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

Finally, we present the specifications for the new Ultra-LD Mk.3 Amplifier along with a couple of minor tweaks to the design to maximise its performance.

By Nicholas Vinen

These figures and graphs show the performance of the complete Ultra-LD Mk.3 amplifier. The test signal source was set to 2V RMS and connected via the RCA inputs of channel 1 on the rear panel of the unit. The performance was measured at the speaker terminals on the rear of the unit, with a resistive load connected via 1m of twin lead. The volume control was set to deliver 100W into 8Ω and 200W into 4Ω with the 2V RMS input signal.

The overall performance of this amplifier is much better than the vast majority of commercial amplifiers, even expensive models sold as “high fidelity”. Distortion figures for commercial units are often quite vague; those that do provide graphs typically show quite a dramatic rise in distortion above 1kHz. As you can see from the graphs published here, our Ultra-LD Mk.3 retains the low high-frequency distortion characteristics of the individual modules featured in the July 2011 issue.. The signal-to-noise ratio is also very good.

The left/right channel performance differs, despite the fact that the amplifier modules are identical. This is because one module is closer to the power transformer than the other; we purposefully arranged it this way because otherwise, the transformer would be close to the sensitive input circuitry of the right-hand module and that would be worse.

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