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The x0x-heart is designed to be small, inexpensive, and a close replica of the TB-303. It is not a perfect replica - some sacrifices were made to keep costs down - but its pretty darn close. It also has no pots or controls, making it great for DIY synth building. All of the useful control points are pinned out on 0.1" spacings for easy prototyping. And, as a special bonus feature, digital control is given for Accent, Slide, Waveform select, Cutoff, and Envelope mod. The x0x-heart is designed to be small, inexpensive, and a close replica of the TB-303. It is not a perfect replica - some sacrifices were made to keep costs down - but its pretty darn close. It also has no pots or controls, making it great for DIY synth building. All of the useful control points are pinned out on 0.1" spacings for easy prototyping. And, as a special bonus feature, digital control is given for Accent, Slide, Waveform select, Cutoff, and Env Mod.
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Of the original transistors that are still available, none are available in SMT, so all new transistors were used. The PMP4201/5201 matched pairs were selected, and use throughout. These have very similar characteristics to the 2SC2291 and 2SC1583 matched pairs used in the 303, but have better matching characteristics. There are many differences between the x0x-heart and TB-303, most of which are due to components no longer being available, or not available in SMT format. In all cases, choices were made to keep costs down with minimal impact on the sonic quality of the synth. Here is a listing of some of the more notable differences:
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 1. PMP4201/5201 matched pairs used throughout (in place of both singles and duals). These have very similar characteristics to the 2SC2291 and 2SC1583 matched pairs used in the 303, but have better matching characteristics. They are mediocre replacements for the 2SA733 and 2SC536, but it reduced part count to use the same parts throughout. The impact on sound is minimal, except on the square wave, for which there is a workaround.

 2. 1% resistors used in place of 5% resistors throughout. The 1% resistors aren't significantly more expensive, and it makes the synths behave more consistently (which could be a seen as a drawback).

 3. Ceramic resistors in place of electrolytics and poly capacitors. This will have a small effect on the sound, but is unavoidable in an SMT design, as the poly caps in SMT are prohibitively expensive, are difficult to solder, and aren't as good as the THMT versions anyways. High voltage, and high quality dielectrice ceramics were chosen to help eleviate any problems here.

 4. 3300PPM tempco thermistor for R100 instead of 3000PPM. This should actually give better temperature matching.

 5. 220k/0.1uF slide components instead of 110k/0.22uF. This should have negligible effect on the slide timing, but will increase offset voltage slightly. The feedback resistor on the CV buffer was changed from 2.2k to 220k, which should eleviate any offset voltage problems seen from the change (it will probably be better than the original).

 6. LM358 instead of AN6562. These are very similar amplifiers, and should have no effect on the sound.

 7. 2SK3666 instead of 2SK30A. These are very similar JFETs, with the same I,,DSS,,, and should have negligible effect on the sound.

 8. Slightly different powersupply. It is a switching powersupply, with very similar frequency, output compliance, and output voltage. A definite improvement over the x0x.

 9. Digital waveform select. There is a bit of bleed-through that you don't get with the mechanical switch, but you can do so much with the digital control that it seemed worth it.

 10. Discrete BA662 implementation. Since this IC is no longer available, i reverse engineered its internal transistor layout, and just built my own on the board. details can be found on the [[x0xb0x|x0x wiki page]].

x0x-heart

About the x0x-heart

The x0x-heart is the heart of the x0xb0x, surgically extracted from the x0x to be transplanted into your designs. The x0x is a faithful replica of the Roland TB-303, complete with sequencer and DIN/MIDI/USB. The x0x-heart is just the analog section of the TB-303, replicated with SMT components, and made small enough to fit into a Eurorack modular format. It even has a Eurorack power header on it.

The x0x-heart is designed to be small, inexpensive, and a close replica of the TB-303. It is not a perfect replica - some sacrifices were made to keep costs down - but its pretty darn close. It also has no pots or controls, making it great for DIY synth building. All of the useful control points are pinned out on 0.1" spacings for easy prototyping. And, as a special bonus feature, digital control is given for Accent, Slide, Waveform select, Cutoff, and Env Mod.

User Manual

Differences from the original 303

There are many differences between the x0x-heart and TB-303, most of which are due to components no longer being available, or not available in SMT format. In all cases, choices were made to keep costs down with minimal impact on the sonic quality of the synth. Here is a listing of some of the more notable differences:

  1. PMP4201/5201 matched pairs used throughout (in place of both singles and duals). These have very similar characteristics to the 2SC2291 and 2SC1583 matched pairs used in the 303, but have better matching characteristics. They are mediocre replacements for the 2SA733 and 2SC536, but it reduced part count to use the same parts throughout. The impact on sound is minimal, except on the square wave, for which there is a workaround.
  2. 1% resistors used in place of 5% resistors throughout. The 1% resistors aren't significantly more expensive, and it makes the synths behave more consistently (which could be a seen as a drawback).
  3. Ceramic resistors in place of electrolytics and poly capacitors. This will have a small effect on the sound, but is unavoidable in an SMT design, as the poly caps in SMT are prohibitively expensive, are difficult to solder, and aren't as good as the THMT versions anyways. High voltage, and high quality dielectrice ceramics were chosen to help eleviate any problems here.
  4. 3300PPM tempco thermistor for R100 instead of 3000PPM. This should actually give better temperature matching.
  5. 220k/0.1uF slide components instead of 110k/0.22uF. This should have negligible effect on the slide timing, but will increase offset voltage slightly. The feedback resistor on the CV buffer was changed from 2.2k to 220k, which should eleviate any offset voltage problems seen from the change (it will probably be better than the original).
  6. LM358 instead of AN6562. These are very similar amplifiers, and should have no effect on the sound.

  7. 2SK3666 instead of 2SK30A. These are very similar JFETs, with the same IDSS, and should have negligible effect on the sound.

  8. Slightly different powersupply. It is a switching powersupply, with very similar frequency, output compliance, and output voltage. A definite improvement over the x0x.
  9. Digital waveform select. There is a bit of bleed-through that you don't get with the mechanical switch, but you can do so much with the digital control that it seemed worth it.

  10. Discrete BA662 implementation. Since this IC is no longer available, i reverse engineered its internal transistor layout, and just built my own on the board. details can be found on the x0x wiki page.

Mods

Documentation

x0x-heart (last edited 2022-02-10 00:00:26 by guest)