lm386 based amplifier

[shawsofhell]

I want to build a practice amp using an LM386 but there are so many different circuit variations for this on the net I am having trouble working out which one to build. I will probably use two chips for the circuit so another thing is I was wondering whether it is best to build two completely seperate amps and run a speaker each or use a circuit like at runoffgroove where they both power the same speaker? Any help with this project would be greatly appreciated!

[MrChameleon]

My advice is to build the Runoffgroove Ruby: http://www.runoffgroove.com/ruby.html

It's loud for a practise amp, my (LM386 N-4 @12v) Ruby amp drives a 2x10" open-backed cab, and I can't turn it right up at home without  a complaint from my wife!

It also sounds great for what it is. Kudos to ROG.

Hth

Chris

[phaeton]

There's an LM386 amp that uses two chips?

[MrChameleon]

http://www.runoffgroove.com/littlegem.html

See LittleGem MkII

[phaeton]

http://www.runoffgroove.com/littlegem.html

See LittleGem MkII

Cool, thx... I was always so happy with Richardo's 386 amp that I never looked into others.

http://www.generalguitargadgets.com/richardo/practiceamp/lm386.gif

[shawsofhell]

I'm thinking of going along the line of two seperate amps with one speaker for each so that I have the option to run it in stereo if I want to.

One thing I was wondering about is the use of capacitors in the gain setting from pin 1 to 8. Some designs have a capacitor only here which will under my understanding just act a short to AC signals but then the designs with pots don't have a cap as well in series. Anyone care to explain?

I'm going to use two LM386 - 4 and will normally run it from a 12V battery supply. However I read that this can handle up to 18V so could I possibly give it more juice for extra headroom?

[MrChameleon]

Re capacitors in the gain setting, this is cut&pasted from the datasheet ... http://www.national.com/ds.cgi/LM/LM386.pdf

"Application Hints
GAIN CONTROL
To make the LM386 a more versatile amplifier, two pins ( 1
and 8 ) are provided for gain control. With pins 1 and 8 open
the 1.35 kW resistor sets the gain at 20 (26 dB). If a capacitor
is put from pin 1 to 8, bypassing the 1.35 kW resistor, the
gain will go up to 200 (46 dB). If a resistor is placed in series
with the capacitor, the gain can be set to any value from 20
to 200."

Re 18v for N4, the answer is yes (also see the datasheet).

[shawsofhell]

OK I have settled on two separate amps each with its own speaker. I will wire a 1K pot in series with a 10uf cap for the gain control. My only issue left to work out now is how to wire up the pre stage. I am not sure whether I want the preamp to distort much but a little bit of break up would be nice plus some sort of tone control. The sound I am after is really close to good fender clean sound. Any suggestions? Maybe I could use a Runoffgroove circuit?