Sunday, 15 May 2016

DMFX-1-2 (mezzanine board) PCB layout and assembly

DMFX1-2 is the DMFX-1 system mezzanine board.

DMFX1-2 requires a more standard, less demanding and cheaper PCB technology than DMFX1-is DMFX1-2 consists of 2-layers on FR4 dielectric (100 x 68mm). green soldermask, and white top silkscreen, layer plated copper thickness is 35μm. PCB thickness is 1.55mm. Minimum trace width is 250μm and minimu isolation distance is 250 μm. Minimum finished hole is 350μm.
It uses an Eurocircuits class 3B compared to class 8D for DMFX1-1.

The mezzanine board is plugged into the main board using 2 high density connectors, it houses a 128x32 pixel LCD graphic display blue LED with white LED backlight, a 5-button integrated switch with 4 arrow buttons (left, right, up, down) and a center OK button that allows navigating through menus displayed on LCD, five red LEDs, and 5 potentiometers connected to SAR ADC inputs on control DSP.

Top layer is used for signals and power plane. Bottom layer is used for signals and ground plane
DMFX1-2: Top layer
DMFX1-2: Bottom layer
This is the DMFX1-2 mezzanine board fully assembled:
DMFX1-2 fully assembled

DMFX-1-2 (mezzanine board) Schematics and BoM

DMFX-1-2 is a mezzanine board that get plugged into the main board DMFX1-1 by means of two 20-pins SMD connectors on the bottom side of the PCB.
The mezzanine board includes a  LCD-graphic 128x32 pixels display panel (with 
blue background white pixels and white backlight) that is configured from control DSP-2 via an SPI bus.
It also includes a button navigator with five switches (four arrow buttons: Up, down, left, right and center OK button) used to navigate through the LCD menus.

Additionally, there are five 3-mm red LEDs and five 9-mm potentiometers. A 5K potentiometer (VR5) in the middle, controls the distortion octaver level. The other four 50K potentiometers (VR1-4X) are connected to analog SAR ADC inputs (AIN0-3) on DSP-1. Only two of them (VR3-4) are connected to DSP-2 (AIN2-3) since AIN0-1 are connected to tuner and noise suppression circuits respectively.
These may be used as digital potentiometers to configure some effect parameters such as gain, volume, tone, depth, delay, rate... on LCD menu.
DMFX-1-2: Schematics

Schematics and BoM source files

Schematics and layout have been made using CAD Eagle 6.3.0. Source files can be found in the DMFX-1-2 github HW repository including Eagle Schematics source files (.sch), Eagle Board layout files (.brd), Eagle component libraries (.lbr), Schematics in pdf format, and all manufacturing files including gerber files, assembly drawings and pick and place files. An Excel file contains the full BoM including reference designators, manufacturer part number  as well as Digikey part number.

DMFX-1-1 (main board) PCB layout and assembly

DMFX-1 consists of two PCBs built by Eurocircuits:
  1. Main board (from now on DMFX-1-1) is 8-layers on FR4 dielectric (144 x 100mm), green soldermask and white top-bottom silkscreen, inner layer copper thickness is 18 μm (1/2 oz.), outer plated copper layer is 30 um. PCB thickness is 1.55 mm. Outer layers traces are 125μm, inner layer traces 100μm, isolation distances are 100μm. Hole density  <1000/dm2. Minimum finished hole is 150μm. This corresponds to Eurocircuits pattern class 8 drill class D.
  2. Mezzanine board (from now on DMFX-1-2) is 2-layers on FR4 dielectric (100 x 68mm). green soldermask, and white top silkscreen, layer plated copper thickness is 35μm. PCB thickness is 1.55mm. Minimum trace width is 250μm and minimu isolation distance is 250 μm. Minimum finished hole is 350μm. This corresponds to Eurocircuits pattern class 3, drill class B.

