timoteus
500+ Head-Fier
- Joined
- Jun 22, 2001
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Here is an amp that comes in either kit or in a completed and cased version. It is designed by Dr. David White of Glasgow. They should have a picture of the cased version up on their site soon.
www.wnaudio.com
More details:
Headphone Amplifier (New Version)
Only a small proportion of integrated or power amplifiers have a headphone socket, and those that do frequently make use of a simple attenuator on the main output. A simple attenuator wastes power, is relatively noisy, and often has too restricted a bandwidth to get the best from headphones. Obviously a dedicated headphone amplifier is the best option.
A good headphone amplifier should have low noise, wide bandwidth, very low distortion, low output impedance, and sufficient output current to drive all types of headphones; which range in impedance from 8 to 2k. The White Noise headphone amplifier fulfils all of these criteria and also has full short circuit protection. The headphone amplifier has a 50mA class A output stage and uses circuitry similar to the buffer amplifier.
The kits are supplied with a high quality, gold-plated, 6.35mm, stereo jack socket for the headphones. These gold-plated sockets are preferable to the silver-plated professional sockets for domestic use. Silver plating gives the lowest contact resistance but is prone to tarnishing, which then greatly increases the contact resistance. In a professional environment this is not a problem because the constant plugging and unplugging of headphones during the working day polishes the contact surfaces and keeps them free from tarnish. This constant plugging and uplugging would also soon wear away relatively soft gold plating. The domestic environment is much more likely to cause tarnish (cooking, aerosol sprays, etc.) in the first place and then, because plugging and unplugging is a relatively infrequent event, the tarnish will remain on the contacts and spoil them. The fewer contact cycles involved in domestic usage are not going to wear away a gold-plated contact surface.
The stereo headphone amplifier is available with either OPA134 (standard) or OPA627 (audiophile) driver op-amps and has a gain of three, although provision is made on the pcb for setting the gain to any desired value. The headphone amplifier is powered from a "plug top" stabilized psu for lowest hum and noise. There is 150-200mA of surplus ±12V power for any other circuitry you may care to house in the headphone amplifier case (e.g. balanced i/o modules, active crossovers, etc.). The standard stereo headphone amplifier has 2.2µF polyester (audiophile, 4.7µF polypropylene) capacitors on the input of each channel but is otherwise DC coupled throughout. The DC offset at the output is typically 2mV which allows the direct connection of all headphone types bar electrostatics.
The passive preamplifier cased kit, detailed later in the catalogue, is drilled with mounting holes designed to take the headphone amplifier pcb and, on request, punched with a mounting hole for either 3.5mm or 6.35mm stereo headphone sockets.
The audiophile grade headphone amplifier is supplied with Welwyn RC55Y resistors, polypropylene capacitors, and OSCON electrolytics. A construction manual, with full schematics is included with the pcbs and kits.
KitA&T
Headphone amplifier pcb only (74mm x 105mm) £ 30
Plug top mains psu£ 16
Headphone amplifier, standard version, including A&T plug top psu£ 75£105
Headphone amplifier, audiophile version, including A&T plug top psu£110£140
www.wnaudio.com
More details:
Headphone Amplifier (New Version)
Only a small proportion of integrated or power amplifiers have a headphone socket, and those that do frequently make use of a simple attenuator on the main output. A simple attenuator wastes power, is relatively noisy, and often has too restricted a bandwidth to get the best from headphones. Obviously a dedicated headphone amplifier is the best option.
A good headphone amplifier should have low noise, wide bandwidth, very low distortion, low output impedance, and sufficient output current to drive all types of headphones; which range in impedance from 8 to 2k. The White Noise headphone amplifier fulfils all of these criteria and also has full short circuit protection. The headphone amplifier has a 50mA class A output stage and uses circuitry similar to the buffer amplifier.
The kits are supplied with a high quality, gold-plated, 6.35mm, stereo jack socket for the headphones. These gold-plated sockets are preferable to the silver-plated professional sockets for domestic use. Silver plating gives the lowest contact resistance but is prone to tarnishing, which then greatly increases the contact resistance. In a professional environment this is not a problem because the constant plugging and unplugging of headphones during the working day polishes the contact surfaces and keeps them free from tarnish. This constant plugging and uplugging would also soon wear away relatively soft gold plating. The domestic environment is much more likely to cause tarnish (cooking, aerosol sprays, etc.) in the first place and then, because plugging and unplugging is a relatively infrequent event, the tarnish will remain on the contacts and spoil them. The fewer contact cycles involved in domestic usage are not going to wear away a gold-plated contact surface.
The stereo headphone amplifier is available with either OPA134 (standard) or OPA627 (audiophile) driver op-amps and has a gain of three, although provision is made on the pcb for setting the gain to any desired value. The headphone amplifier is powered from a "plug top" stabilized psu for lowest hum and noise. There is 150-200mA of surplus ±12V power for any other circuitry you may care to house in the headphone amplifier case (e.g. balanced i/o modules, active crossovers, etc.). The standard stereo headphone amplifier has 2.2µF polyester (audiophile, 4.7µF polypropylene) capacitors on the input of each channel but is otherwise DC coupled throughout. The DC offset at the output is typically 2mV which allows the direct connection of all headphone types bar electrostatics.
The passive preamplifier cased kit, detailed later in the catalogue, is drilled with mounting holes designed to take the headphone amplifier pcb and, on request, punched with a mounting hole for either 3.5mm or 6.35mm stereo headphone sockets.
The audiophile grade headphone amplifier is supplied with Welwyn RC55Y resistors, polypropylene capacitors, and OSCON electrolytics. A construction manual, with full schematics is included with the pcbs and kits.
KitA&T
Headphone amplifier pcb only (74mm x 105mm) £ 30
Plug top mains psu£ 16
Headphone amplifier, standard version, including A&T plug top psu£ 75£105
Headphone amplifier, audiophile version, including A&T plug top psu£110£140
