Naim NPX TT Power Supply

Naim Audio NPX TT power supply is an upgrade to the power supply for the NVC TT phono stage. It has dedicated sections for digital and analogue and will provide the best possible power source for this excellent phono stage.

Firstly, a large transformer is used for good transient response. The separate feeds for the digital and analogue circuits prevent any mutual interference. Finally, Naim uses their own DR power design that outperforms other designs.

Why a separate PSU?

Using the NPX TT power supply to drive the NVC TT preamplifier should remove any possible sources of magnetic and mechanical interference. As a result, the sensitive internal electronics can work at their best. The upgraded PSU also separates the digital and analogue power feeds. This prevents any interference from crossing over between sections.

Power supplies use large mains transformers, that generate both mechanical and electrical noise. With a separate PSU, this is moved away from the Audio signal path. Moreover, noise from the rectifiers can also get into the grounding system adding mush and interference to the sound. As a result, Naim has developed their own power supply design, known as DR or Discrete regulator.

The Naim DR power system

The Naim DR power system is used throughout the range and gives a stable and clean output. It may seem simple to design a power supply but several factors complicate the issue. For example, many different voltages are required for different stages. Moreover they can mutually interfere with each other. The signal from a turntable phono cartridge is very fragile and noise can affect the sound if not controlled. Hence the NPX TT has dual supplies. Cheaper units can use monolithic voltage regulator ICs. These are convenient but can be unstable and have limited output current capability.

How does a power supply work?

Like most power supplies the NPX TT uses a mains transformer to change the high mains voltage, to a set of lower voltages. In the UK the mains voltage is 240 Volts. Whereas preamps usually need voltages in the range of 5v - 25V. After the transformer comes the rectifier. This converts the AC voltage, from the transformer to DC. There can be more than one rectifier with one being used for each secondary voltage. Naim use discrete diodes, for the NPX TT, instead of a one piece bridge rectifier.

Next come the smoothing capacitors, these smooth out any variations in the voltage and remove any hum. These need to be high quality components, both for ESR (Effective series resistance) and longevity. They usually get hot and can leak over time. After the smoothing there is a pre-regulator this filters any noise and prevents it from both getting into the ground system as well as to the audio equipment itself. Finally comes the regulator section. The NPX TT uses discreet components rather than Op-amps for this section. 

Regulation is a complicated subject, but usually involves a reference voltage of some type. Naim uses a low noise Zener diode. This provides a voltage that does not vary with load. Regulation also involves feedback. The output is monitored and feedback to a control circuit. If the current load drops the output voltage will try to rise. As a result the regulation circuit will reduce the voltage. This is instantaneous, with good design. The design also needs to be good to prevent instability and oscillation. Finally, there is the question of heat. The output transistors get hot and need good heatsinking to prevent thermal runaway. Naim has several years of experience with power supply design and has dealt with all of these factors.