|Leak Point-One Stereo Control Centre & Stereo 60 basic amplifier|
The two chassis are interconnected by a multi-conductor cable which carries operating power to the preamp as well as signals from it to the basic amplifier. For use with preamps other than the Leak, a pair of standard phono jacks is provided on the chassis of the basic amplifier. As supplied, the Leak combination goes on automatically when the AC line cord is plugged into a live outlet; alternately, its switch outlet can be easily wired to turn the power off and on from the preamp.
The preamp is neatly and simply styled, with a relatively small number of essential controls logically laid out. At the extreme left is a large input selector knob, with positions for tuner, tape head, magnetic pickup, extra (or auxiliary high-level source), and microphone. Just below and to the right is the mode selector, with positions for monaural (monophonic), left channel, right channel, stereo, and reverse (channel reversal). Continuing across the panel, there are bass and treble tone controls - each is ganged so that it operates on both channels simultaneously; a channel balance control; and the volume control. Just below and to the left of the volume control is a rumble filter switch.
The rear of the preamp contains input level controls for the magnetic pickup, tuner, and auxiliary inputs. The microphone and tape head inputs feed directly to the selector switch. In addition to these input jacks, there are recorder output jacks for each channel which tap into the circuit after the tone controls but before the volume control. The preamp also contains the octal socket for connecting the cable to the basic amplifier, as well as a single phono jack for feeding a mono signal (right channel only) to a mono power amplifier if desired. The preamp - compact, light in weight, and enclosed in its own case - may be placed in the open on rubber feet or installed in a panel cut-out.
The power, or basic, amplifier of this duo contains its own octal socket for receiving the other end of the interconnecting cable, as well as standard phono jacks for use with other preamps. It also has two switched AC convenience outlets (there are none on the Leak preamp) for connecting other equipment. Instead of the series of screws for the different speaker impedances found on most amplifiers, the Leak has only one pair for each channel; different speaker impedances are selected by changing the position of a shorting plug on the top surface of each output transformer. Similarly, the power transformer has a shorting plug which can be positioned for 110, 117 or 124-volt operation, depending on the electrical voltage supplied in any locale. The tubes used, in both chassis, are standard types.
If inanimate equipment can be said to possess a personality, the Leak ensemble may be characterized as "British conservative. This is most apparent in the number and type of controls offered, minimal by American standards but enough to keep things going smoothly. Even such a seemingly insignificant item as the use of the word "monaural" instead of the more recently adopted term "monophonic" (or, indeed, the shortening to "mono") suggests a temper that will not bow to current vogue.
This notion is further evident in the equipment's performance. Mr. Leak has indicated that his philosophy of amplifier design eschews both high power and very wide response (that is, much below 30 or above 20,000 cps). As for speakers, he favours magnetic cone types of moderate to high efficiency. USTC's measurements of the Leak amplifier indeed confirm this approach; the equipment is what its designer obviously has intended. Thus, the less power the amplifier was called on to deliver, the lower its distortion and the wider its response, and at what might be termed – by current practice – low power, the amplifier did cover the audio range with ease. When driving capacitive loads between 0.01 and 0.2 microfarads, it tended to oscillate which, of course, would indicate that it is not intended to drive electrostatic speakers. On the other hand, it did have a high, favourable damping factor which would help it control magnetic speakers. And its square-wave response, both at low and high frequencies, was quite satisfactory: the 50-cps response showed a relatively small tilt, indicating clean bass down to and below the nominal 20-cps limit; its 10-kc response indicated virtually no ringing and good handling of transients. The signal-to-noise ratios were, in sum, not as high, and the IM distortion not as low, as measured on many other amplifiers; but these characteristics were impossible to discern as "unfavourable" in listening tests at normal volume levels in average-size rooms.
The preamp's tone control and rumble filter characteristics were well suited for their intended functions. The RIAA disc playback characteristic was very good, but the tape head playback characteristic varied by several dBs from the standard. This would concern only those who wanted to play pre-recorded tapes from a deck that lacked its own preamps; tape decks with their own preamps can be jacked into either the "radio" or "extra" inputs on the preamp or into the phono input jacks on the basic amplifier.
Both pieces of the Leak ensemble are magnificently
built. Wiring and under-chassis layout are among the finest encountered,
and resemble high-grade military- type construction. The layout atop the
basic amplifier chassis is ample, and the unit does not generate excessive
heat. The whole has a feeling of rock-solid quality about it. The Leak
may not be the most spectacularly performing amplifier, but it surely
must be - within its admitted limits - one of the most reliable and enduring.