x0x:voltagecontrolledfilter
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x0x:voltagecontrolledfilter [2007/09/30 16:29] hl-sdk |
x0x:voltagecontrolledfilter [2016/01/28 18:05] (current) |
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| (Transistors are apparently more versatile than diodes and whenever designing a diode ladder VCF, use transistors. matching is very important, that's all I know) | (Transistors are apparently more versatile than diodes and whenever designing a diode ladder VCF, use transistors. matching is very important, that's all I know) | ||
| - | This filter has the property where resonance is increased, the peak stays at the same volume and the passband is reduced in volume. This is contrasted with the state variable filter where the passband retains its volume, and the peak gets louder. <--what? where did you hear this? | + | This filter has the property where resonance is increased, the peak stays at the same volume and the passband is reduced in volume. This is contrasted with the state variable filter where the passband retains its volume, and the peak gets louder. |
| - | The output is taken from the VoltageControlledOscillator switch, and fed to R62 and C17 (providing attenuation?) Then it is sent to the left base of Q12, and also attenuated to 5.333V via R68, R70, R98 and C16, and send to the right base of Q12. The common emitter of Q12 serves as a (current based) control for the cutoff frequency, and this is where the EnvelopeGenerator is input, both for the Env Mod values, and the Accent. | + | The output is taken from the VoltageControlledOscillator switch, and fed to R62 and C17, AC coupling the filter (VCO has DC offset). Then it is sent to the left base of Q12, and also attenuated to 5.333V via R68, R70, R98 and C16, and send to the right base of Q12. The common emitter of Q12 serves as a (current based) control for the cutoff frequency, and this is where the EnvelopeGenerator is input, both for the Env Mod values, and the Accent. |
| ==== Block Diagram ==== | ==== Block Diagram ==== | ||
| {{x0x:media:vcfblock.png|}} | {{x0x:media:vcfblock.png|}} | ||
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| ==== Transistor Ladder ==== | ==== Transistor Ladder ==== | ||
| Line 21: | Line 22: | ||
| Another "flaw" might be that the original Moog ladder filter had resistors connected from the common base of Q22, all the way down the ladder, and eventually connected to ground. Where as the TB303 and x0xb0x uses a single resistor, and connects that to a capacitor and then ground. | Another "flaw" might be that the original Moog ladder filter had resistors connected from the common base of Q22, all the way down the ladder, and eventually connected to ground. Where as the TB303 and x0xb0x uses a single resistor, and connects that to a capacitor and then ground. | ||
| - | Here is a link to a Moog filter schematic for comparison: [[http://www.synthdiy.com/files/1/20011020/moogvcf_schematic.gif]] | + | Here is a link to a Moog filter schematic and board (to build your own!) for comparison: [[http://dropmix.xs4all.nl/rick/Emusic/Moog/]] |
| ==== Amplifier ==== | ==== Amplifier ==== | ||
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