I am kind of a music/recording guy and I'm interested in building my own multichannel (4 or more) ADC. I've looked online and I found a hackaday post of a high end stereo DAC, but not much about ADCs, let alone multichannel ones.

I was hoping there's a single USB chipset with more than 2 analog inputs but I wasn't able to find one. All chipsets with builtin ADCs feature 2 inputs at most. I looked up some internal photos of professional equipment and all of them use separate ADC chips and USB chips.

After some googling I came to the conclusion that the only viable chips for multichannel ADCs are those from Cirrus Logic (considering CS5368), which are priced around 18$ per chip for an 8 channel one. Then I still need to find a USB interface chip. The ADCs are also controlled (or programmed, I don't know) through I2C or SPI which makes life more difficult.

I have no idea how to approach this.

Does anyone have any experience or advice with this kind of thing?

So I was browsing loneoceans.com and noticed that some schematics for SSTC bridges had diodes across the gate resistor to make the gate discharge faster.


I've built a variant of the KaizerSSTC3 and I was wondering if I could add these diodes, (1N5819) to decrease switching times. I'm worried that while this would decrease switching-off time it will increase switching-on time because of the load it puts on the gate driver. This would in turn cause a decrease in efficiency in the MOSFETs and increase heat production. Is this correct?

Can someone shed some light on my theory and perhaps give me a recommendation?

Has anyone ever built a solid state coil with gallium nitride transistors? I would assume that using more efficient transistors would reduce the need for cooling and risk of damaging them.

I've looked at a company that makes them called Transphorm and their FETs are only about 3x as expensive as regular silicon FETs for the same current rating (compared to IRFP460), at a slightly higher voltage. What's interesting is that they can cram a lot of current capability into small packages because of the high efficiency.

Let me know what you think.

Tested the bridge at 30V
It produces a small amount of breakout but it's a comfortable sound level.

For some reason I can't compile this code for Arduino.
#include <MIDI.h>

#define samplingRate 62500
#define maxPlayingNotes 2

MIDI_CREATE_DEFAULT_INSTANCE();

float midiFrequency(float note){
  return 440*(pow(2, (note-69)/12));
}

typedef struct {
    byte pitch;
    int onTime;
    int offTime;
    int hasBeenOn;
} Note;

Note getNoteTimes(byte pitch, float dutyCycle){
  float period = samplingRate/midiFrequency(pitch);
  Note finalNote = {pitch, round(dutyCycle*period), round((1-dutyCycle)*period), 0};
  return finalNote;
}

volatile Note playingNotes[maxPlayingNotes];



void handleNoteOn(byte channel, byte pitch, byte velocity){
    for(int i = 0; i < maxPlayingNotes; i++){
        if(playingNotes[i].onTime == 0){ // 0 onTime means this note isn't in use
            playingNotes[i] = getNoteTimes(pitch, 0.1);
            break;
        }
    }
    digitalWrite(13, HIGH);
}

void handleNoteOff(byte channel, byte pitch, byte velocity){
    for(int i = 0; i < maxPlayingNotes; i++){
        if(playingNotes[i].pitch == pitch){
            playingNotes[i] = {0,0,0,0}; // 0 onTime means it doesn't play
        }
    }
    digitalWrite(13, LOW);
}

//void handlePitchBend(byte channel, int bend){
//  float bendfactor = (1+ (float) bend/8190);
//  float dutyCycle = 0.1;
//  for(int i = 0; i < maxPlayingNotes; i++){
//      if(playingNotes[i].onTime == 0) continue;
//      float period = samplingRate/(bendfactor * midiNotes[playingNotes[i].pitch]);
//      playingNotes[i].onTime = round(dutyCycle*period);
//      playingNotes[i].offTime = round((1-dutyCycle)*period);
//  }
//}






void setup(){
    for(int i = 0; i<(sizeof(playingNotes)/sizeof(playingNotes[0])); i++){
        playingNotes[i] = {0,0,0,0};
    }
//  playingNotes[0] = getNoteTimes(261.6, 0.1);
//  playingNotes[1] = getNoteTimes(329.6, 0.1);
//  playingNotes[2] = getNoteTimes(392.0, 0.1);
    pinMode(9, OUTPUT);
    pinMode(13, OUTPUT);

  cli(); //stop interrupts
//  TCCR2A = 0; // set Timer/Counter Control Registers (TCCR2A/B) to 0
  TCCR2B = 0;
 
