IMPROVING AUDIO QUALITY

Radio Record, Volume II, Issue 1, 20 July 1928, Page 13

IMPROVING AUDIO QUALITY

(QUALITY of reproduction may be marred on the audio side in many different ways. There is distortion, arising from transformers, from badlyproportioned resistance coupling, low yolume-carrying capacity of the last valye, lack of grid-bias, and last, but not least, low-frequency reaction. Although the internal resistance of B battery or eliminator may not he so high as to cause an actual howl in a two or three-valve amplifier, there may be distortion caused by reaction due to such internal resistance. A remedy for this trouble, if it is suspected to be present, is to place an extra resistance in the plate supply leads excepting that to the powervyalye. A 2-mfd. by-pass condenser is placed across each such resistance on the. side away from the source of current, and B negative filament common lead. ‘ In a2 general way, a resistance of 20,000 ohms at least, is recommended, and whilst it may be considered that a great drop in plate voltage would result from its inclusion in the circuit, when an eliminator is in use, the drop need not cause any appreciable drop in volume, This method will at least prove a good last resort for any tendency to trouble from reaction on the audio side, as it is a practically certain cure. It may also be applied to the detector. The method is also a cure for "motorboating,"