The instantly recognisable Trio/Kenwood KA-2002 is one of those products that is sure to have touched the lives of many readers of Hi-Fi News. A popular first move upmarket from record players and radiograms towards 'proper' hi-fi, this inexpensive amplifier was a frequent choice for enthusiasts taking their initial steps towards serious listening.

Introduced in 1970, the KA-2002 used cool-running and compact solid-state circuitry to deliver a claimed 2x13W/8ohm. This was a healthy figure when compared to the basic set-ups the owner may have just moved on from. Japanese equipment was a relative novelty on the British market at the time, and a few years previously there had been virtually none. Indeed, at first Kenwood sold its products under the Trio brand in the UK to ensure it would not be confused with the high-profile British kitchen appliance manufacturer – a situation that would continue until the 1990s.

Price Is Right
The offer from the Japanese companies would become a familiar one, however. This meant the latest tech combined with a good standard of finish, plus aggressively keen pricing. As a case in point, the Kenwood KA-2002 cost under £40 when the similarly rated, but ageing, Leak Stereo 30 Plus [HFN Sep '20] cost over £60. In addition, Japanese electronic products of this era offered a level of reliability previously unknown to British buyers.

While not a top-end model, the KA-2002 was laid out internally in the same way as its more expensive counterparts. For example, the RIAA eq amplifier for the turntable input was used exclusively for this purpose and switched out of the circuit when not in use. Common practice for small amplifiers at that time (such as the Leak Stereo 30 Plus) was to change its characteristics and use it to provide gain for the other inputs – with an attendant noise penalty. Given that records were likely to be the main source for an amp such as this, the RIAA stage of the KA-2002 had been designed with considerable care.

Pop Star
A particular point of interest was the use of an elevated supply voltage to give good immunity to pops and clicks from imperfect record surfaces, with electronic filtering said to reduce the possibility of hum entering the signal path from this source. The rest of the circuit was divided into the preamp (with active treble and bass controls) and the power amp. Unusually in this class, the pre and power amplifiers could be separated using a switch at the rear. This made possible the use of external filters or a more powerful output stage.

One aspect of the design of equipment intended for the novice user is that it must be more tolerant to misuse than that designed for seasoned experts. Any amplifier's most vulnerable section is its output stage. This must deal with overloads caused by factors such as prolonged periods of operation at full output, unsuitable loudspeaker loads and the accidental short circuiting of the connecting cables. To a great extent, the use of AC coupling between this amp's output transistors and its output connections – by capacitors – removed the possibility of instant destruction by a stray whisker of wire or a poorly connected loudspeaker. But the designers went further in the pursuit of toughness.

Early Warning
The average current flowing in each of the two pairs of output transistors was continuously monitored by a transistorised circuit. If either channel exceeded a predetermined level the input to both of the power stages was muted, protecting the amplifier and giving a clear warning that something was wrong. Once the overload condition cleared, the circuit automatically reset itself. This meant that on most occasions a simple reduction of the volume setting was all that was necessary. The arrangement was greatly preferable to conventional fuses, which users seldom replaced with correctly rated parts. As a result of the care taken in its design and the quality of the components employed, the KA-2002 soon earned an enviable reputation for reliability, with decades of trouble-free use being enjoyed by the majority of owners.

For those requiring more power and more facilities Trio offered a range of pricier alternatives to the KA-2002. The KA-4002 looked much the same but was a little larger and offered slightly more power. For those wanting a real top-end model, the KA-7002 had everything one could possibly want, including a rating of around 60W per channel.

Kerb Appeal
The KA-2002 itself became the KA-2002A in 1973. While many small changes were made to the circuit, the basic layout remained. The fascia was also re-styled with new (and slightly larger) knobs, and buttons in silver rather than black.

This KA-2002 is attractively sized and styled – it has the sort of instant appeal that makes one keen to give it a try. It isn't small like the micro systems of the late 1970s were – for example, the Aurex 15 [HFN Apr '16] – but it isn't built into a standard-sized but largely empty chassis either. The styling has a functional, timeless quality, enlivened by a subtle and restrained use of colour.

