1st Veroboard Project

[JMac26]

Hi there, I am attempting my first veroboard pedal build (Meathead Fuzz Clone) and am getting very loud continuous buzzing coming as well as a quiet fuzz guitar signal. I have completed a couple of DIY pedal builds, which both used PCB's. However, I need some advice on troubleshooting this one.

I am following the diagram shown here: http://tagboardeffects.blogspot.com/2010/10/dam-meathead.html

The voltages across the two transistors are as follows:

2N3904 NPN Transistor
- Collector to Emitter 1.05V
- Collector to Base 0.59V
- Emitter to Base 0.33V


BC182L NPN Transistor
- Collector to Emitter 0.67V
- Collector to Base 0.67
- Emitter to Base 0V

My input voltage is just under 8V (i'm using a battery that isn't completely full to test, but this should still work / wouldn't cause this issue, right?)

The voltage across the two legs of the 47uF cap is also just under 8V.

Any recommendations for potential testing / problems would be much appreciated, thanks.

[duck_arse]

is there a circuit diagram to match?

when we take voltage measures, we usually put the black probe to ground/common/0V and then poke about with the red probe. that way, all our readings are referenced to ground, and are easier to make sense of.

[stallik]

Looking at the solder side of the vero, there appear to be a couple of joints which I'd describe as a bit suspect. Difficult to be sure from the photo but there may be a couple of shorts too. This may just be the angle of the shot or just long component leads.

I'd suggest a close examination of each joint, reflowing the solder where necessary then run a blade or jewellers screwdriver along each of the gaps between the copper traces. Vero is notorious for hiding tiny shorts between the tracks which has caught me out so often that I now 'post clean' the gaps on every build

[JMac26]

when we take voltage measures, we usually put the black probe to ground/common/0V and then poke about with the red probe. that way, all our readings are referenced to ground, and are easier to make sense of.

Sorry, thanks for the tip. In that case:

2N3904 NPN Transistor
Collector: Starts off at 0.9V but then starts dropping the longer I keep the probe connected.
Base: 0.63V
Emitter: 0V

BC182L NPN Transistor
Collector: 1.05V
Base: 0.38V
Emitter: 0.38V

And no there's no circuit diagram other than the link i've posted above. Although i'm sure the schematic is probably available online.

[JMac26]

Looking at the solder side of the vero, there appear to be a couple of joints which I'd describe as a bit suspect. Difficult to be sure from the photo but there may be a couple of shorts too. This may just be the angle of the shot or just long component leads.

I'd suggest a close examination of each joint, reflowing the solder where necessary then run a blade or jewellers screwdriver along each of the gaps between the copper traces. Vero is notorious for hiding tiny shorts between the tracks which has caught me out so often that I now 'post clean' the gaps on every build

Thanks i'll try and reflow some of the joints. I have tested for continuity between the ones that look like they could be bridging but the DMM shows 1 and no beep.

[DrAlx]

Emitter and Base should not be at same voltage.
There should be about 0.6V difference just like on the other transistor.  You probably have a short circuit between emitter and base.

[duck_arse]

so not this circuit?

[antonis]

You probably have a short circuit between emitter and base.

If so, Q1 Collector should stay at Q2 Emiiter voltage.. 

Furthermore, Q1 Base voltage can't be higher than Q2 Emitter one due to NFB bias via R5..

@JMac26: Are you sure about correct pinout location of the transistors..??

[PRR]

....Q1 Base voltage can't be higher than Q2 Emitter one due to NFB bias via R5....

True for Silicon, as we are doing here.

Not always true for Germanium, because of high leakage inside the Q1 C-B junction.

[JMac26]

You probably have a short circuit between emitter and base.

If so, Q1 Collector should stay at Q2 Emiiter voltage.. 

Furthermore, Q1 Base voltage can't be higher than Q2 Emitter one due to NFB bias via R5..

@JMac26: Are you sure about correct pinout location of the transistors..??

Sorry have been away from home the last couple of days. I've taken the transistor measurements again and got: 


Q1 - 2N3904

Emitter: 0V
Base: 0.39V
Collector 1.04V

Q2 - BC182L

Emitter: 0.37V
Base: 0.38V
Collector: 1.04V

Going to attempt to reflow the solder and clean up the tracks to see if it makes any difference.

[antonis]

You're free (and strongly recommended) to reflow anything you wish to but Q1 Collector and Q2 Base MUST exhibit absolutely same DC voltage..!! 

[JMac26]

You're free (and strongly recommended) to reflow anything you wish to but Q1 Collector and Q2 Base MUST exhibit absolutely same DC voltage..!! 

I've reflowed the solder and cleaned up the tracks and the transistor measurements are now this:

Q1 - 2N3904

Emitter: 0V
Base: 0.63V
Collector: 1.47V

Q2 - BC182L

Base: 1.47V
Collector: 2.34V
Emitter: 0.85V

I can hear the guitar signal faintly in the amp, but mostly just getting a loud buzzing sound. The only thing different between my circuit and the recommended layout is the electrolytic axial cap (and the jumper next to it) are one space to the left of where they are in the diagram (see original image), but it seems like this wouldn't make a difference to the signal path, right?

[duck_arse]

we cannot see half the build. we need to see all offboards and jacks, you might be missing a ground, or having a ground too many.

[ElectricDruid]

we cannot see half the build. we need to see all offboards and jacks, you might be missing a ground, or having a ground too many.

My thoughts exactly, Duck. That comment about a "loud buzzing sound" sounds a lot like a bad ground in the offboard wiring.

[antonis]

Additionally to what well said above, check proper resistor values 'cause:

Q1 - 2N3904

Emitter: 0V
Base: 0.63V
Collector: 1.47V

Q2 - BC182L

Base: 1.47V
Collector: 2.34V
Emitter: 0.85V

Q2 Emitter at 850mV calls for Collector current of 850μA (due to 1k Emitter resistor & neglecting 1.8μA Q1 Base bias current) hence for a 4.7V drop on Collector resistors (4k7 + 820R) resulting into 4.3V (9 - 4.7) Collector voltage..
(way far from the 2.34V measured one..)

P.S
Unless, of course, your battery measures about 7V..

[JMac26]

we cannot see half the build. we need to see all offboards and jacks, you might be missing a ground, or having a ground too many.

Just testing the effect before I do the offboard wiring properly. I have both the I/O jacks and the DC jack connected to the board ground (white and black clips). The yellow wire is the output, green is input and red is 9V. (see image)

P.S
Unless, of course, your battery measures about 7V..

Yes I was using a battery which is 7.5V or so, but have also tested with a 9V supply and it's the same issue with the sound.

[antonis]

Yes I was using a battery which is 7.5V or so, but have also tested with a 9V supply and it's the same issue with the sound.

Sound issue is more related to what Stephen & Tom said above..

I focused on the wrong resistor values case judging from voltage measurements for +9V power supply..

[antonis]

I think someting happens here :

[JMac26]

I think someting happens here :

With the wiring? Sorry the image isn't very good, the ground and jack tip aren't touching if that's what you mean. Yellow is going to the tip lug and black is going to the ground lug.

[ElectricDruid]

Buzz the grounds with the multimeter. One probe on the board, and then go round and check that you actually have the continuity that you think you have to the other points. It's ridiculously easy to get a dodgy connection when everything is connected up with croc clips, and that alone would be enough to explain the symptoms you're seeing, so I'm not really convinced that there's a genuine problem here beyond basic "half built circuit". I'd personally be inclined to measure wires for jacks in the enclosure and solder everything up and get it ready to be boxed. If it *still* doesn't work at that point then I'll admit there might be fault