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x0x:voltagecontrolledoscillator [2007/09/30 16:22] hl-sdk Changed block diagrams. Visible on jonnay wiki, not here? They were "draw" files instead of PNG. Have I messed up? |
x0x:voltagecontrolledoscillator [2007/09/30 18:26] hl-sdk |
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===== The Voltage Controlled Oscillator ===== | ===== The Voltage Controlled Oscillator ===== | ||
{{template>.templates:schema|section=VCO|inputs=DigitalSequencer: Slide On/Off,Note|outputs=VoltageControlledFilter: Audio Out, MidiAndSync: CV Out}} | {{template>.templates:schema|section=VCO|inputs=DigitalSequencer: Slide On/Off,Note|outputs=VoltageControlledFilter: Audio Out, MidiAndSync: CV Out}} | ||
- | The VCO is comprised of 5 sections. The first of which is the Digital to Analog converter, which takes the digital signals for the note generated by the MicroProcessor and converts them to a voltage. After that the voltage is sent to a buffer and the Slide Circuit. Then it is sent to Q26 which is responsible for (blah... marked as "antilog" on the Tb303 block schematic). Q24 and Q25 act as a special switch, which is based on a [[http://en.wikipedia.org/wiki/Silicon-controlled_rectifier|Silicon Controlled Rectifier]] which generates a Saw Wave. This waveform is then sent out to Q28 a 2SK30 JFET which is used as an operational amplifier. The output is sent to the switch, and also sent to Q8, where the saw wave is shaped into a square and back to the switch. From the switch, the output is sent to the VoltageControlledFilter | + | The VCO is comprised of 5 sections. The first of which is the Digital to Analog converter, which takes the digital signals for the note generated by the MicroProcessor and converts them to a voltage. After that the voltage is sent to a buffer and the Slide Circuit. Then it is sent to Q26 which is responsible for (blah... marked as "antilog" on the Tb303 block schematic). Q25 and Q27 act as a special switch, which is based on a [[http://en.wikipedia.org/wiki/Silicon-controlled_rectifier|Silicon Controlled Rectifier]] which, when coupled with an integrator, generates a Saw Wave. This waveform is then sent out to Q28 a 2SK30 JFET which is used as an operational amplifier. The output is sent to the switch, and also sent to Q8, where the saw wave is shaped into a square and back to the switch. From the switch, the output is sent to the VoltageControlledFilter |
==== Block Diagram ==== | ==== Block Diagram ==== | ||
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==== Oscillator Drift Compensation and Tuning ==== | ==== Oscillator Drift Compensation and Tuning ==== | ||
==== Anti-Log ==== | ==== Anti-Log ==== | ||
+ | |||
==== Switch ==== | ==== Switch ==== | ||
- | Transistors Q24, Q25 and Q27, along with C (... unreadable on the schematic) are responsible for generating the SawWave. The transistors Q25 and Q27 are set up in a special layout like so: | + | Transistors Q24, Q25 and Q27, along with C33 are responsible for generating the SawWave. The transistors Q25 and Q27 are set up in a special layout like so: |
{{x0x:media:vcoswitch.png|}} | {{x0x:media:vcoswitch.png|}} | ||
- | This arrangement is similar to a Silicon Controlled Regulator. | + | This arrangement is similar to a Silicon Controlled Rectifier. |
=== From: Martin Czech martin.czech@intermetall.de, === | === From: Martin Czech martin.czech@intermetall.de, === | ||
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amount of the transistor current flows through the base, especially in | amount of the transistor current flows through the base, especially in | ||
the case of Q27 where there is no base resistance nor diode. If Q27 is | the case of Q27 where there is no base resistance nor diode. If Q27 is | ||
- | not suited for such an application, it will shure burn out. Most good | + | not suited for such an application, it will sure burn out. Most good |
audio transistors with high Ft and high beta have shallow base junctions | audio transistors with high Ft and high beta have shallow base junctions | ||
that are very sensitive. So the problem of Q27 burnout could be addressed | that are very sensitive. So the problem of Q27 burnout could be addressed | ||
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==== Saw to Square Waveshaper ==== | ==== Saw to Square Waveshaper ==== | ||
+ | |||
+ | After the saw wave gets passed through the JFET and heads out to the waveform select switch, it heads into a jungle that I can only assume is a waveshaper. Here's a picture of the circuit: | ||
+ | {{x0x:waveshaper.png|}} |