my monster headphone amp idea

[guitarmonky55]

ok so ive got a broken foot and about 15 boxes of free samples just arrived from various electronics companies.  today i got a semi-large plastic enclosure from davies molding that has all these pcb slots and standoffs and *lots* of room for goodies.  i got to thinking about using it for a headphone amp, something ive wanted to build for a long time as i dont own a small amp to practice with, so when i play i blow the family out of their minds.  

my goals are this:
-i want a basic clean headphone amp that i can power by ac adaptor or batteries.  
-id like to build a simple distortion circuit like a distortion+ or something in the signal path before the amplifier portion taht i can switch on and off.
-heres the part where i will start needing some guidance it hink...i have a *ton* of small speakers lying around the house and would like to add a switcheable speaker.  i have alot of switches i could use to toggle the headphone out or the speaker.  

so my questions are:
1)ive never dealt with multiple circuits in one box before.  if i run a dist+ and an amplifier circuit, what powering issues may i encounter?  how would i go about powering the unit most efficiently?

2)in order for the speaker idea to work, will i need a power amplifier of some sort?  i dont need extreme volume, just something audible for pracicing by myself quietly in a corner somewhere.  how would i go about hooking up the speaker?

[samzeppelin]

check this out:

http://www.generalguitargadgets.com/pdf/two_in_one_wiring.pdf

might help a bit

Cya
sam

[Marcos - Munky]

You can use a LM386 as the power amp IC, or the TDA2003 if you want more power, but you will need to use a power supply instead of a battery. You can use a battery if you choose the LM386 (which I think it will be your choice), but it eats batteries fast.

[guitarmonky55]

forgive my ignorance on teh subject but i have a few q's about those.(i tried searching but couldnt really find what im looking for)

what is a good, simple lm386 power amp that i could use?

could i do with just throwing the signal straight at the power amp so i can achieve a clean sound, but using my switcheable distortion in front for any other sounds i need? or will i need some type of a preamp circuit too?

also are there any good stand-ins for an lm386?

[Marcos - Munky]

The LM386 don't need any kind of preamp. Take a look at the Ruby and Little Gem in ROG site (runoffgroove.com). They already have a "distortion" inside the IC. The problem is that they give a low volume (for small speakers, not for headphones) when the signal is clean. Maybe you can wire two of them in bridge, like the Little Gem MK2, and get a louder sound.

[guitarmonky55]

ok i took a look at those and they look like exactly what im after.  

i read the descriptions and it says the little gems are closer to the marshall sound, im not really into the clean thign im after something i can pump to squeal a little.  got a few q's:

would the regular little gem be sufficiently loud through a little speaker?  how loud about would it be?

for connecting it to a speaker, do i just put the output to positive and the negative of teh speaker to ground? never really messed with speakrs before but i notice thats how they are in the other diagrams.

would there be a significant increase in volume/power with the mkII?  and are there any good perf layouts for it as im terrible at making up my own and would like soem reference to it.

[Marcos - Munky]

Yeah, the Little Gem gives a Marshall-like sound. I have one, and is cool to play thru it. It can be loud enought to practice in the room, but you need to choose the correct speaker. You need a very good one to get a good sound. Almost all of these tiny speakers have low bass, and sounds really bad when you play more than 2 notes. To connect the speaker, the output goes to + and ground goes to -. If you use a bridge amp, the connection will be in the schematic. I didn't tried the MK2, but in the schematic it says that it have twice the volume of the Little Gem, but it will eat your battery faster, then is better to use a power supply (well, is better to use a power supply in any kind of amp). If you can build a effect in a PCB, I can draw a layout of the MK2 for you. But I believe the MK2 is a clean amp, because of the soundclip in ROG's site. My suggestion to you is to build the Little Gem and put a output jack, so you can connect it to a speaker or to a headphone. I use a 8" speaker with my Little Gem, and sounds great to my ears.

[guitarmonky55]

well i was digging through my boxes of cannibalized innards that ive collected from various broken bits around the house over the last few months and found 2 jrc386D chips, so i ripped one out and, as i have a current lack of perfboard i proceeded to wire up a little gem on a piece of cardboard(talk about being anxious, i couldnt wait till today to build it!).  it sounds pretty good, i dont haev any pots hooked up to it right now, i just hard-wired all the settings to max.  i think im gonna end up using a switch between full open and a resistor for the gain, and i may put a pot in front if the 386 as opposed to after as i found that the little bugger gives some wicked cleans even through my little 2 inch speakers when i roll the guitar volume down.  

i was staring at the mkII schematic and decided what the hey, if i mess up the perf layout whats the big deal.  so im gonna get some perf and tear off the other 386 and give it a go.  

my only gripe is that at times it sounds a bit tinny, it could just be the speakers im using though.

[Marcos - Munky]

My Little Gem have no pots too, it's hard wired to get full gain and full volume. Did you wired it to a speaker or to a jack? My suggestion is to use a jack, and use a volume pot, then you can use it as a headphone practice amp. I tried mine with a good headphone, and believe in me, it's very loud. What kind of speaker did you use?

[guitarmonky55]

right now the circuit is soldered together with the legs punched through a piece of cardboard and i have alligator clips going to the speaker.  its just a tiny little 2 inch speaker that i tore out of my old computer speakers.  sounds pretty good.  im going to throw an mxr dist+ in front of it, hardwired to max gain that will be switcheable.  my thoughts are to have a switch for going between a clean and distorted setting on the actual amp circuit, and another to kick on the dist+.  my plan is to wire it to this little speaker and include it in the enclosure, and then make the output switcheable between the speaker and an output jack.

if i just run this signal straight to a mono output jack, will i only get teh guitar signal in one ear with headphones?  id like to get both if possible.

i plan on perfing and boxing the circuit up later tonight, i have to run to radio shack to more perf as i used all mine up.

[Marcos - Munky]

You can use a stereo jack and wire the output to the two channel lugs of the jack. I used a PC speaker too, and the sound is very bad compared to a bigger one. About to use the Dist+, I think it's better to stay with the 386 distortion. If you use the Dist+ in a clean 386, it will works, but if you use the Dist+ in a 386 with it's distortion in max, you will get only noise.