Help, No Distortion

[ZebCahan]

Hello!
This is my first post and my first project so im a real beginner.
My english isnt that good either so have patience with me =)
The problem I have is this:
After studying a lot of resources on the net,
I have designed my own version of a MXR Distortion+ stompbox. (A too hard project for a beginner like me but i got to exhaulted)
Im using all the components as the original schematic but with some few exceptions. I have put two clipping-diodes (1N914) in parallell in the feedback-loop in hope to ashieve some kind of overdrive a´la tubescreamer (I know im stupid, but i had to try anyway =) ) with a single mini-switch (You know the ones with only 3 pins) to be able to turn the effect on and off. The next thing i did was to put a mini-switch before where the original clipping-diodes are. I also changed to LED´s instead. The point was to be able to switch between two different kinds of distortions and to be able to have no distortion at all.... well it didnt really work... hahaha.. =)
When i plug it in and i have the dpdt-switch in off-position the signal goes right thru as it is supposed to do, but when its in the on-position theres no distortion. I can use the volume-pot because it works but when i turn the gain-pot up, the only thing that happens is that the sound slightly changes a little bit (Sounds like a lowpass-filter) but its still clean. If i pound really hard on the strings, you can hear a quiet crackle in the background like there was distortion... hmm... I have tryed to remove the mini-switches and just solder a wire between the clipping-stages and the signal-path, But this didnt work either.
I know i have choosed a really bad first-project.. but if I have come this far i really want to end it!
Please help me if you can, im thankful for all help I can get as the project stands completely still for the moment.

/Sebastian

[ZebCahan]

Ok, hello again.
I was looking at the schematic for the MXR distortion+ and found that i had put a 1m resistor instead of a 4,7k before the gain-pot (Stupid) in the feedbackloop of the OP-AMP. I havent had time to solder it again but i guess that the 4,7k resistor together with the 1m potentiometer controlls the gain of the opamp... or am i really wrong here? Is there anyone that can confirm this?

[Peter Snowberg]

Welcome to the forum Sebastian.

You did choose a complex project for your first one.

It is very hard to debug something without pictures or a schematic. It sounds like you may have a very simple problem with your circuit.

If you can post a picture and/or schematic it would be very helpful.

For picture hosting, http://www.photobucket.com/ is free and works wonderfully!

For drawing schematics, http://www.expresspcb.com/ gives out free schematic drawing software (ExpressSCH) that is installed along with their free circuit board CAD.

The best tool for debugging is probably the "Audio Probe". See the Audio Probe post in the FAQ Forum. With a probe you just follow the sound until it stops. That is where your problem is.

Your modifications sound fine. For your knowledge.... the diodes in the feedback loop decrease the gain to 1 when it goes beyond the clipping threshold, which is different from the Dist+ style of "shunt" clippers going to ground. The feedback clipper produces more even harmonics. The Boss HM-2 pedal uses both of these clippers at the same time.

Build an audio probe, check your component values again, and I'm sure you will be able to complete your project!

[ZebCahan]

Thanks Peter,
I replaced the 1m resistor i was talking about.... and... IT WORKED!!!
Sounds great!

[Peter Snowberg]

Fantastic!