Here you can verify Eurocircuits pattern classification. DMFX-1-1 requires a quite high and therefore more expensive pattern and drill class (8D)
The main reason for that is that DSPs are 144-pin 0.8 mm pitch BGA devices. The main challenge of this project is using those tiny BGAs with 0.8 mm pitch which are not very well suited for a DIY application, and the biggest challenge of all is manually soldering those BGAs
But 0.8 mm pitch BGAs also impose constraints on minimum trace width and the number of layers to be able to fanout all the BGA pins.
If minimum finished plated drill (PTH) size is 150μm for class D, minimum production hole diameter (PHD) size is 250μm and minimum inner/outer annular ring (IAR/OAR) is 100μm, which corresponds to a via pad size of 450μm (PTH + 2xOAR/IAR = 250+100+100)
That means that between two 450μm vias spaced 800μm there is a distance of 350μm within which we have to pass fanout traces, class 7 requires 125μm traces an isolation and hence 3x125μm=375μm. Conclusion: a class 8D is required with minimum trace width 125μm and minimum isolation of 100μm.
DMFX-1-1: PCB design rules
There are four signal layers: top, bottom and internal layers 3 and 4, but all signal layers include ground planes (analog and digital), this helps copper balancing on PCB but also it helps to shield and reduce noise if some via stitching is added so that good ground connection is assured on all layers.
Layer 3 uses mainly horizontal routing and layer 4 uses vertical routing.
Layers 2 and 5 are mainly ground and power planes.

DMFX-1-1: Top layer - layer 1 (signals)
DMFX-1-1: Layer 3 (signals, horizontal routing)
DMFX-1-1: Layer 4 (signals, vertical routing)
DMFX-1-1: Layer 5 (Power planes)
DMFX-1-1: Bottom layer - layer 6 (signals)
DMFX-1-1: Assembly top


It is recommended to move capacitor C180 down as indicated by the red arrow in the following figure, below the line marked by the green arrow that shows the position of the border of the mezzanine board. C180 electrolytic capacitor is too high and mezzanine board may not be fully plugged in.

DMFX-1-1 (main board) schematics and BoM

DMFX-1-1 includes the following blocks:
  • TI C5535 DSP-1 implements the digital effects and audio codec control (pages 2-3)
  • TI AIC3204 ADC/ADC audio codec and buffer, 12MHz clock oscillator, stereo headphones output jack (page 4)
  • DSP-1/2 external memories: SPI, I2C, SD/MMC (page 5)
  • DC/DC step-down switching regulators (3.3V, 1.8V) and LDO (1.3V), power-on reset, clock driver (page 6)
  • FTDI2232 USB/JTAG interface an SEEPROM (page 7)
  • TI C5535 DSP-2 implements LCD, navigator buttons, tuner control (page 8)
  • DMFX-1-2 mezzanine Connectors and footswitch push-button (page 9-10)
  • Line-In stereo input buffer, filters, distortion circuit (page 11)
  • Line-Out dual-mono output buffers and filters, tuner, noise supressor circuits (page 12)
DMFX-1-1: Schematics page 1 - Table of Contents
    DSP-1 implements the digital effects and control the audio codec. It includes a dedicated mini-USB connector. Four analog SAR ADC input are connected to DMFX-1-2 potentiometers. DSP-1 is the first device on the JTAG daisy chain connected to USB/JTAG device to allow JTAG emulation and debugging. INT0 input is connected to DSP-2 external flag (XF) signal and DSP-1 XF signal is connected to DSP-2 INT0; both DSPs exhange interrupts to allow synchronizing processes and tasks between both processors. INT1 is connected to DSP-1 GPIO10. Two SD/MMC cards are connected to DSP-1 to store data, samples, loops, code...
    I2S2 interface is a fast serial interface to exchange samples between DSP-1 and ADC/DAC on audio codec. SPI interface is connected to an external SPI flash to store code and data. UART interface is connected to CBUS on USB/JTAG-UART device and it can be used as console for emulator debugging. I2C bus is connected to external SEEPROM, to store parameters or inventory information. I2C is used for configuring audio codec, and it is also connected to DSP-2 to exchange FX configuration parameters set by user interface via LCD menu and buttons.
    DMFX-1-1: Schematics page 2 - DSP-1 FX interfaces
    Page 2 shows DSP-1 power supply inputs, ferrite filters and decoupling capacitors.
    DMFX-1-1: Schematics page 3 - DSP-FX power