For those who require a tuner, the KT-2001 is in every respect a perfect match. The KA-2002 is also easy to combine with modern equipment, the only stumbling blocks being the speaker terminals, which are uninsulated finger screws of a small, fiddly size.

Without Fear
On the input side, things are much simpler since all the sockets are standard RCA types, sensibly spaced and of normal sensitivity. There is no fear of overloading the line-level inputs with modern high-output sources such as CD players and DACs as the volume control precedes the first active stages of the amplifier. In fact the worst that can happen is that the action of the volume control may become a bit abrupt.

Twin Decks
The provision of two turntable inputs, both with MM sensitivity, is not only unusual but will probably be found to be unnecessary in most systems in which the amp will be used. A pair of shorting plugs inserted into the vacant inputs avoids the nuisance of noise pick up from this source when using the input selector. There is no option of variable cartridge loading, but the fixed value is the standard 47kohm, which will suit most popular types of pick-up.

All the controls work in an intuitive and straightforward manner, the only quirk being the needless click-stop increments fitted to the treble and bass knobs. These may well give the impression that the adjustments are made by precision-switched attenuators but in reality they are not. Rather, it is a simple deceit created by a spring, a ball bearing and a series of holes. The loudness function, meanwhile, is unlikely to be used by readers of HFN, but the mono switch is useful not only for the playing of old mono LPs, where it can help in reducing background noise, but for system setup.

Tim Listens
In practice the KA-2002 is light on bass, though this may be ameliorated by the use of ported loudspeakers pushed well into the corners of the listening room. Yet what one gains in bass level one tends to lose in precision, so this is not the perfect solution. With a more conventional set-up, however, the KA-2002 manages to give a good sense of bass. The result is a sound which, after just a few pieces of music have been played, is easy to tune into and enjoy.

Cream Of The Crop
Indeed, there is much to like about the KA-2002, my favourite aspect being its modern feeling and character. Using the line-level inputs (tape, tuner and auxiliary are all the same) it is subjectively noiseless at any volume setting and rewards with a focused, agile sound. Yet the lack of extension at the bottom and top ends, and the prominent midrange this effect generates, means that the KA-2002 never escapes from the 'small amplifier sound', which was ever present during an entire week spent listening to a wide range of material.

Power levels were adequate though, in part because music lacking a hefty bassline can sound strident when played very loudly – an effect that occurs well before any obvious clipping or compression sets in – and this certainly wasn't the case here.

Peter Gabriel's 'Mercy Street' on the compilation Shaking The Tree: Sixteen Golden Greats [Virgin PGTVD 6] sounded impressively spacious and broad through this amplifier. The delicate percussion may have lacked some sparkle, but the centre presence of the vocal was excellent while the bass was tight and tuneful. Detail rendering reached a high standard too, there being no suggestion of the blurring and veiling that some basic amplifiers can cause. 'Grown up' was the phrase that came to my mind. I could see this amplifier remaining useful to its original owner as both sources and loudspeakers were upgraded, perhaps several times.

Largescale orchestral works proved to be more of a challenge, however. The 'Waltz Of The Flowers' from Tchaikovsky's The Nutcracker [Philips 814 125-2] showed promise at first, the opening harp set against a perfectly still background being followed by the most beautifully creamy woodwind. It was the strings that revealed the KA-2002's limitations, sounding a little lifeless and grey when compared to the results given by more sophisticated (and expensive) equipment.

In the end, it is only in its limited ability to convey scale where this neat little unit falls short. Otherwise, it is a pretty good listen. It may not be the best amplifier I've ever heard, but the KA-2002 is still one I'd happily use in a small system.

The DC-coupled generation that came afterwards may have done a better job, but consider this: our well used example is, as far as I can determine, completely original. Not a single component has been replaced and not one connection has been remade since it was built. It is Methuselah with tone controls!

