1. Quote of the month: "Think like a proton. Always positive" - Unknown
2. New quiz of the month: AQQ295 about a audio logarithmic volume controller using linear pot circuit
A kind proposal from Tim O’Brien (a frequent participant to our quizzes)
Audio volume is usually controlled by a logarithmic (log) potentiometer (pot) to approximate human hearing response. However true log pots are increasingly hard to source and relatively expensive. But there is a simple trick to establish an approximation of a log response using a linear pot and a single fixed resistor that’s good for about two decades - provided that the source and load impedances are appropriate to prevent undesirable attenuation at full volume.
One has to build a digital 90 degrees phase splitter circuit giving an in-phase (LO_I) and a quadrature phase (LO_Q) square LO signals phased out 90° one to each other. Among the following 4 circuits, there is one which is not performing that role.
Question: can you localize it and tell why?
1. With a 10K Ohm linear pot what is the value of the parallel fixed resistor R? to establish 10% attenuation at 50% rotation:
a. assuming zero source and infinite load impedance?
b. assuming 100 Ohms source and 10K Ohms load impedance?
2. There is no voltage attenuation for 1 a. at full volume, but what is the voltage attenuation at the load at full volume for 1b?
Good luck and try to be among the first ones!
