Switching Inputs on the Twisted Pear Audio Buffalo III-SE DAC

One of the neat features of the Buffalo III-SE is that it allows you to have both a SPDIF and I2S source connected and to switch between them using the on-board IP_S pins, thus obviating the need for an OTTO or other external switching mechanism. And if you’re controlling the BIII-SE with an Arduino you only need to use a single (digital) pin to switch between sources. Turns out it’s very easy to implement, but I couldn’t find any guidance on the web.

The following assumes that you have a SPDIF and I2S source connected the BIII-SE (block “1” in the picture below). ALl you need to do is connect a digital pin (I use pin #6) on the Arduino to the pin below the “S” on the IP_S header on the DAC – circled in red in the picture below with a red arrow pointing to it.

B3SE IPS

The code is simple as well.

Put this in your initialization block:

  #define IPSPIN 6 // Or whatever pin you're using
  pinMode(IPSPIN, OUTPUT);
  digitalWrite(IPSPIN, HIGH); //Enable pull-up resistor - default is SPDIF

And then just switch the pin HIGH when you want SPDIF and LOW when you want I2S.

If you’re using the HiFiDuino code, then just swap out the setAndPrintInputFormat function for this one:

void setAndPrintInputFormat(byte value){
  // This register also controls mono-8channel operation, thus more code...
  lcd.setCursor(8,0);
  switch(value){
  case 0:                            // Enable SPDIF for DATA 1 pin
    writeSabreReg(0x08,0xE8);        // Reg 8: Enable SPDIF input format
    bitSet(reg17L,3);                // Reg 17: auto spdif detection ON -Set bit 3
    writeSabreLeftReg(0x11,reg17L);  // Reg 17: write value into register
#ifdef DUALMONO
    bitSet(reg17R,3);                // Reg 17: auto spdif detection ON -Set bit 3
    writeSabreRightReg(0x11,reg17R); // Reg 17: write value into register
#endif DUALMONO
    writeSabreReg(0x12,0x01);        // Set SPDIF to input #1 (only input valid for BII is 1 and 5)
    spdifIn=true;                    // Indicates input format is spdif. 
    lcd.print("SPd");
    break;
  case 1:                            // Enable SPDIF for DATA 3 pin (For BIII use)
    writeSabreReg(0x08,0xE8);        // Reg 8: Enable SPDIF input format
    bitSet(reg17L,3);                // Reg 17: auto spdif detection ON -Set bit 3
    writeSabreLeftReg(0x11,reg17L);  // Reg 17: write value into register
#ifdef DUALMONO
    bitSet(reg17R,3);                // Reg 17: auto spdif detection ON -Set bit 3
    writeSabreRightReg(0x11,reg17R); // Reg 17: write value into register
#endif DUALMONO
    writeSabreReg(0x12,0x02);        // Set SPDIF to input #3 
    spdifIn=true;                    // Indicates input format is spdif.
    lcd.print("Sp3");
    break;
  case 2:                            // Enable SPDIF for DATA 7 pin (For BIII use)
    writeSabreReg(0x08,0xE8);        // Reg 8: Enable SPDIF input format
    bitSet(reg17L,3);                // Reg 17: auto spdif detection ON -Set bit 3
    writeSabreLeftReg(0x11,reg17L);  // Reg 17: write value into register
#ifdef DUALMONO
    bitSet(reg17R,3);                // Reg 17: auto spdif detection ON -Set bit 3
    writeSabreRightReg(0x11,reg17R); // Reg 17: write value into register
#endif DUALMONO
    writeSabreReg(0x12,0x40);        // Set SPDIF to input #7 
    spdifIn=true;                    // Indicates input format is spdif.
    lcd.print("Sp7");
    break; 
  case 3:                            // Enable SPDIF for DATA 7 pin (For BIII use)
    writeSabreReg(0x08,0xE8);        // Reg 8: Enable SPDIF input format
    bitSet(reg17L,3);                // Reg 17: auto spdif detection ON -Set bit 3
    writeSabreLeftReg(0x11,reg17L);  // Reg 17: write value into register
#ifdef DUALMONO
    bitSet(reg17R,3);                // Reg 17: auto spdif detection ON -Set bit 3
    writeSabreRightReg(0x11,reg17R); // Reg 17: write value into register
#endif DUALMONO
    writeSabreReg(0x12,0x80);        // Set SPDIF to input #7 
    spdifIn=true;                    // Indicates input format is spdif.
    lcd.print("Sp8");
    break;
    
