Hi. My name is Dan, and I'm a noob

[dmartn149]

Hi I am new here, and new at building amps. I just ordered one of these
http://cgi.ebay.com/Audio-Power-Amplifier-20W-2x-TDA2003-Assembling-kit_W0QQitemZ230446223553QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item35a7aa50c1
It looks like a really good deal. About $10.00 with shipping, and includes everything but power, speaker, and enclosure.
I'm planning on using the lm386 amp that I already built as a preamp. If I have any problems, I hope I can pick some of your brains.

[J M Fahey]

Looks good.
Keep us informed on your experiments.
Good luck.

[dmartn149]

I haven't started on my amp kit yet. I have been using any spare moment to get my old Fender amp working. I have been thinking about it though, and I was wondering. Can I just run the speaker leads from my Little Gem to the input of the tda2003 amp? or is there more to it than that?
Thanks

[pyromaniac_]

At least put a resistor between the speaker lead and the TDA2003 Amp. And read this thread; http://www.ssguitar.com/index.php?topic=1122.0

[joecool85]

At least put a resistor between the speaker lead and the TDA2003 Amp. And read this thread; http://www.ssguitar.com/index.php?topic=1122.0

I agree you should read the thread.  I don't agree you *need* a resistor in there.  I ran my lm386 into several amps straight with nothing special at all.  No problems either.

[dmartn149]

I put it all together today, and it sounds okay, but won't get a really "clean" sound and it makes a motorboat sound when turned up. I added a resistor in series between the Gem and tda2003 with no improvement. Any ideas?
The case is an Army surplus night vision goggles case. It's heavy gauge aluminum, so I bolted the tda2003s right to it for heat sinking. The speaker was salvaged out of a dead Yamaha powered subwoofer.

Here is a piucture

[phatt]

Try a guitar speaker or any full range speaker.
You will have a far better chance of success
Phil.

[joecool85]

Looks good, to get rid of the motorboating, check your powersupply board.  You might have a backwards cap or something.

As for the clean sound, turn down you guitar, turn up the power amp (if you put a volume between the preamp and poweramp).  The LM386 amps aren't great for a super clean sound, but do alright with a low output single coil pickup.  With a high output humbucker it's darn near impossible.

Also, try making a Ruby instead of Little Gem for the preamp.  http://runoffgroove.com/ruby.html

Supposedly it has a better handle on clean output.

[rowdy_riemer]

If you want to use an LM386 for a preamp, perhaps you should also checkout the Grace and Big Daddy circuits on Runoffgroove. http://runoffgroove.com/grace.html . Also, lookup the smash drive circuit. http://www.aronnelson.com/gallery/main.php/v/Daves-Layouts/Smash_Drive.gif.html circuit. or maybe the Distortus Maximus http://www.aronnelson.com/gallery/main.php/v/Schematics-etc/Krank+Distortus+Maximus.jpg.html?g2_imageViewsIndex=0 . I've not tried the Ruby or Little Gem as preamps, and they may work quite well. However, they are not desiged to be preamps. If you need a good clean preamp using an LM386, the Grace circuit might be your best bet.

[dmartn149]

I could live with the little bit of distortion. It does clean up when I turn the guitar down. I really would like to fix the motorboating though. When I used the Gem as an amp, it didn't do that. It just started when wired it into the new tda2003 amp.

I was thinking maybe I could try disconnecting the Gem, and running the output from a zoom or digitech rp300 into the TDA, just to see if it is the amp, or just the way it ineracts with the gem

[tonyharker]

What power supply are you using?  Motor-boating is usually caused by the supply not having enough capacitance across the + & - rails i.e. too high an impedance.  You should have at least 2200uF but more is better. 
Another cause is the supply not being able to supply the current needed by the amplifier.  20 watts peak into an 8 ohm speaker would need approx 1.5 amps. 
This cannot be supplied by the same battery as you used for your little Gem!

Tony.

[dmartn149]

Woa Tony, That might be it. I'm running the whole thing on 8 D-cells. Do I need to go with a wall wart?

[J M Fahey]

No, just isolate it. Feed it through a 100 ohm resistor and an extra 220 to 1000 uFx16 or 25V; *and* solder a 2200 to 4700uF x 16 or 25V across the battery terminals.

[joecool85]

Woa Tony, That might be it. I'm running the whole thing on 8 D-cells. Do I need to go with a wall wart?

I'd run it off a wallwart/homebrew psu board.  You'll burn through batteries otherwise.

[dmartn149]

I stopped in to the good will store and got a 12v 1500ma wall wart. It measures 19.7v on my MM. What can I do to bring it down to 12v? or should I just get a lower voltage w.w.
Also, the cap across the + and -, would I need that with a wall wart? Is that like the filter caps on a tube amp? Is there a website, or thread where I could learn  about powering devices like this with a wall wart? and finally, what is a psu board?
Thanks