Hi,
I'm a french student in first year in electrical engineering and I'm working on a project of design for a hifi audio amplifier.
There are 5 main parts in my projects :
- input (thevenin equivalent with variation of +/-0.5V and impedance of 100Ohm)
- filtering (topic here)
- pre-amp (voltage amplifier, with potentiometer allowing a gain of 0 to 10)
- power amplifier AB (push-pull)
- output (speaker modelised by a 8ohm resistor)
The problem is in the filtering part. As you can see on the title, I have to create a 3-band filter WITHOUT any op amp. I thought about the baxandall structure, but it's only for 2 band. Then I thought about adding in parallel another baxandall structure, but a bit modified. It could be a pass-band, with cutoff and gain in treble/bass already fixed, but with a common emittor with potentiometer to control the gain of the band pass.
I'm not good in calculus of circuits and it takes me a lot of time, without a good method too. Moreover, my deadline next thursday (I have an oral presentation) and I worked the whole semester on finding solutions, but I had also a lot of work so I'm actually quite in a bad situation. What I need before monday (I also have exams from monday to friday), is to assure that my idea will work, make the calculus, and also implement the impedance adapations for the branches, because I need to have the same impedance on both branches.
By the way, do you think that using the potentiometer on a branch will modify the impedance ? If yes, is there a possibility to follow the impedance of one branch for the other one ?
What could be the problems for the phase ? (a standard baxandall doesn't have any problem in 2-band, because the low pass and high pass just cancel each other)
Thank you, if needed I can make some simulations on LT Spice, but actually, I don't want to simulate and lose time if it's just impossible to use this solution. I will use it to find the best parameters faster
Thanks for helping if you can,
Paul