Build of Ultra-Low Noise Balanced Dual-Mono Class A Preamp
Budget: $250 – $750 USD
Project Description:
I am seeking an audio electronics builder/designer to build a sample fully discrete, dual-mono,
balanced line-level preamplifier, using AMB β22 ready made PCBs sourced from AMB, as
well as all other components required. All components and information required for the build is
available on their website below:
https://www.amb.org/audio/beta22/
Different alternatives are offered to complement this amplification PCB. We require the highestend alternative suggestions available on the website.
Stage 1: Compilation of required components and cost including a brief description of the main
constituents as well block diagram. All electronic components must be sourced from reputable
distributors such as Mouser, Digikey, RS, Partsconnexion and/or part distributors designated
manufacturers to avoid counterfeits. Chinese generic components are not accepted.
Transistors that need matching are to be ordered in excess for matching by the freelancer.
Stage 2: Execution, testing, and shipping the preamplifier.
Sample Performance Specifications:
Parameter Value
THD+N (1 kHz, 2 Vrms out) ≤ 0.0005 % (–106 dB)
THD+N (20 Hz–20 kHz) ≤ 0.001 % (–100 dB) across band
Noise Floor (A-weighted) ≤ –125 dBV (goal: –130 dBV)
Crosstalk / Channel Separation ≥ 100 dB @ 1 kHz, goal: ≥ 110 dB
SNR (unweighted) ≥ 120 dB
Frequency Response 10 Hz – 100 kHz (±0.1 dB)
Output Impedance ≤ 10 Ω (balanced), preferably 5 Ω
CMRR (Common Mode Rejection) ≥ 85–90 dB up to 20 kHz
Design Notes / Tips for Achieving These Specs:
● Dual-mono construction is required:
➤ Separate signal boards per channel
➤ Dedicated transformers for L & R channels
➤ Separate power regulation per channel (σ22 or equivalent)
● Shielded, low-noise linear PSU with toroidal transformers and proper ground
referencing
● Star grounding and isolated signal/power grounds
● Use of premium matched resistors (e.g. Vishay RN60) and low-ESR capacitors (e.g.
Elna Silmic II, Nichicon KG)
● Signal path wiring kept minimal and symmetrical, with twisted pairs or shielded
cables
● PCB layout should follow symmetrical dual-differential topology.
● Input/output connectors: hihest-end copper Neutrik XLR, chassis grounded, balanced
in/out
Measurement Requirements:
The finished unit must be measured
You will be required to submit a measurement report including:
● THD+N vs frequency
● SNR
● FFT plots (1 kHz and 20 Hz–20 kHz)
● Channel separation / crosstalk plot
● Noise floor / residual noise spectrum
Deliverables:
● Complete assembled dual-mono preamp (no enclosure required unless specified)
● PSU with 2 toroidal transformers (or one with dual secondaries + shielding)
● PDF measurement report
I am seeking an audio electronics builder/designer to build a sample fully discrete, dual-mono,
balanced line-level preamplifier, using AMB β22 ready made PCBs sourced from AMB, as
well as all other components required. All components and information required for the build is
available on their website below:
https://www.amb.org/audio/beta22/
Different alternatives are offered to complement this amplification PCB. We require the highestend alternative suggestions available on the website.
Stage 1: Compilation of required components and cost including a brief description of the main
constituents as well block diagram. All electronic components must be sourced from reputable
distributors such as Mouser, Digikey, RS, Partsconnexion and/or part distributors designated
manufacturers to avoid counterfeits. Chinese generic components are not accepted.
Transistors that need matching are to be ordered in excess for matching by the freelancer.
Stage 2: Execution, testing, and shipping the preamplifier.
Sample Performance Specifications:
Parameter Value
THD+N (1 kHz, 2 Vrms out) ≤ 0.0005 % (–106 dB)
THD+N (20 Hz–20 kHz) ≤ 0.001 % (–100 dB) across band
Noise Floor (A-weighted) ≤ –125 dBV (goal: –130 dBV)
Crosstalk / Channel Separation ≥ 100 dB @ 1 kHz, goal: ≥ 110 dB
SNR (unweighted) ≥ 120 dB
Frequency Response 10 Hz – 100 kHz (±0.1 dB)
Output Impedance ≤ 10 Ω (balanced), preferably 5 Ω
CMRR (Common Mode Rejection) ≥ 85–90 dB up to 20 kHz
Design Notes / Tips for Achieving These Specs:
● Dual-mono construction is required:
➤ Separate signal boards per channel
➤ Dedicated transformers for L & R channels
➤ Separate power regulation per channel (σ22 or equivalent)
● Shielded, low-noise linear PSU with toroidal transformers and proper ground
referencing
● Star grounding and isolated signal/power grounds
● Use of premium matched resistors (e.g. Vishay RN60) and low-ESR capacitors (e.g.
Elna Silmic II, Nichicon KG)
● Signal path wiring kept minimal and symmetrical, with twisted pairs or shielded
cables
● PCB layout should follow symmetrical dual-differential topology.
● Input/output connectors: hihest-end copper Neutrik XLR, chassis grounded, balanced
in/out
Measurement Requirements:
The finished unit must be measured
You will be required to submit a measurement report including:
● THD+N vs frequency
● SNR
● FFT plots (1 kHz and 20 Hz–20 kHz)
● Channel separation / crosstalk plot
● Noise floor / residual noise spectrum
Deliverables:
● Complete assembled dual-mono preamp (no enclosure required unless specified)
● PSU with 2 toroidal transformers (or one with dual secondaries + shielding)
● PDF measurement report