Help with my first pedal (D*A*M meathead)

[objector]

Hi everyone,

Today I finally tried to build my first pedal, but since I don't have an enclosure ready, I tried just wiring it up for testing... and it failed.

I'll try to provide you with all necessary information, but if I'm not clear enough, don't hesitate to ask.

1) The schematic I used:


Things I changed:

- Instead of a 12n I used a 15n
- Instead of the 22n I used a 470pf
- Instead of the 100n I used a 1n

Every component I changed was based on what I read from the creator of the schematic.


2) What does it do:

I haven't soldered the footswitch yet, since I don't have an enclosure, I just wanted to test the Meathead. Therefore I have connected everything temporarily and used a piece of veroboard to mount the pot-meter and connect all the grounds together. I hope my little setup is correct, but since this is my first build... When I turn the pot-meter all the way down, I can get some signal, but once I turn the pot-meter more open, I get very loud hum, which gets louder and louder until I have reached the max of the pot-meter. If I play my guitar and concentrate, I can hear some signal coming through. When I change the input and output caps with the switches, I get another frequency of noise.

3) Pictures: When I was soldering, I thought I was doing a fairly good job on the veroboard (since it was my first time), but on the pictures I notice that there is a lot of brownish color?









I hope someone can help! If there are more pictures or even video needed, I'd be happy to provide them.

Thanks in advance!!!!

[joegagan]

most likely a bias issue, but it could be other things combined.
read the debug page, retrace every singly connection and node. double check for things that are making contact that should not. this is very easy to f up when using veroboard like this, solder wants to jump over to places you did not intend. overall, your skills look pretty nice tho.

[objector]

most likely a bias issue, but it could be other things combined.
read the debug page, retrace every singly connection and node. double check for things that are making contact that should not. this is very easy to f up when using veroboard like this, solder wants to jump over to places you did not intend. overall, your skills look pretty nice tho.

Thanks for the fast response! I'll try to double check everything. I suppose it isn't a problem that I haven't connected a led yet on the circuit?

[joegagan]

no, in fact, the problem i see with a lot of beginners is that they complicate things with parts/ connections that don't involve the signal path.
disconnect the resistor involved with the led and proceed.

[objector]

I just read the debug page and I have measured what I thought necessary, I hope someone can find the problem this way.

Voltages of the vero traces (Row 1 is the uppermost):


Row 1 = 8,68v
Row 2 = 0,00v
Row 3 = 0,66v
Row 4 = 1,63v
Row 5 = 3,24v
Row 6 = 0,99v
Row 7 = 8,67v
Row 8 = 7,86v
Row 9 = 0,00v

Input switch: switch UP-position

0,66v - 0,00v
0,66v - 0,00v
0,00v - 0,00v

Input switch: switch MIDDLE-position:

0,00v - 0,00v
0,66v - 0,00v
0,00v - 0,00v

Input Switch DOWN-position

0,00v - 0,00v
0,66v - 0,00v
0,66v - 0,00v


Output switch UP-position

7,82v - 0,00v
7,82v - 0,00v
0,00v - 0,00v

Output switch MIDDLE-position:

0,00v - 0,00v
7,82v - 0,00v
0,00v - 0,00v

Output switch DOWN-position:

0,00v - 0,00v
7,82v - 0,00v
7,82v - 0,00v


2N3904:

E: 0,00v
B: 0,66v
C: 1,62v

BC182L:

B: 1,62v
C: 3,22v
E: 0,98v

[objector]

http://dl.dropbox.com/u/34285081/untitled.wav

This is a quick recording of what the pedal does. The 2k2 resistor for the LED is still connected to the Vero, but there is no Led connected. I suppose this can't cause the noise?

[Jdansti]

http://dl.dropbox.com/u/34285081/untitled.wav

This is a quick recording of what the pedal does. The 2k2 resistor for the LED is still connected to the Vero, but there is no Led connected. I suppose this can't cause the noise?

Cool sounds! -Sorry, I know these things can be very frustrating. Seriously though, are you using a soldering station with variable power?  I once spent hours trying to solve mystery sounds only to eventually learn that my soldering station was creating the noise. When I turned the station off, everything worked great.

This might not be your problem, but it is something quick and easy to check. Sorry I don't know of any other possibilities,provided you've double checked your board for misplaced components, backwards components, and clean solder joints.  As for the LED resistor, that is something you can quickly check by removing it from the circuit.

[IvIark]

Did you use a BC182L for the second transistor?  Some of the other BC182* transistors have a CBE layout rather than BCE.

I've had sounds like that from a pedal before and it was a ground issue.  If you have a multimeter, check for continuity between all points of ground, including socket sleeves, DC adapter, 2nd and 9th row of the vero etc.

[objector]

Did you use a BC182L for the second transistor?  Some of the other BC182* transistors have a CBE layout rather than BCE.

