The KRELL KSA 80 is something of a legend in the world of vintage audio, a Class A power amplifier that has garnered a reputation for its exceptional build quality, uncompromising performance, and robust power delivery. The KSA 80 was introduced in 1984 and was produced until around 1990.

Krell KSA 80 power amp review

Reading the forum chatter it doesn’t take long to realize that the KSA 80 is very well regarded among audiophiles and enthusiasts, with many people saying that this amplifier may just represent the pinnacle of audio engineering from the prestigious KRELL brand. I’ve owned a couple of Krell amps over the years and had a couple in my system as long-term loaners from a friend. (RIP Squidboy), so I’ve a good deal of experience with the following:

  • Krell KAV 300i (owned)
  • Krell FPB 200 (owned)
  • Krell MDA 300 monoblocks (loaned)
  • Krell FPB 700 (loaned)
  • Krell KSA 80 (owned)

Krell has a reputation for building amps with power and grunt that can handle most any speaker load, and that’s true of some of their offerings, but not all. They also have a reputation for building amps that sound cold and clinical and a-musical, and that is also true of some of their offerings, but not all.

Krell KSA 80 power amp review

Krell KSA 80 power amp review

Krell KSA 80 Design and Build Quality:

The KRELL KSA 80 boasts a visually striking design that exudes heft and solidity. The amplifier’s chassis is crafted from heavy-gauge aluminum, which not only enhances its aesthetics but also provides excellent shielding against electromagnetic interference. The construction is rock-solid, showcasing KRELL’s meticulous attention to detail and its commitment to delivering products of the highest caliber. The heatsinks on this beast are something to behold. They’re also bloody lethal, I’ve caught myself on them a couple of times while moving this thing around, and it hurt.

Krell KSA 80 power amp review

Features and Connectivity: The KSA 80 is a fully Class-A dual-mono power amplifier, meaning it contains two independent amplifier circuits, one for each channel. This configuration ensures maximum channel separation and minimal crosstalk, resulting in a cleaner and more precise audio reproduction. The amplifier offers a conservative power output of 80 watts per channel into 8 ohms, and it can double that power into 4 ohms, again into 2 ohms, and again into 1 ohm, allowing it to effortlessly drive a wide range of speakers, including the venerable Apogee Scintilla in its 1-ohm configuration.

Krell KSA 80 power amp review

On the connectivity front, the KSA 80b provides both balanced XLR and unbalanced RCA inputs, whereas my KSA 80 only supports single-ended connections. It also includes heavy-duty binding posts for speaker connections, ensuring a secure and reliable connection, but these are not the best binding posts on the market, and anyone looking at restoring one of these amps should spend a little extra on new and sturdier binding posts.

This amp is large and heavy. It’s fairly easy to move around via the two pairs of front and back handles, assuming you can dead-lift an 86lb hunk of metal from off the carpet. I can, but only just these days.

Krell KSA 80 power amp review

Performance and Sound Quality:

I had some trepidation when first powering up the KSA 80 as I bought this from an estate sale, operation unknown. Expecting the worst, I set the amp up outdoors on my open porch, with some low-fi support equipment and a pair of Michael Green speakers that sound great but have seen better days. With a fire extinguisher on hand, I switched the power rocker on the front of the amp and stuck my fingers in my ears as quickly as I could. A few seconds later the internal relays switched in with a clunk and the amp became operational for the first time in almost a decade.

Krell KSA 80 power amp review

Right from the get-go there was a very audible buzzing through the speakers. I half expected this to be the best-case scenario for the amp, but I was still a little disappointed. But would it play music? I stuck a John Martin CD in the cheap DVD player and waited a few seconds for the $60 player to read the first track….and….voila – SOUND!

There’s something pretty cool about playing music through a full system outdoors, with the sound unimpeded and unaffected by the room. I wasn’t expecting to do any critical listening outdoors, of course, but I could get a sense of how the amp sounded and whether or not it was worthwhile pursuing a repair/restoration. So for about an hour, I flipped through a few different CDs, and, I have to say, the amp sounded fantastic – albeit with a rather nasty buzz as a backdrop.

