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 (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.
Looks good.
Keep us informed on your experiments.
Good luck.
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
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
Quote from: pyromaniac_ on April 01, 2010, 07:39:35 AM
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.
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
(http://i858.photobucket.com/albums/ab141/dmartn149/battamp/th_battamp004.jpg) (http://s858.photobucket.com/albums/ab141/dmartn149/battamp/?action=view¤t=battamp004.jpg)
Try a guitar speaker or any full range speaker.
You will have a far better chance of success :)
Phil.
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.
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.
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
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.
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?
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.
Quote from: dmartn149 on April 05, 2010, 09:19:03 PM
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.
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
Hi. Those 19V are no load voltage.
You'll get to 12V (hopefully) with full 1500mA load.
That's why it pays to overspec everything a bit.
so it's not going to kill my amp?
If it were a stiff 19.7V PSU, maybe.
Real life test: hook it to your TDA2003 board (without preamp) , no signal or shorted input, speaker connected, and measure what you really get.
As the datasheet states, it can stand 28V *no signal* but it should not "work" with more than 18V.
In a nutshell: I doubt you will have more than 18V there with any sound coming from that speaker, definitely less than that when cranking your favorite guitar licks through it
As usual, only measurements will tell.
PS: I'd buy a few TDA2003, simply because of its low cost and the real possibility of having a mob of friends asking for similar amps.
I tried the 12v ww with the input open, and shorted, and still measured over 18v both ways. I found a 9v , 300ma ww in my "pyle-o-junk" that gives 12v with no load, but it motorboats, and hums too. I haven't tried the isolating methods yet, as I don't have the caps and resistors on hand.
could I run my 12v 1500ma wallwart through this to get clean, stable 12v?
http://www.instructables.com/id/Make_a_simple_12_volt_power_supply/
Yes, you can.
Bolt that 7812 on a heatsink, at least a piece of aluminum, and the first time you use it, touch it now and then to check it does not overheat.
Practical rule: if you feel it hot, yet you can stand touching it, it's OK; if you can't bear it over a few seconde (or even worse, if your skin sizzles or grills), then it's *too* hot.
Make an external power supply so you can power this ampand any future project freely.
I noticed after I posted that that circuit uses an ac transformer. Could I delete the diodes and use a dc wall wart instead?
I don't understand you.
A DC wall-wart does have diodes and filter capacitors within.
When you wire a power jack for it, you send its positive and negative pins to the corresponding points in your PCB.
Adding a 2200 or 4700 uFx25V from positive to ground will lower hum and provide cleaner sound.
I guess I just wanted confirmation that I don't need the four 1N4001 diodes used in this circuit
http://www.instructables.com/id/Make_a_simple_12_volt_power_supply/
because they are for rectification, which is already done in the dc ww.
You do not need the:
* 4 x 1N4001 diodes
* 14V - 35V transformer
* 240V input
because all that is included into your wall wart
I built the regulated power supply, and temporarily wired it up to the amp. No more motorboating! ;D Now the gain control on the Gem doesn't seem to be working. I'll check into that when I get more time. Thanks for all the help and guidance. I'll probably be asking more questions when I decide to add some kind of tone control.
Thanks again, Dan
OK, now you know what to do with that "International House of Pizza" membership card I signed on your behalf. (hint, hint) 8|