...Master Talk: Zeljko Nastasic

Trio-Kenwood is one of the older Japanese HiFi manufacturers. During the 70s and early 80s Kenwood launched a series of amplifiers featuring state of the art circuit techniques and superb build quality. This amplifier was the flagship integrated amp in 1977.

Conservatively rated at 100WPC into 8 ohms, will drive two pairs of speakers, 4-16 ohms single pair, 8-16 ohms both pairs. The amplifier features a dual-mono construction right from the power cord - including dual power transformers, power supplies and completely separated amplifier sections. [...] The preamp section is more high-end oriented than it's smaller brother, the 8100 [...].

The input selector, tape monitor and dubbing switch make up the input switching. The options continue with a stereo/reverse/mono selector, two filters (upgraded to active compared to the 8100) 18Hz subsonic and 8kHz high, tone controls with defeat switch, followed by a comprehensive volume control section featuring a stepped volume pot (one of the very first ALPS stepped attenuator units!), a coaxial balance control, a muting switch with three positions (-10dB, 0dB and +10dB), and finished off with a 3-position loudness control. Compared to the 8100, the selectable tone control and loudness center frequencies have been replaced by a set of nicely lighted power output meters, with two sensitivity settings - 3W full scale and 100W full scale. Build quality is excellent, very well thought out, tidy, and above all heavyweight.

DETAILED INFO
In the 70s Kenwood produced some of the best commercial amplifiers - and of course, in those days, 'commercial' had an altogether different ring than today.[...]
Unlike some other Japanese manufacturers, Kenwood did not purport to discover revolutionary amplifier topologies, though their circuits were state of the art for the times. Several generations of their amplifiers were very similar, and they concentrated on perfecting an already good concept. The 9100 is good evidence to that fact. Like the smaller 'brothers' in the series, it uses a dual JFET input, but continues with fully differential circuits practically to the output stage.

Lower ranked amps in the series use discrete darlington stages with quality beta-sustained transistors. The 9100 replaces these with a hybrid package where the output drivers, power transistors, the bias servo and overcurrent protection network are bonded to a very large aluminium heat spreader - increasing the area of thermal contact between the semiconductors and heatsink by a factor of at least 5. This, although similar in looks, is very different from the various STK modules used by mid-fi amps, one can actually even test the output transistors measuring through the pins of the hybrid module - the point was just to achieve exemplary thermal integrity.

The mechanical and electrical execution of this amp is very high quality and robust, with special extra parts to route cables, a MU metal shield for the phono preamp, etc. - the attention to detail is evident. The input selector is right at the inputs, the speaker selector right behind the speaker terminals. It is also wired so that the output protection relay disconnects speakers while the selector passes from one setting to another. The power amp sections are moved onto outboard mounted massive forged heatsinks, and the power supplies and transformers are centrally mounted. The power supply is massive, using two 12000uF low ESR electrolytics made by Nippon Chemicon, per channel - a total of 48000uF for both amps! Quality components are used throughout, including metal film resistors in critical places, and polystyrene caps in the phono amp.

The front panel, in common with other amps from this series, is massive aluminium, as well as all the knobs. The heatsinks are forged in such a way that they form the rear 'feet' and much of the sides of the enclosure, and are an integral part of the construction.
Sonically, this amp is nicely neutral and not over-analytical like some of the amps that succeded it. It is very similar sonically to the 8100, with more available power, easily noticed at high volumes.