DNM PA3 S Power Amp Not For Headbangers

'Not For Headbangers'

The company's amplifiers represent the antithesis to mega-muscle power. As Denis Morecroft, DNM's founder and designer, says, 'I'm not designing for headbangers! They've got to look elsewhere! But in my defence, I'd argue that the dynamic expression I try to achieve makes my amplifiers sound louder and more satisfying than amplifiers of nominally greater power.

'The sense of power in live unamplified music derives from the fine detail, not from the loud parts. For reproduction, resolution is thus more important than brute force... resolution without intermodulation effects.

'Frequently my amps are used like SE triode models with higher sensitivity speakers (greater than 90dB/W) and my distributor finds a good match with the highly efficient French made Rhedeko speakers, which I also like.'

In the PA3 S, Denis Morecroft tried to concentrate on a number of concepts concerning the perfection of the layout of the amplifier. He was concerned to obtain the right relationship of parts, and to understand the current flow and interaction between circuits. He also tried to minimise unwanted coupling even at very high frequencies.

On The Boards
In Morecroft's view, 'If power supply and ground routing don't intrude then a close approach to a perfect layout can be achieved. I've used modern technology in the form of surface mount techniques to make the power amplifier uniquely small. But then you have to connect power to it.

'My solution involved three stacked printed circuit boards with the power lines and power grounding running vertically, that is at right angles to the area of the circuit, so minimising the interaction between sensitive low level parts and high current regions.

'My research showed that problems of feedback stability, clarity and dynamic expression often related to these unwanted interactions which I've tried so hard to avoid. In a sense it completes a path of development which began with optimised star grounding, ultra clean power supplies, non interactive casework and, despite the expense, full supply regulation when deemed essential.'

Building Blocks
DNM has adopted an evolutionary approach to design. As Morecroft reflects: 'While the PA3 S may be substantially different to previous models, it embodies successful aspects of designs that go back over ten years. For example, regardless of expense I've retained the alumina block thermal coupling between the output FETs and the heatsinks to minimise interaction with the metal of the heatsinks.

'And there are high performance power regulators in the supplies of the top model, which give the cleanest and most stable power. In a sense they are power amplifiers in their own right'.