Universal Purifi Input Buffer

This input buffer is designed for the following Purifi and Hypex Class D amplifier modules: 1ET400A, 1ET6525SA, 1ET7040SA, 1ET9040BA, and NC500.

Key advantages:

• Fully differential output for full power, even with a single-ended source.
• Controlled common-mode voltage to prevent power supply bus pumping.
• Four independent ultra low-noise voltage regulators for analog and digital power.

Get the best performance from your Purifi and Hypex modules with this input buffer.

Technical Documentation

Data SheetDesign Documentation

• Description
• Specifications
• Circuit Topology

• The buffer is a single-channel (mono) buffer, with the following features:
  

  • Differential (balanced, XLR) input, which can easily be configured for single-ended (unbalanced, RCA) operation.
    
  • Fully differential output even when used with a single-ended source. 
    
  • Common-mode feedback ensures zero common-mode output voltage to avoid power supply bus pumping.
  • Jumper-selectable gain: 11.6 dB, 13.0 dB, and 13.2 dB for a total amplifier gain of 26.0 dB when used with the Purifi Class D modules. 
  • Gain can be further customized by adding a resistor (1206 size SMD and leaded/PTH supported) or set to unity gain (0 dB).
  • Plug-and-play connection with Hypex SMPS1200 power supply.
  • Four ultra low-noise voltage regulators power the analog and digital circuits of the Buffer and the amplifier module. Optionally, you can add the Hypex HPR/HNR regulators.
  • Speaker output is provided on 6.3 × 0.81 mm quick-connect spades and a terminal block accepting up to AWG 10 (5.2 mm²) in size.

  In addition, the following options are provided for advanced users:

  • By adding a resistor and a 7-pin connector, the amplifier module can be operated in software mode. See the relevant amplifier module data sheet for details. 
  • The buffer can be disabled by removing two resistors. A 3-pin connector footprint provides direct access to the input of the amplifier module.
    

  The Universal Purifi Input Buffer circuit board is fully assembled, RoHS compliant, and is designed and manufactured in Canada.

  

• The full specifications for the Universal Purifi Input Buffer are tabulated below.

  Parameter	Value	Notes
  Quiescent Power Supply Current	20 mA 27 mA	Nominal Maximum
  Maximum Power Supply Current	47 mA	Zload = 1.5 kΩ, +25 dBu
  THD	-140 dBc (0.00001 %)	1 kHz, Vin = 2.0 V RMS
  THD	-130 dBc (0.00003 %)	20 kHz, Vin = 2.0 V RMS
  THD+N	< -120 dB (< 0.0001 %)	1 kHz, Vin = 2.0 V RMS
  THD+N	< -120 dB (< 0.0001 %)	1 kHz, Vout = 9.6 V RMS
  IMD: SMPTE 60 Hz + 7 kHz @ 4:1	-112 dB	Vin = 2.0 V RMS
  IMD: DFD 18 kHz + 19 kHz @ 1:1	-122 dB	Vin = 2.0 V RMS
  Multi-Tone IMD Residual	< -148 dB Ref.: 7.6 V RMS	AP 32-tone, Vin = 2.0 V RMS
  Gain	0 dB (1.00×) 11.6 dB (3.80×) 13.0 dB (4.47×) 13.2 dB (4.57×)	Can be further customized by resistor option.
  Gain Flatness	±0.007 dB	20 Hz - 20 kHz
  Bandwidth	DC – 900 kHz	100 mV RMS, -3 dB
  Slew Rate	±21 V/µs	Fully symmetric
  Common-Mode Rejection Ratio (CMRR)	≥ 80 dB	20 Hz - 20 kHz, typical
  Total Integrated Noise and Residual Mains Hum	2.5 µV RMS (11.6 dB) 1.5 µV RMS (0 dB)	20 Hz - 20 kHz, A-weighted
  Total Integrated Noise and Residual Mains Hum	3.1 µV RMS (11.6 dB) 1.9 µV RMS (0 dB)	20 Hz - 20 kHz, Unweighted
  Dynamic Range (AES17)	132 dB	Vin = 8 V RMS
  Input Impedance	48 kΩ
  Module dimensions and weight	64 × 84 × 28 mm 45 g	(W × D × H)

  All parameters are measured at an auxiliary power supply voltage of ±20 V, 1.5 kΩ differential load impedance, differential input, and 11.6 dB gain unless otherwise noted.

  The specifications were measured on the prototype and should be considered the typical performonce the Universal Purifi Input Buffer. The specifications should not be considered a guarantee and may be changed at any time without notice.

  Sound Quality

  I designed the Universal Purifi Input Buffer to be sonically transparent and firmly believe I have achieved that goal. I generally prefer precise amplifiers as they render the source material naturally, without any colouration, and offer a spacious and realistic sound stage. This aligns well with the design philosophy of Purifi and Hypex as well.

• A simplified block diagram of the Universal Purifi Input Buffer is shown below.