LittleGem I Question

[Oliver]

Hi All,

im in need of a practice Amp, because my Setup is places in our Bands Practice Room and its to heavy every Monday to carry al the things to the Room an after our Session back home.

So i searched on ebay for some cheap amps and remembered the littleGem from runoffgroove.

Now my question:
first, das anybody build that MiniAmp and can tell me his experience with that?
and the 25Ohm Pot is marked with "Rheostat" i cant find any Pot matching this - can someone explain what that means (Rheostat)??

When the DIY one sounds like the Soundfile found on Runoffgroove, i will be very happy with that!!

OK guys..

bye
Oliver

[petemoore]

Variable rheostat....that's a pot..I believe RS has them.
 I use the little gem for guitar/string Instr. practice...plenty loud for sing alongs etc. Not really near loud enough to be heard with drums.
 I was getting a sorta clean, distorted, and that octave thing it does sounds from it.
 I'm thinking of building a second, finding the 'right' speakers [makes big diff] then I could have a stereo mini combo amp!!!
 Right now I've got a little [3''] TV or puter speaker in there and it's probably the weakest comp in the amp.

[B Tremblay]

The rheostat isn't crucial to the circuit; it can be omitted with no ill effects.  Gary Burchett added it as a master volume that would not significantly alter the output impedence.  Without it, the volume can be controlled with your guitar volume and the Gain control.

I've built three 386-based amps and they are very fun.

[Oliver]

The rheostat isn't crucial to the circuit; it can be omitted with no ill effects.  Gary Burchett added it as a master volume that would not significantly alter the output impedence.  Without it, the volume can be controlled with your guitar volume and the Gain control.

I've built three 386-based amps and they are very fun.

Hi,

than i will build a NON-MasterVolume LittleGem  

@Petemoore - i want to use it at Home for practice and for the Test, i connect it to a 1x12 Hughes&Kettner cabinet that includes a Celestion Vintage30 Speaker (8Ohm), thats owned by my neightbour.
If it sounds good, i will look for a cheap Guitarcabinet.

I dont build a Combo, even a small Top (perhaps like the Mini TubeAmp from ZVEX   )
And i want to add a simple Tonecontrol with a Pot and two caps (50 and 330 uF instead of the 220uF one at the End of the circuit), maybe that it sounds good...

Thank you !!

cu
Oliver

[Peter Snowberg]

than i will build a NON-MasterVolume LittleGem  

This is not like a standard master, it is more like a power-brake on the output.

I use an LM386 circuit with a 10 inch celestion G10D from a Marshall practice amp. It sounds really nice and the rheostat allows you to play at whisper level volumes. I use a 500 ohm pot because it was in my junk box.

-Peter

[Gary]

Yep, it's exactly like a power brake.  The ohmage is not critical.  I used that pot 'cause it was available.  I'm pretty sure you could use about any pot you wanted there.  Glad people are digging that little amp.  The 386 seems very sensitive to cap sizes, so play around and see what you like on both the input and output.

Peace

[Oliver]

Yep, it's exactly like a power brake.  The ohmage is not critical.  I used that pot 'cause it was available.  I'm pretty sure you could use about any pot you wanted there.  Glad people are digging that little amp.  The 386 seems very sensitive to cap sizes, so play around and see what you like on both the input and output.

Peace

Ahha, than i know what is ment with a rheostat Pot - they are not cheap, arent they, and such big in comparisation with normal PlasticFilm Pots?
Its like, or it is a WireWound-Pot?

But for what - it seem not to be very loud, or not?

I will see..

cu
Oliver

[Gary]

Guten Abend, Oliver.

The rheostat I used is 25mm in diameter.  Yes, it is built a little heavier than a normal pot.  I think the rheostat is rated for 2W.  It is not required, but I used it for the sake of my wife and daughter.  They are tired of hearing it play at full volume through my 2X12 cabinet.  I guess they don't like music...  Maybe they just don't like bad music.

Best regards.

Aufwiederlesen  (did I just make up a new German word?)

[Oliver]

Guten Abend, Oliver.

The rheostat I used is 25mm in diameter.  Yes, it is built a little heavier than a normal pot.  I think the rheostat is rated for 2W.  It is not required, but I used it for the sake of my wife and daughter.  They are tired of hearing it play at full volume through my 2X12 cabinet.  I guess they don't like music...  Maybe they just don't like bad music.

Best regards.

Aufwiederlesen  (did I just make up a new German word?)

Moin  

thank You - now i know what to buy  

What do you use for Enclosure? I thought of a Hammond CastAlu. Box. or an equivalent one ....

cu
Oliver

P.S. do you come from Germany too?

[Gary]

Oliver,

I don't come from Germany originally, but I lived there a few years ago.  I miss it sometimes.

I used a small metal electrical junction box for that project.  It's the box that power outlets are mounted into the walls with.  Sie sind sehr billig.  Any metal box should work fine.

Best regards.

[RDV]

I used a small metal electrical junction box for that project.

Mines in a Plastic Seymour Duncan Pickup box. Two of them in stereo in the one little box!