Ah well. It was a fun afternoon hauling all the gear outdoors on a balmy Virginia summer day with temps in the high 80s and humidity about the same, and it was fun pulling it all down again and dragging it all back indoors. Right.

That night I spent a couple of hours researching repair and restoration services for the old Krell amp and came across a place that’s around a 2.5-hour drive from me, so I settled into the idea of finding some time in the coming weeks and planning a road trip. I’d pretty much decided that based on what I’d heard from the amp, spending a thousand, or fifteen hundred bucks or so, was going to be worth it.

But Wait…..

I tossed and turned that night, wondering if perhaps I’d botched the system setup in some way. What if…

I’d used a high-quality power strip plugged into an outlet on the porch wall. I’d used quality power cords for each of the components. Rather than haul out my main tube preamp, I used a Cambridge Audio 840a integrated amp and hooked the pre-outs into the Krell. I then used the el-cheapo DVD player as a source, a player which I use occasionally when testing stuff – it works fine.

So the next day being Sunday, I decided to break the monotony and setup the big amp in the big rig in the big room. I plugged the amp into my PS Audio P10 regenerator and hooked up the balanced outputs from my Veloce tube preamp, using XLR-RCA adapters, into the big Krell. I stuck with the Michael Green speakers as I really didn’t want to damage a nice pair of Martin Logan Impression 11a that I’ve only had for a few weeks.

Krell KSA 80 power amp review

Using a broom handle I flipped the toggle switch on the KSA and assumed the crash position with fingers firmly inserted. SILENCE. Not a peep from the speakers, something must be broken or improperly connected. I toggled to a track on the Mconnect app on my iPhone and watched as the Lumin U1 mini came to life and triggered the screen on the Mytek Brooklyn DAC+ to wake up. A second later…..MUSIC!!

GLORIOUS…BIG…BOLD..AND BEEFY SOUNDING…..MUSIC.

Ok, those are not the usual audiophile adjectives I use, but I was stoked and that’s how the system sounded out of the gate and prior to any more reasoned evaluation.

This amp is pretty darn good….

It has very good weight, grip, and authority, more so than most other amps I’ve had in my system in recent times. I have to think all the way back to a pair of SimAudio Moon W10 monoblocks that had a fair bit of the same but always sounded a tad lean to these ears. The big Krell FPB 700cx that I’d used a few years back on a variety of different speakers always sounded cold and clinical to me, even though it had plenty of bass and good control over the lower registers. Most recently, a SimAudio Moon W5.3SE had a similar presentation to the Krell from around 400hz down, but with more air and detail than the Krell.

The KSA 80 delivers a level of transparency, detail, and dynamic range that is pretty impressive for such a relic. The amplifier effortlessly resolves even the most intricate musical passages, revealing nuances and subtleties that lesser amplifiers tend to miss. The soundstage is expansive and well-defined, offering precise imaging and instrument separation. But it has a smoothness and warmth in the midrange that really makes the sound signature of this amp so alluring.

The bass response is tight, impactful, and extended, yet that midrange…. it’s lush, natural, transparent… The highs are clean, airy, and devoid of any noticeable harshness. I picked up on a touch of sibilance on vocals during the first extended listening session, but it seemed to disappear as the amp became fully warmed up.

The soundstage this amp throws is pretty incredible. Deep, wide, and high – playing Paul Simon’s Graceland, I’ve never heard a sound fill the room in this way. And all of this via the fairly modest Michael Green speakers.

Wrapping Up.

I’ll put the Martin Logans back into service in the near future and report back here with my findings. The Logans should give the amp more of a workout as they dip to 0.6 ohms in the high frequencies – though I doubt they’ll knock the KSA out of its stride.

