Presentation on theme: "Miles Blair Cody Dinges Greg Entzel Derek Glass THE BLUE BOX - CDR."— Presentation transcript:
Miles Blair Cody Dinges Greg Entzel Derek Glass THE BLUE BOX - CDR
PROJECT UPDATE Class A Amplifier – Analog Board Update: Thorough understanding of tube theory and single-ended design 30W design not economically feasible with single ended design Currently driving 10W using 250VDC Plan to drive closer to 15W signal power. Foot Pedal & Effects Circuitry – Digital & Analog Board I/O Larger SPI potentiometers set with good accuracy at 8-bit precision Plan to implement effects/preset command signals using digital logic MSP430 – Digital Board Update: SPI drivers set potentiometers with ease Plan to transition to I 2 C with surface mount potentiometers Plan to focus on interfaces, buffers, and database before UI
FOOT PEDAL – LEVEL 2 Foot Button Inputs: User button press Outputs: Logic message to the processor Implementation: Digital Button integrated circuit triggers message Test Plan: Power the integrated circuit and press the button while using an oscilloscope to check that an I2C message was generated. Preset number display Inputs: I2C with new preset number sent from the processor. Outputs: 7 segment display to user Implementation: Premade integrated circuit with display Test Plan: Send a I2C and observe a display change.
SMARTPHONE – LEVEL 2 Phone computer system Inputs: User interface input Outputs: Wireless messages to the phone Bluetooth modem Implementation: Android operating system with application software Test Plan: Unit tests for individual software modules. Phone Bluetooth modem Inputs: Inbound wireless messages from the device Bluetooth modem Outputs: Outbound wireless messages to the device Bluetooth modem Implementation: Android device and operating system Test Plan: It is built into the phone, hope it works.
DIGITAL BOARD – LEVEL 2 Device Bluetooth modem Inputs: Inbound messages Outputs: Outbound messages Implementation: Premade device with software Test Plan: Send a message and read the TX pin with an oscilloscope. Processor Inputs: Button hit messages and inbound Bluetooth messages Outputs: Foot pedal display changes, outbound Bluetooth messages, and I2C messages for effects changes, EQ changes, volume changes, and effect bypass switch changes Implementation: Premade hardware and custom software Test Plan: Use the phone and foot pedal to change the preset or change an effect setting and observe outgoing I2C messages to the digital potentiometers and seven segment display.
MSP430G2553 MICROCONTROLLER Inexpensive UART connection to Bluetooth modem I2C drivers for digital potentiometers and effect bypass switches 20 pin designs offer enough general purpose pins for the foot-pedal buttons 16 kB non-volatile flash memory to store presets and performance sets
DIGITAL POTENTIOMETERS AND SWITCHES Digital potentiometers have 256 resistance settings Control Analog effects circuits and amplifier Digital Switches bypass effects that are not used in active preset Can all be connected to the same I2C serial bus Bluesmirf RN-42 Bluetooth Modem Class 2 Bluetooth Device 18 meter range makes it perfect for a stage
Analog effects circuits Inputs: Guitar signals from electric guitar and I2C messages containing digital potentiometer changes and relay changes to bypass/connect effect circuits Outputs: Analog signal to the equalizer circuit. Implementation: These will be a series of filters and analog effects circuits. The effects can be adjusted by digital potentiometers, and they are selected on/bypassed by a digital relay integrated circuit that is controlled by the processor using I2C messages. Test Plan: Input a signal generator signal 100 mV peak to peak and use an oscilloscope to observe an alteration in the input signal’s wavform. EQ filter Inputs: Analog signal from the effects circuits and I2C messages with potentiometer changes for the filters in the equalizer. Outputs: Analog signal to the power amplifier. Implementation: Series of bandpass/highpass/lowpass filters that are adjusted with digital with digital potentiometers. Test Plan: Input a sinusoidal waveform signal 200 mV peak to peak and use an oscilloscope to observe an alteration in the input signal’s amplitude for different frequencies. Analog amplifier Inputs: The altered analog signal from the equalizer. Outputs: Amplified analog signal to drive the speaker. Implementation: High power tubes to amplify the signal in 2 stages and an audio transformer steps down the voltage to a level where the current is high enough to drive the speaker. Test Plan: Input a 100 mV signal from a waveform generator and observe 15W signal from the power amplification stage. Then connect the speaker and check that it sounds correct. Speaker Inputs: Amplified analog signal from the amplifier Outputs: Sound Implementation: Premade inductive driver Test Plan: Connect to amplifier and hear if it sounds correct.
