Guitar Distortion/Overdrive Pedal

[audioguru]

The input resistance of the circuit is the 500k resistor so the input current is very low.

The output load determines the output current and we don't know the resistance of the load. The opamp can supply a peak output current of 15mA.
Why do you want to reduce the output current?

 

[TrevorP]

Well I don't want to if I don't have to. I have a feeling I just came to a bad assumption on the basics of sound and AC current.

 

[audioguru]

A good audio amplifier has a very low input current and very high output current. It won't work if they are the same.

 

[TrevorP]

Ahhh ok...

(this doesn't mean that its going to be a LOT louder will it?)

Basically what Im asking is what controls the amount of dB's you hear? Voltage or Current? (my geuss is voltage)

 

[audioguru]

When you turn up the volume, the voltage increases across the speaker that increases its current. Power= voltage times current.

 

[TrevorP]

Ok great I just didn't want this to be boosting the output volume too much.

 

[audioguru]

The volume control on the amplifier adjusts the volume from zero to the max avaiable from the amplifier.

 

[TrevorP]

I have a quick...but REALLY urgent question:

Will I be able to get away with switching the LT1001 Op-Amp for a LM741 without having to change my circuitry?

(my simulator doesn't come with LM741 Specs built in so I don't know...)

 

[TrevorP]

Ok scratch that the LM307 will work even better than the LT1001 and the local supplier actually has it.

 

[HiTech]

Who needs an expensive valve amp when a cheap circuit like this will add all the distortion you need?

Use a potential divider to get the 4.5V.

I thought the potentiometers and volume controls were used to alter the clipping and output voltage.

Valve amps like the Marshall, Mesa, Fender, Ampeg provide a clean, mellow sound many lead guitarists seek. Then they add in a distortion "stomp box" when necessary. If valve amps were such cr@p from the start, guitarists wouldn't be getting in line for them since their advent.
And why isn't the original poster using germanium diodes? The good fuzz boxes use germaniums, not silicon diodes. Then again, finding a germanium diode anymore these days is a chore.

 

[audioguru]

The old 741 opamp is noisy, has a full output to only 9kHz and has high frequency distortion. The old LM307 is discontinued, is noisy, has a full output to only 5kHz and has high frequency distortion.

The TL071 single, TL072 dual and TL074 quad audio opamps are about the same price, are low noise, have a bandwidth to 100kHz and are low distortion.

 

[TrevorP]

Yes but for what I need to do right now the LM307 is going to work fine... I will upgrade at a later date...

And my distributer has a 307 in stock. (Frankly for the purposes of "wowing" my class I just need distortion.)

EDIT:

In response to HiTech's response...yes I know that germanium is the MUCH better option...but frankly the silicon ones provide distortion. And thats really all I need.

 

[Hero999]

audioguru,
Somehow I don't think he's too bothered about distortion here.

 

[TrevorP]

no I know that there is good distortion and bad distortion...but I just need distortion right now.

Heres a little history:

My friend and I are doing a Grade 12 Physics project...you get to choose what to build...it just has to relate to physics. So I thought "Well I love playing guitar and my amps distortion sucks, so lets make our own amp.."... but after about half an hour it dawned on us that making our own amp would be stupid. So I thought "well lets make a distortion pedal, Ill still get different distortion and the class will still be amazed by the pretty schematic picture". So I started researching about distortion and finally came down to a pretty rough diagram (Which you guys were my savior for). But the downside is that instead of having to have it finished by next Tuesday my friend is going to Germany for the holidays so we have to have it ready to present by this Thursday. So I'm buying the parts tomorrow after school and were going to build it tomorrow night.

 

[audioguru]

You like distortion? Are you deaf or something? Most deaf people like fuzz sounds because they can't hear how bad it really is. Guess how they blew up their hearing?

Sorry, I thought this was the thread about the Auto-Wah filter circuit.

 

[TrevorP]

ahahah...I really cant understand sarcasm very well on the internet.

And yeah no I only like distortion in moderation... its shows a lot more highly of a player when they play with a clean sound... Or at least if they use distortion for its original purpose (adding more energy). I really cant stand those people that just crank distortion up all the way and mash the strings a bunch of times.

 

[TrevorP]

Ok I got a weird problem...

Ok I have a 9 Volt power supply going across the the Op-AMP and about 4V going in the + input... But for some reason there is NO output coming out. If I place a wire across to the input from the output it will pass an un-amplified sound... so I really don't understand whats going wrong.

Im using a LM307 Op-AMP.

 

[audioguru]

If I place a wire across to the input from the output it will pass an un-amplified sound.

Then the input signal has blown up the output of the opamp.
You shauld never feed a signal to the output of something.

Measure the DC voltage at the output pin of the opamp. It should be the same as the +input pin.

 

[TrevorP]

Ok it turns out that I dont have the initial .02uF Capacitor and in my simulator that essentially gives me the same situation...so Im gonna see if I can get one from my friend later tonight.

 

[TrevorP]

Ok that solved nothing what so ever...

Ok Between the 500k and 2 100k's there are 4.5V. But across the 40k there is only .2V.

And when I listen VERY closely I can hear something. So the Op-AMP is working I think just something is wrong in the stuff leading up to it.