Hi Guys,

For those who didn't read my intro post, I'm a noob noob having fun learning electronics...

I'm currently building this little practice amp I found someone else on this forum talking about in a different thread...here is the link to the amp and schematic...

Little Gem

I'm just building it on a solderless board right now to see if I can get it to make noise.

My question: I have a little 8 ohm 1 watt speaker from an AM radio project...can I use that to test it? I didn't see anything about the correct impedance in the diagram or description, but I may be blind.

The other noob question: assuming the answer to the first question was 'yes', looking at the speaker from the back, is one pin positive and one negative? Does it matter?

Thanks for any help in advance!

Annie

 

Hi Again!

Ya know, it's been a long day, lol....I just looked at the site again and my speaker will work....AND I found under the magnifier that the speaker is marked with a plus and minus sign.....heh....

Well, thanks! If anyone can give me some coaching or point me to my next project, feel free!

Annie

 

hi Annie,
The polarity marking on the speaker is to indicate which way the speaker cone will move when a signal is applied.

Assume you connected a small battery to the terminals of the speaker, say, the cone moves foward,
reverse the battery and the cone moves backward.

The need to know this is, if you have a stereo speaker system you would want the speaker cones to be moving in the same direction when a signal is applied, if not, you would get sound 'cancellation' which would effect the sound quality.

In a mono system it dosn't matter, unless you are using a speaker 'column' ie: two or more speakers connected in parallel or series.
In parallel all the '+' on the same line, like wise all the '-' on the same line.
In series, '+' on one speaker to the '-' on the next, ... '+'.... like connecting batteries in series.

The circuit designer says he uses a 16ohm speaker, your 8ohm should be OK.
You may need to increase the 220uF to say 470uF, if you like a 'basey' guitar.

Welcome to the forum, I hung back on saying 'hello' didn't want to get trampled in the stampede!

Hope this helps.

Regards

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

 

The Little Gem amplifier has a very low input impedance that is too low to be driven by a guitar's pickup. The high input impedance of the FET transistor used on The Ruby amplifier is recommended. The Ruby amplifier has a proper volume control.

The LM386 has an output power at clipping into an 8 ohms speaker with a brand new 9V alkaline battery of only 450mW. It is not loud. It is like a toy. When the battery voltage falls to 6V then the output power is only 200mW. A joke.

The value of the 0.01uF input capacitor in The Little Gem and the 47nF capacitor in The Ruby are so low that the bass frequencies will be reduced.

__________________
Uncle $crooge

 

Thanks for the info, guys....I'm not making this for any real world situation, so I'm not worried about the low output...I'm just making it for the learning experience....so I'll play around with it and then try the Ruby...

I do confess however that I don't quite have a grasp on the input impedance stuff...but I learn a little every day!

Thanks again!

 

Here is what a guitar electronics geek says about the input impedance of a guitar's amplifier:

Attached Images

guitar preamp.PNG (15.4 KB, 39 views)

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Uncle $crooge

 

That looks like something I can build, Audioguru! I just read an article about input impedance as well..

Now, remember....I'm just a goofy girl in Tucson teaching myself electronics so please don't get frustrated at simple questions...heh..but here goes:

I could build that circuit you just posted and use it as a preamp for the Little Gem, right? LOL!

Thanks for the help!

Annie

 

Then it is almost the same circuit as The Ruby. Make The Ruby instead. It has a proper volume control.

__________________
Uncle $crooge

 

Success! I put everything on my breadboard with alligator clips and I got sound! Yay! But before I move on to a fancier circuit like the Little Gem MKII or the Ruby (both available on the link above), I have some questions...

My point in doing this is not just to have fun and make some noise, I wanna understand what I am doing. To that end, I'd like to draw out the schematic in such a way that it is made up of series and parallel circuits that I can then do the calculations on to see what current is going where, which voltages are doing what, etc.....that's possible right? I'll try it.

Then, I was thinking that I should add an on/off switch and an led to show when it is on....is there a 'best' place to hook in the LED?

Third...I have some LEDs that aren't marked...are cheap LEDs pretty much one standard voltage rating?

Fourth...when calculating voltages and resistances how do you calculate the resistances and voltages for caps and ICs? Using the DMM? Figuring out the voltages and current of the resistors and then calculating?

Fifth....if all these questions are too basic and bug you guys, can you recommend any other forum that is more geared towards beginners? I don't want anyone to roll their eyes and curse under their breath....heh...

Thanks for everything!

Annie

 

You can place a LED with a series 1K resistor near the polarities (+9V) & (0V).

There are various types of LED’s. You better keep a 3V battery pack to check your LED’s polarity. Red lead is positive & black is negative in the battery leads. (But in the analog multimeter this polarity is wise versa) I hope they are 5mm cheapy LED’s. It needs 1.75V onwards.Use this link to calculate LED resistor values http://www.kpsec.freeuk.com/components/led.htm

Yes I’m using DMM. To measure the resistance you must remove it from the circuit even one lead. You can measure the VOLTAGES in the components while in the circuit (parallel).for CURRENT measurements you must place the DMM in series with the component.

No any other forum I see better than this. Ask any stupid question. No one laughs.

__________________
Gayan

My Website
http://gsmicro.blogspot.com/

 

Gayan,

Thank you for all the info! Okay, I won't worry about asking questions, then...lol....Hopefully I'll have some time this afternoon to play around with my circuits...

Annie

 

can u tell me how to make it on a solderless breadboard?
0_o
im new to electronics and im lost...
thx

 

You buy a solderless breadboard. It is made with hundreds of connectors that pinch wires and join a few together. Because the parallel tracks and connecting wires have capacitance between them, they cannot be used for high frequency circuits.

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Uncle $crooge

 

come again?
0_o
i didnt get that