Block diagram of the HEADPHONE-OPAMPLFR board
The Sefirot architecture includes the following boards, all available in this webstore:
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Super Balanced Input (SUPER-BNCD-INPT)
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Baxandall Volume Control (BAX-VOL-CTRL)
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Headphone Amplifier Stage (HEADPHONE-OPAMPLFR)
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Bandwidth Definition & Subbass Low-Pass Filter (BWLP-FLTR-MONO)
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Summing Amplifier Module ( SUMMING-AMP-L+R)
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LLLL-INDICATOR Log-Law LED Level System (LLLL-INDICATOR)
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Power Supply Module (PAMP-PSU)
The HEADPHONE-OPAMPLFR board offers a passive volume control for each input channel, offering an operational range from -20 to 0 dB. Following the buffer/amplifier stage, there is the power stage, consisting of a set of operational amplifiers connected in parallel. This configuration is designed to achieve an analog sound characterized by minimal noise and THD (Total Harmonic Distortion).
The final stage in the signal path of this headphone amplifier board involves a Zobel network connected to the output of each channel. This network serves to stabilize the impedance of the headphone speaker load at high frequencies. The design of this board draws inspiration from Douglas Self’s 5532 OpAmplifier, as detailed in an article published in Elektor magazine.
The following are the main features of the HEADPHONE-OPAMPLFR board:
- Input volume control: -20 to 0dB.
- Unity gain and optional user programable gain.
- Output Zobel network for each channel
- DC servo for output offset correction
- THD+N:00006% at 1 kHz and 0.0001% at 10 kHz driving a 600 Ω load. Output voltage: 0.138 Vrms (0.032 mW for a headset with 100 dB/mW sensitivity, equating to a safe volume of 85 dB SPL for long periods).
- THD+N:00002% at 1 kHz and 0.00006% at 10 kHz driving a 600 Ω load. Output voltage: 0.775 Vrms (1 mW for a headset with 100 dB/mW sensitivity, equating to a maximum safe volume of 100 dB SPL).
- THD+N:000023% at 1 kHz and 0.00009% at 10 kHz driving a 16 Ω load. Output voltage: 0.18 Vrms (1 mW for a headset with 100 dB/mW sensitivity, equating to a maximum safe volume of 100 dB SPL).
- Crosstalk: < -94 dBV @ 1 kHz
- Bandwidth: > 2 MHZ configured as unity gain.
- Frequency response: -0.05 dB at 20 Hz and -0.16 dB at 20 kHz.
- High-quality double-sided plated-through-hole PCB (Lead-free HASL) with solder mask on both sides and full screen print.
- Input impedance > 10 kΩ or > 3 kΩ if using a 4.7k resistor in parallel with volume control pot.
- Output impedance < 1Ω unless you are using the 120 Ω standard.
- Total Current consumption: 132 mA Max @ 1 mW output for both channels.
- PCB size: length=100mm, width=70 mm. It incorporates four M3 fixing holes.
A couple of interconnection diagrams to build a preamplifier using different boards designed by Olas Audio are displayed below.
Interconnection between different Olas Audio boards to build a preamplifier with two separate Low pass/Bandwidth Definition filters
Interconnection between different Olas Audio boards to build a preamplifier with one Summing Amplifier and a Low pass/Bandwidth Definition filter
The published price is for the PCB only. A bill of materials and assembly instructions will be provided upon purchase.
