9V amp offboard wiring

[Gargaman]

Hi there,
I'm trying to make a 9v amp (Little Gem kind of). I decide to setup a offboard wiring first (with a headphone mod) before breaking my head with the amp itself. I need a walkthrough help bringing live to this thing!



1) The 10R resistor between headphone lug to ground atenuates headphone volume. Is it correctly connected? May I try differente values to suit my headphone needs?
2) Can I connect the battery snap that way?
3) Are these grounds correctly connected? Do I need a star ground?
4) Will my mono signal come to my headphones on L+R?
5) Will a led work fine between ground and 9v on the board (with its resistor)?

thanks

[GibsonGM]

Hi G,  welcome!

Umm...not enough info is given to answer your questions!  We need the schematic you are working from, and any modifications you are doing.


Well...yes, an LED with appropriate resistor will work from 9V to ground.

Are you going to us a wall-wart transformer?  Battery probably wouldn't last all that long...

[Gargaman]

Hello Mike!
my plan is to use a wallwart, yes.
I'm looking for clean sounds, a volume control and a gain control. I expect that the speaker mutes when the phones are inserted.
I've been messing around with this schematic:

[PRR]

Can't see from here.

The images show a box. Can't see any guts.

The schematic you posted does not relate to your headphone, batt-snap, and LED questions.

Step back, look at your questions, and supply the clues needed to help you from 6,789 miles away.

[GibsonGM]

For offboard wiring, look at the docs presented here (download the PDF): http://www.tonepad.com/project.asp?id=35
That will show you how to wire the jack with battery, and in/out jacks and so on.  Great reference to keep!

Of course you can try playing with the 10R resistor value, altho what is shown is 'standard'...did you know that there are better headphone amp circuits you could build?   

I would finish the Ruby/mod thing here, see what it is like with a speaker, before you try to mod it for headphone use.   Be CAREFUL and do not listen thru phones at too high a volume level!!   To add an 'aux' jack to cut the speaker out, you simply need a switching jack.

The vol and gain controls are there now, right?  Like PRR says, think about what you're doing, and try to be more clear if you can, ok? 

[Gargaman]

All right, thanks
looks like the image was not showing.
Well, I'm a real begginer and I can't write in english as well as I can read, so sorry about mistakes.
I've built a 'smokey amp' like this

that was a fun but very 'distorted'. Had to turn the guitar vol down to get clean sounds.
I would like to know if there's a way to get a clean miniamp with 9v and a lm386 chip.
A vol. knob to control the master volume (to headphone and to speaker).
A gain knob control (from pin 1 to 8 ) for 'clean' to a 'soft overdrive'.
I researched a little and noticed that this is almost like a 'ruby amp' or a 'little gem'.
I thought that would be nice to have a phone out, with a switching jack, just like the one named phones at the picture, like the mod in this page
http://www.electrosmash.com/little-gem-analysis
I think we can leave the battery snap off by now.

[PRR]

SOMEWHERE, there must be a build-guide for a '386 amp with "all the frills".

It might be better to find that than to ask "all" to walk you through every detail.

[Gargaman]

all right, thanks.
I need to study the basics in amp design.
Just two direct questions:
how much watts those little amp can deliver to a speaker?
Is there a problem to use a 3w speaker with a 1w amp?

[GibsonGM]

Hi Gabriel,

When we want to find out about a part, we usually will "Google" the data sheet.  I found this:  http://www.ti.com/lit/ds/symlink/lm386.pdf
I keep them in a folder in my computer so I can go back to them later.

There are a few models of 386, but the average seems to be about 500mW of dissipation.  1/2W.  This is probably more than what you will really get, anyway, just a conservative 'boundary' for you to use when designing.

You'll have no problem with a 3W speaker! 

To get moving fast, you may want to look up "LM386 project" on the internet, and build some different circuits. This will help you learn about the 386, and you may find some designs you like!   

To make a cleaner amplifier, it is helpful to raise the power supply voltage to 12 or 18V, being aware of what power you are dissipating in your components. Many designs already have done this, and they have taken this into account...*hint*

[Gargaman]

Thanks for the attempt on helping me out.
In fact I got a lot of questions about those miniamps, not just the initial offboard wiring question.
You asked for a schematic and so I showed what is the most like what I got on breadboard.
I tryed a first 'smokey amp' like the one I posted, minimum parts.
Then I realized that there's a input buffer on 'ruby' model, plus a Zobel network. Also I noticed that 'little gem' has a vol. pot. just before the speaker (in fact, it's a rheostat - another question that comes to me), when the ruby has it just before the 386 input, and right after that buffer.
As I did on another post, I think it's a matter of making the right questions (wich I didn't)
I feel like Jesse Pinkman, Paul looks like Walter White to me..