The Marantz PM7001 KI Integrated Amplifier delivers a stunningly high level of performance at a price we would not have believed possible.
Contrary to popular belief, Ken Ishiwata (‘KI’) does not actually design the special models that carry his initials, so although he certainly ‘signed off’ on this special, souped up version of the standard Marantz PM7001, he did not actually design it. I know this because I have personally asked him this exact question. ‘That would be impossible,’ was his answer to me. ‘What happens is that I oversee all the models we make, with different teams working on different ones. Sometimes it happens that some of these models work out so well that I think it would be a pity not to make them any better. So when I consider there is real potential for improvement in one of these models, that’s how a model becomes a ‘KI’ version, which involves me tweaking it by changing various components. Because it is my name and my reputation that are then at stake, it is entirely my own choice as to which models I choose to improve.’
Anyone who has heard a standard Marantz PM7001 might well wonder what there is to improve, because it’s a great amplifier in its own right, but Ishiwata obviously did, and the PM7001 KI is the result. One of the changes he made was to the current feedback circuitry. Both the PM7001 and PM7001 KI use current feedback rather than voltage feedback, partly because it makes the output stages work at their optimum irrespective of speaker loading. In the KI version, however, Ishiwata instructed that the current feedback be wound back to its minimum level in order to increase the bandwidth, and make the circuit ‘faster.’ Doing this meant upgrading the power supply, so this was done also, with higher-specced and higher-value smoothing capacitors (Marantz-branded 1800μF 63V Nichicons), and by substituting a Bando toroidal transformer for the standard one.
Although the main printed circuit board (PCB) is the same, the KI version benefits from individual copper screens that are attached to selected transistors and diodes (apparently specifically selected by Ishiwata on the basis of listening tests, because I couldn’t see any specific technical reasons to shield the particular ones he’d chosen) and of course the casing of the KI is completely copper-plated. The components inserted in the PCB have not had their actual values changed, but according to Qualifi , the Australian distributor, many of the critical semiconductors used in the KI versions are sourced from different suppliers than those who supply the semis for the standard PM7001. One circuit component that is the same in both models, but newly designed for the 7001 series, is the ‘HDAM’ that Marantz uses in place of conventional operational amplifiers (op-amps). Ishiwata says the Marantz HDAMs do essentially the same job, but completely outperform standard IC op-amps, particularly in the areas of slew rates and noise levels. The audible result? ‘Much more dynamic, accurate and detailed sound,’ says Ishiwata.