Miscellaneous

AF input selection
Use is made of a single-pole, 12position rotary switch, S1, with whichand 12 pull-down resistors the inputsource is selected. Since only one resistoris linked to the positive supply lineat any one time, the current drawn bythe circuit is only 15 μA, which, in thecase of a battery operated preamplifier,is an important advantage.

ACTIVE POTENTIOMETER
The potentiometer introduced by Panasonica little while ago is of a qualityexceeded only by the likes of the Penny &Giles potentiometer (which cost in excess of£ 100). The Panasonic devices have multilayertracks made from conductive plasticsand carbon, which are linked to the terminalsby silver electrodes. The five-foldwiper is also made of silver and guaranteeshigh […]

active power buffer
Frequently,a directvoltage isrequired ina circuitthat mustbe free ofhum and noise,but not regulated.For instance,the supplyto an audiooutput stage mustbe able to vary with themains voltage and theload. Another exampleis when in the workshopa variable-ratiotransformer (variac) isto produce a well-filtereddirect voltage withgood loading capacityfor general purposes.

This accurate bass tone control with A difficult problem in the design of conventional stereo tone controls is obtaining synchronous travel of the potentiometers. Even a slight error in synchrony can cause phase and amplitude differences between the two channels. Moreover, linear potentiometers are often used in such controls, and these give rise to unequal […]