Sorry - another noisy cricket question!

[NZDavo]

Hi all

I'm a first time solderer and have been researching diy pedals and amps for a while. The Noisy Cricket seemed like a good place to start: http://www.beavisaudio.com/projects/NoisyCricket/MarkII/NoisyCricketMarkII_RadioShack_Rev2.pdf

I live in New Zealand so the radioshack board wasn't an option. I have had a good time learning about circuits and decided to try make my own layout on perf board. Please see my diagram. Does this look ok?
http://www.aronnelson.com/gallery/main.php/v/Schematics-etc/NC+Layout.jpg.html

It's not working at all! (Lots of noise when I turn it on. I have tried 2 different LM386 IC's and 2 different transistors - MPF102 and J201) I have been reading other peoples posts about their problems but thought I'd better get my layout checked before trying any other fixes!

Hope you aren't too sick of NC questions!

Thanks
David

[NZDavo]

Hello all - I have a question about capacitors

I got my multimeter out and started following my circuit to check it's all working. I have voltage running into C2 (47nF Cap - See circuit drawing here) but nothing coming out the other side. (please forgive my layman's terms!)
Should I be able to measure voltage across a capacitor? (My understanding is that a cap works like a reservoir and once full it releases at the same value it is fed.)
This capacitor is a non polarized film cap - so not in backwards!

I have the same at C6 (100nF)

Is this an indication that I have fried the capacitors?

Thanks for your help.

Cheers
David

[Perrow]

No, the caps are most likely OK. The cap-reservoir analogy is slightly flawed, a cap lets electrons pass if the voltage across it is higher than the charge in it, if the voltage across it is smaller than it's charge, it gives back. I've fought with it a long time, but I think I've got to understand the most important aspects of caps. They're not always as intuitive as they first appear, not to me at least.

[drolo]

Hi David,

The fact that you don't read voltage across the cap is normal, as caps are DC blocking. That's one of the things they are actually used for. With your DMM, measure voltage on the supply pins of the IC. Otherwise check the orientation of the FET. I get confused everytime with it ...

A probe could help you follow up to where your signal passes through. It can be as simple as plugging your guitar into the input of the effect, disconnect the output. Instead connect the ground of your cable going to the amp to the ground of the effect and connect a cap to the tip of the jack. The cap is used to avoid DC going to your amp. Start with the other end of the cap from the beginning of the circuit and follow up to where you keep your guitar signal.

rgrds,
David

[NZDavo]

Thanks Perrow and David

Ok, more learning with the caps then!

Just to clarify - a probe is not part of my DMM is it? (Do I need to buy a new tool?!)

I have measured the voltage on the IC pins and it was 0 at pin 2. I then measured the voltage before C6 and got nothing. Following it back I found no voltage across the B10k Pot. Following that back I found voltage coming out of the Source (S) of the transistor but nothing from C2 onwards.

As I understand it the signal from my guitar runs into the transistor at the gate (G) and flows into the rest of the circuit through the Source (S)

Is that right?

So it appears that the flow stops at C2.

I'll try your suggestion tonight too.

Thanks
David

[Jdansti]

Welcome to the forum!

I assume that when you say it is noisy, you have the guitar plugged in and you only get noise, no signal.

Make sure you have good ground connections between your in/out jacks, power supply negative terminal, and ground on the board.

Other things to look for are:

-Correct polarities of the 386 IC, Q1 and C8
-The resistors you used really are the ones listed in the BOM
-Bad solder joints
-Unintended solder bridges

If you still have problems, post some photos of both sides of the board. Also try to get shots showing how the off board components are connected.