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Kurzweil K2500 is a first major upgrade of the famous K2000 synthesizer. It is a DSP based, 31 algorithm, synthesizer/sampler workstation. It doubles the K2000 24-voice polyphony to 48 voices and offers a number of new parameters and expansion board options.


The synthesis, this instrument uses, is called V.A.S.T., which stands for Variable Architecture Synthesis Technology. It is a unique system of pre-defined algorithms with a number of variables, individually editable DSP functions and digital oscillators, combined with the internal or external PCM samples.

There are 8 MB of onboard Basic ROM + up to 3 sample ROM blocks (8 MB Orchestral board, 8 MB Contemporary board and 4 MB Stereo Grand Piano board) + max of 128 MB sample RAM. The ROM boards contain internal PCM samples and factory presets.

With an optional SMP-2K/R advanced sampling expansion board, which adds analog and digital sample inputs, K2500 works as a full sampler. Without the SMP-2K/R installed, it works as a fully functioning sample player.

The external RAM sample can be fully edited using the following functions: Sample Start, Attack, End, Cut/Copy/Paste; loop forward, backward, and bi-directional looping and loop bypass; truncate, fade in, fade out, reverse, cross-fade looping with selectable curves and many other functions. Some of the above mentioned functions can be used with the internal ROM samples as well.

PCM samples or digital oscillators (digitally generated waveforms like sine, sine+ LF sine, saw, saw+, LF saw, square, square+, LF square) can work together within any one of the total of 31 DSP algorithms.

As mentioned above, algorithms have variable segments, or in other words, individual DSP units. The algorithms are not rigidly defined as is the case with the Roland JD/JV and XV series but the types of DSP units in an algorithm can be changed. Each DSP is fully editable. K2500 can thus emulate several types of synthesis. This feature makes it really unique among other sample-based instruments.

As could be expected, there are several limitations in DSP combinations. These, however, were resolved with later released and virtually limitless K2600 Triple Mode.

Internal or external samples can be filtered (HPF, LPF, 12db/oct, 24db/oct, BPF, notch, peak, all pass, steep resonance), equalized (several EQ types), mixed with digital oscillators (digitally generated waveforms like sine, sine+, LF sine, saw, saw+, LF saw, square, square+, LF square), distorted and cross modulated.

Other DSPs available are shaper, high freq. stimulator, digital wrap, noise generator, PWM, X-Fade, amplitude modulation, panner, etc.

All individual parameters are fully editable (Hz, cent, dB, sec, msec settings - nothing like usual 1-127).

There are 3 very fast envelope generators (AMPENV - amplitude envelope / ENV2, ENV3 user definable - 8 segments, looping), ENCTL (envelope control) for dynamic or continuous ADR parameters control, 2 LFOs (generators with many cyclic waveforms and adjustable phase angle between 0 – 270 degrees), 2 ASR envelopes for start and attack of user definable modulation functions, FUN (mathematical functions - formulas full of sin, cos, tg etc., for modulation of individual parameters of DSP algorithms e.g. pitch, filter, amplitude, pan, or direct control of LFO waveforms).

The modulation matrix is very complex. "Everything can be modulated by everything" (you can use functions for modulation source control as mixers, negators, invertors, sample and hold, quantization, ramp, shape, etc.).

Each sound program can consists of up to 32 layers.

KB-3 Drawbar Mode

KB-3 Mode is part of the software upgrade since OS 2.5x downloadable from official www.kurzweilmusicsystems.com web site. It provides a powerful tone wheel organ synth model, fully polyphonic over the keyboard. Each single voice contains nine harmonics that may be blended in real time using the sliders. There are 4 organ maps available with rotary speaker emulation, vibrato/chorus, percussion attack, key click, parametric EQ, etc.

Sober multitimbral

K2500 is a 16 channel multi-timbral synthesizer with a sophisticated "invisible" multi mode. Each preset or user program in Program Mode can simultaneously work on a different MIDI channel (1-16). This means that no complicated Multi or Performance mode is used for multi-timbral operations. There are two dedicated buttons on the panel to browse between individual channels/programs.
However, for those who use the "Performances" and "Multis" the Setups are available as well.


There are several differences between programs and setups. Program can include several layers but plays only in one Zone on one MIDI channel. Setup enables user to utilize up to eight keyboard zones, each of which can have its own MIDI channel, program and control assignments. There can be up to 100 setups saved in each memory bank.


The K2500 internal sequencer is one of the best hardware sequencer ever made. It includes 32 fully editable tracks (16 song tracks + 16 arrangements tracks), linear and step recording – cut, copy, paste, quantization, event list editing, Advanced Auto Arranger (sequences can be triggered in real-time from the keyboard), and resolution of 768 ppqn.

The basic capacity of approx. 60 000 events is expandable up to approx. 300 000. A song is stored in program RAM, which means that it uses your limited internal program memory or expansive optional P-RAM capacity. 


The basic built-in digital effect processor is based on simple Digitech chip and offers standard effect algorithms. It is an upgraded version of the original K2000 EFX unit with a few more editing parameters and better signal to noise ratio.

It provides fully programmable basic effect algorithms and their combinations (stereo chorus, stereo flange, stereo delay, 4-tap delay, ultimate reverb, room simulator, gated reverb, reverse reverb, parametric EQ, graphic EQ, parametric EQ + delay + mixer, parametric EQ + chorus + mixer, chorus + room + mixer, delay + room + mixer, chorus + hall + mixer, delay + hall + mixer, EQ + gated reverb + mixer, EQ + reverse reverb + mixer, parametric EQ + chorus + delay + mixer, parametric EQ + flange + delay + mixer, chorus + delay + room + mixer, flange + delay + room + mixer, chorus + delay + hall + mixer, flange + delay + hall + mixer, EQ + chorus + 4-tap delay + mixer, EQ + flange + 4-tap delay + mixer).

Since the K2500 is a really powerful synthesizer it is not necessary to add extra "charm" to its sound with reverb and chorus as with some cheap mass produced instruments. The dry sound is rich enough.

There are two effect buses available (dry and wet). Unfortunately, it is not possible to set the send level for individual channels in multi-timbral mode.

K2500 can be expanded with an optional KDFX board. KDFX is a very advanced and excellent sounding digital reverb and effect unit with digital I/O offering superb sonic possibilities. It is based on Kurzweil´s VLSI chip and it features 4 stereo buses, full bandwidth, 8 outputs and 2 inputs of Kurzweil Digital Stream (KDS) digital I/O (for connection with DMTi option) and flexible routing scheme.

Microtonal tuning

There are 17 pre-programmed intonation tables. All of them are freely user editable.


The polyphony is 48 voices (together with a maximum of 192 oscilators - 48 sample playback and 144 synthesizer waveforms). Special voice allocation system, first patented for K250, is used. This system analyses the most frequently used sounds in multi-timbral mode so the "voice stealing" effect is nowhere near as obvious as with other synthesizers. Each program can consist of up to 32 layers.

Sounds never before imaginable

The instruments has a unique "fat" sound and is excellent in multitimbral settings. It is not necessary to "sweeten" the sound up with reverbs. The rich editing functions offer immense sound possibilities for analog emulations. The instrument offers superb acoustic sounds, excellent pads, as well as aggressive non-harmonic digital colors. K2500 is suitable for all music styles and is excellent for electronic and techno music. This instrument can easily outperform VA synthesizers which were produced a whole decade later. To evaluate the instrument's capability, please listen to our K:Works Modern Synth demo here, and K:Works Gold demo here.

Web resources
http://kurzweil.com/ - 
Kurzweil Music Systems company web page