Aufweidersen

RDV

[Robin]

Hey Oliver,

 A decent speaker is important on these 386-based amps. Here’s one I stuffed into an Altoids box a while back.

http://members.aol.com/woodstalk13/effects/candybox3

That little speaker is only useful when I use the amp as an audio probe for circuit de-bugging. ( See GEO for details on this cool little trick). I did the circuit based on National Semiconductor’s application notes for the chip but thought it needed a higher input impedance, so I put an FET buffer on the front end. Don’t know how much it’s really needed on something like this but you can refer to AMZ’s lab notes on buffers and Runoffgroove’s Grace 3.0/Big Daddy for related info.
 If you look around you’ll find this circuit has been tweaked to death with add-ons like tone and gain controls, preamp stages and even octave effect using schottky diodes. Oh, and it works great as a stand alone distortion box (Smashdrive, for instance). I tried bridging two 386’s to feed a single speaker for more power (Little Gem Mark II) but didn’t have much luck. Might be the fact that some manufacturer’s chips are less stable, but I think the bridging schematic was actually based on app notes for a LM380 or some such. 386’s do work pretty well paired up for a stereo amp, though.
Be aware that the LM386 comes in 325, 700 or 1000 mW power ratings. The ones I get at the local Radio Shack are 325 mW .
If you’re looking for more power in a portable unit, consider some of the chips used in boomboxes and some car amplifiers. I’ve had pretty good luck with scavenged units by downloading the chip’s datasheet and application notes. Pretty often I found that you can simply isolate and remove the amp stage (or even preamp and tone sections) and box it how you want.
Fun, fun.

[Oliver]

Hey Oliver,

 A decent speaker is important on these 386-based amps. Here?s one I stuffed into an Altoids box a while back.

http://members.aol.com/woodstalk13/effects/candybox3

That little speaker is only useful when I use the amp as an audio probe for circuit de-bugging. ( See GEO for details on this cool little trick). I did the circuit based on National Semiconductor?s application notes for the chip but thought it needed a higher input impedance, so I put an FET buffer on the front end. Don?t know how much it?s really needed on something like this but you can refer to AMZ?s lab notes on buffers and Runoffgroove?s Grace 3.0/Big Daddy for related info.
 If you look around you?ll find this circuit has been tweaked to death with add-ons like tone and gain controls, preamp stages and even octave effect using schottky diodes. Oh, and it works great as a stand alone distortion box (Smashdrive, for instance). I tried bridging two 386?s to feed a single speaker for more power (Little Gem Mark II) but didn?t have much luck. Might be the fact that some manufacturer?s chips are less stable, but I think the bridging schematic was actually based on app notes for a LM380 or some such. 386?s do work pretty well paired up for a stereo amp, though.
Be aware that the LM386 comes in 325, 700 or 1000 mW power ratings. The ones I get at the local Radio Shack are 325 mW .
If you?re looking for more power in a portable unit, consider some of the chips used in boomboxes and some car amplifiers. I?ve had pretty good luck with scavenged units by downloading the chip?s datasheet and application notes. Pretty often I found that you can simply isolate and remove the amp stage (or even preamp and tone sections) and box it how you want.
Fun, fun.

Hi,

and thanx for that detailed Informations !!
There are some problems opening the Picture you linked above.
What Format is it (.jpg)?

I found a very good OnlineShop for purchasing many parts to build
my stuff - right today - www.kessler-elektronik.de - they sell needed parts very cheap and even the LM386 in some variations:
LM386-N   IC 0,5 W x 1 1,8 - 6 V DIP8
LM386-N1  IC 0,5 W x 1 1,8 - 6 V DIP8
LM386-N3   IC 1,0 W x 1 5 - 18 V DIP8
LM386-N4 (only Info for that is - PowerAmp IC, butz the German word - Endstufen IC)

i tought of ordering the N3.....
can You tell me, if that will be the right one?

thanx!!

Oliver

[Robin]

I'm not sure what the problem is with opening the photo file --- maybe it has to do with the fact that I'm just using the little FTP space America Online gives you. No big deal anyway; I just wanted to encourage you to be creative about making your own enclosures. Hell, some of my favorite ones are carved from wood! Hence, the name: Woodstalker.
 Anyway, you should be ok with the LM386N-3. Although your site refers to it as 1 W power, National Semiconductor's datasheet shows the -3 as being rated 700 mW. Either way you're well within the usable operating voltage at 9 volts.
 Good luck.

[Oliver]

I'm not sure what the problem is with opening the photo file --- maybe it has to do with the fact that I'm just using the little FTP space America Online gives you. No big deal anyway; I just wanted to encourage you to be creative about making your own enclosures. Hell, some of my favorite ones are carved from wood! Hence, the name: Woodstalker.
 Anyway, you should be ok with the LM386N-3. Although your site refers to it as 1 W power, National Semiconductor's datasheet shows the -3 as being rated 700 mW. Either way you're well within the usable operating voltage at 9 volts.
 Good luck.

Hi,

i use the opera browser, that shows only much letters (nonsense)
with the Internet Explorer it works !! :-))

Looks good  -  ooooh noooooo - your candy is to loug for me!!  

Perhaps the N-3 one has 700mW real and they counted up.
I'll try it...

bye
Oliver

P.S.: if it works and looks showable    i'll post a review with Photodocumentation.. (and perhaps Soundfile)