Here's my problem, I'm trying to learn how guitar pedal effects work, so I figured I'd start off easy and go with a distortion pedal. Right now, I'm trying to learn the fundamentals, and work on making them sound good later. I figured the best start would be to just hook an opamp up, and run the signal through that. Here's what I have wired up right now, but for some reason, I can't get any sound out of it. Nothing through an amp, and when I hooked it up to my computer, and looked at the signal output through Zelscope (a software based oscilloscope program that uses a soundcard for input) I got a large voltage spike when a cable was plugged into the opamp, and nothing but very slight noise afterwards. Can someone look at the schematic, and tell me what I'm doing wrong?

Thanks

Change C1 to .1uf
Add a 1uf - 10uf capacitor on the output. (+ towards op-amp)
Optional - change R1 from 10K to 100K

Also check out Diystompboxes.com for DIY guitar effects schematicc.

Well, it worked for a little while. I didn't switch out the 10k pot, it's all I have right now. It worked for a few minutes, and then it kind of died. It made the kind of sound that a pedal makes when it's battery dies, and now it won't put out any sound. Battery is still good (I'm powering it with a 9v) and nothing seemed to get hot, any ideas? Thanks for the initial reply by the way, at least I know how to get them working now


ETA: Seems that C2 (the one you told me to add) is getting saturated with voltage, and causes it to shut off after a little while. I'm going to experiment with adding a 10k resistor or so to ground on the - side of C2 and see if that helps any


Ok, it's C1, not C2. When it dies, I can short it out by touching the leads of C1 with my fingers, and it seems to "reset" it. I'm kind of at a loss for what to do to fix that problem. Also, been to DIYstompboxes before, awesome site and I picked up a lot of schematics from it already. One of the projects I have planned is building a tubescreamer for a friend of mine, I already have all of the parts, I just need to order the PCB, enclosure and a footswitch.


Anyway, now that I've got it making sound, I'm going to tinker with it some more, and see if I can iron out the problems, and afterwards add some clipping diodes, and go from there. Thanks for the help again.

Hi Stormrider,

Your problem is DC biasing. Most simple op-amp circuits you'll see assume a double-ended power supply (i.e. +/-9V), where you have a single-ended supply (+9V and 0V). When an op-amp is powered by a double-ended supply it's output can go positive and negative, so the AC input signal (from your guitar) can be centred around 0V. In your case the op-amp output cannot dip below zero because that is outside power supply range. The fix is to 'lift' the AC signal above 0V by adding a DC bias - a good point would be about the supply centre, +4.5V. To do this, add a resistor divider at the non-inverting input. Use, say, a pair of 10K resistors, one connected from +9V to the non-inv input, the other from ground to the non-inv input. That will keep the input signal in the working range of the op-amp. Capacitor C1 then acts as a DC blocker. It stops your 4.5V bias from leaking out of your box and back the the previous stage (your guitar).

Hope that helps,

BM

Ok, with feedback from the two of you I've thrown this schematic together.



I haven't had time to test it, I've been swamped with missions, but I should be able to do it tonight. Couple of questions though. I'm still puzzled about having to "reset" C1 with the previous circuit. I understand what the bias voltage does, I did not include it in this design since somewhere in the datasheet for the LM324 it says something about not having to have a bias voltage. I think I understand now that that only applies for DC circuits, and not AC.

Another thing is the resistor at the end, R3. I see that in a lot of schematics, what is it's function? I don't plan on adding it tonight, but I added it to the schematic so I could show what I'm talking about.

Once I get this thing working, I plan on throwing it in front of a small amp design based around the LM386. I don't have the schematic for what I'm using, but I'll put that together tonight (it works thankfully) My question here, is there anything more I need to do, aside from wiring it to the input? Do I need to use separate power supplies? This last part is more rhetorical than anything, since I'm sure I'll find out tonight.

Anyway, once again thanks for all the help guys, it's nice to have help like this when you're a complete newbie. I apologize for my crappy schematics as well, I'm not very good at using ExpressPCB yet.