Sure, from the outside the CLASSIC looks very modest and plain. However, technically and sonically this is the best and most advanced stand-alone amplifier that we've ever build.
Of course this amplifier also uses the concept of active balanced headphone ground. Within this concept each headphone connection wire carries an additional signal such that the sum of the potentials of the wires equals zero. This strongly minimizes the energies stored and released in the electrical fields inside the headphone cable when an audio-signal is applied. The influence of the wire on the sound is thus reduced.
Moreover, with active ground pollution of the internal signal ground by strong driving currents is eliminated and the power-supply-rejection-ratio at the output stages is strongly improved. Thus the best conditions are given for a clean and undistorted sound.
Active balanced headphone ground offers most of the advantages of a true balanced headphone setup without the need of balanced connections. It can be used with any conventional dynamic or magneplanar headphone.
The volume control is technically very sophisticated. The position of the potentiometer is measured with the use of an AD-converter. The output of this converter is then used to switch a bank of relais to set the proper volume level. There are a total of 64 levels which allows for very small stepsizes and a very analog feeling. The advantages of this concept are strongly reduced channel-imbalances and a much cleaner and more detailed sound. The use of a conventional stereo-potentiometer does add its own sonic signature which is now prevented.
The amplification section is build around AD797 opamps biased into class-A. For the output stages BUF634 buffer amplifiers are used. These integrated circuits are very fast and thus allows the output signals to follow the input signals very closely. The amp is DC-coupled and any capacitors found in the signal path are of the highest quality polypropylen and polystyrol.
A very extensive powersupply, a large number of power-regulators, and a total filter capacity of 80.000 microF (!!) assure the best working conditions for any part of the circuitry.
The built-in crossfeed filter is a frequency-extended version of the natural crossfeed found in previous CORDA amplifiers and provides even better imaging. It also offers three intensity levels (Stereo, medium, high). To compensate for the psycho-acoustic bass-loss a separate switch allows to slightly increase lower-frequencies.
Technically the CLASSIC is an extremely advanced headphone amplifier and offers excellent value-for-money!
Output impedance < 0,1 ohm|
Maximum output 15V / 500 mA.
Discrete volume control. Typical stepsize 0.5 dB, 63 steps.
Gain switch. Maximum gain factors -2 / +14 dB
Crossfeed filter switch:
1. crossfeed MEDIUM
3. crossfeed HIGH
(compensation for psycho-acoustic bass-losses)
1. compensation MEDIUM
3. compensation HIGH
2 pair of analog inputs
Input impedance 18 kOhm
Gold-plated input jacks.
Silver plated headphone jack (Neutrik).
Silver plated heavy duty switches
25 Watts toroidal transformer.
110V and 220V mains power switchable.
Power uptake 10 Watts
Built-in groundloop breaker.
Double regulated voltage lines.
Low impedance electrolytic buffer capacitors (Nichicon Fine Gold).
Total Buffer capacity 80.000 uF.
Bypass capacitors in the power supply.
Polystyrol and polypropylen capacitors in the signal path.
Metalfilm resistors in the signal path.
AD797 opamps biased into class-A.
2 BURR-BROWN BUF634 buffer amplifiers at left and right headphone output channel.
(Active) balanced headphone ground.
Star-grounding and ultra short signal paths.
Signal paths and signal path components at the bottom side of the PCB for maximal shielding.
Sturdy anodized aluminium enclosure
Weight: 2.2 kg
Size: 28.0 x 17.7 x 6.7 cm