Foresight Forsooth
Dear Editor:
Concerning my fanciful piece in this issue's "Audio ETC" on "What hath God wrought." and the first Morse code message, allow me to stave off a number of indignant letters by noting that I am quite aware of the improbability of the "testing-testing" messages I manufactured for the story.
Not, however, their impossibility. If I am right, the Washington-to-Baltimore demonstration line was one wire, with earth return, and thus subject to plenty of nature's interruptions. A couple of thunderstorms in the general region could have set off quantities of spurious dots and dashes, like the clicks I hear today in my rural phone when there is lightning around. An imaginative and excited mind might well interpret these literally. Spqrfcc? Maybe.
I trust that those who set up audio communications will attest to the validity of the testing-testing concept--Mr. Murphy, Sr. included.
-Edward Tatnall Canby; West Cornwall, Conn.
Help Wanted
Dear Editor:
I wonder if I might make an appeal through the pages of Audio. Older readers will remember that in the pre tape era, the very best disc recorders were made by Presto Corp. last located in Paramus, N.J. Of course, they have long been out of business.
I have a Model 8D Presto recorder which I would like to restore, and I am seeking any information regarding servicing, etc. If anyone can send me photocopies of schematics and brochures, I will happily reimburse the costs. I also have a Model 85E recording amplifier, and again, photocopied information would be welcome.
Peter Newbrook, "Applecross", 185A Newmarket Rd.
Norwich, Norfolk NR4 6AP England
Ins and Outs
Dear Editor:
In regard to the article "Too Many Signal Sources" (June), while switch boxes can be useful in multiplying the number of inputs and outputs of audio equipment, it has been my experience that they also can degrade the signal.
It is important how the switches are made. For example, some low-current switches employ an armature that simply touches the different contacts as it is switched. These switches can seriously degrade the signal. On the other hand, in most switches, the armature is grasped between spring contacts; these transfer the signal with better fidelity. Probably the closer a switching mechanism comes to being a continuous wire, the better. In other words, the best switches will have heavy armatures and heavy contact gripping springs.
Another factor that can degrade the ability of a switch to conduct an audio signal is oxidation. Switches made of copper, bronze, or silver will tend to become less efficient as they age. The best switches will have armatures and contacts made of gold alloy or gold-plated materials. Spraying with TV tuner cleaning fluid helps reduce oxidation and improve the signal conduction of all switches.
In view of these considerations, it seems important that audiophiles study the construction of the switches that they are thinking of using. Since many switches are mounted in boxes it may be difficult to see the armatures and contacts or to reach them easily with cleaning fluid. Also, it is wise to test switches before buying them.
Bradford Lyttle Chicago, Ill.
Erratum:
In my article, "Cables and the Amp/ Speaker Interface" (August), the discussion of a transmission line's characteristic impedance, on page 48, should have read: The characteristic impedance of a transmission line is given by:
where R is the line resistance per unit length, L is the series inductance per unit length, C is the shunt capacitance per unit length, and G is the shunt conductance per unit length. Of the two constants, j is the square root of -1 and ω (omega) is equal to 2π times the frequency.
-R. A. Greiner
(Adapted from : Audio magazine, Nov. 1989)
= = = =