KRELL KSA-250 (01) PDF Document

The KRELL KSA-250 is rated as delivering 250 watts per channel into 8 ohms, with a maximum power into 8 ohms of 320 watts per channel. It is capable of doubling its output into successively lower impedances, delivering 500 watts per channel into 4 ohms, 1,000 watts per channel into 2 ohms, and 2,000 watts per channel into 1 ohm.

Given its power capabilities, the AC power supplied to the amplifier is crucial for maximum performance. The KRELL KSA-250 requires a dedicated 20-amp line. It should only be operated with the power cord supplied with the unit.

Remove the KRELL KSA-250 unit, power cord, and accessories from the shipping container. Inspect the unit for any shipping damage. If any damage is evident, contact your dealer immediately. If the unit is in proper condition, you can proceed with the installation. It is recommended to store all packing materials in a cool, dry place for future use.

These are important points of which you should always be aware:

• Do not connect the power cord into the AC mains before completing the entire installation.

• The KRELL KSA-250 must always be turned off while making connections.

• Krell XLR and custom RCA connectors are made to very exacting standards. Connectors of lesser quality may damage the amplifier or cause poor connections.

Amplifiers dissipate much of the power they consume as heat. The KRELL KSA-250 must be installed in a location that provides unobstructed ventilation. If the unit will be installed on shelving or in a cabinet, extra ventilation is necessary. This can be accomplished with the use of ‘whisper’-type fans. Generally, with the front and rear of the installation shelving or cabinetry open, 8 inches of clearance on the sides and top of the amplifier should provide adequate ventilation.

The dimensions of the KRELL KSA-250 are: 19” wide x 21.5″ deep x 8.5″ high. Add 2.5″ of depth for the front and rear handles. The unit weighs 140 pounds.

The KRELL KSA-250 has both balanced and single-ended inputs. The balanced inputs use 3-pin XLR connectors and single-ended inputs use RCA connectors. Only one of these inputs should be connected to the preamplifier for each channel.

The pin assignments for the XLR connectors are:

• pin 1 = signal ground

• pin 2 = non-inverting input

• pin 3 = inverting input

The RCA connector is wired in parallel with pin 2, the non-inverted input. The two sets of 5-way binding posts for each channel’s output are wired in parallel to allow for easy bi-wiring.

Note: The KRELL KSA-250’s AC power cord may be connected to the amplifier at this time, but do not yet connect the power cord to the AC mains.

The KRELL KSA-250 is shipped with shorting pins in the XLR inputs. These pins must remain in the XLR inputs if the unit is to operate in single-ended mode (using RCA connectors). The shorting pin connects pins 1 and 3 and grounds the inverted input.

For balanced operation (using XLR connectors), these shorting pins must be removed from the XLR inputs.

The wiring to and from the KRELL KSA-250, and all components in general, should be arranged in a neat, organized manner. Specifically, AC wires should be separated from audio wire to avoid hum or the introduction of other unwanted noise into the system.

It is always preferable to run long interconnect cables to the amplifier and to keep speaker cable length to a minimum. Speaker cable adds impedance between the speakers and the amplifier, regardless of wire gauge. When impedance is added in any significant amount (for instance with excessive cable length), amplifier power is wasted in driving the cable, thereby reducing the maximum power that can be delivered to the speakers.

The feet on the KRELL KSA-250 can be used in three different ways. They are made from machined Delrin and are supplied with separate rubber bottoms and mounting screws.

1. For protection of fragile surfaces such as hardwood floors or furniture, the rubber bottom can be screwed into the Delrin foot.

2. For use on rugs or carpeting, using the feet without the rubber bottoms is recommended.

3. You may purchase a set of Acoustic Mass Dampers (AMDs). AMDs are custom-machined stainless steel feet fitted with a threaded insert and a washer made from acoustically absorbent material. When threaded into the Delrin feet, the AMDs will decouple the amplifier from vibrations present on the surface where the unit is installed.

Power-On Sequence:

Activate the system by turning on the source components and preamplifier with the volume fully attenuated (turned down). The KRELL KSA-250 amplifier must always be turned on last. Just after turn-on, a soft click will be heard, which is the main power relay closing. At this point, the amplifier’s outputs are not connected to the speakers. After the protection circuits detect that the unit has completely stabilized, the speaker relays will engage, and another click will be heard. The amplifier is now ready to use. The KRELL KSA-250 will be at temperature and sound its best after approximately 15 minutes.

Power-Off Sequence:

When turning off the system, the KRELL KSA-250 amplifier should always be turned off first. This avoids the possibility of a turn-off transient from another component reaching the speakers.

Care must be taken in the operation of the whole system in relation to the significant power output of the KRELL KSA-250. Mistakes, such as switching between active sources without muting the preamplifier output or bumping/miscuing a phonograph cartridge, can generate large transients at low frequencies, which can cause a power-surge capable of damaging most loudspeakers. All switching of sources should be done with the preamplifier level either muted or fully attenuated (turned down). Inputs to the amplifier should never be changed while the amplifier is on.

Additionally, care must be taken when setting high playback levels. Because of its tremendous reserve of clean power, the KRELL KSA-250 can safely drive speakers to higher sound pressure levels than other amplifiers. This can result in driving the speakers to their limit. Always turn the volume level down at the first sign of distortion.

The KRELL KSA-250 has two protection modes: Input and Output.

Input Protection: When Input Protection is engaged, the amplifier will remain on, with the front panel LED illuminated, but it will not pass a signal. This indicates a problem with the input signal, most often a DC condition, caused by the preamplifier or a source component. The amplifier will resume passing the signal when the problem is resolved.

Output Protection: When Output Protection is engaged, the amplifier will turn off, and the front panel LED will also turn off. This usually indicates a problem with the speaker wires, their connection, or the speakers themselves. Once the problem is located and resolved, the amplifier will turn on normally with activation of the front panel switch. The Output Protection will also engage if the amplifier fails.

1. When the Output Protection circuitry has been engaged, allow at least 20 seconds before turning on the amplifier again. Repeated fast cycling of the On/Off switch can damage the amplifier.

2. If the amplifier does not come on after following the procedure above, please check for issues with speaker wires, their connections, or the speakers themselves.

3. There is a circuit breaker on the amplifier’s rear panel. This breaker protects the amplifier in the event of catastrophic failure. If the circuit breaker engages, do not attempt to reset it.