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Ruby Amp

Here is runoffgroove’s ruby amp: simple practice amp based on the 386

amplifier chip. runoffgroove took the datasheet example for the LM386,

added a buffer in front, and tweaked a few values to come up with

probably the most popular DIY practice amp. Check out the Noisy Cricket

and Cigarette amp beavis board projects for similar circuits. Learn more

about the ruby at http://www.runoffgroove.com/ruby.html

beavis board project

3.9KΩ

Hooking up a SpeakerThis circuit is designed to power an 8 ohm speaker, but will also work on 4 ohms or 16 ohms.

Because the power output is so low (on the order of 500mW) you can hook it up to just about

any type of speaker without worry about damaging anything.

Using a Guitar Cab

The amp sounds best hooked up to a guitar speaker, so if you have a speaker cab, hook it up

there. Simply run a ¼” mono cable between the i/o breakout box’s output jack and the input

jack on your cab.

Using a Small Speaker

If you have a small speaker, you can connect it either directly to the breadboard, or if the

speaker’s wires are too big, use the terminal strip on the main board. Run one wire from

ground on the breadboard to one of the terminal strips. Run the output wire from the

breadboard to another screw on the terminal strip and connect it as shown below:

breadboard

outputground

-

+

MP

F102

d

g

s

1.5MΩ

47nF

B10K

Volume

LM

386

B1K

Gain

100nf

in

out

47nf

10Ω

10u

f+

input

Q1

MPF102

R11.5MΩ

R23.9KΩ

C1

47 nF

9 volts +

G

D

S C6

220uF

6

OutputVR1

B10K

(Volume)

2

3

18

5

4

+

-U1

LM386

7

C4

100 nF

VR3

B1K

(Gain)

R310Ω

C7

47 nF

revision: 1.0 28 may 2008 © 2008 beavis audio research