My first breadboarded circuit- "Dead Easy Dirt"- success!

[Om_Audio]

Hey guys!

What a night. Not only did my pres win the election (whew!), I breadboarded my first circuit!
I made plenty of mistakes but luckily removed power before the IC got too hot and fried. (True story.)

I just so happened to have cleaned out some stuff earlier today and found an old intercom kit someone left here years ago- and I had looked over the parts and noticed a couple of ICs which I identified as LM386 chips.
Fast forward a few hours and I am looking at culturejams website and see his "Dead Easy Dirt" circuit and realize I have the LM386 it needs, plus I bought some bags of random value caps and such from Radio Shack thinking I would prob never use them but the 2.2uF cap I needed was in there too. I also had parts from an old tuner I took apart etc. I did not have the suggested  diodes though.

I really wanted to use the scematic but sadly I just could not get past the IC pins- made no sense to me even when comparing with the perf board layout. I ended up using the perf and stripboard layouts and used the schem for reference occasionally.

First try-  I had the cap wired wrong and the IC heated up but it did actually pass signal. Fixed the cap and still passed signal but sounded awful and noisy as shit. The IC did not heat up though- progress.

Removed other things/adapters from power strip- that helped noise.

I looked up the diodes I had used (1N4004) and compared them with the ones I was supposed to use (1N914) and learned the difference between rectifying and switching diodes. I used rectifying which can handle more V but are relatively slow to switch unlike the ones specified which handle much less V but are very fast.
I just used some tiny glass ones that looked similar from the Boss TU-2 tuner I had mined for parts.
They worked MUCH better!

The thing was still squealing and noisy so I took readings at the suggestion of this page over at DIYSB:
http://www.diystompboxes.com/smfforum/index.php?topic=29816.0

Then I realized one of the diodes was not connected- my add-on legs were a bit wonky- I made sure they were connected and it sounded even better and the readings I had taken changed. (I tested continuity of everything at first though which was also helpful for learning how the breadboard works)

In any event, very exciting. I need to spend more time thinking about it to try and better understand how it actually works.

-too much voltage can be an issue (yay sag knob on my test rig!)
-grounding and power source can contribute a lot to noise
-the diode readings are VERY curious and interesting- that info is below the pic- I wont go into that but even though the diodes are flipped the K and A on each side have the same readings. Also seeing negative voltages in some spots was def not expected!

Silly long post but damn this was fun. I ended up trying to play "Let The Good Times Roll" by the Cars. hah

Regards,
C




Supply voltage: 8.92V BATTERY (does not seem to like the 9.76V of wall wart unless I sag it a bit)
(one pot position which produces squeal: pot 1-2 is 76K, 1-3 is 76K, 2-3 is 255R)

IC1: LM386N-1
1: 1.26V slow fall
2: 0.2mV
3: -0.1mV
4: 1mV
5: 4.41V
6: 8.83V
7: 4.5V
8: 1.26V slow fall

C1: 2.2uF electrolytic
+: 4.39V
-: 2.0mV

D1: unknown glass diode
A: 1.8mV (-369mV first, remove probe then goes positive)
K: banded 0.2mV

D2: unknown glass diode
A: 0.2mV
K: banded 1.8mV (-369mV first, remove probe then goes positive)

100K pot fully CW:
1: to ground: 0.1mV
2: to output: -370mV
3: from D1: -370mV

D2 was disconnected at one point and many values changed after slightly but most dramatic were pot values 2 and 3 which went from -127mV to -370mV
this also made a lot of the craziness and noise stop
removing other adapters from power strip stopped a lot of noise too

[jkokura]

Great job. It was fun reading about your experience.

Jacob

[DutchMF]

Those diodes look exactly like a bunch I got from Tayda which where labelled as 1N914, so you might have used the correct diodes without knowing! Your post has me wanting to buy a breadboard even more than I already did....

Paul

[culturejam]

Nice work!

[pickdropper]

Nice, clean bread boarding there.  Cool that you are off and running with it.

[Om_Audio]

Thanks guys! I appreciate your support. And thanks CJ for the super resources!

Dutch, go for it man! It is really fun, rewarding, and informative. Just make sure to have some hemostats or something on hand if you have big fingers like I do, or I guess get a bigger breadboard and spread everything out more.

One last thing I forgot to mention- I used a socket for the IC (don't ask me why) and it kept popping off the board like it was popcorn. It was f*****g funny and annoying all at the same time. Sockets not required when breadboarding!


Also, I kind of don't like the fact that the 9V from my test rig is always on- so I trimmed some LED neg legs, added resistors and plugged them into the breadboard as indicator lights to let me know 9V is hot or not. Finally found a use for a blinking LED I had.



C