exponential vf converter for electronic music


Posted on Feb 4, 2014

The diagrams a circuit which performs this function with 0. 25% exponential conformity over a range from 20 Hz to 15 kHz using a single LM392 and an LM3045 transistor array. The exponential function is generated by Q1, whose collector current will vary exponentially with its base-emitter voltage in accordance with the well known relationship betwee


exponential vf converter for electronic music
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n BE voltage and collector current in bipolar transistors. Normally, this transistor`s operating point will vary wildly with temperature and elaborate and expensive compensation is required. Here, Q1 is part of an LM3045 transistor array. Q2 and Q3, located in the array, serve as a heater sensor pair for A1, which servo controls the temperature of Q2. This causes the entire LM3045 array to be at constant temperature, eliminating thermal drift problems in Q1 ²s operation. Q4 acts as a clamp, preventing servo lock-up during circuit start-up. Q1 ²s current output is fed into the summing junction of a charge dispensing I/F converter. Here is s schematic drawing : C1 ²s output state is used to switch the 0. 001 uF capacitor between a reference voltage and C1 input. The reference voltage is furnished by the LM329 zener diode bridge. The comparator`s output pulse width is unimportant as long as it permits complete charging and discharging of the capacitor. In operation, C1 drives the 30 pF-22k combination. This RC provides regenerative feedback which reinforces the direction of C1 ²s output. When the 30 pF-22k combination decays, the positive feedback ceases.




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