Naim NAP 250 Power Amplifier (1985)

Here we have a nice early example of the NAP 250 power amplifier from British experts Naim Audio. The NAP 250 must be one of the longest running power amplifiers still in production today, with their website quoting 1975 as the year of its introduction. It is in very good condition considering its age and will be supplied in its original factory packaging. It also comes with a mains cable, 4-pin DIN – XLR cable, reprinted manual and of course our normal three month warranty.
Naim Say….
The purpose of an audio amplifier is to drive loudspeakers without loss of musical information. In our view many commonly accepted parameters have little to do with loss of information and in some instances, such as the pursuit of large bandwidths or low distortion, unqualified acceptance of them can actually lead to the creation of mechanisms that bring such losses about. Dynamic output impedance, open loop bandwidth, slew rate, propagation delay and stability margins are only some of the many factors to which we attach Importance, and which must all be bought into positive balance.
With this balance in view, our amplifiers not only achieve low harmonic distortion low noise and wide power bandwidth, but also have a constant dynamic output impedance over the whole audio bandwidth. They are able to drive reactive loads without any appreciable change in distortion and are not sensitive to the absolute impedance of the load.
The frequency response of our amplifiers at the bass end is dependent on the gain decoupling capacitor, and the half power bandwidth extends to below 5Hz. At the top end the response is controlled by a passive single pole filter and is 3dB down at 40kHz. The amplifiers do not slew rate limit within this frequency bandwidth.
The amplifiers will tolerate any load from 0 ohms to infinity without damage or instability, the output stages being protected by circuitry that measures the power dissipated. Prolonged running at high dissipation will cause the NAP 250 to become quite warm and should the heatsink temperature exceed 70°C the mains supply will be interrupted until the amplifier has cooled down.
The cases of the power amplifiers are all constructed in a similar way, using a heavy aluminium extrusion, which acts as a heatsink, to form the outer cover for an inner chassis inside which the entire amplifier is assembled. All connections are on the rear.
The NAP 250 has four regulated power supplies, each of which is rated at 40 volts and able to deliver more than 10 amps continuously.
High quality components are used throughout, with great attention to detail construction. Many components are specially selected or manufactured to our own specification.
Specifications:
Power output: 70 W into 8 ohms; Transient: 400 VA; Voltage Gain: 29 dB
Input impedance: 22 kOhms
Operating temperature: 0 to 50 °c
Mains supply: 240 V, 220 V or 120 V, 50 or 60 Hz
Dimensions: 430 (W) x 300 (D) x 76 (H) mm

To read an interesting article about the history of the NAP 250 from Hi-Fi Choice please click here