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ELECTRICAL DATA 2.")
recording we do not require this step down, and so a transformer of the order 1 to 1 will frequently be found satisfactory.
Actually these components, the output transformer and the speech coil of the recorder, should be properly "matched'' in impedance. It is not within the present scope to deal with impedance matching, and in the experience of the writer trial is the only certain method of obtaining best results.
If we propose building a home recording set by purchasing units in distinction to simply taking the complete outfit from one of the manufacturers given later in the book, one or two points must be borne in mind. First of all the supplier of the microphone will be able to suggest the best ratio of transformer and almost certainly supply it. In the same way the company supplying the recording arm will be able to suggest the best output transformer if the type of amplifier to be used is mentioned.
Connection to Radio Sets. Most modern radio sets, especially of the mains variety, possess terminals labelled "pick-up" and ''loud speaker." In this case the secondary of the microphone transformer should be connected direct to the pick-up terminals, and the switch on the radio set should be turned to "gramophone."
The terminals labelled "loud speaker" must be treated more carefully. If the set itself contains a loud speaker this is best disconnected. It must then be determined whether or no the loud speaker is of the moving coil or moving iron type. If the former, a further inspection should be made to determine whether the loud speaker output transformer is also disconnected by removing these connections. Nearly always this is the case, and the output transformer will be found attached to the cone basket of the loud speaker itself.
If, then, the radio set possesses a moving coil loud speaker with associated output transformer, the leads can be removed and in their place fitted the primary leads of the recorder output transformer, as in Fig. 11. With the circuit thus made up we are in a position to proceed with recording.
If, however, the loud speaker is of the moving iron class
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