When the Kurzweil K2000 hit the market in 1991, it was nothing short of revolutionary. What set the K2000 apart was its cutting-edge Variable Architecture Synthesis Technology (V.A.S.T.), which allowed musicians to build complex sounds from the ground up using a highly flexible signal path and a wide variety of digital processing blocks.

While most home computers in 1991 averaged at 1MB of RAM, the K2000 offered a whopping 64MB of expandable sampling memory and supported up to a 1GB hard drive, at the time specs on par with the Silicon Graphics workstations (used for CGI in blockbuster films). No wonder it could cost you around $10,000 fully maxed out, equivalent to about $24,000 today’s money. But the feature set justified the price: Virtual Analog synthesis (way way before Clavia Nord Lead), vector synthesis (with a bit of programming), LA synthesis, wave sequencing, true FM synthesis (with 2 operators x 3 layers = enough for DX7 Epiano or Tubular Bell), ring modulation, osc sync and full sampling and playback via SMP-K (or SMP-R for the rackmount version). In 1991 it was a sound designer’s dream and aside few top notch programmers and sound designers not many were actually aware of how powerful this thing was.

Fast forward to the Kurzweil K2600, the more powerful descendant of the K2000. While it carries many advancements under the hood, we decided to put it to the test: Can the K2600 really replace the K2000 when it comes to reproducing its sonic character?To find out, we loaded the K2000 factory patches into the K2600 using the official K26TOK2K compatibility set from Kurzweil. Both synths were run side-by-side, with identical patches, and careful A/B listening. Let’s break down what we found.

Identical at the Core… Almost
At the fundamental level, both machines share a lot. They use the same raw waveforms, and in direct playback, those waveforms sound identical. The DACs (digital-to-analog converters) in both units are from the AD1865 family: the K2000 uses the AD1865, while the K2600 uses the slightly updated AD1865R. These integrated circuits when they came out were referred as the best digital analog converters ever designed and the word seems to stay to this day. Despite K2000 being 18dB lower in (max) volume compared to K2600 I was totally caught off guard once I realised its audio it did not contain any extra additional noise in the background once I normalised it against the K2600! It’s signal to noise ratio turned out to be the same as on K2600. I’ve never seen anything like that before – I mean boosting one synth against the other for 18dB you would expect some increase in background noise of the former – not here! Unfortunately I am not an expert but I guess I can understand why people were so impressed with AS1865 back in the day. Technically, these two DACs offer the same resolution, and noise levels seem to be similar on paper. However, perceptually, the K2600 appears to benefit from some form of noise-shaped dithering, making the noise floor less audible to the human ear. But it’s when you dig deeper, into how each synth handles effects, that the differences really start to emerge.

When Effects Go Off-Script
Despite the K2600 boasting a superior effects processor, this is ironically where it begins to fail in emulating the K2000 accurately.

Stereo Panning Effects: Here’s where the biggest difference lies. Patches that feature stereo panning in their effects are the most affected. The K2600 tends to push the stereo field too wide, making patches that once felt balanced now sound artificially exaggerated. This results in a loss of the original K2000 vibe.

Low-End Response: Certain effects in the K2000 add subtle, but critical, bass boosts. These same patches played on the K2600 lack that depth, making the low-end feel slightly scooped or more clinical.

Reverb Heavy Patches: The K2600’s reverb is technically better, denser, smoother, more realistic. But that polish also alters the intended sonic character of the original patch. What once sounded ethereal now sounds lush in a way that wasn’t intended. For patches designed around the quirks of the K2000’s effects engine, this might be a deal-breaker. Unfortunately I didn’t have time to try replacing the reverb algorithm with some other. Besides that would be time consuming and a bit pointless for this test.

What Remains Consistent
High Frequencies: Surprisingly, neither synth comes off as significantly brighter or darker than the other. The high end is preserved equally well across both, with no noticeable roll-off or hyped treble. I will have to disagree with some online forum posts claiming one is “warmer” or other is “colder”.

Noise: As mentioned earlier, while both machines have similar noise floors, the K2600’s output feels quieter due to what’s likely noise-shaped dithering. Still, this is a subtle difference, more apparent in theory than in practice.

Spectrograms and Listening Tests
For the curious and technically minded: in our Soundcloud audio test, every patch first plays on the K2000, then on the K2600. In spectrograms, the left side of the display represents the K2000, while the right side shows the K2600 since horizontal axis is time while the vertical bar shows the frequency. This visual data confirms the sonic observations made by ear, especially in the spatial and low-frequency domains. I will comment directly using timestamps from the above Soundcloud demo.

