we will have to debug your breadboard build just like we debug any perfboard or pcb build.
but we have the benefit of being able to fix your mistakes very easily.
first, to answer your question about the gain knob. the pot, which can be used generally as a voltage divider (like the fixed voltage divider in the power section) can be specialized to work as a variable resistor. this is done by connecting the wiper (middle lug) to one of the other lugs. by shorting those two lugs all of the resistance between the connected pair and the other lug is the resistance between the wiper and the unconnected lug.
so, no, it's not a a flaw. it is just that the gain knob is a variable resistor between the feedback loop and ground.
if you would like to read a sequence of notes about resistors, starting with fixed resistors and working all the way through to mods on pots, you might try the ones i put up on gaussmarkov.net:
resistors. there are links to R.G.'s stuff there and some other sites as well.
your ceramic disc capacitor will be fine. and your series of 100pF caps also. if you want to match the 47pF capacitance, i think you only need to put two of them in series. that should give you 50pF.
so ... on to debugging.
the debugging page linked at the top of the pages of this forum is required reading. so are the links in that page. among the things that are described there is the audio probe and voltage readings on ICs and transistors.
you need to build an audio probe (it's easy) so that we can trace the signal through your circuit by listening to it at different points and seeing where the signal stops. with the breadboard set up, you can actually just build the audio probe onto the board -- it's just a capacitor and two jumpers. one jumper will go to a net on the breadboard from one side of the capacitor and the other will go to your output jack from the other side of the capacitor.
you also need to read and report the voltages on each pin of the IC. the ones that i got for a working circuit are in
Topic: 3. Hooking Up the IC and these are the approximate values that you should be reading.
one last thought: you may not have grounded everything properly. use the continuity check on your DMM to make sure that everything that is supposed to be grounded is connected to the ground post of your breadboard, including the ground lugs of the input and output jacks.
i am looking forward to helping you get your breadboard build working.
