Power supplies for Naim: why two cables are required?

A short explanation about Naim’s power supply connectivity

Looking at our TeddyCap (or TeddyCapPlus or DualTeddyCap) user manual, it will show this connection diagram for the Naim integrated amplifiers (Nait XS, Supernait), using two cables:

The TeddyCap has two functions:

1. Deliver power to the Supernait preamp section.
2. Deliver audio out signals from the preamp section to the power amp.

The reason for this unusual connection scheme, lies in the way that Naim preamps are designed.

Since Naim’s early days (NAC12, early 1970s) the preamp is powered with a single polarity (+24v) power supply, where the supply return line is doubled as the audio ground, as shown in the drawing below:

This single-polar power schematic has been used across all Naim preamps and integrated amps, and changed to a bipolar supply only in the NAC-552 and the new Classic line (NSC222/333), as depicted in the drawing below:

Single-Polar vs Bi-Polar power supply

When comparing the two systems, the single-polar power supply is a more cost-effective solution, as the power supply only has positive supply circuits (regulators), rather than positive and negative regulators, as required by a bi-polar supply.

On the other hand, the single-polar power supply uses the signal ground as its power-return line, which creates a potential for ground noise (hum and buzz).

The reason for this noise evolves from Ohm’s Law: in the real world, cables are characterized by a series resistance that is higher than zero, and the actual voltage in their return line is not exactly zero volts. 

The diagram below depicts the problem caused if we connect a single polarity power supply with just one cable: the voltage drop at the supply return line, forces a higher than zero voltage at the audio ground line, which results in hum and buzz noise.

How to solve the ground-induced noise:

To avoid ground-induced noise, Naim dictates power supply connectivity using two cables, so the audio signal is routed via the power supply, as a result, the voltage drop at the power supply cable, does not affect the power amp, as the signal ground is referenced to the zero volt line at the power supply, and not to the supply ground at the preamp – see the diagram below:

Conclusion

This article explains why power supplies for Naim are required to route preamp audio out signals, and why two cables are required for connecting the power supply. This requirement does not apply to bi-polar powered preamps such as NAC-552 and the new Classic products such as NSC222.

The Koltura Cable advantage

Our Koltura cables (LINK) offer a unique advantage in the context of Naim’s single-polar power supply, by presenting ultra low impedance at the ground connecting wires. This results in lower noise and a more lively presentation.