    Page 3 shows TI TLV320AIC3024 audio codec that includes ADC/DAC, LINE input, MIC input, LINE out and stereo headphones amplifier. I2S is a high speed serial interfaces to echange audio samples with DSP-1 at a sampling frequency configured by DSP-1. Interface is buffered via a CBTLV3245 octal bus switch. 12MHz clock oscillator is included here, it is connected to a clock driver on page 6.
    DMFX-1-1: Schematics page 4 - Audio CODEC ADC/DAC
    Page 5 includes two W25Q64 64-Mbit SPI flashes connected to each DSP SPI interface. Two SD/MMC cards are connected to DSP-1 for large storage (samples, loop, data). One I2C 64Kbit SEEPROM 24C64 can be used to store remote inventory or configuration data.
    DMFX-1-1: Schematics page 5 - Memories I2C, SPI, MMC
    Page 6 shows two DC/DC step-down switching regulators TI TPS56220. They generate +3.3V and +1.8V respectively from a +9V external supply or +5V USB input with a maximum current of 500mA each. A TI TPS73201 LDO generates the analog 1.3V DSP supply voltage from 1.8V input at a maximum current of 250 mA. A TI CDCLVC1108 octal clock buffer generates up to 8 clocks from 12MHz clock oscillator: USB DSP-1 clock, DSP-1 system clock, audio codec master clock, USB/JTAG clock, USB DSP-2 clock and DSP-2 system clock.
    DMFX-1-1: Schematics page 6 - power supply, clock driver
    Page 7 shows an FTDI2232 USB/JTAG interface device that works as XDS100v2 TI emulator for DSP debugging. ABUS is connected to JTAG daisy chain on DSP-1 and DSP-2. CBUS is sonnected to UART interface on DSP-1. A D-type flip-flop detects power reset rising edge from FTDI device and generates a power detect signal back to the FTDI device. An external SPI SEEPROM AT93C46 stores USB device configuration parameters. USB port is protected for ESD. USB debug port is a type-B USB connector. The +5V USB debug port can be used to power the whole DMFX-1 system. DMFX-1 system can actually be powered from any of the three USB ports or by an external +9V power supply.
    DMFX-1-1: Schematics page 7 - USB/JTAG
    DSP-2 implements user interface and control tasks. It includes a dedicated mini-USB connector. Two analog SAR ADC inputs (AIN0-1) are connected to tuner circuit output and noise supression circuit output respectively, AIN2-3 are connected to DMFX-1-2 potentiometers 2-3. DSP-2 is the second device on the JTAG daisy chain connected to USB/JTAG device to allow JTAG emulation and debugging. INT0 input is connected to DSP-1 external flag (XF) signal and DSP-2 XF signal is connected to DSP-1 INT0; both DSPs exchange interrupts to allow synchronizing processes and tasks between both processors. INT1 is connected to DSP-2 GPIO10.
    DSP-2 GPIO0 controls clean or distorion audio input to audio codec. GPIO1-2 configure the overdrive/distortion gain, GPIO3-4 control different overdrive/distortion modes, increasing mid tones or setting fuzz clipping diodes circuit. GPIO6-11 drive five red LEDs on DMFX-1-2 mezzanine board. GPIO11 is connected to CPU active green LED.
    SPI interface is connected to SPI flash (device 0) and to 128x32 graphic LCD (device 1) on DMFX-1-2 mezzanine board, GPIO12 is connected to LCD A0 signal and is used to send command or data to LCD via SPI bus. GPIO13-17 are connected to the five navigator buttons respectively: left, up, center, down, right.
    GPIO28 is connected to footswitch.
    SPI and UART interfaces are not used. I2C bus is connected to DSP-1 to exchange FX configuration parameters set by user interface via LCD menu and buttons.
    DMFX-1-1: Schematics page 8 - DSP-2 Control interfaces
    Page 9 shows DSP-2 power supply inputs, ferrite filters and decoupling capacitors.
    DMFX-1-1: Schematics page 9 - DSP-2 Control Power
    Page 10 shows DMFX-1-2 mezzanine connectors. J5 connector includes DSP-2 SPI2 bus, LCD A0 addess signal, reset signal and the five navigator button inputs: left, up, center, down, right. J7 connector includes LED1-5, DSP-1 GPAIN0-3 SAR ADC signals, DSP-2 GPAIN2-3 SAR ADC signals, distortion circuit output, octave circuit output and the mix of distortion-octave coming from a potentiometer on DMFX-1-2. +3.3V, analog +1.3V power supplies and ground.
    DMFX-1-1: Schematics page 10 - Connectors
    Input buffers and filters and distortion circuits are based on TI rail-to-rail LME49721 audio op-amps powered at +3.3V, in contrast with +9V supply normally used on guitar pedals. 