Buying Secondhand
The famous reliability of the Trio/Kenwod KA-2002 has endured to the present day and any reasonably well cared for example is likely to still be fully functional. The designers' protective measures do not rely on relays, so this frequent source of problems when it comes to amplifiers is not an issue here. Nor is there the requirement to adjust the offset voltage in the output stage, for this is stabilised automatically. The only adjustment possible is to set the bias current, which should be 20mA in each channel. With age it tends to fall, resulting in obvious distortion at low volume settings.

Point Of Contact
Component quality is high, so the routine replacement of things such as electrolytic capacitors is unnecessary. One occasionally encounters a sample with excess noise on one of the channels, and this is normally the result of a defective transistor in the small signal stages. Otherwise, most problems stem from tarnished switch contacts, most commonly in lesser used controls. A small dose of contact cleaner is usually all that it required, not forgetting the pre/power amp link switch at the back. This may never have been moved since the amplifier was made!

Hi-Fi News Verdict
An amplifier with genuine vintage interest that sounds good, is easy to use and seldom goes wrong. A dream come true? In a way. The KA-2002 is the perfect introduction to vintage hi-fi, just as it was to everyday serious listening when new. Still abundant and inexpensive, it has so much to recommend it. Be selective as there are a lot of them out there, so don't settle for anything but the very best.

Trio/Kenwood KA-2002 Integrated Amplifier Lab Report

Boasting a full 22 transistors in its BOM (bill of materials), four of these are the 2SC1060 NPN silicon types, one pair for each channel, employed in Trio/Kenwood's quasi-complementary, AC-coupled output stage. Rated variously at 17W/8ohm or 2x13W/8ohm, our venerable sample of the KA-2002 mustered 2x12W into 8ohm and 2x14W into 4ohm, both just 1W shy of the original specification. Under dynamic conditions, output increased to 17W, 24W, 23W and 16W into 8, 4, 2 and 1ohm loads, respectively, [see Graph 1, below] and although these 10msec figures are more significantly lower than the 38W/8ohm dynamic output claimed by the brand at the time, Trio/Kenwood never specified duration or distortion for this latter figure.

Otherwise the KA-2002 performed as anticipated: overall gain is a sensible +36.6dB (40dB+ was more common) while the A-wtd S/N ratio proved about 10dB behind the 'modern average' at 75.5dB (re. 0dBW). Distortion increases gently with increasing output and decreasing frequency [see red infill, Graph 2], the former lifting from 0.15%/1W to 0.5%/5W and 1%/12W (all 1kHz into 8ohm). Distortion increases from 0.15%/1kHz to 0.28%/20Hz (all re. 0dBW) as a function of the capacitor-coupling, the latter impacting both output impedance (0.16ohm/1kHz to 1.2ohm/20Hz) and frequency response versus loading. Into 8ohm the bass response starts to roll away below 50Hz, reaching –2.8dB/20Hz, but is more extended at HF to –0.75dB/20kHz and –5.25dB/100kHz [black trace, Graph 2]. Low frequency extension is further limited by lower impedance loads [red, blue and green traces] although the 'loudness' contour delivers a +5dB boost at 50Hz and +2dB lift at 30kHz [dashed trace, Graph 2]. PM

• Power output (<1% THD, 8/4ohm) 12W / 14W
• Dynamic power (<2% THD, 8/4/2/1ohm) 17W / 24W / 23W / 16W
• Output imp. (20Hz–20kHz/100kHz) 0.160–1.24ohm / 0.77ohm
• Freq. resp. (20Hz–20kHz/100kHz, 0dBW) –2.8dB to –0.75dB/–5.25dB
• Input sensitivity (for 0dBW/13W) 24mV / 152mV
• A-wtd S/N ratio (re. 0dBW/13W) 75.5dB / 86.6dB
• Distortion (20Hz-20kHz, 10W/8ohm) 0.12–0.28%
• Power consumption (Idle/rated output) 5W / 60W (for 2x13W/8ohm)
• Dimensions (WHD) / Weight 330x118x240mm / 4.8kg 

Review: Tim Jarman, Lab: Paul Miller

Source: www.hifinews.com