Hi all, Knowing the folk around these boards, I'm sure one of you can shed some light on this little problem for me. I've decided to dive into electronics with a project, a small NPN transistor based boost guitar pedal based on the schematic from diy stompboxes. Here is is: I've put the build together on a breadboard and some weird things are happening. The transistor I've used is a BC548, although I have tried a BC108C as well with similar results. Basically, the 10k resistor between the 9V supply and the collector of the transistor is where I'm getting the issue. When the resistor is in and linking the supply to the transistor, the output is incredibly low and dull sounding. When I take the resistor out (note, no 9V supply to the tran) the circuit functions as it should for a few seconds, with the right tone before it fades down to nothing. I've measured with a multimeter and the voltage at the collector follows the drop down. I assume this is the capacitors discharging and providing the power, is that right? I'm still not sure how to solve this. Originally I had a hunch that the resistor value was wrong and I needed a lower output to the collector, however no matter what value I try, the same thing happens. Besides, many others have built the same circuit with success. Any suggestions on how I can fix this? Or if not, even a little understanding on whats going on here so I can trace it back round would be great. As I say, I'm really new to the whole electronics/circuit building thing so I'm sure it's something simple I've missed! Any light you folks could shed would be awesome!
Have you changed the circuit from the DIY Stompbox version? I'd grab a multi and get prodding about to see if anything is malfunctioning if it's unaltered spec, although it's got pretty simple components that shouldn't fail. If I'd kept up with my electronics after A-level I'd probably dig in and give it a go, but I'm now pretty much useless.
Update time I have changed a couple of things, but I've made sure to substitute parts and wire them in correctly to make sure I'm keeping close to the values specified. I managed to get it going tonight after an hour or so tinkering around. Turns out that even though the schematic specifies a 0.1uF value for the input cap, when I plug in it filters the sound so much that I get horrible 'boing' like sounds from the peaks of the signal pushing through. I replaced it with a 4.7uF (tonnes bigger, lots of trial and error!) and now the sound is coming through clear and strong. Not a bad sound or boost either. I'm not certain if everything is still 'right' as I'm rubbish with the components/voltages etc, but I trust my ears!
