Graham Slee Novo headphone amplifier
Discrete design offers exceedingly high sound quality
The Graham Slee Entheos (enthusiast's) Series Novo stereo headphone amplifier is a discrete solid state transistor configuration using an IC voltage regulator. There are six transistors per channel. The "fast" voltage amplifier stage uses a current feedback input and a current source to drive a small signal transistor class AB push-pull output stage. The output is capacitive and resistively coupled to prevent headphone damage/short circuit damage and an output impedance reduction network minimizes any signal distortion these components could add. The Graham Slee Novo headphone amplifier uses multi-path negative feedback to reduce distortion without degrading the musicality of the signal.
The Graham Slee Novo headphone amp is supplied with an Energy Efficient plug style AC/DC mains adapter power supply for universal mains use: 90-250VAC supplied with a selection of plug heads to suit a customer's mains outlet. The power supply is of the switched mode type and sensitive users may detect a slight tingling sensation from the Novo case: this is normal and within world safety standards, but can be eliminated completely by connecting a wire to the Novo "aux ground" post; the other end to earth (either mains earth or an earth spike - seek qualified assistance if unsure). When connected to an earthed source this wire will not normally be required. The switched mode power supply emits an ultra-sonic whistle which cannot normally be heard, but in the presence of other persistent noise (such as air-con, refrigerators etc) a beat frequency (chirping) may be heard. Careful positioning will minimize this effect.
A Chained set of phono/RCA jacks enables the stereo input to be routed to other equipment such as a power amplifier. The input impedance is greater than 39 kilo Ohms so as to be virtually transparent to the source.
The output jack is designed for standard 1/4 inch/6.35mm headphone plugs (B-gauge) and can also be used with tapered A-gauge plugs. Headphones of impedance 8 - 2,000 Ohms may be used but best results will be obtained with impedances of 16 - 600 Ohms. An impedance reduction network reduces the driving impedance "seen" by the headphones and compensates for the headphone's cable capacitance, leading to a more focused musical image than purely resistive or power-amp configuration headphone amplifier outputs. It also reduces the apparent differences between dissimilar headphones.
The volume control can be set at any position to give comfortable listening. Unlike Hi-Fi amplifier volume controls, it can be set at any position and still give excellent performance. This is preferable to the contact resistance and wear of a gain switch, which would otherwise be required.
Graham Slee Novo Specifications
Output: 150mW rms into 32 Ohms, 40mW rms into 600 Ohms (both channels fully driven - 0.05% THD)
Input Impedance: greater than 39 kilo Ohms
Recommended input range: 200mV - 1V rms (2.8V p-p)
Frequency Response (worst case): Flat: 43Hz to 16kHz (-1dB), 22Hz to 30kHz (-3dB) (volume control at 3 o'clock position)
Channel Balance: 0.5dB typical
Hum & Noise: -80dB CCIR Q-pk 20Hz-20kHz (into 30 Ohms)
Stereo Crosstalk: -64dB typical
Distortion (THD+Noise): 0.02% at 1 kHz into 30 Ohms, and 12 o'clock volume control position
Power Supply: Switched mode type AC/DC adapter for use with 90-250VAC mains outlet
Dimensions: L. 10.5 W. 10.5 H. 5 (cm) approx. excluding controls and connectors
Specifications and features are subject to change without notice.