Audiolab 8000C Preamplifier
The 8000C preamplifier precisely matches in size, style and quality of construction its stable mate the 8000P; like it too, discrete transistor amplifier stages are employed throughout; integrated circuits have been eschewed. Although all the components, with the exception of a toroidal power transformer at the right rear, are mounted on a single glassfibre printed circuit board covering the whole remaining area, there are I really six distinct divisions. The first two are concerned with housekeeping, namely power supplies and turn-on delay plus output switching. Regarding the former, users are warned that after a run the left side of the case will be quite hot, and this is because it is used as an extension of the heat sink provided for the main regulating transistor. Two of the remaining divisions are separate pre-amplifiers for moving-coil and moving-magnet pickup inputs. Which one you choose is selectable by a push-switch on the rear panel between the respective phono sockets, which are distinguishable by their gold plating. A parallel pair is provided for the MM input to permit the connection of an additional load if the chosen cartridge would benefit. If you have two turntables, both may be left connected and the one selected is indicated by a small red LED on the front panel. The controls provided on the latter are, running from left to right, as follows. First a pair of identical rotary switch knobs independently select the chosen input to be passed on and the chosen source for recording. Two tape recorders, turntable(s), a tuner and a CD player are catered for; all line inputs are accorded the same input level and load. One set of markings between the knobs is applicable to both, so their selecting positions are reversed, one clockwise, the other anti-clockwise. This is not a problem but the situation is repeated for the next pair of knobs which are the bass and treble tone controls. One is so used to 'clockwise to increase and anti-clockwise to reduce' that to find this case of inverted operation for the treble is something of a trap. A push-switch between these knobs can be used to disable and by-pass the tone controls. Next is the balance control and this, like the continuously variable tone controls, has a central detent to identify the normal position. A larger circular knob is used for the volume control, followed by a further pushswitch labeled Output On/Off, which in reality effects a changeover between the rear mounted output sockets and the internal headphones amplifier whose output jack-socket is alongside. This amplifier and the tone control/line amplifier form the last two of the six internal divisions. A last push-switch controls the mains supply arriving from the fused IEC connector at the rear.
On test the 8000C performed accurately to specification-usually slightly better-though there were two exceptions. The overall gain was low, 100mV in producing only 675mV (650mV with the tone controls in circuit) instead of the 707mV claimed; secondly there was a slight departure from the stated tone control range. What is of some concern is the quoting of input sensitivities for an output of 700mV which, as we have seen, is well below that needed to drive fully the 8000P power amplifier. One day we may get international agreement on this transfer voltage level but in the meantime I think manufacturers might avoid such misleading anomalies, however unintentional, for their own products, particularly where a common instruction book applies to both. In the present case, to quote an input sensitivity of 175mV at the main inputs and pro rata at the phono inputs for full output would be more realistic and helpful to the prospective customer.
Listening tests through both these pieces of equipment were highly satisfactory. Using the CD input, and with the tone controls out of circuit, it proved impossible to decide whether the pre-amplifier was in circuit or whether the power amplifier was being fed direct. Including the tone controls did give an impression that something had changed but this was identified as a slight loss of gain which, on checking the measurements proved to be only 0.4dB! Both moving-coil and moving-magnet inputs were checked, the former with low and high output cartridges. All performed admirably, as the accurate RIAA and adequate overload margins would suggest. Because the sensitivities of all the other inputs are identical, it might be considered desirable to pad down some sources such as CD players which, if switched in without first turning down the volume, will certainly scare the cat. This apart, the 8000C is a first grade product, very well considered and executed. I particularly liked the gentle nature of the tone controls, avoiding the excesses of most designs which only encourage misuse.
