CHRT synthesizer


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CHRT Synthesizer is a true analog monophonic tube sythesizer, first designed as a sound module for MIDI wind controllers, from revision 2.0 it is also a greatly responsive sound module for keyboard players. Revision 2.1 brings improved modulation possibilities, more control over the envelope generators, nicely consolidated circuit board design and user-friendly panel labelling.

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CHRT rev.2.1 was presented at Synthplex in Burbank, California at the end of March 2019. Thanks for your wide interest. Here's the Synthtopia video from the event:
Synthtopia about CHRT at Synthplex
Thanks again to all who helped with their suggestions how to improve the synth (especially Mr Pedro Eustache) and to all who make the synth visible (Synthtopia, Sonicstate, Mike Learmouth...)


Slightly outdated videos done on my personal testing CHRT showing some of the modulations.
CHRT Synth Youtube channel

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The Oscilator Trigger Bias knob which people enjoy fiddling with into the self-oscillation region can now be switched to floating voltage mode where the trigger bias level is modulated by MIDI CC #some_number and/or the second Envelope Generator. The result is a controlled hoarse or growl, best used in lower octaves.


Opposed to quite brutal Growl modulation, this provides delicate continuous timbre change, especially when you play with patches with high filter and/or VCA gain fed by low oscillator stage drive. In terms of sound character, this modulation enables an oboe-to-sax-to-clarinet-to-moogy-to-brass controlled continuous sweps, again by MIDI CC #some_number and/or the second Envelope Generator.

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The CHRT rev. 2.0 firmware has 3 major variants:

In brief, the wind controller FW variant works with BreathControl CC as the main VCA parameter and uses velocity to influence the amplitude of Envelope Generators (both EG1 for VCA and EG2 for Growl and Timbre Modulation)

With keyboard FW, Velocity decides on the note sustain level and also influences the amplitude of Envelope Generators (both EG1 for VCA attack and EG2 for Growl and Timbre Modulation). AfterTouch implementation is an essential feature where with separate CC messages, the player can adjust the AfterTouch influence on VCA and/or Pitch either in static UP-ONLY mode or in a more sophisticated CENTERED mode allowing "in-tune" vibrato, falls athe end of note, crescendo and diminuendo on a sustained note, etc. The keyboard FW has a CC operated switch beween LAST-NOTE and HIGHEST-NOTE Priority modes.

All variants receive PitchBend combined with LipPressure(BC) or AfterTouch(KEY), of course, and deal with the difference between legato/tenuto oscillator triggering

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Before ordering, please consider the following:

Once you know the answers to the above questions, please go to ORDER

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The main features of CHRT Synthesizer are:

The basic CHRT Synthesizer design is a 2U 19" rack


shipped as a DIY kit, while you can decide on the level of help and assistance with assembly, boards soldering, activation and debugging.

However, the structure is quite flexible and can fit, for example, into some vintage cases. Please do not hesitate to discuss the possibilities.
Here is the CHRT Synthesizer built into a case rescued from a wreck of a 50s tape recorder:


The software part - firmware can be adopted to your needs, e.g. a custom MIDI implementation. Please do not hesitate to discuss the possibilities.

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