Krell KST-100 Class A Solid State Amplifier

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I’ve always been a fan of class-A amplifiers and this one is a fantastic example.

This model runs on class A up to 50W (or half its rated power) while being able to deliver 100W into 8 ohms. If you already have one of these, having two of them is 4 times the fun since each amp will deliver 400W into 8 ohms in mono configuration.

Build quality is absolutely stunning. Just look at the obscene component layout and attention to detail. Utilizing 10 output transistors per side with ample heat sinks this amp will run moderately warm with most music, unlike other class A amps that will cook your room in the summer.

The external finish is super high quality also. Thick brushed and anodized aluminum faceplate, heavy sheetmetal throughout, and the best connectors available at the time.

On the back you’ll find balanced and single ended inputs as well as dual binding posts that will allow you to bi-wire the speaker cables.

This unit is in very good condition with only the slightest signs of wear. The rack handles have slight rubbing imperfections on the edges barely visible a few feet away. Very common from an amplifier that weighs in at over 60lbs.

The unit was bench tested carefully and it passed with flying colors. All capacitors were inspected and tested for leakage. It was driven to its full power rating while monitoring distortion without hiccups.

Included is the amplifier with a printed instruction manual.

With regards to sound quality, here is a quote from Stereophile which I encourage you to read in its entirety by searching online:

“First impressions were of a thoroughly up-to-date, low-feedback sound, one of greater delicacy, air, and transparency than the sound traditionally associated with solid-state electronics. The KST-100 did have a good proportion of Krell character: a firm, confident approach, highly stable imaging, and a strong, highly controlled bass. I rate Krell's KSA-150B highly, and found it to have much in common with the (relatively) budget-priced KST-100. In this context, it was a touch more dynamic and a shade clearer than the KSA-80. Given that the '80 came top in its class only a year or so ago, this is high praise indeed for the KST-100.

Taking the stereo performance in more detail, it was close to today's best in image depth and the transmission of hall and stage acoustic. It could help define the performance of top digital replay systems, and sounded genuinely transparent. Direct comparison with the '80 showed the latter to have a mildly cloudy effect with a shortfall in stage depth. Here the KST has moved rather closer to the ARC Classic 120. Specific focus was also close to the best, held both in terms of width and depth. Stage width was virtually to the limit of available program, and only fractionally less than the best monoblock amplifiers in percentage terms.

Possessing a fine tonal balance (to be discussed separately), the KST-100 was also capable of a strong presentation of perspective, with convincing layering of players in large orchestral recordings. I do not believe height is a property of electronics which are inherently neutral; however, certain combinations of room acoustic, phase, and perceived system frequency response, particularly in the 2–8kHz range, can give rise to sensations of image height which may be enhanced by the accurate and transparent reproduction of recorded ambience. In this latter respect, the KST was very capable.

The KST-100 conveyed a dynamic, lively quality well beyond its class, remaining interesting and alive over long listening sessions.

Dynamics do not only relate to inner vigor but to an overall feeling of power, specifically dynamic range. Technically, this can be described as the range in dB between the inherent background noise and the maximum level possible with a given loudspeaker load. Subjectively, this also concerns an amplifier's ability to reproduce low- and moderate-level detail while being exercised by powerful ones, and its ability to sound unchanged and unstrained when crescendi arrive.”

Technical Specifications:
Stereo power amplifier
Output power: 100Wpc/8 ohms (20dBW), 200Wpc/4 ohms (20dBW), 400Wpc/2 ohms (20dBW), 800Wpc/1 ohm (20dBW).
Output impedance: 0.125 ohms.
Damping factor: 150.
THD & IMD: less than 0.1% under all conditions.
S/N ratio: 96dB A-weighted.
Slew rate: 50V/µs.
Input sensitivity: 1.5V for full output.
Input impedance: 47k ohms.
Dimensions: 6.4" H by 18" W by 14.8" D.