    First opamp stage has 0dB gain but implements some low pass filtering. Second op-amp stage implements a configurable gain controlled by DSP-2 GPIO signals connected to OD_DRV0-1. when both switches are active (shorted) we obtain the minium gain value of 13dB (x4.5), if OD-DRV1 is open, gain value is incremented by 10dB (x14.5), if OD_DRV0 is open, gain value is incremented by 9dB (x40). Third op-amp stage implements high saturating gain (hard clipping) or soft clipping via asymmetric diodes, when OD_MODE1 is 0, a 20dB gain is implemented with 10K switch shorted and switch in series with diodes open. When OD_MODE0 is 1, a 10dB gain is implemented, but soft asymmetric clipping is added with Schottky diodes added in parallel to the opamp feedback path.

    OD_MOD0 activates a notch filter that attenuates middle tones by 12dB at 400Hz.

    These four GPIOs: OD_DRV0-1 and OD_MODE0-1 allow different combinations of gain, hard clipping, soft clipping, and mids attenuation to get different types of analog overdrive and distortion effects.


    A forth op-amp implements a full-wave rectification that generates a octave up, that can be mixed with distortion output.

    Line-In circuit:

    The input from a guitar can be connected to Line-In input. The first stage is a J-FET buffer, followed by a filter that boosts up to 6dB high frequencies and attenuates down to 9dB low frequencies. 0dB occurs at 3.7kHz. The filtered line-in signal is the input to the tuner circuit and to an analog switch that can select the clean or the distortion at its output. The output of the switch is connected to the Audio Codec analog left channel input. Right channel input is connected to the clean signal, this allows mixing clean and distorted signal within DSP and obtain a more or less overdriven signal.
    The op-amp at the bottom of the page is a follower buffer that generates a middle point reference signal at 1.65V equal to 3.3V/2. Op-amps are rail-to-rail TI LME49721 powered at 3.3V.
    DMFX-1-1: Schematics page 11 - Input buffers, filters, clean, distortion
    Page 12 shows right and left channel pre-amp circuit with high impedance Line-Out signals that can be connected to a guitar amplifier or Line-In input of a sound card or sound equipment.This pre-amp amplifies 9dB with a 3dB bandwidth of 1.35kHz, 0dB is at 4kHz. The first op-amp stage filter is a low pass filter with a pole at approximately 14kHz and 3dB bandwisth at 24 kHz.

    The two op-amp circuit at the bottom of the page is used as support to the tuning and noise suppression circuit within the control DSP-2. The first stage is a very high gain amplifier that can be used as power detector for a noise suppression algorithm. The second op-amp is used as comparator and generates a square wave between 0 and full scale with the same fundamental frequency as the input signal and zero voltage when no signal is present. This square wave simplifies tuning algorithm using and auto-correlation method. Both tuner and noise suppression signals are connected to analog inputs of SAR ADC circuits within the Control DSP-2
    DMFX-1-1: Schematics page 12 - Output buffers, filters, tuner, noise suppression

    Schematics and BoM source files

    Schematics and layout have been made using CAD Eagle 6.3.0. Source files can be found in the DMFX-1-1 github HW repository including Eagle Schematics source files (.sch), Eagle Board layout files (.brd), Eagle component libraries (.lbr), Schematics in pdf format, and all manufacturing files including gerber files, assembly drawings and pick and place files. An Excel file contains the full BoM including reference designators, manufacturer part number  as well as Digikey part number.

