Nuforce P-9 Preamplifier

August 2007 Secrets of Home Theater and Hi-Fi Reviews the P-9

Download the HI Fi World review of the Nuforce P-9

About the Designer
Demian Martin is a widely experienced industry consultant specializing in systems design covering electronic, electrical and acoustical products for consumer electronics manufacturers.

Martin has a long, distinguished history in the audio industry. He was Co-founder and Director of Engineering of Spectral Audio where he designed an impressive number of high quality and durable electronics products. He was responsible for the design and engineering of Spectral’s very low noise preamplifiers including the DMC-10. He also designed Spectral’s wide band power amplifier the DMA-100 Instrumentation Amplifier. The DMA-100 was six years in development and brought about a new performance benchmark in amplifier design. Many of the products that he designed while at Spectral have had a market life of over ten years.

NuForce P-9
THD+N = 0.0004% @ 1kHz  and a power bandwidth of 5MHz. Near perfect reproduction of 125kHz square wave.
Nuforce P-9 is a breakthrough low noise high performance audio pre-amplifier.   The P-9 is housed in 2 separate chassis. One chassis contains the three separate power supplies and microprocessor control logic, while the second chassis contains the analog volume control input selection relays and sensitive analog circuit components. The P-9 chassis matches the form factor of NuForce Ref 9 series power amplifiers.

Nuforce developed a ‘Dual Drive’ control mechanism for the P-9. Volume can be controlled either by the full function custom designed remote control interfacing with a digital volume control or the manual Alps volume pot. A microprocessor control drives the high performance Alps motorized pot in the analog chassis. A communication protocol constantly sense and feedback the volume level to the microprocessor to sync-up the level settings on the digital volume indicator and Alps volume pot. The volume control is ultimately analog based where the digital volume control only acts as an interface to the remote control for convenience.   Built-in memory stores the last-used input selection and volume levels.

The heart of the P9 boasts an all discrete precision operational amplifier module.   Ultra low noise monolithic dual JFETs, specially selected VMOS FETs and very flat hFE bipolar transistors are used in a dual cascode design with a driven shield to reduce capacitive loading on the final voltage amp.     All of this is necessary to get a 5MHz power band-width with a S/N ratio that exceeds 100dB and over 120 dB of dynamic range. The inherently stable P-9 gain circuit has no capacitors or DC-servos in the signal path.

Much attention has been paid to isolation from external influences. The amp modules are contained in heavy copper shields with internal thermal insulation to prevent sudden thermal drift or signal related heating affecting its operation. Each amp module has a self contained shunt regulator to increase its isolation from the supplies. Each module is fed from a separate isolated floating current source supply further isolation the amp chain from any noise getting into the ground system. The control system only sends DC to the relays and the motor of the potentiometer. No logic circuitry with its clocks and fast edges is in the analog section radiating noise into the sensitive low level signals. The overall isolation gives a much lower noise floor while still providing the convenience of remote control.

Specifications:

• Inputs: 5 RCA (including Home Theater bypass input
• Outputs: 1 RCA, 1 XLR (XLR output is unbalanced)
• THD+N at 1kHz = 0.0004% at 20-20kHz = 0.003% at DC to 1MHz: < 0.05 %
• S/N = 100dB at 20-20kHz S/N > 90dB at DC to 1MHz
• Frequency Response at 20-20kHz = +0.02dB/-0dB at DC to 1Mhz = +0.5dB/-0dB at DC-2.5 MHz +0/-3dB
• Maximum output: 7V RMS
• Phase shift = 0
• Input impedance = 10K ohm
• Output impedance = 100 ohm
• Dimensions: 1.75”H x 8.5”W x 16”D
• Weight:
• Power 120V 60Hz (100V and 240V models available)