Under the Hood

In a Nutshell

The power supply has a major role in sound quality, in many cases even more than the audio circuit. Actually several high-end manufacturers consider it as part of the audio circuit design, and the same equipment whether it is an amplifier, a CD player, or a DAC will sound totally different with or without a good regulated power supply.

Ideally the power supply rail should consist of only clean DC. In practice however, every power supply, including batteries adds noise to the audio stages. Any noise on the power rail translates into distortion, coloration, reduced sound stage, and a sound which is less natural.

Most regulated power supplies today are either Switch Mode Power Supplies (SMPS), or linear power supplies. Our power supplies are based on the SuperTeddyReg, a different technology which has proved to be far superior for audio designs.

Linear power supplies, such as those used in Naim power supplies are based on a transformer, rectifier, smoothing capacitors, and a linear regulator. When the AC at the output of the transformer is rectified and smoothed, a ripple is still present on the DC rail. This ripple has the form of a saw tooth which translates into noise at all audible frequencies and has a negative effect on the sound quality. The better the power supply can filter this ripple the better the sound will be. To get an idea of how much the power supply can affect the sound quality suffice to mention that almost all Naim preamplifiers are based on the same amplification circuitry and differ in their ability to connect more or better power supplies.

The amplitude of the ripple mentioned above decreases with the size and quality of the smoothing capacitors being used. Naim Audio uses a brute force technique for the HiCap; they use a 500VA transformer and rely on large low ESR capacitors. Not only that this technique is less effective in noise filtering, but over time, due to their chemical construction, the quality of these Electrolytic capacitors decreases (ESR increases), and as a result the ripple increases. This is the reason for which Naim power supplies require expensive re-capping every 10 years or so. 

The most common way to reduce ripple is to use a linear voltage regulator such as the LM317. The core of a linear regulator is an operational amplifier which monitors the output voltage and correct it using feedback. In order to reduce cost, most monolithic linear regulators, including the LM317 used by Naim for their power supplies, make use of a simple operational amplifier which generates its own additional noise. According to the LM317 datasheet it has a typical output noise of 0.003% of the output voltage. For an output voltage of 24V the output noise will be 0.72mV, not negligible...

In addition, all linear (feedback) regulators, including the superior Jung SuperRegulator, have a limitation which is inherent to the way they operate, they can only fix a problem after it occurs. Since the speed in which they can fix the problem (regulate) is constant, their ripple rejection capability decreases with frequency. The LM317 has a ripple rejection of around 80db at 50Hz, which drops to merely 20db at very high frequencies (note that a -60db difference means x1000 times less!!!).

Switch mode power supplies, such as the small wall-wart power supplies provided with the Logitech Squeezebox or with many popular DACs, are based on switching technology rather than transformer/rectifier/bridge combination. The idea behind these power supplies is to charge a coil/capacitor at high frequency and use the energy they store. The advantages of this technology are numerous which makes them very popular. They are small, efficient, low cost, and they are readily available from many manufacturers (mostly in China). The main drawback of these power supplies is that they are noisy, very noisy... Not only do they have a high level of high frequency noise on the DC, but they often inject high frequency noise to the mains which may impact performance of other hi-fi equipment. In short, less than optimal for high-end audio equipment.

The SuperTeddyReg

The regulator is the heart of the power supply. The TeddyCap and TeddyXPS power supplies are designed around the SuperTeddyReg a regulator that has been developed especially for high end audio circuits and surpasses any regulator that we have tested so far. The SuperTeddyReg is an evolution of the TeddyReg and provides even better performance. The SuperTeddyReg is also offered as a small independent circuit to the DIY community and is being used for a large variety of applications.

The innovation in these power supplies is the incorporation of a very effective low-pass filter that in conjunction with a voltage regulator provides a theoretical (impossible to measure with conventional equipment) ripple rejection of more than 120db over the entire audible spectrum and above 1MHz. This powerful filter allows using smaller transformers and smaller smoothing capacitors. Since it does not rely on large smoothing capacitors to eliminate the noise, it does not require re-capping if the quality of these capacitors decreases.

Smoothing capacitors are usually in the order of 4700-20000 uF, the SuperTeddyReg filter stage uses much smaller capacitors. The advantage of using smaller capacitors is that capacitors other than electrolytic can be used. Electrolytic capacitors are limited in their ability to filter high frequencies above the audio spectrum, and have leakage noise. Our power supplies make use of a combination of Tantalum, and PPS capacitors capable of filtering very high frequencies (over 1MHz). Surprisingly, filtering high frequencies even above 100 KHz is clearly audible.

The following graph show the difference in noise level between a good quality Switch Mode Power Supply, a Naim SuperCap, and a TeddyCap mk3

As can be seen on the graph, the Logitech Touch PSU (pink line) which is a Switch Mode Power Supply is very noisy, the Naim SuperCap (red line) which is based on a linear regulator is still relatively noisy all over the audible spectrum. The TeddyCap (blue line) has a much lower noise level, and outperform the other power supplies by far. It is actually very close to the 0 Volt reference (black line).

Comparing with the original Naim power supplies, these power supplies will provide a higher level of resolution, better transparency, more detail, larger 3D soundstage, deeper and more controlled bass:

"Bass is tight and very deep, with the higher scales well defined and vocals crystal clear. Drum solos are amazing - you can now actually define the drum being used. It retains, but more so, even enhances the 'PRAT' that Naim are renowned for.Read more testimonials...

Implementation

Obviously, to achieve this level of performance a larger number of components is required, and high attention is required in component selection. Many listening hours showed that every capacitor type and value has an impact on the sound. PCB layout has a major effect on power supply performance too. Component placement and signal routing are critical. Several cycles of design, prototyping, and measurements were needed to achieve the best results.