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.
(https://i.postimg.cc/HrdnW8Fd/IMG-0519.jpg) (https://postimg.cc/HrdnW8Fd)
(https://i.postimg.cc/BPFbbTqQ/IMG-3286.jpg) (https://postimg.cc/BPFbbTqQ)
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.
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
Quote from: duck_arse on May 06, 2021, 11:47:53 AM
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.
Quote from: stallik on May 06, 2021, 12:07:38 PM
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.
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.
(http://2.bp.blogspot.com/-K2kZ3PF-0B8/TxyNt4la7kI/AAAAAAAAArA/VwLBebGGKQ4/s1600/Dam_Meathead.gif)
so not this circuit?
Quote from: DrAlx on May 07, 2021, 10:03:48 AM
You probably have a short circuit between emitter and base.
If so, Q1 Collector should stay at Q2 Emiiter voltage.. :icon_wink:
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..??
Quote from: antonis on May 07, 2021, 03:50:03 PM....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.
Quote from: antonis on May 07, 2021, 03:50:03 PM
Quote from: DrAlx on May 07, 2021, 10:03:48 AM
You probably have a short circuit between emitter and base.
If so, Q1 Collector should stay at Q2 Emiiter voltage.. :icon_wink:
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.
You're free (and strongly recommended) to reflow anything you wish to but Q1 Collector and Q2 Base MUST exhibit absolutely same DC voltage..!! :icon_wink:
Quote from: antonis on May 08, 2021, 04:20:44 PM
You're free (and strongly recommended) to reflow anything you wish to but Q1 Collector and Q2 Base MUST exhibit absolutely same DC voltage..!! :icon_wink:
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?
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.
Quote from: duck_arse on May 09, 2021, 10:26:03 AM
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.
Additionally to what well said above, check proper resistor values 'cause:
Quote from: JMac26 on May 08, 2021, 06:00:31 PM
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..) :icon_wink:
P.S
Unless, of course, your battery measures about 7V..
Quote from: duck_arse on May 09, 2021, 10:26:03 AM
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)
Quote from: antonis on May 09, 2021, 12:13:29 PM
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.
(https://i.postimg.cc/fJLqGxm6/IMG-3147.jpg) (https://postimg.cc/fJLqGxm6)
Quote from: JMac26 on May 09, 2021, 03:08:59 PM
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.. :icon_wink:
I focused on the wrong resistor values case judging from voltage measurements for +9V power supply..
I think someting happens here :
(https://i.imgur.com/W8ja5nG.jpg)
Quote from: antonis on May 09, 2021, 03:57:13 PM
I think someting happens here :
(https://i.imgur.com/W8ja5nG.jpg)
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.
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 ;)
And you are definitely using a BC182L with the unusual pin out?
Quote from: ElectricDruid on May 09, 2021, 06:59:21 PM
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 ;)
Thanks, i've tried connecting the dmm black probe to ground and using the red probe on all of the components that go to ground on the schematic. All of them have continuity to ground. I've used this setup in the past without this kind of issue. Granted, there is usually some noise, but it's nowhere near the level of the effect and disappears once it is boxed up.
Should I have continuity through the capacitors? i.e one probe on each leg of the caps, because I don't at the moment.
Quote from: JMac26 on May 10, 2021, 08:18:47 AM
Should I have continuity through the capacitors?
Only for shorted capacitors.. :icon_wink:
P.S.
Capacitors block DC..
Quote from: andy-h-h on May 10, 2021, 02:48:58 AM
And you are definitely using a BC182L with the unusual pin out?
Yes I believe so, it was in the kit from Bitsbox, when I search the component code it comes up with the correct data sheet with
1. Base
2. Collector
3. Emitter
Quote from: antonis on May 10, 2021, 08:25:02 AM
Quote from: JMac26 on May 10, 2021, 08:18:47 AM
Should I have continuity through the capacitors?
Only for shorted capacitors.. :icon_wink:
P.S.
Capacitors block DC..
Ok thanks :)
Haven't got any further with this. I removed a couple of the caps and tested them out of the circuit. Also corrected the misplacement of the jumper and 47uf cap I mentioned previously. I attempted to solder up the jacks and DC power connector properly (no croc clips) and still the same issue with loud buzzing.
Do transistors that have overheated still make sound? Or produce unwanted sound? Struggling to figure out which component could be causing this kind of issue. There's no continuity between the transistor legs so I don't think they've shorted.
Quote from: duck_arse on May 07, 2021, 12:13:28 PM
(https://i.postimg.cc/VdQLT1nS/Dam-Meat-Head.png) (https://postimg.cc/VdQLT1nS)
so not this circuit?
I checked the layout against the schematic that Duck posted (trimmed above) and it checks out. That's the one.