Block diagram of the CSS-4700 board
The CSS-4700 Power Amplifier is the culmination of meticulous circuit design and engineering refinement — delivering exceptional power output with vanishingly low noise and distortion. Every element of the CSS-4700 architecture is optimized for absolute linearity, control, and reliability, resulting in a sound that is powerful, detailed, and effortlessly musical.
At the core of the system lies the CSS-4700 board, the amplifier module responsible for delivering one channel of pure fidelity. Its architecture is optimized for ultra-low Total Harmonic Distortion and an outstanding signal-to-noise ratio, ensuring flawless reproduction even under demanding load conditions.
Supporting PCB modules extend its versatility and protection:
SP-DR1200 Speaker Protection System – Guards connected speakers against DC offset, and power-on transients, ensuring absolute operational safety.
PS-4700 Power Supply Unit – Provides stable, ripple-free power delivery optimized for dynamic headroom and transient response.
Optional Baxandall Volume Control Board – Although the CSS-4700 board includes provisions for a built-in passive volume control, this optional module provides a higher level of precision, offering smoother adjustment and impeccable stereo tracking.
Log-Law LED Level Indication System – Offers intuitive, accurate visual feedback of output levels over a wide dynamic range.
Whether integrated into studio monitoring chains or high-end hi-fi systems, the CSS-4700 Power Amplifier embodies the union of technical excellence and sonic purity — designed for those who demand both absolute control and authentic musical expression.
The construction of this amplifier employs widely available electronic components from various semiconductor vendors. While nearly any low-noise, low-distortion dual operational amplifier can be used, achieving a total harmonic distortion of 0.000045% requires the use of the LM4562 or LM49720 Op amps. The NE5532, a staple in audio equipment for decades, can also deliver excellent performance for these parameters. Additionally, the RC/NJM4580 operational amplifier, if desired and available, has demonstrated good results in our experience for this application.
The CSS-4700 PCB is designed to implement a balanced voltage-input stage using a buffer and a differential amplifier that handle both the positive and negative halves of the signal. This topology offers high input impedance, excellent CMRR, and preserves low noise and very low harmonic distortion.
The CSS-4700 also delivers impressive results with minimal offset voltage, eliminating the need for large capacitive components at the output. However, to protect speakers from potential damage caused by prolonged offset or DC voltage in the output signal, it is recommended to include Olas Audio’s SP-DR1200 speaker protection system.
The CSS-4700 module provides on-board support for a regulated bipolar power supply featuring a mutual shutdown system, designed to protect your valuable Op amps in the event of an unexpected failure. This mechanism safeguards both the operational amplifiers and the rest of the circuitry.
The following are the main features of the CSS-4700 board:
- Ultra-low noise and low harmonic distortion for highest quality sound.
- One Channel per board
- Balance input for lower noise and EMI.
- Input overvoltage protection
- Input differential amplifier CMRR: > 77 dB @ 1 kHz
- THD @ 1kHz & into 8 Ω: 000045% @ 1W and 0.00011% @ 40 W.
- THD @ 10 kHz & into 8Ω: 001% @ 1W and 0.0014% @ 40 W.
- THD @ 1kHz & into 4 Ω: 000076% @ 3W and 0.00012% @ 56 W.
- THD @ 10 kHz & into 4 Ω: 002% @ 1W and 0.008% @ 40 W.
- Output DC offset voltage: < ±2mV
- Bandwidth: 62 kHz, 1W -3dB
- Frequency response: -0.02 dB @ 20 Hz and -0.5 dB @ 20 kHz
- Input impedance: > 46 kΩ
- Output impedance (without Zobel and Thiele Networks @ 1kHz): < 0.005 Ω
- Output impedance (with Zobel and Thiele Networks @ 1kHz): < 0.02 Ω
- Damping factor: > 400 @ 1kHz, 8Ω
- Gain: 22.2 dB (x13)
- Input sensitivity: 1.35 Vrms @ 40W, 8Ω
- It is compatible with the LME49720 and the LM4562 ultra-low noise/low THD Op-Amps, both delivering stunning results.
- Provides on-board support for a a regulated bipolar power supply unit with a mutual shutdown system, ideal to protect your valuable Op-Amps during an unforeseen failure.
- The design allows the installation of a passive volume control or a Baxandall volume control, using the BAX-VOL-CTRL board also available from Olas Audio.
- Compatible with the Speaker Protection System SP-DR1200 and the LLLL level indication system, both designed by Olas Audio.
- High-quality, 4 layer, plated-through-hole PCB (ENIG Gold Fingers: 1U”) with solder mask on both sides and full screen print.
- PCB size: length=100mm, width=85 mm. It incorporates four M3 fixing holes.
The following diagrams illustrate the configurations in which you can integrate this board with other Olas audio products.
Interconnection between different Olas Audio boards to build a stereo audio power amplifier. This version includes one PS-4700 Power Supply Unit, two channels of amplification (left and right), a Log Law Level LED indicator board and a Speaker Protection board.
Interconnection between different Olas Audio boards to build a stereo audio power amplifier. This version includes one PS-4700 Power Supply Unit, two channels of amplification (left and right), a Baxandall Volume Control board, a Log Law Level LED indicator board and a Speaker Protection board.
Interconnection between different Olas Audio boards to build an audio power amplifier with a bi-amplification scheme. This version includes two PS-4700 Power Supply Unit boards, three channels of amplification (left, right, and one for subbass signals), a Baxandall Volume Control board, a Log Law Level LED indicator board, a Summing Amplifier board, a Bandwidth Definition/Low Pass Filter board and a couple of Speaker Protection boards.
The published price is for the PCB only. A bill of materials and assembly instructions will be provided upon purchase.
