Why did my simple boost set on fire?

[Hot_Chips]

Hey all, I attempted my first pedal build from here:

https://barbarach.com/articles/building-a-simple-pedal/lets-build-a-simple-pedal/

Yeah, let's! So, I used polyester capacitors because that's all they had (.2A104J). I used a KSP13825 transistor I had from a 1w amp kit because the guy mentions that the transistor he's chosen isn't great for audio. I also swapped the 100k pot for a 500k DiMarzio I had because it was my understanding that this would let my signal (highs and all) through unchanged.

I used veroboard. I completed the circuit, plugged it into my 9v supply and it started pouring with smoke  . I checked and none of the solder joints are touching solder joints on neighbouring tracks. On closer inspection, the transistor is the smoker. Looks to be the right way around.

Here is the top view and bottom view of the board:
https://imgbox.com/AiEJfoqm
https://imgbox.com/4eRffsYs

I am a beginner at building pedals, but I have built a valve amp kit and am generally good with soldering and electronics...just lacking in the overall understanding field! I feel like Homer making cornflakes.

[antonis]

Hi & Welcome..

I can't find any info about KSP13825 but I don't sympathize with author's opinion about 2N3904..

As for heavy smoker TO-92 transistor (supposing it indeed is a n-p-n transistor), power dissipation over 600mW is a premise..
(meaning too much current with too much Collector - Emitter voltage..)

edit: It's n-p-n Darlington https://www.onsemi.com/download/data-sheet/pdf/ksp13-d.pdf
Considering Q1 Base biased at about 800mV, it can't work here..
(at least, not without raising R3 value or lowering R1 value..)

[Hot_Chips]

Hi and thank you so much!

So, I guess I'll stick the transistor from the build instructions in (I did buy one anyway). I suspected it may not be as simple as just swapping a transistor!

Hopefully, no damage was caused to the other components.

Thanks again.

[PRR]

It can't actually burn with those resistor values, even mis-wired.

So you have some deeper problem. Pictures or it isn't happening.

[Dormammu]

I used a KSP13825 transistor I had from a 1w amp kit because the guy mentions that the transistor he's chosen isn't great for audio. I also swapped the 100k pot for a 500k DiMarzio I had because it was my understanding that this would let my signal (highs and all) through unchanged.

Your "understanding" is wrong.
In such a simple circuit, almost any transistor with a sufficient bandwidth of the operating frequency will work well.

Something at the input of this circuit can screw up all the frequencies that some people are too worried about.
(And yep, it's too low R3) 

The amplified/buffered signal is indifferent to which pots value are used(if they are not too high). And so it is more convenient to use lower resistance pots 10-50k, for reasons too long to explain.
When you try to adjust the signal level with this "fancy-pancy" 500k pot, you will also screw up all the frequencies and start running along the walls in search of frequency compensation.

[antonis]

And so it is more convenient to use lower resistance pots 10-50k, for reasons too long to explain.

I shouldn't use 10k pot together with 10k Collector resistor..
(unless I was aiming at totally different DC & AC load lines - not indicated for a booster..)

When you try to adjust the signal level with this "fancy-pancy" 500k pot, you will also screw up all the frequencies and start running along the walls in search of frequency compensation.

Could you plz elaborate that "screwing up" difference between 1/2πC2(100k+R2) [15Hz] & 1/2πC2(500k+R2) [3Hz]..??
If anything, a 22nF cap is way cheaper than a 100k pot..

[Dormammu]

And so it is more convenient to use lower resistance pots 10-50k, for reasons too long to explain.

I shouldn't use 10k pot together with 10k Collector resistor..

When you try to adjust the signal level with this "fancy-pancy" 500k pot, you will also screw up all the frequencies and start running along the walls in search of frequency compensation.

Could you plz elaborate that "screwing up" difference between 1/2πC2(100k+R2) [15Hz] & 1/2πC2(500k+R2) [3Hz]..??
If anything, a 22nF cap is way cheaper than a 100k pot..

I do this from time to time, with no issues (In the specified range of pots)

Somehow I don't see any 22nf cap in the shown diagram. "Screwing up" on a high-resistance pot happens when the knob is turned less than 90% volume.

[antonis]

Somehow I don't see any 22nf cap in the shown diagram.

Somehow I don't see any 500k pot in the shown diagram..
So, given the 100k pot lack and 500k pot availiability, it should be way chaper and easier to look for a 22nF cap in place of 100nF one..

"Screwing up" on a high-resistance pot happens when the knob is turned less than 90% volume.

Are you talking about next effect input impedance set in parallel with wiper - lug 1..??

[Dormammu]

Somehow I don't see any 22nf cap in the shown diagram.

1.Somehow I don't see any 500k pot in the shown diagram..
2.So, given the 100k pot lack and 500k pot availiability, it should be way chaper and easier to look for a 22nF cap in place of 100nF one..

"Screwing up" on a high-resistance pot happens when the knob is turned less than 90% volume.

3.Are you talking about next effect input impedance set in parallel with wiper - lug 1..??

1.OP said he put it in. I take his word for it. 
2.So, not only do we not care about high freqs, we also throw away low freqs. Geniu...?- nope!!!
3.Yep

[antonis]

I don't think that trolling in a humble CE amp thread could help OP, but let it be..

[Dormammu]

I don't think that trolling in a humble CE amp thread could help OP, but let it be..

The design of active pickups is also trolling, I guess?

[MrStab]

You need to make gaps between components when both of their legs are on the same copper track (often with a drill bit), or they're just shorts.

[Hot_Chips]

Ha ha ha wow. Erm, thanks antonis & MRStab.

I'll use the exact components in the build until I can learn more about them. I had a feeling that the way I'd soldered the components to the board was wrong. Luckily, the transistors are cheap and available locally, so I can smoke a few of then while I experiment.

Thanks again.

P.S. Here's my transistor with a hole burnt in it: https://imgbox.com/HDF1EM3J

[Itchy Scratcherson]

Yeah, I wasn't allowed to use super-glue for many years, but now I'm more careful and don't stick my fingers together every time. 
...Seems you & I may have some things in common: I learned the hard way to recognize the good sense in following the recipe as it is and mod'ing it after everything checks out. Be well,

[MrStab]

The symptoms sounded like resistors weren't resisting, as Paul alluded to, and I noticed on your photo of the bottom of the board that there were no trace cuts. Most people use a small drill bit by hand to cut the copper out of holes between traces (easier), others use a knife to cut the copper between holes (pain in the bum).