help, I built a distortion

[varialbender]

http://privatewww.essex.ac.uk/~mpthak/Distortion/

Alright, so I built it, and it was doing just fine. So I needed to break it.

I took out the diodes, and noticed it still distorts without them. Why's that?

I switched the drive pot from 100k to 500k, to play around with gain. Very fuzzy.

By now, wires are breaking from being bent constanlty for long periods of time while making changes.

Out of nowhere, I plug it in again, and it's gating. You know, that fuzz factory sound, where you've got gigantic fuzz for a second, and then a big die out to nothing, no noise at all? What's the deal with that? Did I kill a part? I'd need a lot more voltage for it to make jumps...

PS: my tone control never seemed to work.

Thanks in advance. I'm sure you've got better things to do than help a n00b out.

[varialbender]

By the way, I know there is a procedure to follow for when things go wrong, but I'm not asking for help fixing it. I did all my work on breadboard and it is already taken apart. I'm just interested in knowing why I don't need diodes to get distortion (as i assumed they were doing the clipping) and how I got weird gating. Hopefully the answers don't involve me having damaged anything.

Thanks again

[doug deeper]

alot of fuzz boxes distort with or with out diodes....
but in these circuits the diodes tend to "smooth" things out a bit.
also....if its gated....its missbiased. (probably from all the movment you mentioned!)

[Herr Masel]

I don't really understand yet the differences in types of distortion sound-wise and the theory behind them, but there is more than just diode clipping. You can make opamps clip, tubes, transistors, ICs, combinations of these... I guess you can clip anything that causes sound because clipping just means pushing it too hard so the frequency's edges (the most top and most bottom parts of the sound wave) sort of "clip" off. There is also symmetrical distortion, a-symmetrical distortion, and it really never ends. In fact, thank you varialbender, I am going to read what I can about it now.

[PenPen]

Herr Masel is right. Distortion comes from a highly amplified signal peaking so high that it hits the voltage ceiling of whatever it is being sent through. Kinda like jumping on a trampoline in a house. If you jump high enough your head hits the ceiling. When a sound wave hits the ceiling, its top get squashed. This is distortion. So, different tranistors and opamps have different ceilings. In some cases you can control the ceiling with the supply voltage, many opamps can be run at a higher voltage on their V+ pin, and this raises the ceiling for them ("increased headroom"), so they get louder without distorting. Or, I suppose you could lower the voltage to that pin to get it to distort easier, though it won't be as loud.

Diodes help with the clipping by using some of the voltage passed through them to 'open', thereby squashing or clipping the signal. I always think of diodes like one way valves, some of the energy is used when passing through just to open the gate. Different diodes have different voltage drops too.

There was a great article at Geofex that explained distortion, really helped me when I was first starting. I'd recommend finding and reading it.

[varialbender]

Cool, thanks. I understand most of how the circuit works, I just didn't think I'd hit the ceiling so fast. I mean, yes, I did stick a 500k pot in there, giving it something close to 500 in gain, but even at the lower end of that, it was still distorting quite a bit. Also, good to hear it was misbiased.

Thanks