Soundcloud demo timestamps:

• 0:00 the first patch seems close, however the flanger is way off in the K2600 version and panning is too extreme losing the coherence the original patch on K2000 had.
• 0:29 this patch has the same issue with the chorus on K2600, it’s a bit too dominant.
• 0:34 the beautiful ambient patch from K2000 when played on K2600 becomes a bit over the top with extreme stereo panning removing the impact / focus it originally had, the superior K2600 reverb is obvious in this example but does not compensate for too much stereo spread. The original emotion is completely lost.
• 0:45 the low end of this patch on the K2000 clearly sounds fuller and spectrogram clearly tells the same story. Click image for full size:

• 1:09 example of an identical sounding patch on both devices.
• 1:14 clear demonstration of superior K2600 reverb, the string sample itself is identical, but the patch no longer sounds like K2000 String.
• 1:21 noise test – this is extremely amplified patch (over 40 dB) as it was deliberately recorded on low volume. In here, something that behaves like shaped noise dithering is clearly present on K2600, and as a result it appears to sound less noisy. The spectrogram shows this in much better detail. Notice how K2000 has the evenly spread noise and it appears to be less noisy, but looks can be deceiving. If you look closer you will notice majority of K2600 noise is near the upper end of average human hearing. Click image for full size:

• 1:25 choir sounds slightly brighter on K2600.
• 1:33 another ambient patch and another example of too wide stereo filed on K2600.
• 1:41 bass although identical in frequency response the extreme wide stereo field on K2600 makes it sound hollow almost out of phase. Low end is identical. Click image for full size:

• 1:53 this patch seems to sound identical on both units.
• 2:00 extreme stereo separation on K2600 unfortunately ruins the patch, also some harmonics seem to sound slightly different.
• 2:10 while the patch itself sounds similar, the different reverb on K2600 changes the character.
• 2:16 a classic K2000 ambient patch which on K2600 unfortunately loses focus. Flanger and pan are all over the place, and that beautiful centre focus of the panorama is lost, with the signature K2000 patch sound completely losing its original character. This is probably one of the worst of the bunch.
• 2:35 the low end is pretty solid but I thought I’ve heard a tiny difference in the attack phase of the filter in the K2600, slightly more open sounding.
• 2:47 this clustered patch sounds ok on K2600 and the larger panoramic effect actually turned it for the better, a rare example in here.
• 3:00 beautiful K2000 ambient patch which on K2600 received a bit too much flanging, losing its original character, but on the other hand, perhaps adding something interesting.
• 3:21 I don’t know what happened here but the K2600 sounds just way way off, the resonance seems to have too much power/compensation, the patch loses volume while resonant peaks completely dominate. Perhaps this is not effects related but the VAST itself. This would be interesting to analyse. If someone has time to do it or already analysed it, feel free to comment below.
• 3:57 the VA portion of the bass seems to be identical, the low end is similar with K2000 having a bit more power, but the stereo chorus is way to extreme in K2600 version. Click image for full size:

• 4:05 again the way too pronounced flanger on K2600 removes the character of original K2000 patch. Perhaps someone prefers the later.
• 4:17 in this example K2600 completely ruined this beautiful shimmering patch of K2000. The two don’t even compare. Unfortunately I don’t have time to do in depth analysis, but I would bet on the effects. The interesting part is that on K2600 this patch has way more high frequency content present. Click image for full size:

• 4:33 this just for reference. K2000 default program followed by K2600 default program. As we can hear they sound identical. But looking “under the microscope” we can see a difference in the converter performance. To demonstrate noise performance within the spectrogram display I’ve completely muted the above piano sound, applied a lot of gain in post to let the background come in. We can clearly see the noise performance of the two units. As already discussed K2600 looks noisier but it is K2000 that actually sounds noisier due to evenly spread noise of the later. Click image for full size:

Final Thoughts: Which One Should You Get?
The K2000 has a unique sonic fingerprint that simply can’t be replicated on the K2600, even with compatible patches. There’s a character in its limitations, quirks, and effects engine that defines its sound. That said, for quick sketches, live covers, or modern workflows where you need a bit more horsepower and flexibility, the K2600 is a fantastic option. It’s a more advanced machine in every technical sense. But if you’re chasing the true K2000 experience, quirks, grit, and all, there’s no substitute for the real thing.

Where to hear more of the Kurzweil K2000?
There were a lot of artists who used K2000, but the best performance demonstration by far was made by Italian composer Roberto Concina. K2000 can be heard all over his first two albums. And it’s not just that piano or a guitar. No. It’s at least a dozen K2000 patches that any owner of this synthesizer will immediately recognise.

Below I will provide links to a few of his tracks, although many of the K2000 presets are on other tracks as well which you will find on albums titled Dreamland and 23am. His arrangements carry the classic Italian music school with rich string arpeggios and dominant melody mixed with modern rhythms of the era, both albums were innovative and original pieces of work which started a new genre, loved by millions of people all over the world.