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The FreeDSP-G is an ADAU1467 DSP Board, A Dedicated design for Electric Guitar Players.
The purpose of this unit is to simulate a tube guitar amplifier sound. Remember this is NOT a Hi-Fi Audio product. Powerful and plenty of I/O embedded on the ADAU1467 realize direct operation capabilities. A and B dual-mode 7 control knobs are provided on the top panel. Plus an effect control foot switch is provided. Plus, 5 small push switches are provided to have a chance of controlling the sound variations. Currently, only one sample DSP firmware is provided. Of course, you can reprogram the DSP firmware as you like. If you create your original firmware, you can fork the branch, and you'll be able to pull requests to the mainline. I hope many people share their ideas with this community in the future.
- A simple single DSP board concept
- 6.5mm Phone Jack I/O connector
- KARAOKE (Play-along) feature
- Effect loop function with plug insert detection feature
- Stereo Output
- Headphones output
- Switchable Dual 7 Potentiometer Controls
- 5 Optional Push Switch
- Dual Color LED indicator x1
- Single Color LED x1
- 3 Momentary-ON Footswitches with LED indicator
- Optical S/PDIF Input and Output
- 3.5mm Stereo Analog signal Input with plug insert detection and rotary volume control feature.
- USB-C Audio Input (44.1kHz/48kHz)
- Embedded BM83 Bluetooth Audio Interface (Option)
- BGM mix level control (POT-7)
- DSP reset button
- Selfboot disable jumper
- Bright(Hi-Boost) Jumper
- Triodizer Head Amplifier with bypass option
- USBi 10P IDC pin-Header with shroud
FreeDSP-G consists of two PCBs: a "POT-SWITCH" board and a "MAIN" board.
POT/SWITCH BOARD SCHEMATIC CIRCUIT DIAGRAM
Seven rotary potentiometers have each de-multiplexed AUX-ADC paths to DSP-embedded ADCs.
Two of three foot switches have an A/B latch selector circuit to select the DSP algorithm and potentiometers.
The rest of the foot switch has an alternate flip-flop circuit for switching the effect on/off.
C24 and C25 are provided for default selection.
A dual-color LED has been provided.
There was some crosstalk between the MPxx GPIO pin and the AUX-ADC. So you should be careful when using this LED. I wonder if it must be the inside of the chip-level crosstalk.
NAIN BOARD SCHEMATIC CIRCUIT DIAGRAM
PLUG INSERTION DETECTING CIRCUIT
Weak pull-up GPIO goes high if the phone plug is inserted. By acknowledging those statuses, you can mute unused inputs.
HEAD AMPLIFIER
A J-FET head amplifier circuit is provided. This circuit has high input impedance and some triode-like characteristics.
If you do not like this feature, you can bypass it by moving the jumper on the J16.
Then the input guitar sound and Effect-return signal are converted to I2S via IC4 ADC.
HEADPHONES AMPLIFIER CIRCUIT
A simple Headphones driver circuit is provided.
POWER ON/OFF MUTE DRIVER
This circuit is provided to reduce the "Pop" noise on the headphones.
SLEFBOOT JUMPER
This jumper is provided for the zombie junk-code written EEPROM issues. If you face this trouble, jump out of this. Then reboot, erase EEPROM, and overwrite the fixed firmware. This will be the only way to recover from this trouble.
BOOT EEPROM CONFIGURATION CIRCUIT
Using I2C for programming the DSP. Normally, the USB-Host device XIAO RP2040 board is connected. And its I2C bus is connected to the DSP. But if you connect the USBi to J13, an I2C path from RP2040 will be cut.
USB AUDIO INPUT
A simple, low-cost USB Audio bridge is provided. You can drag and drop programming the firmware which is created by Takazine as a famous DIY Audio Blogger site master of New Western Elec.
USBi emulation is not provided yet.
S/PDIF INPUT & OUTPUT
Optical digital audio I/O is provided
BLUETOOTH INTERFACE
AAC/SBC Bluetooth connection is supported. Multifunction button acts as a pairing button(Long-push)
You can access the hardware noted in the chart below.
Multiple asymmetric soft-clipping stages are provided. 2 or 3 stages are selectable. Clipping will start from the last stage.
You can add a crossover distortion as you like. This will be related to the decay of the sound characteristics.
You can load IR data (Text Cofficent data) files for the cabinet and microphone sound simulation.