    For your convenience here is a link to DigiKey with a BoM of the whole DMFX-1 platform including main board DMFX-1-1, described in this post, and the daughter board (DMFX-1-2 with LCD and navigator buttons). You'd better verify BoM completion, lead-times and obsolescent components beforehand.

    With all this information you can build your own DMFX-1 platform and develop your own Digital effects!!

    Thursday, 23 July 2015

    Rezz-Fuzz 3 in 1: RAT + βr + Octaver

    For this guitar pedal project I wanted to mix some of my most iconic distortion effects into a single one:

    1. Turbo-RAT is the distortion that was used by one of my favourite 90s bands: Teenage Fanclub
    2. βr (Beta or hFE reverse) is a technique used on the Fuzz War pedal by DeathByAudio, designed by Oliver Ackermann, singer and guitarrist of one of my favourite 2000s bands: A Place to Bury Strangers
    3. Octave Up was kind of a wink to noisy fuzz pedals like the Shin-Ei Fuzz used by Jesus & Mary Chain, one of my favourite bands of 80s, 90s that adds a doubler to increase high frecuency harmonics.
    Gerard Love, TFC bassist, showing a Turbo RAT pedal (picture from Bandwagonesque album vinyl jacket)
    Oliver Ackermann from A Place to Bury Strangers showing a Fuzz War pedal
    Shin-Ei Fuzz Wah pedal

    William Reid "pedalboard" (Fuzz-Wah on the right)
    So the Rezz-Fuzz 3 in 1 pedal basically had to be a:

    RAT + βr + Octave Up

    Apart from that, I wanted to experiment with different type of diodes for the hard clipping section of the RAT distortion part.
    The main issue was that mixing both pedals into one would require too many knobs: 3 for the RAT, 3 for the Fuzz War, plus one for the octave up, plus at least 2 switch buttons: one for clipping diode selection and at least one for effect switching, that is far too many controls for a single pedal to be packed in a 1590BB box.

    Some simplification had to be made, the first one was to remove tone control on the RAT and replace it by octave up control. But since only one effect is used at a time, it would be good to reuse the same knobs for both effects. The solution was to use analog SPDT switches for two potentiometers on each of the 3 potentiometer contacts, plus another 2 SPDT switches for effect input and output selection. A 4053 device includes 3 SPDT switches, 3 of them were required.


    These are the schematics of the Rezz-Fuzz 3 in 1 effect in Eagle CAD:

    On the top it's the βr or reverse hfe part of the circuit consisting of 7 transistor stages. At first sight there seems to be a big mistake on this circuit: Those NPN transistors seem to be inverted, but they are actually not, collector and emitter are inverted on purpose, actually base-emitter and base-collector both consist of a PN junction and they could be inverted, except that the gain of the resultant inverted transistor is what is called the βr (or hfe reverse) which usually is much lower than the direct gain. Here is an article from AMZ website that explains the characteristics of  reverse beta amplifiers, apparently the clipping on a reversed transistor is quite different from a regular transistor generating different harmonics. The reason for having 7 transistors is because the gain on reverse beta transistors is much lower.

    The problem with this is that actually the reverse hfe on most transistors is not specified, is not part of the manufacturing control process, and hence it may have wide variations. So the only choice here is manual selection after gain measurement with a multimeter able to measure hfe. On the other hand, this add a uniqueness to each pedal, and maybe the need to manually adjust resistors for each manufactured effect. The other issue is that I am not sure that Spice models can actually simulate the real behavior of transistor in reverse configuration. For this reason I will not include LTSpice simulations of the circuit.
    I had to manually adjust the resistor values to make this circuit work, the final resistor values were very different from schematics published on internet. The recommended transistor base pull-ups were 430K on the first 5 stages and 910K on the last two stages, I had to change the value to 820K on the first 5 stages to properly bias the circuit and make it work. The recommended transistor emitter pull-downs were 390 ohms, I changed the values to 270 ohms. The recommended transistor collector pull-ups were 100K on the first 6 stages and 180K on the last 2 stages, I had to change the values to 1.2K in all stages in order to make it work.

