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, revision 2.0 makes it a greatly responsive sound module for keyboard players. more



Unexpected chassis parts delivery term problem on the metal machining works supplier's side. I'm trying to keep calm, looking for a new supplier. I will keep you posted.


The modulations described below prove to be a good addition. Please, check out some very basic videos done on my personal testing instrument.
CHRT Synth Youtube channel


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Taking into account your design improvement suggestions I gathered at Musikmesse Frankfurt and Superbooth Berlin, and a very special testing session with Mr Pedro Eustache, the synth has been redesigned, the firmware and digital board in a substantial way, the analog board slightly. The core of the synth, the oscillator, resonator and VCA remained untouched, the new modulation circuitry only added more timbre variants, keeping the CHRT sound you know exactly as it was. I wish that you find the inovations and changes worth waiting for.

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Growl or Formant Modulation

The Oscilator Trigger Bias pot we enjoyed fiddling with at the fair can 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.

Timbre Modulation

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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Thanks again to all for their patience, both the author and the project needed some time for necessary changes. Before ordering, please consider the following:

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

Note on first possible deliveries

Revision 2.0 required changes in front panel and chassis design and my metal machining partner asks for 6 weeks to deliver ready parts. The first CHRT can be shipped approx. on 22nd October.

Thank You

end of important news

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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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