Overdrive crackle

Berger · June 25, 2005, 07:22:44 PM

Well this is my first modified build.

I built and over drive based off of Joshua's nut-drive in the layout section.

I used different caps, the diodes are n34a germaniums. everything else is the same.

I plugged it into my amp and did some playing. I like the overdrive it produces, but when I strum lightly..it crackles..or it could be more of a cut-out..I'm not sure.

I was wondering if anyone could help me figure out what the problem is.

I included a pics

-Berger

Edit-this is my first perfboard pedal..so I would understand if I screwed up there

Berger · June 25, 2005, 09:02:19 PM

So I put it straight into my speaker cab, and it drives it fine.
I'm guessing running it through the head is whats causing the issue.

Is there anyway for me to modify it so that I can use it through the head, like a normal pedal?

Thanks for any help
-Berger

markr04 · June 25, 2005, 09:15:05 PM

Maybe someone else can be more specific, but I think I see an LM386 on that board. I remember using that as a mini amplifier once. It sounds like it's overpowering your amp's input, so it's best not to plug it into your amp until someone can tell you what that circuit was designed to do exactly.

Best wishes and welcome to the forum.

Berger · June 25, 2005, 09:18:07 PM

My bad I should have been more specific..ya its a lm386 chip.

The layout I used was

I thought I read somewhere that the lm386 was not to be used with amps, just speakers..but the layout for some reason made me think otherwise

Thanks for your help

BigTexas · June 25, 2005, 11:48:56 PM

I know what you mean about the crackling at times. I think ive experienced that with a 386. I doubt that it will hurt your amp unless its a wuss. I know coling from EA used a 386 in his parallel universe and ive built one for myself and it sounds great. maybe lower your input volume maybe lower your output volume?

Eric H · June 25, 2005, 11:56:17 PM

The circuit has no input or output coupling caps (?!)
That will cause strange behavior right there. The dc will make the pots in your guitar crackle, and DC into your speaker is a bad idea.

Hal · June 26, 2005, 12:35:44 AM

what are the 2 extra caps on your perfboard?

try putting the supply cap in. I doubt it, but you may be pulling too much current and cutting out the 386 when you play. Is your battery fresh?

Berger · June 26, 2005, 11:43:59 AM

Quote from: Eric HThe circuit has no input or output coupling caps (?!)
That will cause strange behavior right there. The dc will make the pots in your guitar crackle, and DC into your speaker is a bad idea.

I was wondering about that. I chose the layout because it was so simple..but I guess its too simple. So I should add a .1uf cap after the input? Do I use the same value on the output?

Quote from: Halwhat are the 2 extra caps on your perfboard?

try putting the supply cap in. I doubt it, but you may be pulling too much current and cutting out the 386 when you play. Is your battery fresh?

The 2 caps on the left are to get my as close to the 100uf cap that is on the diagram..I didn't have a 100uf cap, so I put 2 in series to get there.

By supply cap are you talking an cap after the input? I'm not using a battery, just a dc power supply.

Thanks for all your help guys
-Berger

PCS · June 26, 2005, 12:14:10 PM

Ooh, I can't imagine that those two tiny ceramics are 50uF. Unless they're actually tantalum? If I'm not mistaken, capacitors should be put in parallel to get the sum of their capacitance.

Berger · June 26, 2005, 12:19:51 PM

Quote from: PCSOoh, I can't imagine that those two tiny ceramics are 50uF. Unless they're actually tantalum? If I'm not mistaken, capacitors should be put in parallel to get the sum of their capacitance.

Ya I just checked them, and they are waayy off. Thats what I get for trying to read cap values..I have a 250uf cap, but is that too much?

I know thats a problem, but is it "the" problem? Since its running to ground I thought it was acting as filter...

I guess I have a lot more to learn

-Berger

octafish · June 26, 2005, 07:11:20 PM

Same caps into and out of the circuit are fine. 0.1uF, or as I like to say, 100n are my preference for coupling caps because for my gear I can't hear any frequency cut off, plus I have a tonne of them. I'd sub in the 250uF and see if it helps, for power filtering I believe the rule is start big ie. 1000uF and then reduce the value till you find a balance of what works and what is cheap. If I don't have the specified cap I usually use a larger one.

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Overdrive crackle