    In the middle of the schematics page, there are three 4053D 3-SPDT analog switch devices, the one on the left only uses two SPDT switches to select the input and the output of the selected effect (RAT or βr), the other two switch devices connect the three potentiomenter terminals to the desired effect. The switch device at the center is used to select the gain (RAT or βr) and the switch device on the right side of the page is used to select distortion/octave up mix for the RAT or tone for the βr effect.

    At the bottom of the page it's the RAT effect with input and output buffer, soft clipping amplifier (that uses unbalanced diode clipping, R42 resistor is not installed) on top and octave-up on the bottom. Octave-up amplifier uses the feedback voltages between the feedback diodes and resistors to build a fully rectified version of the distorted signal.

    The mix of soft-clipped signal and octave-up goes through a hard-clipping section where three options can be chosen: hard clipping with germanium diodes, no clipping or hard clipping with LED diodes.

    On the bottom left side of the page it's the +9V DC input jack connector, battery terminals, an EMI filter, resistor divider to generate mid point voltage of +4.5V, decoupling capacitors and inversion protection diode.

    On the top right side there is a 6-pin 0.1'' header footprint to solder a flat cable between the effect PCB and the 3PDT push-button foot switch PCB. A small PCB was designed in order to directly connect the foot switch and the PCB with a 0.1'' pitch flat cable.

    PCB layout

    The PCB was made on two layers with dimensions of 85 mm x 75 mm with chamfered corners to leave place for box screw holes. Three footswitch PCBs were also added.
    PCB top layer

    PCB bottom layer
    The finished pedal with a Turbo RAT look:
    Rezz Fuzz 3 in 1: RAT + βr + Octaver

    Source files

    If you want to build your own RezzFuzz 3-in-1 pedal find Eagle 6.3.0 files (schematics, PCB, gerbers, BoM) on this github repository.

    Wednesday, 1 July 2015

    DMFX-1: Open Source Digital Multi-Effects guitar pedal (1)

    Rezzonics© presents the most compact digital multi-effects guitar pedal, completely open source, giving you the opportunity to create your own stereo effects or use a huge range of pre-programmed effects.

    Every analog or digital effect your guitar needs in one compact format. The best of both worlds: ANALOG for overdrive, distortion, fuzz, octave-up, DIGITAL for echo, delay, chorus, tremolo, phaser, flanger... and many others you can imagine: looper, pitch shift, reverb, leslie...

    DMFX-1 main features:
    • TI C55x 16-bit fixed point DSP, providing quality, low power and low cost
    • Dual DSP for low latency, real time signal processing and fully independent Audio and Control processing.
    • Up to two SD/MMC cards for Software and audio data storage
    • One graphical LCD 128x32 pixels Blue with White LED backlight for better visibility
    • Up to 5 configurable LEDs
    • One 5-button display navigator for seamless effect configuration
    • Up to five digitally controlled and configurable potentiometers
    • Analog configurable input distortion (overdrive, crunch, vintage, fuzz...)
    • Analog octave-up effect, mixable with distortion
    • Dual Mono L/R Line Output
    • Stereo Headphones output
    • Guitar Mono Line input
    • Analog input / output buffers and filters
    • Standard +9V DC or USB +5V DC power input
    • Up to 2x USB 2.0 ports (Audio, Control) for PC connectivity
    • Optional USB debugging port XDS100v2, TI Code Composer Studio compatible
    • Foot switch input
    • Compact size: 130 mm x 110 mm x 32 mm (W x D x H)
    A stand-alone unit: just plug your guitar, your headphones and configure your desired effect easily via the navigator and LCD menus.

    Stereo effects like reverb or speaker rotating effects like leslie can be emulated thanks to the dual mono and stereo outputs.

