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Suggested Layout of I S D Chip
Above: The use of an interstage transformer for an External Amplifier.
|There are Several Choices:
1) Buy a "Mini Audio Amplifier" model # 277-1008 @ $11.99 from Radio Shack and use its speaker (16 ohms, ~ 2 inch in Dia.).
2) An amplifier stage between the ISD device and the 8 Ohm speaker.
3) Two 8 Ohm speakers in series.
4) A 8 ohm resistor in series with a 8 Ohm speaker.
The ISD chip has very little power for the speaker, therefore:
(A) The cheaper the speaker the better--cheap speakers have high compliance (small magnet) which means they are loud for the input power at the expense of fidelity (of which the ISD has little).
(B) The larger the diameter the speaker--within limits--the better.
(C) Always enclose the speaker: A speaker held in mid-air will sound weak & tinny as compared to the same speaker inside, say, a Styrofoam cup.
(D) Make sure the openings at the front of the enclosed speaker are large: many holes or large holes or both.
(E) Experiment with various options--it will be very Instructive!
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