battery-operated (text) Contentspre-amplifier - part 1
This preamplifier is intended for those audio enthusiasts who are interested in only the best. Its discrete design produces distortion figures that are measured in tenthousandths of a per cent (the remainder of its specification looks very good, too!). Moreover, bearing in mind that in certain areas the mains supply voltage is not as pure as it should be, the preamplifier is powered by rechargeable NiMH batteries.
In this first of a two-part article, the preamplifier proper will be described. The second part, to be published next month, will deal with the specially designed battery charger. Design by T. Giesberts 14 The design of high-end audio equipment is typified by the continual striving for Dyed-in-the-wool audio enthusiasts then seek enhancement in psycho-acoustic matters such as solid silver the best possible quality. In the high-end design world, bass boost net-works, equalizers and impressive dis-plays are not contemplated. In fact, such ancillary facilities are considered undesirable. The only aspect that is of importance is the quality of the signal processing. This quality is the be all and end all as far as real audio enthu-siasts are concerned: no concessions are given or asked for. Only true qual-ity is worthy of the name hi-fi. A difficulty arises when the specifi-cations of an amplifier are so good that the designer is testing at the limits of his measuring equipment. Real improvements are then not possible or, in any case, cannot be measured. connecting cables, gold-plated connec-tors and bizarre units to treat CDs. The sense of such matters is a topic of argu-ment among themselves and ques-tionable to outsiders. Certainly, they cannot be measured or made audible. A more tangible means of enhanc-ing the performance of an amplifier is the eradication of all aspects that, out-side the normal signal path, may affect the performance. One of those aspects is the mains supply. In many countries, this is far from stable, while interfering spikes and other undesirable facets are the rule rather than the exception. This justifies the assumption that it must be possible to improve the amplifier’s per-formance by powering it not from the mains but from a battery. This assump-(text) Contentstion has been put into practice in the present preamplifier. The mains volt-1 input selector preamplifierage is used solely to operate the bat-tery charger and this only when the amplifier is switched off. THREE SECTIONS The design of the preamplifier proper is not really spectacular. True, the fact that no integrated circuits are used in the signal path is conspicuous but nothing special. The exemplary good specifications are nothing new because they have been achieved in earlier pre-amplifiers. The property that differentiates the present pre-Figure 1. Block diaamplifier from its predeces-gram of the batterysors is that these specifications operated AF preampliare allied with battery opera-fier. Only the upper tion. two sections are dis-The block diagram of the cussed in this article. ing ICS and semiconductors. Unsoldering is best done with a suction iron to time in this magazine. Also, the readers letters column often contains or special unsoldering braid. useful comments/additions to the published projects.