CONRAD JOHNSON

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, we 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).

Our design team has long appreciated the critical importance of parts quality in achieving top performance.

Our commitment to executing our 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 us to extract the full potential from our circuit designs and ensures that our products
will perform to this potential for years to come.
The ART27A andART108A amplifiers are built without compromise to achieve a new standard in musical performance,
and they are built to last.

Power: 36 Watts rms per channel from 30 Hz to 15 KHz at no more than 1.5 % THD
into 4 ohms (also available connected for 8 or 16 ohm loads)

Sensitivity: .6V rms to rated power

Small Signal Distortion: less than .25% at mid-band

Frequency Response: 20 Hz to 20 kHz, +/- .25 dB

Hum and Noise: less than 200 microVolts

Phase: phase correct

Input Impedance: 100 kOhms

Tube Complement:

3 x 6922
4 x KT88 (matched pairs, selected)

Dimensions (D X W x H): 45 x 48 x 23 cm

Weight: 29 kg


Color: Gold

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