SINGLE-ENDED AMPLIFIER SCHEMATIC Pre-Amplifier (Twin Triode 12AX7): 45 X 45 = 2025 Gain Power Amplifier (Power Beam Pentode 6L6GC): 10W Signal Output
PRE-AMP DESIGN Triode (12AX7): Anode/Plate: Determines operating point of tube. Delivers output signal of gain stage Cathode: Determines sensitivity to input. Grid: Input signal. Heater: Improve cathode conductivity. Minimize effects of any gas.
V SUPPLY =250V V PLATE =175V V IN,MAX =100mV V CATHODE =1V I TRIODE =1.65mA V R_P =75V R P =V R_P / I TRIODE 46 Kohm Plate Resistor R K =V CAT. / I TRIODE 610 Ohm Cathode Resistor
Mutual Conductance: g m = 1.950 mA/VPlate Resistance: r p = 53 KOhm
PREAMP EQUIVALENT CIRCUIT r P = 53 Kohm R P = 51 Kohm R LOAD = 200 Kohm R K = 680 Ohm R TOT = r p || R P || R LOAD = 23 KOhm g m = 1.950 mA / V V IN,MAX = 100 mV ∆i P = g m * V IN,MAX =.195 mA V OUT = R TOT * ∆i P A V = V OUT / V IN,MAX = 45
PRE-AMP SIMULATION RESULTS V PP = 7.6V V P = 3.8V A V = 38
PRE-AMP TEST RESULTS V PP = 8.6V V P = 4.3V A V = 43
PRE-AMP GAIN / DISTORTION RESULTS First gain stage outputs 4.5V peak. Second gain stage biased to 1.5V Input signals near and above 1.5V P cause distortion Begins at 90V PP Set currently by a 500 Kohm logarithmic potentiometer
POWER OUTPUT TUBE Power Beam Tetrode: (6L6GC) Anode, Cathode, Heater, Control Grid: Same roles as triode, except plate drives an inductive load. Suppressor Grid: Help increase output current. Reduce effect of oscillations Tied to ground to reduce control grid-ground capacitance internally Screen Grid: Similar function to suppressor, close to high voltage.
OUTPUT DESIGN STARTING PLACE Output transformer (125ESE) rated for a bias of 80mA before saturation and frequency attenuation Some saturation emulates compression and works well with high tube gain Bias for 75 mA
POWER OUTPUT Transformer Input Waveform Speaker Waveform 17.5V PP indicates near 5W output V RMS = 6.189 P = V RMS 2 / R P = 4.8W 388 V P ! A lot of energy stored in the output transformer
NOTE ON POWER OUTPUT There is no standard for determining ratings for amplifiers 5W was only obtained at 100Hz and 100mV p Used a guitar with humbucker pickups (generate a 200mV P signal) Drove the speaker to V PP = 23 V (a 10W output) without noticeable distortion Drove the speaker to V PP,MAX = 35 V (near 20W output) with noticeable distortion Safe to rate the amplifier at 8-10W as a maximum recommended “playing volume” This rating is somewhat flexible due to tone desirability from overdriving pentode This power output is expected as it is biased near 20W with an expected 50% efficiency in a single ended setup
PLAYING DEMONSTRATION Note lack of hum: Quality DC voltages, requires high-fidelity supply design Note frequency response: Special consideration given to sizing biasing and coupling capacitor Special consideration given to audio transformer saturation current Note the gain/distortion: Smooth gain, subtle yet full. Additional overdrive will square out signal more dramatically Lacking Tone Design: Equalizer will improve audio quality. Capacitors may need to be decreased to reduce signal drift and popping
PRELIMINARY PARTS LIST PartCost 12AX7 Ruby$12.57 6L6GC$17.50 5 x 100uF 330V caps$6.00 3x4.7K, 2x200K, 2x51K, 680, 910, 200, 510 Resistors$10.00 500K & 1M Logarithmic Potentiometer$3.00 Power Transformer 269AX$45.00 Output Transformer 125ESE$70.00 Wood & Screws$50.00 400W Peavey Scheffield$30.00 Android Droid$50.00 20 x I 2 C Potentiometers$25.00 I 2 C Switches$10.00 Effects Components (R,L,C, Op-amps)$150.00 Amplifier PCB$33.00 Effects PCB$33.00 MSP420 Dev. Kit$3.50 Approximate Total: $548.57
DIVISION OF LABOR TaskDerek GlassCody DingesGreg EntzelMiles Blair Build and test filtersX X Build power supplyXX X Build amplifierXXXX Android initialization XX Design User InterfaceXXXX MSP430 data Interfacing XX Foot Pedal Interfacing XX Construction of AmpX X Altium DesignXX
CURRENT HIGH RISK FACTORS Hardware: Power Supply Stability Software: I 2 C Address Space UART Capability of MSP430 vs. ARM M0 Flash Memory Capacity