Wrong transistors

[kwitak]

As a little introduction, I'm a sophomore majoring in Electrical Engineering. I've been playing guitar for a while now and wanted to get into some of the engineering aspect of it, so I thought I'd toy around with stompboxes. Most of the courses I've taken thus far have been pretty basic, DC and AC circuit analysis, power, resistance, capacitance, inductance, etc. (except digital logic, I've taken fairly advanced courses in that). I don't know a whole lot about transistors, so when I went to buy the transistors for the stompbox I'm trying to build (the fOXX tonemachine, http://www.geocities.com/CollegePark/Library/1355/tonemachine.gif) at Radioshack and they didn't have the 2N3565, I wasn't sure what to buy. I picked some NPN transistors since I knew the 2N3565 was, but its obviously incompatible. The transistors I bought were TIP31 silicon NPN's. Is there any way to use these in the tonemachine? If not, is there any stompbox schematic on DIY that these will work with? Thanks in advance.

[aron]

I don't know about the TIP31. What you want is small signal NPN transistors.  2N3904, MPSA18 etc... easily found.

[toneman]

look @

http://www.generalguitargadgets.com/

there's a FOXXmachine in the Effects section.

mentions almost any NPN tranny will work.

wiring layout, pcb layout, parts list....
GGG has it all....
check it out.........

[niftydog]

TIP31 is for "medium power linear switching appications"

2N3565 is a general purpose amplifier.

Like aron said, you want a small signal transistor.

DC current gain in the 3565 is at minimum 3 times more than the TIP31 and there are a number of other charateristics that are very different.

[kwitak]

I got the circuit working, I made a stupid mistake and missed a jumper wire (After 8 hours of analysis, I said to myself "Hey, how come nothing is driving this transistor?" and felt extremely stupid). Anyways, it sounds alright, very heavy low end, but sounds really bad on the high end and when playing chords with more than 3 notes and "akward" chords. Would this be helped by replacing the transistors with 2N3565's or one of the other transistors mentioned in this thread? I'm not sure I understand the effects of higher or lower current gain, although I remotely understand the concept.

[niftydog]

had a really quick glance at the circuit. Given the bias arrangement is designed for the proper transistors, and it is non-adjustable, I would think that the sound would likely be improved by using the right transistors.