Jun 13 2009
The Atom Amp : Electronics Complete
I breadboarded the Ruby circuit twice this morning. Why twice? Well, because my big powered breadboard is acting up, as breadboards are want to do. So, I had to redo the whole thing again. I wanted to build out the prototype circuit first, as we’ve found that a lot of examples on the net don’t work! Always test it out first.
After the second round, I powered up everything and it worked. Horray! Next, I built out the actual perfboard soldered circuit. Here is the finished product:
Atom Amp : Ruby Amplifier Circuit
It was all point to point wiring. Not the neatest, but it works. I do use Molex connectors for everything. I’m not a big fan of directly wiring things to the board. Mainly due to past experience — it’s a lot easier to take things apart to debug when you have connectors.
There are connections for Input, Volume, Gain, Power, Speaker Out, and Aux Power (for driving other things like LEDs). The chip in the middle is the LM386 audio amplifier. Toward the upper left, near VOL, is the FET. The rest of the stuff is just caps, resistors, and wires. Layout, as usual, took the most time.
You have to be careful when doing audio amps, especially those with high gain. They are prone to noise and powerline hum. For example, if you have a long lead (like a alligator clip cable) attached to the input, you can pick on AM radio stations! It’s quite a little booster for its size.
Here are the controls, with wires braided and Molex connectors installed:
Atom Amp - Inside Wiring - With Molex Connectors
Next up, putting it all together.
10 Responses to “The Atom Amp : Electronics Complete”
great one, but it’s missing a back side photo, and schematics – i’m trying to follow information from http://www.runoffgroove.com/ruby.html and http://electro-music.com/forum/phpbb-files/ruby_158.gif – but these informations are too messy for a newbie…
All of the wiring is point to point, so a back photo might be more confusing than helpful.
I added a lot more wiring, to handle the Molex connectors, so it looks more complicated then it really is.
Take a look at the standard LM386 schematics and build their most basic version. Once you get a hang of that, add in the MPF 102 FET portion of the circuit.
The LM386 can be driven either positive or negative. In a basic configuration, you’d connect your input to pin 3 (+ input). When using the MPF 102 FET, you connect your input to pin 2 (- input). When doing an audio amp, you’ll use either 3 or 2 for your input, and tie the unused pin to ground.
I used the runoffgrove schematic for my design. The only thing I altered was adding the connectors.
Hope that this helps a bit.
nice addition of molex connectors. Only prob I have is hooking up the pots correctly, how do you know which wires go where?
Also, it asks for a 10k vol. pot. Do I have to use that value, or can I use a 100k. Any help would be greatly appreciated. Thanks
If you are using the Ruby schematic, here’s how the Volume pot is wired:
You have three connectors on the pot. The center one is the wiper and gets connected to pin #2 of the LM386 (the input).
If you are looking at the pot from the front the left pot leg will go to the 47nF cap. The right pot leg will go to ground.
You’ll know if you screwed up the left/right if the amp gets quieter as you go clockwise. You should go louder as you go clockwise. (You won’t hurt anything, just swap the wires.) I sometimes forget and just do some test wiring and see what works.
I’d recommend using an audio (log) taper pot for volume. This is because the human ear follows a Logarithm and not linear. I wouldn’t go with a 100K pot since that’s a big resistance jump — you might find that you can only use about 1/4 turn of the pot before it gets too quiet. A 5K or 25K might be okay. Search out a an audio/log pot if you can.
For the gain pot, it’s easier. Connect one wire to the left leg of the pot. Connect another wire to the center AND right legs of the pot. You’re tying center and right legs together.
The two wires go up to pins 1 and 8 of the LM386. It doesn’t matter which goes where.
Again, the gain should go up as you rotate clockwise. If it goes down, just re-solder the wires on the pot.
I found the general guitar gadgets diagram to be helpful for LED, pot wiring, and the inclusion of the DC jack. It also includes options.
http://www.generalguitargadgets.com/pdf/ggg_ruby.pdf
Thanks for that PDF link, Andy. It will help out a lot of people — including myself.
I love the use of the molex connectors. What are the part numbers for the two/three sockets and plugs? I have been combing over digi-key and ouser for them but there are thousands of possiblities! My brain has melted……
Here are the part numbers (from Mouser):
These are all MOLEX KK type connectors.
*** HEADER ***
Mouser #: 538-22-23-2041
Mfr. #: 22-23-2041
Desc.: Headers & Wire Housings VERT PCB HDR 4P TIN FRICTION LOCK
Mouser #: 538-22-23-2031
Mfr. #: 22-23-2031
Desc.: Headers & Wire Housings VERT PCB HDR 3P TIN FRICTION LOCK
Mouser #: 538-22-23-2021
Mfr. #: 22-23-2021
Desc.: Headers & Wire Housings VERT PCB HDR 2P TIN FRICTION LOCK
*** CRIMP TERMINALS / PINS ***
Mouser #: 538-08-50-0114
Mfr. #: 08-50-0114
Desc.: Headers & Wire Housings CRIMP TERM 22-30 TIN
Mouser #: 538-22-01-3047
*** SOCKETS ***
Mfr. #: 22-01-3047
Desc.: Headers & Wire Housings HSG 4P W/RAMP/RIBS
Mouser #: 538-22-01-3037
Mfr. #: 22-01-3037
Desc.: Headers & Wire Housings HSG 3P W/RAMP/RIBS
Mouser #: 538-22-01-3027
Mfr. #: 22-01-3027
Desc.: Headers & Wire Housings HSG 2P W/RAMP/RIBS
Thank you!!!!!!!!! You saved me so much time. I ordered a bunch like you said. Seems like there will so many uses for them.
I just finished the Little Gem amp last night. It sounded even better than I expected. Ruby is next.