Very cool. Do you mind if I ask a few questions?
Why two LM386s in parallel? From what I can tell, the toggle sends the same signal to both volume pots (but through different caps), and the only difference in the setups is one chip has the input at pin 2 and the other at pin 3. And one output goes to the negative speaker pin and the other output to the positive speaker pin? I'd love to know why this is.
Why the resistor at pin seven?
And also, why is pin 1 of the volume pots soldered back to the pot?
Any advice you can give is much appreciated. I'm trying to hack a few of these out myself with varying degrees of success.
2 chips in parallel but the output runs to each side of the speaker/output jack. Chip 1 runs to speaker negative side while chip 2 runs to speaker positive side. I got the idea from a effect pedal that was on Beavisaudio.com website called the Tuffnel distortion. The designer of that pedal had problems with his schematic and I was wanting more of a dual Ruby op amp, so I combined the 2 designs in a way that I thought might work. Basically a stab in the dark experiment that actually worked.
Both of the input caps deliver signal to both chips and you can switch from the regular Guitar mode .047 cap to .1 cap for Bass Mode or Bass Boost. I messed that up a bit in the drawing.
Pin7 on both chips gets a 100nf cap, not a resistor.
You have to ground one side of the pot pins. BTW you are looking at the pots from the back side in the schematic. The pot will work if you ground the other side by mistake, it'll just work in the opposite direction. Ground pin 1 for Clockwise/normal operation - Ground pin 3 for Counterclockwise operation AKA Lefty guitars.
When building amps with JFET chips(MPF102) and op amp chips(IM386N1), its best to use push in sockets to keep from overheating the chips. You solder the sockets in and push the chip into the sockets.
Use good quality components and you'll get good results. I prefer metal oxide resistors(blue ones), poly film caps over disc caps and electrolytic directional caps for 100uf and up.
I used to get most of my stuff at Radio Shack til it got too hard to find there. Now I get most of my stuff from Smallbearelec.com or Mouser.com
I don't know as much as some people do since I'm new at this, but I'll help as best as I can.
Thank you very much! I will try the schematic. I just built a two-string diddly bow-type instrument out of an old wooden level and am now working on effects circuits to liven up it's output. The circuits will go in a wine box, and I'd like a built-in amp so I can play it without needing another sound system.
I've built about half a dozen LM386 amps using Forest Mims diagrams and some ideas from "Handmade Electronic Music" by Nicolas Collins (a great book) But I haven't come up with anything reliable I'd be comfortable with performing live or building into an instrument. This might be the ticket.
Thanks for specifing the JFET; looking at the diagram I though it was just a garden-variety transistor. I order a bunch of stuff from Jameco every so often, if you haven't heard of them. Thanks again. I'll let you know how my build goes. It'll be a few weeks, though.
Isn't 100 nano Farads (nF) the same as .1 micro Farads (uF)?
On your diagram, you have a .1 uf by the toggle, but then 100 nf at pin 7s.
I don't want to seem obtuse, but want to ensure I'm using the right parts.
According to this conversion chart at www.justradios.com/uFnFpF.html you would be correct. A 100nf cap is the same as a .1uf cap. When I started this build, I was following 2 different schematics that both showed the 100nf cap for pin 7. The .1uf cap on the toggle was a recommended bass/bass boost mod that was suggested by someone other than the original Ruby amp and Tuffnel pedal designers. So either cap should work fine in those placements.
Keep that conversion chart link in your favorites if you plan on building amps. Very useful info.
Great. Thanks for confirming. I order stuff from Jameco and they have a wide variety of .1 uF caps, but no 100 nFs.
With the Volumes at 10 and the gains at 7, it will sound like a Fender Champ. Turn gain 2 to 10 and it will sound like a Fender Tweed. Gains on 10 and Volumes down will deliver gobs of nasty distortion.
Just remember that the bigger the speaker, the better the sound.
This amp's output is 1 to 2 watts max at 8ohms.
So you'll want at least a 6" speaker, but it will handle 12" and 15" well. 5watt to 20 watt 8ohm speaker is all you need.
Thanks for the tip! I haven't started cutting the wine box yet, I'll see if I can make room for at least a 6 inch speaker.
I replaced a speaker in a small guitar cabinet once. The original was a 6" and I put a 8" in it's place. Had to tilt it a bit at the top to make it fit, but it worked.
So... What you've built here is called a "Bridged Amplifier". Basically 2 identical amps delivering an opposite signal to either side of a bridged load. You get twice the power output that way.
Yes, your terminology is better than mine was.
I built it in a Mrs. Fields "Thank You" tin as a head and have it hooked up to a 15" speaker that I pulled from a '57 Motorola stand alone phonograph. The speaker had a tear in it that I repaired, just didn't want to put it in anything with more than 10watt output.