A FEW FACTS ABOUT THE LAST AUDIO

Radio Record, Volume I, Issue 31, 17 February 1928, Page 13

A FEW FACTS ABOUT THE LAST AUDIO

By

Megohm

With the increasing use of B eliminators, the quality of reproduction will, on the whole, tend to be raised, especially when dry batteries give way to the more economical method of high-ten-sion supply. Working from the maius, 20 milliamps or more may easily be supplied to the plate circuit of the last valve, acconipanied by a suitably high voltage of 150 or so. It should be noted that the current, or milliamps, have more effect upon quality than has the voltage, which latter merely provides the means of overcoming the internal resistance of the valve, For a last stage valve the requirements are high plate current (milliamps), high grid bias, but not unreasonably high voltage. In practice these conditions are not entirely fulfilled, though they are aimed at, The range of volume is determined _ by the amount of current passed by the plate of the last valve, although it is only the fluctuations of this current which operate the loudspeaker, ‘The larger this current, the larger the maximum fluctuation possible, and hence the increased volume. So that the actual steady plate current passed is a good indication of output capacity. ° To secure good quality reproduction the last valve must both receive and deliver undistorted signals, and when this is accomplished it must be seen that the speaker will reproduce and further amplify these signals without distortion. A good amplifier will give good amplification on the lowest notes that a broadcast station puts out, and if loudspeakers had arrived at the same point on the way to perfection, then average reproduction would now be at a much higher level of quality than it actually is. Amplifiers are being , improved so that their amplification is fairly even over a very wide range of audio frequencies, and coupled to one of the few hfgh-grade types of loud- |

speaker that exist, resulis are highly pleasing to a person of musical taste.After all, it is only the music that counts, and experimenters as well as others should accustom themselves to judging the output of their receivers with their musical ear, and make it their greatest care to correct any unwanted tendencies that may te detected in the reproduced sounds. ‘These tendencies are only too often in evi-dence-woolliness of speech, distortion of low notes; general indistinctness or waut of sharpness and clarity, geuttiness or taspiness of tone, ‘‘tinny" tene, and so On. Good components will usnally give better tone and better general results than will the cut-price variety, and will need less nursing and bolstering up with fixed condensers and _ other expedients. But even if it has been necessary to purchase some of the less expensive variety, amends can be made to a good extent by careful adjustment and an exercise of common-sense, and the bad tendencies noted above can all be very considerably reduced if not entirely cleared up. Every receiver will deliver a certain amount of. volume without distortion, but whether or not-that amount of volume satisfies the owner, depends upon the individual taste, coupled with the capabilities of the receiver. The last audio valve chiefly determines the amount of undistorted volume, provided that the loudspeaker is capable of handling that volume and retain the quality. ake your last audio stage and loudspeaker as one combined unit, you may hitch up before it the biggest receiver with one audio stage that you can get, but the undistorted volume passed by your own audio-speaker unit will only be the same as with your own smaller hook up, provided, of course, that the latter is able to deliver at least right up to the limit where distortion commences.