billet brass, gold plate nut.
hva-1 headphone Amplifier
The HVA1 is a reference quality single-ended class A triode amplifier designed to power low-impedance headphones (around 20 to 32 Ohms).
The HVA1 accommodates two line-level inputs. Power output is 3 Watts into 20 Ohms. The enhanced triode circuit (similar to that introduced in our flagship GAT preamplifier) employs two 6922 vacuum-tubes (one for each channel) for voltage gain coupled to a high-current FET buffer stage (source follower). Each of the two channels is powered by its own independent DC regulator. CJD Teflon capacitors and Vishay resistors are featured in the circuits. The level control is a discrete stepped attenuator constructed entirely with Vishay resistors. The circuitry is housed in a heavy, elegant aluminum chassis dressed with anodized brushed aluminum panels on front, sides, and top.
HVA-1 Headphone Amplifier Review: