Naim’s DR power amplifiers: taking you inside the music

By tackling one of the fundamentals of amplifier design –­ the provision of the cleanest possible power to each part of the signal chain within an amp – Naim’s latest Discrete Regulator amplifiers bring you even closer to the music.

The ideal for a power amplifier looks simple: the relatively low-level signal from the preamp goes in one end, and out the other comes the same signal, increased to enable it to drive a loudspeaker. That’s it: nothing added and nothing taken away ­– just a direct amplification of the signal.

Of course, it’s not that simple, and while the old idea of ‘a straight wire with gain’ sums up what a power amp should be doing, a whole load of other factors are brought to bear in any design: the need for each section of the amp to do its job as optimally as possible, the different (and varying) load speakers present to the amplifier, and the need to keep the whole plot stable and reliable under a wide range of conditions, both physical and musical.

Fundamental to the way any amplifier works is the way its powered, and it really isn’t as simple as ‘…want more power? Fit a bigger transformer!’ Each part of an amplifier has its own power requirements, from the input stage all the way through to the output transistors, which correspondingly means each section needs its own power supply.

Again, that sounds simple enough, and most hi-fi products have several secondary windings on their power transformers, providing different voltages to the various parts of the amplifier, or serving the different sections of, say, a CD or network player to avoid noise passing between those sections. Some manufacturers even use multiple transformers; having one for each channel in a stereo power amplifier for example, or for the digital and analogue sections of a player. This isn’t a path Naim follows – we prefer to use just one large primary transformer to supply the whole product.

Naim Electronic Design Director Steve Sells explains the thinking behind this: ‘A single large transformer has a lower impedance and so charges PSU reservoir capacitors faster than two smaller transformers. This in turn allows the mains conduction angle to be shorter, essentially allowing the PSU to be disconnected from the mains for a longer time.’

Naim Audio NAP 500 DR:

However, providing just the right power in all the relevant places throughout an amplifier can mean the use of many different regulated power supplies, any of which has the potential to introduce noise into the signal path. With the different power requirements of the various sections, each needs a power supply with its own regulation to guarantee exactly the right power is available, keep any noise in one section away from the others, and ensure the amplifier can handle the demands placed on it by the requirements of the signal passing through it.

Naim is no stranger to the importance of power supplies in the performance of its products: for many years we have built offboard power supply units, each offering multiple supplies to the connected product, as an upgrade for many of its models, and as standard for its flagship offerings. It’s not just a question of the offboard box delivering more power: connected through those thick Burndy cables are separate supplies for each section of the product with which they’re designed to be connected, and each optimised for its task.

For some years Naim has been rethinking our power supply design in the quest for lower noise and better performance -  specifically working on the incorporation of Discrete Regulators, which first appeared in power amps in the massive NAP S1 monoblocs, part of our Statement amplifier system.

The technology also appeared in a range of upgraded ‘DR’ power supplies for the existing Naim range of preamplifiers and source components, but it was the implementation in Statement – which uses truly massive Discrete Regulators, able to deliver up to 100amps – that led to its more widespread adoption across the Naim power amplifier range, from the NAP 200DR all the way up to the NAP 500DR.

So, what exactly is a Discrete Regulator and what advantages does it bring? Well, as previously mentioned, a regulator acts like an amplifier, taking in a DC reference voltage and amplifying it to the voltage required by the circuit(s) it is powering. The DR takes in unregulated ‘raw’ DC from the transformer, and delivers near pure DC at the point where it’s needed. This ensures a low-noise, low-impedance power supply, immune to effects of the load on the regulator and the temperature at which it is operating.

DR regulator Block Diagram:

The secret of the Discrete Regulator is keeping the reference voltage as electrically quiet as possible, whilst providing sensitive reactive amplification, that will supply the cleanest possible power to the circuitry, and enable the power supply to cope with the dynamic demands created by the signal the circuitry is handling. Less noise, and faster reactions to the requirements of the music – that’s the idea behind the Discrete Regulator technology.

To keep the reference voltage as quiet as possible, Naim uses a sub-surface Zener diode.  This is the quietest possible voltage reference and is designed for extremely tight voltage tolerances, regarding both time in use and changes in operating temperature variables. Steve Sells explains: ‘The ‘sub-surface’ bit means it’s diffused below the silicon surface, so that the diode actually ‘Zeners’ or regulates physically below the silicon crystal lattice surface defects and oxides. Without the sub-surface construction, Zener diodes are inherently noisy and prone to drift – in fact, ordinary Zeners have even been used as white noise generators.’

Further noise reduction is achieved by powering this reference diode from the output of the DR itself, thus keeping the supply as quiet as possible.  This ‘bootstrapping’, which is used for the entire front end of the regulator, enables DR devices to be kept extremely compact, allowing their use in more places in Naim’s products. 

NAP 300 DR Circuit:

Sells explains that the DR power supply is 30x quieter than the supplies used in our previous generation of power amplifiers, and that it has a range of advantages allowing it to be widely used across the Naim range: the supply can be scaled for different voltage and current requirements, can be tuned for use in various products, and as well as its noise characteristics offers excellent transient response thanks to its fast recovery time after the instantaneous demands placed on it by the signal being passed.

Noise Plot: Red = NAP 250, Green = NAP 250 DR

Not surprisingly, therefore, the supplies are being used throughout the new DR power amplifiers: look at the NAP 500DR, and you will see just how widely the company is making use of this technology. There are no fewer than 10 DR power supplies for each channel, equalling a total of 20 in the amplifier. On each channel, there are two on the input buffer; one positive and one negative, and four on each of the two gain stages; ‘hot’ and ‘cold’, of the bridged topology of the 500. Each gain stage uses two power supplies – again, positive and negative – on its input, and another two on the output.

NAP 500 DR PSU Block Diagram:

The DR power supply has been used not only in the NAP 500DR, but also in the NAP 300DR and NAP 250DR, each of which uses linear regulated power supplies throughout. In the NAP 200DR, a simpler design, the DR power supply is used purely to power the preamplifier connection, enabling an attached Naim preamp to enjoy the advantages of the DR design. In fact, the DR module used in the NAP 200DR is identical to that found in the Hi-Cap offboard power supply, enabling the preamp to enjoy the DR advantages without the need for a separate power supply.

NAP 250DR/300 DR PSU Block Diagram:

Beyond that, the amplifiers remain unchanged, aside from some re-tuning to allow them to make the most of the added potential unleashed by the DR power supplies. This will enable models from the outgoing generation to be factory upgraded to DR specification. Only the NAP 200 won’t be upgradable, as the incorporation of the DR supply for a connected preamp would entail a whole new main circuit board, as the new DR sits in a cut-out to one side of the board. Existing NAP 200 users can have a more cost-effective upgrade by opting for an offboard power supply for their preamp.

The benefits of DR technology are already being recognised in reviews, with critics noticing the gains in performance, for example comparing the NAP 250 DR with the model it replaces. Writing in Hi-Fi News & Record Review, Andrew Everard commented:

‘What immediately became evident was the additional clarity the NAP 250 DR brings to the party, while still maintaining that punchy, explicit and vibrant NAP 250 sound, encouraging higher volume levels simply because the silence from which the music emerges is all the more striking.

‘It can hit hard, play it cool or just captivate with the sheer detail and musicality on offer. Once the NAP 250 DR’s qualities start to grow on the listener, I suspect there’ll be no going back.’

He concludes ‘This latest version is a spectacularly good amplifier, with bass and attack to surprise, plus subtlety and finesse to delight. Fuss-free in operation and as unassuming as ever in its looks, it shows gains in clarity and sheer impact over its predecessor. Who’d bet against it still being around in another 40 years?’

Writing for The Ear, reviewer Jason Kennedy agrees: ‘This is easily the best sounding Naim amplifier I have reviewed, and one of the best power amps I’ve reviewed period. It has transparency, pace and bandwidth that caught me by surprise.’

He adds ‘the NAP 250 DR is a classic reborn, a power amplifier for the high resolution era that will take any signal and make the most of it.’

Clearly DR technology is now bringing to Naim’s already highly acclaimed amplifier range, something very significant: the power to amaze.

Hear the benefit of the latest upgrade for yourself at your nearest Naim retailer.