My first prototype and schematic (amateur hour) - Page 1
Forum section: electronics / general

author: strangersound
author_rank: Regular Contributor
timestamp: May 10, 2019, 10:20:19 am
content: So, I finally got around to actually building something up from scratch and after a couple of days of trial and error, I finally succeeded. I built my first distortion pedal. A single NPN followed by a couple of LEDs for clipping. I used a scavenged c1815 transistor, that seemed to work pretty well. The first thing I used was a old Sanyo Germanium NPN and although I did get it passing signal, it never seemed to really have any gain. So I swapped in the c1815 after brpwsing my horde and some data sheets.Nothing too fancy, as simple as it gets. But I was stoked when it worked. I had already whipped up a cigar box amp, but I did that with a hung low lm386 module, which for the price is an amazing deal. Amazon has no shortage of prefab modules of every configuration you could dream up. It seems lazy, but you can get them for cheaper than you can make them.Once I ran the distortion into the cigar amp (lm386 module), I was getting some pretty decent volume. It's two speakers, a small and medium one. Like 2.5 and and inch, I'd guess. I don't know, I scrapped them out of something. A bigger speaker would be even louder. Not bad for a buck.It needs an enclosure, right now it's just a rat's nest of wires and stuff. Oh yeah, I used a prototype style board and just ran the components turret style along the board and then point to point wired it with some fancy bodge wires.I'm calling it distOrange. It uses a red and yellow LED for clipping, so you can go from there...I do love browsing datasheets and weird parts and stuff. And a good data sheet is art. My favorite is when they do a schematic of an integrated circuit. That never ceases to get me all hot and bothered. So, let me know what a hack I am so I can stroke my ego with some feedback.

author: strangersound
author_rank: Regular Contributor
timestamp: May 10, 2019, 10:40:47 am
content: Oh, man. I just noticed the schematic has a stray line after that first voltage point. I was rushing, obviously. I fixed it.

author: strangersound
author_rank: Regular Contributor
timestamp: May 10, 2019, 12:46:46 pm
content: I found an old pedal case that was empty and would work. It had two holes drilled for knobs, so I added a tone control. Did some random decorating to cover up the previous stuff on it. It sounds pretty decent, actually. If you want to get some good metal tones, it will do it.Thanks for letting me share, Dave.

author: GlennSprigg
author_rank: Super Contributor
timestamp: May 11, 2019, 10:35:34 am
content: Keep up the work. 1st idea to 'working' is an important step !For such small PCB's, you can get little project boxes very cheap !!....https://www.ebay.com/bhp/plastic-project-boxLookout Fran Blanche !!! (Pedal designer etc. Youtube)

author: strangersound
author_rank: Regular Contributor
timestamp: May 12, 2019, 06:07:43 am
content: I had success on the first project, so I wasted no time starting a new one. Well, I was just going to do the smoke test and yeah, she smoked. POW! Followed by another POW before I could pull the plug.So, I have little preamp running into one of those lm386 modules and figured since the circuit was two different sections, maybe I should run some decoupling caps on the power feeds. I used some 16v 470uF electrolytic caps. I hooked up a 12vdc power supply and not long after I powered it on, the caps went POW! I wasn't sure until I gave it a look what popped.Any ideas why I just toasted those caps? All the numbers seemed right. Hooking them up is pretty straight forward, so I'm at a loss. Now I gotta take them out of circuit and hope I didn't fry anything else. I know those caps weren't intended for how I was using them. POW!

author: ebastler
author_rank: Super Contributor
timestamp: May 12, 2019, 07:17:02 am
content: The first thing that comes to mind is the polarity of the capacitors. Are you sure you had them connected the right way round?

author: Shock
author_rank: Super Contributor
timestamp: May 12, 2019, 07:52:26 am
content: Congrats. Two most common reasons would be polarity and working voltage. If the are rubbish Chinese or old leaky caps that may explain the problem as well.FYI, you can delete attachments when editing posts.

author: strangersound
author_rank: Regular Contributor
timestamp: May 12, 2019, 09:40:45 am
content: Both caps are beyond determining what the polarity situation was. They transformed into little spiral flowers with their guts all hanging out. They're still connected to ground, but the label and all is long gone. I had the negative side going to ground.I think...but we'll never know. I did find another wiring error, but it was an input error and shouldn't have mattered.I started breaking down the whole mess and both lm386 modules seemed dead, but they were still partially in circuit...but I'm guessing I fried the whole mess. I did some quick and dirty troubleshooting, but more research is needed. I did get my front panel LED working, so there's that.I decided to take a break. Where's Dave to encourage me? I got all these traps for young players over here. I'm trying to maintain my enthusiasm and I'm blowing things up. They didn't teach me how to maintain a positive attitude in the face of total failure in the Radio Shack Electronics for Losers Guide.

author: ebastler
author_rank: Super Contributor
timestamp: May 12, 2019, 12:41:51 pm
content: Hmm, if the LM386's are also blown, that suggests some other fault. Can't see how the failing caps would take them down...Do you trust that 12V power supply? Is it adjustable, so you might inadvertently have set a much higher voltage? Is it really DC? Some simple wall warts provide unregulated AC voltage, i.e. they contain just a transformer (and hopefully a fuse...). It might be worthwhile to check the supply's output voltage, both the AC and DC component, with a multimeter.

author: strangersound
author_rank: Regular Contributor
timestamp: May 12, 2019, 04:04:01 pm
content: Quote from: ebastler on May 12, 2019, 12:41:51 pmThe first thing I checked was to make sure that power supply didn't trick me. 12vdcoutput. I checked it and it was putting out about 14v.

author: ebastler
author_rank: Super Contributor
timestamp: May 13, 2019, 09:56:25 am
content: Quote from: strangersound on May 12, 2019, 04:04:01 pmRunning out of ideas then... One last thing maybe: If all components in your circuit were wired correctly, but then you connected the power supply with reverse polarity, that might explain the death of both, the caps and semiconductors.It's probably too late for a detailed post-mortem now that you have taken things apart. But always a good idea to make sure that you have the power supply outputs (and circuit inputs) clearly labelled or color-coded. You know, "Red is black and plus is minus"...

author: GlennSprigg
author_rank: Super Contributor
timestamp: May 14, 2019, 12:03:59 pm
content: Quote from: strangersound on May 12, 2019, 06:07:43 amWhy did you think they were the wrong ones ? (Voltage Capacity Style etc...)