I should make it clear that I wouldn’t recommend running this amp in its original form into a pair of expensive speakers unless you’ve had it rebuilt with new capacitors and whatever else is needed to bring it back to spec. Given its age, it is just a matter of time before the amp fails. And it could fail in a big way. Restoration costs vary for this thing, my recommendation would be to send an amp of similar vintage back to the manufacturer and not risk it in the hands of someone with limited experience of the brand and model. I contacted Krell and they quoted me $1800 for the ‘rebuild’, excluding shipping costs, which would likely tag on another $300. So on that basis alone, this isn’t a project that fits what I do here, so I’ll probably recycle it out into the wild and have someone else do what’s needed.

But overall this is a great-sounding amp and could be considered a high-end bargain, even if you need to drop $2000 or so on a re-cap and repair.

CAH June 2023

Let’s take a look at the chronological timeline of the different models of Krell power amplifiers, starting with the oldest first. Included are some specs and basic information on each model, based on the official website of Krell and some online reviews. Check the list for accuracy, I’m sure some dates and specs will be wrong!

The first Krell amplifier was the **KSA-100**, launched in 1981. It was a stereo power amplifier that delivered 100 watts per channel into 8 ohms, or 200 watts into 4 ohms. It used a fully balanced design with a dual-mono configuration and a large toroidal transformer. It was praised for its transparency, dynamics, and bass control.

The next model was the **KSA-50**, introduced in 1982. It was a smaller version of the KSA-100, with 50 watts per channel into 8 ohms, or 100 watts into 4 ohms. It had a similar circuit design as the KSA-100, but with less output devices and a smaller power supply. It was also more affordable than the KSA-100, making it more accessible to audiophiles.

In 1983, Krell released the **KRS-100**, which was a monoblock version of the KSA-100. It delivered 200 watts into 8 ohms, or 400 watts into 4 ohms. It had a separate power supply unit that connected to the main amplifier unit via a thick cable. It was designed to drive the most demanding speakers with ease and authority.

The **KRS-200** followed in 1984, which was a monoblock version of the KSA-200, a stereo amplifier that was also launched in the same year. The KSA-200 delivered 200 watts per channel into 8 ohms, or 400 watts into 4 ohms, while the KRS-200 delivered 400 watts into 8 ohms, or 800 watts into 4 ohms. Both models used a new output stage design that increased the current delivery and reduced the distortion.

In 1986, Krell introduced the **Audio Standard** series, which consisted of three models: the Audio Standard I, II, and III. These were stereo power amplifiers that delivered 100, 200, and 300 watts per channel into 8 ohms, respectively. They used a new Class A biasing scheme that improved the linearity and efficiency of the amplifiers. They also had a modular construction that allowed for easy upgrading and servicing.

The **Audio Standard IV** came out in 1989, which was a monoblock version of the Audio Standard III. It delivered 600 watts into 8 ohms, or 1200 watts into 4 ohms. It had a massive power supply with four toroidal transformers and multiple capacitors. It was one of the most powerful amplifiers ever made by Krell.

In 1990, Krell launched the **FPB** (Full Power Balanced) series, which marked a new era for the company. The FPB series used a fully balanced design that eliminated any common-mode noise and distortion from the signal path. The FPB series also introduced the **Sustained Plateau Bias** (SPB) circuit, which maintained a constant Class A operation regardless of the output level or load impedance. The FPB series consisted of four models: the FPB-200 (200 watts per channel), FPB-300 (300 watts per channel), FPB-600 (600 watts per channel), and FPB-1200 (1200 watts per channel).

The **FPB-K** series followed in 1995, which was an upgraded version of the FPB series. The FPB-K series used larger power supplies, improved output stages, and refined SPB circuits. The FPB-K series also featured **Krell Current Mode** (KCM) technology, which enhanced the speed and bandwidth of the amplifiers. The FPB-K series consisted of three models: the FPB-200K (200 watts per channel), FPB-300K (300 watts per channel), and FPB-600K (600 watts per channel).

In 1997, Krell released the **Master Reference Amplifier** (MRA), which was their flagship model at the time. The MRA was a monoblock amplifier that delivered an astonishing