  OCR2A = 0; // = 16000000 / (freq*prescaler) - 1 (must be <256)
  // turn on CTC mode
  TCCR2A |= (1 << WGM21);
  // Set CS01 and CS00 bits for 64 prescaler
  TCCR2B |= (1 << CS20);
  // enable timer compare interrupt
  TIMSK2 |= (1 << OCIE2A);
  sei(); //allow interrupts


  MIDI.setHandleNoteOn(handleNoteOn);
  MIDI.setHandleNoteOff(handleNoteOff);
//  MIDI.setHandlePitchBend(handlePitchBend);
  MIDI.begin(MIDI_CHANNEL_OMNI);
}

void loop(){
    MIDI.read();
}

volatile bool shouldPlay;
ISR(TIMER2_COMPA_vect){

  shouldPlay = false;
 
  for(int i = 0; i < maxPlayingNotes; i++){
    if(playingNotes[i].onTime == 0) continue;
    playingNotes[i].hasBeenOn++;
    if(playingNotes[i].hasBeenOn > playingNotes[i].onTime){
        playingNotes[i].hasBeenOn = -playingNotes[i].offTime;
    }
    if(playingNotes[i].hasBeenOn >= 0){
        shouldPlay = true;
    }
  }

  if(shouldPlay){
    PORTB |= 1 << 1;
  }else{
    PORTB &= ~(1 << 1);
  }





 
//  byte ^= 1 << bit_to_flip;
//  byte &= ~(1 << bit_to_clear);
//  byte |= 1 << bit_to_set;
}

polyphonic_midi_interrupter_pitchbend:19:1: error: 'Note' does not name a type; did you mean 'tone'?
 Note getNoteTimes(byte pitch, float dutyCycle){
 ^~~~
 tone
exit status 1
'Note' does not name a type; did you mean 'tone'?

#include <MIDI.h>

#define samplingRate 62500
#define maxPlayingNotes 2

MIDI_CREATE_DEFAULT_INSTANCE();

float midiNotes[] = {8.18, 8.66, 9.18, 9.72, 10.3, 10.91, 11.56, 12.25, 12.98, 13.75, 14.57, 15.43, 16.35, 17.32, 18.35, 19.45, 20.6, 21.83, 23.12, 24.5, 25.96, 27.5, 29.14, 30.87, 32.7, 34.65, 36.71, 38.89, 41.2, 43.65, 46.25, 49, 51.91, 55, 58.27, 61.74, 65.41, 69.3, 73.42, 77.78, 82.41, 87.31, 92.5, 98, 103.83, 110, 116.54, 123.47, 130.81, 138.59, 146.83, 155.56, 164.81, 174.61, 185, 196, 207.65, 220, 233.08, 246.94, 261.63, 277.18, 293.66, 311.13, 329.63, 349.23, 369.99, 392, 415.3, 440, 466.16, 493.88, 523.25, 554.37, 587.33, 622.25, 659.26, 698.46, 739.99, 783.99, 830.61, 880, 932.33, 987.77, 1046.5, 1108.73, 1174.66, 1244.51, 1318.51, 1396.91, 1479.98, 1567.98, 1661.22, 1760, 1864.66, 1975.53, 2093, 2217.46, 2349.32, 2489.02, 2637.02, 2793.83, 2959.96, 3135.96, 3322.44, 3520, 3729.31, 3951.07, 4186.01, 4434.92, 4698.64, 4978.03, 5274.04, 5587.65, 5919.91, 6271.93, 6644.88, 7040, 7458.62, 7902.13, 8372.02, 8869.84, 9397.27, 9956.06, 10548.08, 11175.3, 11839.82, 12543.85};

typedef struct {
    byte pitch;
    int onTime;
    int offTime;
    int hasBeenOn;
} Note;

