Graham Slee Novo headphone amplifier

GRAHAM SLEE NOVO HEADPHONE AMPLIFIER

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 capacitively and resistively coupled to prevent headphone damage/short circuit damage and an output impedance reduction network minimises any signal distortion these components could add. The Novo headphone amplifier uses multi-path negative feedback to reduce distortion without degrading the musicality of the signal.

The 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 39k ohms so as to be virtually transparent to the source.

The output jack is designed for standard 1/4 inch 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 Headphone Amplifier Specifications
- Output: 150mW rms into 32 ohms, 40mW rms into 600 ohms (both channels fully driven - 0.05% THD)
- Input impedance: >39k ohms
- Recommended input range: 200mV - 1V rms (2.8V p-p)
- Frequency response (worst case): Flat: 43Hz-16kHz (-1dB), 22Hz - 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% @ 1kHz 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 (cm): L. 10.5l x 10.5w x 5h (excluding controls and connectors)