An Announcement, Amp Update, and Voltage Controlled Filter (VCF) Prototype 1

Hey readers, I have a quick announcement before getting to the core of the post. This project will be continuing through the Fall semester! Quite excited. I did not get where I wanted in the summer session and my professor offered me the opportunity to continue this as a Project II class. Great news! More fun ahead.

Well, since the end of the summer session I've been busy finalizing my guitar amp build, just finished last week. My professor and I agreed that building the amp unmodified first would be a good idea, that way I am actually see what kind of voltages I will be dealing with as I design the VCF.

Here's it the completed amp!

It sounds great. I was blown away it worked when I first switched it on. I've heard horror stories of people spending a week tracking down incorrect wiring or bad components on their first builds. Phew!

Now, I do have a prototype VCF, it is not at all designed to be placed inside the amp, it was more of a proof of concept. And it does work as a VCF under certain conditions. One of those conditions being an input signal with a magnitude of around 200mV-500mV, any greater or lesser voltage causes the transistor to enter saturation and the circuit no longer functions as a VCF. It also has a rather small frequency range/sweep.

Have a look:

I don't have a schematic for this yet. I'll scan in my paper draft when I get the chance. I plan to modify this design within the week. I want to see if I can increase the filter frequency range by placing another FET in series with the first. The FET's I am using have a rather small ohm range, from around 70 ohms to 800 ohms. I will be ordering some different FET's to experiment with this week as well. I need to start some PSPICE simulations soon. We'll see. I have not worked with FET's in PSPICE before.

Well that's all for now,
Mark