Note getNoteTimes(byte pitch, float dutyCycle){
  float period = samplingRate/midiNotes[pitch];
  Note finalNote = {pitch, round(dutyCycle*period), round((1-dutyCycle)*period), 0};
  return finalNote;
}

volatile Note playingNotes[maxPlayingNotes];


void handleNoteOn(byte channel, byte pitch, byte velocity){
    for(int i = 0; i < maxPlayingNotes; i++){
        if(playingNotes[i].onTime == 0){ // 0 onTime means this note isn't in use
            playingNotes[i] = getNoteTimes(pitch, 0.1);
            break;
        }
    }
    digitalWrite(13, HIGH);
}

void handleNoteOff(byte channel, byte pitch, byte velocity){
    for(int i = 0; i < maxPlayingNotes; i++){
        if(playingNotes[i].pitch == pitch){
            playingNotes[i] = {0,0,0,0}; // 0 onTime means it doesn't play
        }
    }
    digitalWrite(13, LOW);
}

void handlePitchBend(byte channel, int bend){
  float bendfactor = (1+ (float) bend/8190);
  float dutyCycle = 0.1;
  for(int i = 0; i < maxPlayingNotes; i++){
      if(playingNotes[i].onTime == 0) continue;
      float period = samplingRate/(bendfactor * midiNotes[playingNotes[i].pitch]);
      playingNotes[i].onTime = round(dutyCycle*period);
      playingNotes[i].offTime = round((1-dutyCycle)*period);
  }
}




void setup(){
    for(int i = 0; i<(sizeof(playingNotes)/sizeof(playingNotes[0])); i++){
        playingNotes[i] = {0,0,0,0};
    }

    pinMode(9, OUTPUT);
    pinMode(13, OUTPUT);

  cli(); //stop interrupts
  // set Timer/Counter Control Register to 0
  TCCR2B = 0;
 
  OCR2A = 0; // = 16000000 / (freq*prescaler) - 1 (must be <256)
  // turn on CTC mode
  TCCR2A |= (1 << WGM21);
  // Set CS01 and CS00 bits for 64 prescaler
  TCCR2B |= (1 << CS20);
  // enable timer compare interrupt
  TIMSK2 |= (1 << OCIE2A);
  sei(); //allow interrupts


  MIDI.setHandleNoteOn(handleNoteOn);
  MIDI.setHandleNoteOff(handleNoteOff);
  MIDI.setHandlePitchBend(handlePitchBend);
  MIDI.begin(MIDI_CHANNEL_OMNI);
}

void loop(){
    MIDI.read();
}

volatile bool shouldPlay;
ISR(TIMER2_COMPA_vect){

  shouldPlay = false;
 
  for(int i = 0; i < maxPlayingNotes; i++){
    if(playingNotes[i].onTime == 0) continue;
    playingNotes[i].hasBeenOn++;
    if(playingNotes[i].hasBeenOn > playingNotes[i].onTime){
      playingNotes[i].hasBeenOn = -playingNotes[i].offTime;
    }
    if(playingNotes[i].hasBeenOn >= 0){
        shouldPlay = true;
    }
  }

  if(shouldPlay){
    PORTB |= 1 << 1;
  }else{
    PORTB &= ~(1 << 1);
  }

}

Currently it can only play 2 notes at the same time or else it gets stuck unable to receiver MIDI commands to turn off. I'm nut sure why but I'm guessing because the lack of CPU time to process Serial data because of interrupts.

Is anyone interested in creating a discord server for the forum?

I assume the color has some sort of meaning. Videos on youtube suggest to avoid the light green ones. One person also said to avoid ones from computer power supplies, but that's the only source I can find for them really. So which one from the pic should I pick?

Is it a stupid idea to fill the inside of the secondary with polyurethane spray foam to prevent arcing?