I've had sounds like that from a pedal before and it was a ground issue.  If you have a multimeter, check for continuity between all points of ground, including socket sleeves, DC adapter, 2nd and 9th row of the vero etc.

Thanks for the reply and thanks for your amazing website IvIark!

I can confirm that I used a BC182L, I just double checked it.

Everything that should be grounded, looks grounded when I check continuity. Row 2 and 9 are connected, the jacks are grounded, DC is grounded, potmeter is grounded... As you can see in the pictures below, I used an extra piece of vero to make a little board for the potmeter and grounding, until I have an enclosure. Black wire is grounding and blue wire is the out-signal.

The only thing that isn't grounded, is the row from the LED. The resistor is in place, but there isn't anything connected to it. I'll try to connect a LED or remove the resistor today.








I hope someone can help with all this information. I'd be awesome to have a working effect, because I really had fun building this.

[objector]

Update: I just simplified everything by removing the switches and just using two fixed capacitors as input and output. Still get the weird sounds, so the problem lies elsewhere.

[IvIark]

No problem, glad you find the site useful.  The LED resistor shouldn't make a difference, it's just fed by 9V and is on its own row so it isn't interfering with anything, and having no LED attached wouldn't account for the noise.  The solder on the input socket green wire looks like a cold joint to me and so it may be worth reflowing that.  Again check with your multimeter (in the audible diode mode) for continuity between input socket and the point on the board where it attaches.  Run a stanley knife or similar down the grooves inbetween each vero row, just in case a stray bit of solder or sliver of wire/track burr is making a connection between tracks which shouldn't be there.  You could even use your multimeter to double check for continuity between every consecutive row to see if there is an unwanted bridge made somewhere.

Also could you post a face on pic of the board, I can't see the values properly, but to me what should be the 820R resistor looks like brown-black-black-red-violet which could be 10K?  I can't see that causing noise but still worth checking.  Looking at the track side it does appear that you have everything connected to the right rows so that seems to be ok.

One thing I will say is that I built a Meathead once it oscillated when I first tested it, but was silent when I boxed it up.  I know it's unscientific but it isn't unheard of that the grounded box can solve some noise problems, although I will admit that your noise is a lot more extreme than mine was, and I certainly wouldn't suggest boxing it before all other avenues were explored first.  The layout is definitely verified and so it all other things being correct you know it should work, so stick with it and you'll solve the issue.

[IvIark]

One other thing, is the noise still there if you pull the transistors?

[objector]

Thanks again for the help!

I am pretty sure that the resistor values are correct, since I measured them with my multimeter once they were attached on the board.

For the other values: The big cap reads 100uf25v, the smaller cap read 10uf35v, and the little ceramic caps are less clear. The one on the right reads 474 and the other one reads 47.

On the input-cap there is printed a large '10', and on the other side it reads: WIMA 0,01 63-
The output cap reads 22n563.

The potmeter reads B500K

The noise stops once I pull a transistor.

Checking continuity between the rows was one of the first things I did, as was running a stanley knife between them, so that should also be OK.

When the effect is engaged and I touch the veroboard, the hum also changes in pitch. But I guess that's normal because I act like a ground that way?

[IvIark]

The one on the right reads 474

Should read 471.  It needs to be 470pF not 470nF

[objector]

The one on the right reads 474

Should read 471.  It needs to be 470pF not 470nF

Damn! This means Musikding has shipped me the wrong caps. Could this be reason for the fx not working? So 471 means 470pf and 474 means 470nf?

[IvIark]

Yes, 471 means 47 and one zero (470pf), 474 means 47 and four zeros, (470nF).  Definitely the wrong cap and no doubt that is the problem.  That's just a BC filter cap which is supposed to smooth things out a bit, so you can prove it by just removing it.  The Meathead will work fine without it, it just may be a bit more spikey

[objector]

Yes, 471 means 47 and one zero (470pf), 474 means 47 and four zeros, (470nF).  Definitely the wrong cap and no doubt that is the problem.  That's just a BC filter cap which is supposed to smooth things out a bit, so you can prove it by just removing it.  The Meathead will work fine without it, it just may be a bit more spikey

Thank you very much for all the information. Once I get home tonight, I'll try removing the cap and give an update in this thread. What is the meaning of a BC filter cap (trying to learn and understand the art of stompbox building).

[IvIark]

It's just a cap between base and collector which helps smooth things out

[objector]

My hopes were high when I came home... Removed the cap, but the problem is still the same Any guess what to try next?

[IvIark]

Darn, I was convinced it was going to be that.  Are you sure the other one is 47pf and not 47nf?
It may be just me but looking at the DC adapter, it looks like there a little sliver of wire going from the 9V wire towards the ground wire.  There's nothing touching there is there?

Try quickly going over it and reflowing the solder on the board to make sure all the joints are good.  Plus are you sure the transistors are ok, do you have any more to check it with?