  case 4:                            // I2S 32 bit
    bitClear(reg17L,3);              // Reg 17: manual SPDIF -Clear bit 3
    writeSabreLeftReg(0x11,reg17L);  // Reg 17: Auto spdif detection OFF
#ifdef DUALMONO
    bitClear(reg17R,3);              // Reg 17: manual SPDIF -Clear bit 3
    writeSabreRightReg(0x11,reg17R); // Reg 17: Auto spdif detection OFF
#endif DUALMONO
    writeSabreReg(0x08,0x68);        // Reg 8: Enable I2S/DSD input format
    spdifIn=false;                   // Set variable to indicate input format is I2S/DSD mode
    bitClear(reg10,4);               // Setting to I2S (2 bits required)
    bitClear(reg10,5);
    bitSet(reg10,6);                 // Setting to 32 bit (2 bits required)
    bitSet(reg10,7);
    writeSabreReg(0x0A,reg10);
    lcd.print("I2S");
    break;
  case 5:                            // LJ 32 bit
    bitClear(reg17L,3);              // Reg 17: manual SPDIF -Clear bit 3
    writeSabreLeftReg(0x11,reg17L);  // Reg 17: Auto spdif detection OFF
#ifdef DUALMONO
    bitClear(reg17R,3);              // Reg 17: manual SPDIF -Clear bit 3
    writeSabreRightReg(0x11,reg17R); // Reg 17: Auto spdif detection OFF
#endif DUALMONO
    writeSabreReg(0x08,0x68);        // Reg 8: Enable I2S/DSD input format
    spdifIn=false;                   // Set variable to indicate input format is I2S/DSD mode
    bitSet(reg10,4);                 // Set to LJ
    bitClear(reg10,5);
    bitSet(reg10,6);                 // Set to 32 bit
    bitSet(reg10,7);
    writeSabreReg(0x0A,reg10);
    lcd.print("LJF");
    break;
  case 6:                            // RJ 32 bit
    bitClear(reg17L,3);              // Reg 17: manual SPDIF -Clear bit 3
    writeSabreLeftReg(0x11,reg17L);  // Reg 17: Auto spdif detection OFF
#ifdef DUALMONO
    bitClear(reg17R,3);              // Reg 17: manual SPDIF -Clear bit 3
    writeSabreRightReg(0x11,reg17R); // Reg 17: Auto spdif detection OFF
#endif DUALMONO
    writeSabreReg(0x08,0x68);        // Reg 8: Enable I2S/DSD input format
    spdifIn=false;                   // Set variable to indicate input format is I2S/DSD mode
    bitSet(reg10,5);                 // Set to right justified format
    bitClear(reg10,4);
    bitSet(reg10,6);                 // Set to 32 bit
    bitSet(reg10,7);
    writeSabreReg(0x0A,reg10);
    lcd.print("R32");
    break;
  case 7:                            // LRJ 24 bit
    bitClear(reg17L,3);              // Reg 17: manual SPDIF -Clear bit 3
    writeSabreLeftReg(0x11,reg17L);  // Reg 17: Auto spdif detection OFF
#ifdef DUALMONO
    bitClear(reg17R,3);              // Reg 17: manual SPDIF -Clear bit 3
    writeSabreRightReg(0x11,reg17R); // Reg 17: Auto spdif detection OFF
#endif DUALMONO
    writeSabreReg(0x08,0x68);        // Reg 8: Enable I2S/DSD input format
    spdifIn=false;                   // Set variable to indicate input format is I2S/DSD mode
    bitSet(reg10,5);                 // Set to right justified format
    bitClear(reg10,4);
    bitClear(reg10,6);               // Set to 24 bits mode
    bitClear(reg10,7);
    writeSabreReg(0x0A,reg10);
    lcd.print("R24");
    break;
  case 8:                            // LRJ 24 bit
    bitClear(reg17L,3);              // Reg 17: manual SPDIF -Clear bit 3
    writeSabreLeftReg(0x11,reg17L);  // Reg 17: Auto spdif detection OFF
#ifdef DUALMONO
    bitClear(reg17R,3);              // Reg 17: manual SPDIF -Clear bit 3
    writeSabreRightReg(0x11,reg17R); // Reg 17: Auto spdif detection OFF
#endif DUALMONO
    writeSabreReg(0x08,0x68);        // Reg 8: Enable I2S/DSD input format
    spdifIn=false;                   // Set variable to indicate input format is I2S/DSD mode
    bitSet(reg10,5);                 // Set to right justified format
    bitClear(reg10,4);
    bitSet(reg10,6);                 // Set to 20 bits mode
    bitClear(reg10,7);
    writeSabreReg(0x0A,reg10);
    lcd.print("R20");
    break; 
  case 9:                            // LRJ 16 bit
    bitClear(reg17L,3);              // Reg 17: manual SPDIF -Clear bit 3
    writeSabreLeftReg(0x11,reg17L);  // Reg 17: Auto spdif detection OFF
#ifdef DUALMONO
    bitClear(reg17R,3);              // Reg 17: manual SPDIF -Clear bit 3
    writeSabreRightReg(0x11,reg17R); // Reg 17: Auto spdif detection OFF
#endif DUALMONO
    writeSabreReg(0x08,0x68);        // Reg 8: Enable I2S/DSD input format
    spdifIn=false;                   // Set variable to indicate input format is I2S/DSD mode
    bitSet(reg10,5);                 // Set to right justified mode
    bitClear(reg10,4);
    bitClear(reg10,6);               // Set to 16 bit mode
    bitSet(reg10,7);
    writeSabreReg(0x0A,reg10);
    lcd.print("R16");
    break;   


    // lcd.write(127);                    // Print Arrow to indicate this is input seletion and not signal
  }

  if (spdifIn) { //If we're expecting SPDIF input, we want to pull IPS high on the DAC 
    digitalWrite(IPSPIN, HIGH); 
  } 
  else { //If we're not expecting SPDIF, pull IPS low
    digitalWrite(IPSPIN, LOW);
  }
}

Thanks to LeonvB and the folks at TPA for talking me through the process.

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3 thoughts on “Switching Inputs on the Twisted Pear Audio Buffalo III-SE DAC

  1. Hi.
    I jut tried to upload your code but with no success 😦
    Every time I tried to upload this code:
    #define IPSPIN 6 // Or whatever pin you’re using
    pinMode(IPSPIN, OUTPUT);
    digitalWrite(IPSPIN, HIGH); //Enable pull-up resistor – default is SPDIF
    to Arduino I get this error:
    b11dnew:396: error: expected constructor, destructor, or type conversion before ‘(‘ token
    b11dnew:397: error: expected constructor, destructor, or type conversion before ‘(‘ token

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