Audiolab 8000T Tuner
In the majority of digitally synthesized tuners (basically those where the tuning oscillator frequency is compared with a quartz crystal) variable tuning is under the control of a pair of Up and Down buttons; if there is a knob it is nothing but a mechanical substitute achieving the same thing. To avoid horrible inter-channel noises these tuners have a muting circuit which suppresses all sound whilst selection takes place. The Audiolab 8000T is not like that- very cleverly it accurately mimics the performance and feel of a classic analogue mechanically tuned design. Inside a moulded light-proof housing the shaft of the tuning knob, running in ball races, carries a shutter disc with 60 slots. These pass between an LED light source and a pair of infra red sensors (two are needed because the system needs to know which way you have spun the knob as well as how far) and each pass initiates a 25kHz change of frequency so that a complete revolution on the FM band alters the tuning by 1.5MHz, comparable to a mechanical design. The shaft also carries a 60-tooth cog aligned with the slots and there is a closely adjacent magnet so that although the flywheel action is not impeded it is possible to feel each tuning step when rotated slowly. When this takes place and indeed when any change of operation is initiated in this tuner the output is temporarily reduced by 15dB so that one can listen through the operation without undue disturbance even if the optional full muting is disabled. This has to be the most delightful variable tuning device yet found on a 'modern' tuner but it has the snag that being always operational and readily moved by the slightest accidental touch it is all too easy to spoil a wanted recording. Maybe one of Audiolab's clever chaps could arrange for the microprocessor to disable it by toggling the muting button. The remaining controls, all pushbuttons, are all logical and clearly labelled. At far left under the heading Auto are an Up/Down pair which set the tuner looking for the next worthwhile (i.e. strong enough) station; adjacent are three to select the waveband, then four to select bandwidth (by a choice of two alternative IF chains on FM and by audio filtering on AM), Mono override, the previously mentioned Muting and Hi-Blend which reduces hiss on the weaker stereo transmissions. Spaced off are a group of ten plus a "P" multiplier for direct access to a maximum of 39 chosen programmes from any waveband and any of the chosen conditions above. Lastly are another Up/Down pair to cycle through the 39 and a Save button to commit your choice to the memory. Pressing this and the adjacent "P" button conjures up a recording calibration tone on both FM and AM which closely relates to 6dB below maximum signal thus facilitating setting the gain control(s) of an associated recorder. Near the right edge is a large button which, in common with all the Audiolab products, is the Power On/Off switch.
Behind a full-height transparent panel slightly off-centre is a satisfyingly readable liquid-crystal display backlit in pale green. This shows the programme n umber if one is selected, and the current wave band and frequency in numerals 10mm high. Below it appear confirmation of the relative selected conditions such as Mono or Stereo, Muting and Bandwidth. At the bottom are a pair of bar-graph type displays; the one on the left is an accurate ten-section portrayal of the received signal strength on each waveband which can be related to the actual figures from a chart in the instruction manual if one so desires. The second linear display only appears on FM and provides an exact indication of tuning to the centre of the received transmission and is calibrated in 25kHz steps out to ±125kHz.
The rear panel carries a two-pin fused IEC power connector and a group of four gold-plated phono sockets. Two of the latter are the normal left and right channel audio outputs, the others provide a DC voltage related to signal strength and a wideband demodulator output that might feed an RDS decoder. There is a male coaxial aerial connector and four terminals to two of which the supplied separate directional loop AM aerial is connected and the others for external AM aerial and earth if required.
As I hinted in the opening paragraphs the circuit of the FM section is quite novel, for after leaving the fully featured front-end (designed in house) and one or other of the 10.7MHz IF stages, the signal is limited and passed to a frequency doubler from which it emerges at the expected 21.4MHz with the deviation also doubled to a 'maximum' of 150kHz. It now meets a second mixer with a crystal oscillator operating at 22.1122MHz where a lowpass filter selects the 712.2kHz resultant which retains the 150kHz deviation. I am told the choice of frequency is calculated for the maximum avoidance of possible beats and who am I to argue! The remaining signal information is then applied to their own unique 'charge integrating demodulator', which boasts very low noise and distortion, requires no alignment and is therefore not subject to drift over the years as it uses only close-tolerance passive components. At this point the detected audio signal plus possible pilot tone and stereo carrier is passed through a very elaborate 'birdie filter', so called because any failure on its part to remove spurious signals can produce a chirping background not unlike a distant cage full of budgerigars who have just spied a cat. Next comes a selected integrated circuit stereo decoder and more filtering to remove traces of pilot tone and its harmonics and then at last to a pair of high quality output amplifiers which provide a low impedance source at the output phono sockets.
How it performed
Rather sadly one has to admit that all the effort which the Audiolab team have put into this exceptional design is increasingly let down by the quality of transmission now considered adequate by most of the broadcasters. Because the FM band is now so crowded (Philip Swift was amazed by the number of signals filling every channel right up to around 104MHz to be received on an omnidirectional aerial here, where I live near Oxford, in the centre of the southern half of England) most broadcasters have installed Optimod or some other form of signal boosting to maintain their service area, but at the expense of fidelity. However, enough first class broadcasts are still put out to show what this tuner can do (For example, BBC Radio 3 lunchtime concerts from St Johns, Smith Square seem exceptional at present) but although I and other writers repeatedly read the riot act we shall be fortunate if we can hold the status quo for, under pressure, all the authorities seem more concerned with 'coverage' than quality.
Frustratingly one has to note that if every receiver possessed another feature of this Audiolab 8000T - its amazing ability to drag worthwhile listening from a mess of signals then that concern with coverage would recede into the background. Allied to this is the unwillingness of the average user to invest in even the most modest FM aerial, so rarely to be seen on the rooftops amidst a forest of TV multi-element toasting forks and the prolific dish. A never before equaled test here really convinced me of this tuner's worth. London's Kiss FM, a comparatively small 4kW transmitter, broadcasts on 100MHz exactly; adjacent on 100.1 MHz is the 250kw Classic FM Birmingham station. Using my omnidirectional aerial no receiver so far encountered has been able to do more than just acknowledge that Kiss might be there in a welter of noise and clashing signals. The Audiolab brought it out in the clear in mono using its narrow bandwidth and with the hi-blend engaged a pretty fair result was achieved in stereo. Most remarkable. Out of interest and to illustrate the difference a proper aerial makes, I would comment that practically every tuner tested has made a reasonable job of it with the added discrimination provided by my other highly directional six-element aerial on a rotator, certainly in mono.
Audiolab's tuner may have been a long time cooking but their combined chefs have produced the most appetizing confection I've experienced in many a long day. Listening to it one has the confidence that no competitor is likely to do better and only a few will equal its hold on the information transmitted. On FM it has that easy naturalness which soon makes one forget the medium and enter the music and, perhaps more unusually, the degree of enjoyment available from some AM stat ions has been a revelation. Certainly it is expensive but it is beautifully constructed using the finest materials and a degree of intelligent thinking and manufacturing no us which too many media miseries think we British have lost forever. Let's just hope that our BBC and other broadcasters here and in other countries will try harder, both now and in the future, to produce the input to do it justice.
