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Audio Measurements

HP Buf improvements – 500 mW into 32 Ω headphones with 0.00015 % THD+N!

by nihtila
written by nihtila

HP Buf headphone amplifier’s already excellent THD+N figures can be pushed extremely low by replacing OPA2134s with LM4562s. This gives huge performance boost:

  • 5-8 dB lower noise floor, depending on gain setting
  • Up to 12 dB better THD+N
  • For example, THD+N at 100 mW into 32 Ω went down from 0.00065 % (-104 dB) to 0.00017 % (-115 dB)
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Modular HP AmpObsolete

HP Buf – High-current buffered amplifier board for HP MoBo

by nihtila
written by nihtila

Amplifier daughterboard for HP MoBo modular headphone amplifier

  • High-power high-performance balanced headphone amplifier daughterboard for HP MoBo
  • Balanced input, balanced output
  • Jumper link for two gain options, default 0/10 dB
  • Jumper link for two output impedance options
  • OPA2134 opamps followed by BUF634 or LME49600 buffers
  • SNR: 113-121 dB A-w depending on the buffer, load, and gain
  • THD+N ratio at 100 mW (LME49600)
    • 300 Ω: 0.0004 % / -108 dB
    • 32 Ω: 0.0007 % / -103 dB
    • 16 Ω: 0.0012 % / -98 dB
  • Max power around 1 W (<0.1 % THD+N)
  • Update: get even higher performance with LM4562 opamps
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Modular HP AmpObsolete

HP TPA – Simple IC amplifier board for HP MoBo

by nihtila
written by nihtila

Amplifier daughterboard for HP MoBo modular headphone amplifier

  • TPA6120A2-based simple-IC headphone amplifier amplifier
  • Balanced input, balanced output
  • Jumper link for extra gain option; default 0/10 dB
  • SNR: 116-122 dB A-w depending on the gain and load combination
  • THD+N ratio at 100 mW
    • 300 Ω: 0.0015 % / -96 dB
    • 32 Ω: 0.006 % / -84 dB
    • 16 Ω: 0.009 % / -81 dB
  • Max power around 0.5 W (16 / 32 Ω)
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Modular HP AmpObsolete

HP MoBo – Modular headphone amplifier motherboard

by nihtila
written by nihtila

Motherboard for modular headphone amplifier system

  • Motherboard with inputs, outputs, power distribution, and signal routing for amplifier daughterboard
  • Balanced input
  • Balanced and unbalanced outputs
  • Output mute circuit
  • Requires separate amplifier board

HP MoBo is the basis of a modular headphone amplifier design. It provides input and output connections and simple power supply components (external power supply required), and connections for stackable amplifier daughterboard.

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H-DACObsolete

Addon H-PreAmp – Preamplifier/headphone amplifier addon for H-DAC

by nihtila
written by nihtila
  • Very high performance preamplifier; measurement results with H-DAC and 2 Vrms output:
    • Dynamic range / SNR: 116 dB (A-weighted)
    • THD+N ratio: -102 dB (2.0 Vrms / 1 kHz, 48 kHz sample rate)
    • Crosstalk at 10 kHz: -113 dB
  • Very high performance headphone amplifier
    • Dynamic range / SNR: 115 dB (A-weighted)
    • Maximum output power / THD+N ratio:
      • 22 mW / -98 dB into 560 ohms
      • 230 mW / -85 dB into 33 ohms
      • More gain can be added for higher output power
  • Software controlled (Arduino compatible)
  • Balanced outputs (XLR) on-board and unbalanced connectors (RCA) on H-DAC board
  • Takes supplies and audio signals directly from H-DAC via pinheaders
  • 10×10 cm 4-layer PCB shaped to fit tall components on H-DAC board; PGA4311 volume control, LM49724 and LM4562 opamps (or any with the same pinouts), TPA6120A2 headphone amplifier, optional THAT1606 balanced drivers

H-PreAmp is an addon board for H-DAC, transforming the fixed-output DAC into a very high quality preamplifier with integrated headphone amplifier. H-DAC and H-PreAmp together provide single-ended (RCA) and balanced (XLR) outputs as well as headphone amplifier.

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