    Analog feel can be emulated thanks to five configurable potentiomenters digitally controlled.

    JFET buffer input, low THD distortion, low-voltage, rail-to-rail audio opamps and filters to better adapt guitar signal input and reduce input noise. Exclusive low-cost Schottky diode distortion circuits that emulate germanium clipping diodes.

    Analog support for Tuner and Noise compression.

    One graphical LCD 128x32 pixels Blue with White LED backlight for better visibility in dark places. A 5-buttons navigator (up-down-left-right-OK) allows easy navigation and effect configuration through menus.

    One dedicated audio DSP and one dedicated control DSP provide low latency and real time, while reducing the bill of materials. Control DSP is used for status / commands operations: LCD, buttons and potentiometer control, while Audio DSP is fully dedicated to real time audio effects.

    Up to two USB 2.0 (type Mini-B) interfaces allow pedal connection to a PC, for command / status or audio exchange.

    Up to two SD/MMC cards can be connected to audio DSP for huge program and audio data storage.

    One additional USB (Type-B) interface allows JTAG-Boundary Scan DSP debugging using TI XDS100v2 and Code Composer Studio for implementing your DSP effects.

    Open source libraries will offer free digital effect exchange and improvement.

    Several assembly options for low cost and high performance scalability.

    DMFX-1 is low power, it can be powered by batteries, external +9V DC-DC converter or USB port.

    DMFX-1 is compact: Main board + mezzanine board can be packed on a 148 mm x 100 mm x 24 mm enclosure (W x D x H)

    Compact size: 148 mm x 100 mm x 24 mm (W x D x H)
    3D view of the 2 PCB DMFX-1 guitar pedal (image created with FreeCAD)
    DMFX-1 front view showing connectors

    DMFX-1 rear view showing USB connectors

    DMFX-1 block diagram


    Saturday, 9 May 2015

    Transformerless Negative Ion Generator - Enclosure (3/3)

    The enclosure was made using 10 mm thick plywood, with external dimensions of 160 x 200 x 200 mm (W x H x D)
    Find here below mechanical drawings with dimensions. Front and rear sides are shown in blue. Top and bottom sides in red and left and right sides in green.
    The box consists of a basic frame where left-right sides and top-bottom sides where joined using finger joints 40 mm long 10 mm deep. 3x40 mm fingers on each panel side are joined to 2x40 mm fingers on the adjacent panel. Wood paste was used to cover the
    There is a squared chamfered 75 mm window in the front cover (140 x 130 mm), where the ionizer needle grid will be installed. An aluminum panel 140 x 50 mm and 2 mm thick is used to install 2 potentiometers, one switch and one blue LED.

    The rear cover (180 x 140 mm) has a circular hole Ø90 mm for the fan air exhaust. All sides and corners are filed and rounded to allow covering with red tolex.
    10 mm square wood cleats made out of the same plywood are used to reinforce the corners. they are glued leaving 10 mm distance to the front and rear borders to allow installing the front and rear covers. Only 2 mm are left for the aluminum plate on the front bottom side as shown in the picture below.
    The box front panel as well as the inside has been painted in red. A red tolex has been glued on the top, bottom, left and right sides.
    The PCB fully assembled with front panel, potentiometers, knobs, power-on switch and power-on blue LED. PCB has been connected with wire cables to the AC outlet, fan and ionizer needle grid ready for testing with a digital multimeter.
    The rear panel has been covered with tolex too. The picture below shows the fan installed with a plastic fanguard with filter. A wire frame has been installed in order to place an additional disposable carbon filter.The AC outlet includes a fuse.
    The needle grid is made out of 1 mm thick wire and nails. Four segments of wire where soldered to a square frame of wire. Four nails where soldered to each wire segment for a 16 pins needle grid.

    The picture below shows the front panel  with the needle grid installed as well as the aluminum faceplate with two knobs, power-on swith and power-on blue LED. The left button controls the output voltage of the ionizer, and the right button controls the speed of the fan. There is no risk in touching the needle grid or the screws connected to high voltage because they are protected with high impedance resistors, but an additional plastic cover could be added.