Review

Kenwood-Trio KA-7100 Amplifier Review

This is a smart looking amplifier with its polished alloy front panel having a clean layout and clear functional identifications. Internally, it was well engineered, with very tidy printed circuits and good component identification.

A rotary selector switch selects the magnetic cartridge phono input or either the tuner or auxiliary input, there being negligible crosstalk between these inputs. With the exception of the phono input which has a rather high resistive component of its impedance, input impedances and sensitivities are good with satisfactory overload margins.

Provision is made for connecting two tape recorders with one connection having a DIN compatible connector in addition to the phono sockets which are used for all signal inputs. The arrangement of the tape recorders is controlled by a single switch which permits monitoring of either tape unit, but only allows dubbing from tape A to tape B. However, whilst dubbing, the switch allows monitoring of the signal before or after recording. This limitation in dubbing could be annoying.

Two sets of loudspeaker outputs are fitted, with switch selection of either set or both sets in parallel, plus an ‘off’ position for headphone monitoring by a jack socket. Unfortunately the amplifier takes exception to 2 ohm loads, so pairs of 4 ohm loudspeakers cannot be used, and it would be wise to select single 4 ohm loudspeakers which do not exhibit large drops in their impedance.

The treble and the bass tone controls which are of the eleven position rotary type are activated by a ‘tone defeat’ toggle switch. The range of correction of both controls has been wisely restricted to practical limits, with the result that the increments between tone control steps are adequately small and even.

Both high pass and low pass filters are fitted, the low pass filter being subjectively satisfactory with its 6dB per octave attenuation rate and its "3dB point at 8kHz. However the high pass filter’s "3dB point was at 20Hz and it also had 6dB per octave attenuation rate " it is felt that in an amplifier of this price a 12dB per octave high pass filter could well be justified.

Headphone listening showed that the volume control had an adequate range in conjunction with its associated 20dB switched attenuator, and neither of these or the tone controls upset the amplifier balance. It was however considered that the balance control itself was rather coarse in action about its midpoint setting.

Two further features are the mode switch which permits selection of the common stereo/reverse/mono combinations, but not selection of the left or right inputs, and also the loudness control which has two positions of mild bass boost.

Subjective testing did not reveal any complaints about the Kenwood-Trio KA-7100 which was found to have a good overall measured performance. Noise from all sources was low, very low by many standards, and the harmonic distortion and low level intermodulation distortion was also good. However, at high frequencies there was a sharp increase in half power intermodulation and the amplifier tripped at 65kHz. It is however likely that this is due to the use of slow output transistors which are not always a bad thing as they tend to be more reliable than fast transistors.

In summary this is a good amplifier for 8 ohm loudspeakers, and it offers a wide dynamic range and exceptionally good noise and distortion performance with a good power bandwidth.

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