KRELL Model600

Commentary

This is a stereo power amplifier that is the top-of-the-line of the Kroell full power balance series.

Equipped with Sustaine-Plateau Bias II.
This circuit is a combination of a predictive sensor circuit that monitors all operational states of the amplifier over a wide range, such as the actual load applied to the output stage, and a bias setting circuit with a unique shift schedule. It realizes an ideal class A operation.

The circuit configuration consists of a fully balanced differential circuit for all stages from input to output.
The input gain stage amplifier is a current-mode amplifier that operates with the current between the inverting amplifier and the non-inverting amplifier. In addition, the precise gain matching between each amplifier is achieved by means of a unique microcontroller control. This realizes a high-precision balance drive. This cancels the negative influence on the ground line of the amplifier due to the reactive load when the speaker is actually driven, as well as the mutual interference of each stage around the ground line, and ensures excellent drive performance under all conditions.

For the KAS (Kroell Audio Standard), which is a reference model of Kroell power amplifier, a metal can-type special product jointly developed with Motorola has been fully adopted.
In addition, the fully regulated power stage provides a highly stable power supply from a constant voltage power supply to not only the first stage to the driver stage but also to the output stage. It constantly monitors the drive current and load of the output stage of the amplifier and instantaneously supplies the required voltage according to changes in the current.
The Model600 uses 14 Pc250W class large capacity power transistors.

Equipped with a full auto-calibration function, the amplifier automatically optimizes itself by self-evaluating the internal electrical adjustment conditions such as output bias, regulator voltage, and DC offset.
On the production line, internal parameters are carefully checked for each unit, and the results are stored in the amplifier. In actual use, all operating conditions, including AC voltage, are monitored as needed to ensure accurate calibration of each unit and proper selection of the plateau level of Sustaine-Plateau Bias II. This feature provides long-term factory performance.
In the event of an abnormal situation such as oscillation, DC leak, or short circuit of output terminal, the power supply is cut off immediately. This ensures high safety while eliminating common protective circuits such as relays and fuses, enabling direct connection between output stage and speakers.

Model Rating

Type	Stereo power amplifier
Rated output	600W + 600W (8 Ω) 1200W + 1200W (4 Ω) 2100W + 2100W (2 Ω)
Output voltage	239Vp-p, 84 Vrms
Input Sensitivity / Impedance	2.14Vrms/100k Ω
Frequency characteristic	20 Hz ~ 20 kHz + 0 -0.5 dB 0.1 Hz ~ 240 kHz + 0 -3.0 dB
Total harmonic distortion factor	0.02% or Less (1 kHz) 0.15% or Less (20 kHz)
Gain	26.2dB
Input sensitivity	3.39Vrms
Input impedance	100k Ω
Input terminal	Balance 1 system Single-end one system
Power consumption	85W (standby) 430W (idle) 6000W maximum
External dimensions	Width 483x Height 260x Depth 650 mm
Weight	74kg