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Schematic Overview:Power Supply
The power supply is relatively simple to understand. The power comes in at 9V AC, and goes to the rectifier From here, it is split into 2 sections The 5V and 6V, and the 12V and 5.333 Volt. At each section there are SmoothingCapacitors and ByPassCapacitors.
See the jumpers page for a list of which jumpers go where.
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The power input into the x0xb0x is 9V Alternating Current. This needs to be converted to Direct Current, before getting regulated to its proper voltage. This is done by the 4 1N4001 Diodes with what is called a bridge rectifier. You can see how a bridge rectifier works on the left hand side. While the Bridge Rectifier has in fact made sure our current is DC, it is in a state called "Full Wave Varying DC". We don't have a smooth line of direct current, rather, we have a series of camel humps, where the voltage goes from 0V, to +9V back to 0V.
C3 and C5, the monstor 2.2F Capacitors Perform a Smoothing operation. When the voltage starts on its downward drop from +9V to 0V, the capacitors discharge, and the voltage drop is minimized. The DC waveform looks a lot smoother, and more like gentle waves rather than camel humps, and the varying voltage is quite minimal compared to the rectified output.
The voltage regulators are very complex beasts. Essentially they take the gentle waves of the smoothed DC, and turn them in to a (relatively) perfect line of a specified output voltage.
After the power is rectified and smoothed by C3 (a 2.2F cap) it is sent to the 7805 voltage regulator. The .1mf Caps before and after the regulator seem to be ByPassCapacitors (to further smooth the waveform from any kind of interference) and are part of the application suggestions in the 7805 datasheet. This then becomes the +5V supply. This suplly draws 33mA average and 40mA max dependong on what kind of LEDs you use.
The smoothed waveform is also sent to a 78L06Z, a low current voltage regulator. Again, with .1mf Caps before and after. This becomes the +6V supply. The 6V rail draws 14mA average, irregardless of volume or whether or not notes are being played. One possibility of why this is, is that the la4140 is an inefficent amplifier.
After the power is recitifed and smoothed by C5 (the other 2.2F capacitor) it is sent through an RcNetwork (100 Ohm and 100uF) before providing power to the Op Amp.
The power also goes through another RcNetwork (1K Ohm and 100uf), before sent to the voltage reference circuit. This is taken from the LM336Z datasheet. TM6 allows to adjust the "breakdown voltage" of the Voltage Reference. D45-47 are used to "obtain a lower tempurature co-effient". This is then sent to an op-amp set up to be a VoltageFollower, to eliminate any loading effects. (This makes sure that 5.333 volts is available throughout the entire circuit?)
5.333V is generated first with the voltage reference and buffer because it is the ac ground (virtual ground) for the whole circuit. It needs to be stable so is generated with this reference from ground rather than from a potentialy unstable positive supply. It is buffered so it can supply current under load. As for why they chose 5.333V I think it was probably related to the VCO circuit. Ideally you would pick a bias voltage that is half the suppy rail, but I think they probably chose 5.333V as being the highest they could get without burying the top of the saw wave to the positive supply rail.
The 5.333 volts is sent to a NonInvertingAmplifier, with a 2.2K and 1.8K resistor. This provides a 2.222 voltage gain to the 5.333V, equaling a voltage of 11.851V, giving us the 12 Volt power supply. Capacitors C60 and C61 seem to be ByPassCapacitors
This supply draws between 14mA average and 16mA max when playing notes. When silent, the draw is at 10mA.
|Schematic||Power Supply||Voltage Controlled Oscillator||Voltage Controlled Filter||Envelope Generator||Voltage Controlled Amplifier||Headphone And Mixer||Digital Sequencer||Midi, USB and Sync|
|Fabrication||Building the Ps||Building the Vco||Building the Vcf||Building the Envelope||Building the Vca||Building the Headphone And Mixer||Building the Sequencer||Building the Midi and Sync||Finishing It Off|
|Testing||Testing the Ps||Testing the Vco||Testing the Vcf||Testing the Envelope||Testing the Vca||Testing the Headphone And Mixer||Testing the Sequencer||Testing the Midi and Sync|
|Mods||Ps Mods||Vco Mods||Vcf Mods||Envelope Mods||Vca Mods||Headphone And Mixer Mods||Sequencer Mods||Midi And Sync Mods||Finishing Mods|