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Ultra-LD Mk.3 135W/Channel Sterio Amplifier, Pt.1

Chassis assembly and wiring details

By Greg Swain

AT THE HEART of this new stereo amplifier are two Ultra-LD Mk.3 power amplifier modules, as described in the July and August 2011 issues of SILICON CHIP. The Mk.3 is by far the best class-AB amplifier module ever published and features astonishingly low total harmonic distortion and noise (THD + N) figures and a power output of 135W RMS into 8Ω. Alternatively, it can deliver around 200W RMS into 4Ω.

We followed that with a suitable power supply module in September 2011, then described a loudspeaker protector and muting module in October 2011. The latter is basically a slightly modified version of the very successful design used in our Class-A Stereo Amplifier described from June 2007 to September 2007.

The preamplifier and input selector modules followed in November and December 2011. As with the loudspeaker protector, the preamplifier is a tweaked and enhanced version of the high-performance unit originally designed for the Class-A Stereo Amplifier.

This month and next month we will show you how to assemble every­thing into a custom steel case that’s been designed in conjunction with Altronics. This precision laser-cut chassis is supplied with all holes drilled and with pre-punched front and rear panels with screened lettering. Also next month we will present the performance measurements of the complete amplifier.

Where To Buy Kits

A kit of parts for the Ultra-LD Mk.3 Stereo Amplifier is available from Altronics, 174 Roe St, Perth, WA 6000, Australia. The kit is complete and includes the seven modules (unassembled) and a pre-punched steel chassis similar to that shown in the photographs.

Alternatively, you can purchase the individual kit modules and the chassis separately – see the Altronics website at
for further details.

Note that the kit does not include an infrared remote control handpiece. The unit will work with most universal remotes including the Altronics A1012.

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