Looking for a portable amp schematic.

[GuitarLord5000]

At one time, I had a Smokey Amp.  They were pretty cool little buggers, but after about a week, my son tore the enclosure, a KOOL cigarette box.  Well, my wife threw the rest away, not realizing that 1. It still worked! and 2. I was gonna put it in a more rugged enclosure anyway!

Well, with the job I have, toting my 4*10 amp with me isn't feasible, so I'm looking to make a small, pocket sized guitar amp to carry with me for the purposes of testing circuits.  Anybody have any ideas where I can find a small guitar amp with a clean sound?

[Marcos - Munky]

In my site, you will find the GES Double Jam. You can turn it in a small amp changing the output cap to get more bass. Start with 220uF and try until you find a cool sound. This is a dual channel overdrive, you can get clean booster to high gain overdrive.

[RDV]

:shock:

[smoguzbenjamin]

Try the little gem at www.runoffgroove.com

[GuitarLord5000]

OK.  So I'm looking at the Little Gem here:
http://www.runoffgroove.com/littlegem.html

Looks like an easy build, which I'll put on the breadboard as soon as I get home.  Some questions first.  With the gain pot turned all the way down, will the circuit clean up (i.e.  No distortion, fuzz, etc.) enough to test circuits with?  The 25 ohm pot....volume control?  And the BIG question...Now dont laugh......how do you attach a speaker to this bugger?  Thanx in advance.

Oh...and Munkey, maybe I just wasnt looking hard enough, but I didnt find that Double Jam you were taking about.  I'll try back tomorrow and see if Im just blind or what.

[RDV]

You wire the pot as a variable resistor.

Good Luck

RDV

[javacody]

GuitarLord5000,
   Now is the perfect chance for you to learn how the search funtion of this message board works. I asked the same questions as you and got great help from many people. Do a search on the following terms:

Little Gem
lm386
smoky

You will find the holy grail of which you seek.  

[Marcos - Munky]

Copy and paste in another window:
http://www.geocities.com/munkydiy/gesdoublejam.jpg

Or this improved version:
http://www.geocities.com/munkydiy/improvedgesdoublejam.jpg

[Mark Hammer]

I made one of the LM386-based "PocketRockit" mini-amps (http://ampage.org/hammer/files/PocketRockit.PDF) for a friends son, packaging the circuit in a Hammond 1590D case with a 4" full range speaker and an 8-pack (12vdc) of AA batteries.

That sucker is LOUD, the overdrive very pleasing, and the use of a cast aluminum case makes it extremely durable.

You can power such a device form a 9v battery, but being able to push it further requires more current and voltage.  For that, I recommend 12vdc from an AA 8-pack.

PLEASE NOTE that LM386's are rated in terms of power dissipation.  The higher the numeric suffix (386-1, 386-2, 386-4) the more power dissipation it can tolerate.  You want the 386-3 or -4 since 12v will squeeze more power out of it and could result in heat damage.  Alternatively, figure out a way to heatsink the chip and you're okay.

You can also consider making a combination of Little Gem II and PocketRockit by implementing a bridged amp configuration with a pair of 386's.  There I would strongly encourage you to use something heftier than a 9v battery.

You'll be pleasantly surprised by how loud one watt can be.

[B Tremblay]

Here's another 386-based amp.  We're considering it as a replacement for the Little Gem.

[javacody]

B, that looks a little familiar.     Are you using a j201 for the JFET?

[smoguzbenjamin]

PLEASE NOTE that LM386's are rated in terms of power dissipation. The higher the numeric suffix (386-1, 386-2, 386-4) the more power dissipation it can tolerate. You want the 386-3 or -4 since 12v will squeeze more power out of it and could result in heat damage. Alternatively, figure out a way to heatsink the chip and you're okay.

I used an LM386-n1 in my headphone amp, I designed it off ideas here and the lm386 appnotes, but I use a 9V battery or a 12v wallwart and it goes plenty loud though, and no heat problems whatsoever.

[B Tremblay]

B, that looks a little familiar.  

Gary and I have been working with the 386 lately and the "Ruby" arrangement stood out enough that we wanted to share it.  Ruby is simply the Little Gem with a generic input buffer (as found in the Little Gem MkII) and the volume control changed from the output rheostat to the type and placement as shown in the datasheet application notes.  Also, we're using the inverting input and the stabilizing RC network at the output has been removed and replaced by a bypass cap at pin 7.  Any FET should work well for the buffer.

I realize that you have also been using the Little Gem as a building block, experimenting with tonestacks and an input gain stage.  Ruby is certainly not an attempt to pass off a version of your circuit as a RunoffGroove design (especially after the Peppermill debacle :roll: ).

Is this schematic the final version of your amp based on the Little Gem?

[javacody]

B,
It wasn't an accusation at all. I'm simply progessing enough at this to recognize some of the building blocks.  

My Little Gem variant is similar but I got the idea from your Little Gem MKII. I'm trying to find a better sounding version of the GEM. Do you guys have any sound clips of this little guy yet?

Also, I'm starting to think that the JRC variant of the LM386 sounds a little bit better in these amps, what do you think?

Also, I wanted to thank you and Gary for all your awesome work. I still have the Peppermill schem and am planning on building it. I was thinking that it may make a good built in OD module in a little practice amp.   :wink:  I never had a problem with the resemblance of the Peppermill to the BlueMagic. You simply happened to use two of the same building blocks in the same order as the Blue Magic. No biggie.

[B Tremblay]

No sound clips (yet).

When I sent the Ruby schematic to Gary for testing and confirmation of my results, he said it was good enough to replace the Little Gem - or at least be added to the article as a variant.  I'm currently working on the Ruby perf layout, so that and the schematic/notes will be added to the Little Gem page soon.  It would be great to have your take on the circuit if you try it.

I have noticed a difference between the RadioShack LM386 and the JRC386.  Ruby was assembled with the JRC version, but I haven't done any critical A-B testing to determine the better sounding IC.

I'm really happy to know that you've found RunoffGroove.com useful.  Also, the Peppermill is back online and it does indeed work very nicely driving the Little Gem and Ruby.

Also, I'd love to see the final product of your 386 amp work.

[phillip]

I wish Fender would put the schematic of the Mini Twin Amp on their website.  Battery powered, 1-watt, two 3" speakers, clean and distortion...all the goodies

Phillip

[smoguzbenjamin]

Hell most of us are competent enough to design a 1W amp with 2x3" speakers and distortion/clean!

Let's make it a competition: who can design the best mini amp?

[javacody]

Actually, what I've been thinking about is a mini-amp with built in effects. I was thinking a Fuzz Face, a Tubescreamer or other OD, maybe a BSIAB, reverb, etc. etc.

[GuitarLord5000]

OK...I have three speakers salvaged from cordless telephone/answering machines.  They are a .5 watt 32 ohm, a .5 watt 8 ohm, and a .25 watt 16 ohm speaker.  This amp is a 1 watt right? (The single chip one.)  So, are any of these useful?  Or will the 1 watt amp blow these up?

[javacody]

Not sure GuitarLord, but I'm sure someone here knows.

I wanted to post that B has up the Ruby amp now:

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

I tried building one from the schem but couldn't get it working well. I'm going to use the layout that's up at RunoffGroove rather than try to debug what I have.