I promised in yesterday's post to explain more of a cascode and how it works. We use a cascode when we need to divide the duties of one transistor into two. The reasons are varied: too much voltage for the one, poor performance characteristics, we want a different sound. In the case of the new BHK amplifier, Bascom explains we chose a cascode to remove the non linear response of a certain type of MOSFET. This works because the cascode has an amazing property where the input transistor dominates the circuit's response. This means that the two transistors in a cascode act as one and the clever designer chooses his best for the input device. This is a picture of a typical cascode circuit. Q1 is the input transistor and Q2 the cascode device. The music would come in through the lower small circle labeled VJ and feed Q1. Whatever Q1 measures and sounds like, will be passed along to Q2. The output of this circuit is from Q2 labeled Vo (Voltage Out). This is a great circuit for designers to include in their bag of tricks. Tomorrow I'll explain why Q2 sounds the same as Q1.
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