Ok so I started out trying to make my own amp. So far I have been working on the preamp section.
I based my design off of several designs I found on the internet and the datasheet for the ICs (LM386).
My idea was to use one IC with a drive pot and to be able to switch in the other IC for a "boost" or "high gain" channel.

I am getting weird results. First the gain pot doesn't work, at 0 I get some weird weird artifact noise in addition to harsh metallic distortion. At 10 I get just the harsh metallic distortion. The knob only affects the artifacts.
Also there is kind of a gating effect, sustained notes seem to be cut off after a while in a quick fade out, and playing hard makes it go silent and drop out. Switching on the booster amplifies this effect, I get a second of sounds, then it drops out, then it comes back a second and drops out again, then it dies in the gating effect. Also when playing two strings together I get a "tremolo" effect or oscilation or what you call it

What am I doing wrong? Any ideas?

Schematic is attached,
EDIT: Noticed an error in the schematic C1 is electrolytic!

DocZ

Just to clearify things, if you don't mind me asking that is. How does the values of the caps affect the different functions?

DocZ

Wov thank you very much teemuk for a very insightful explanation!

I will start to prototype this thing as soon as I get my desktop cleaned out. It is absolutely flooded with half-way-done projects

I think this will be great!

DocZ

Thank you very much for a great explanation! I get it C2 and the coupling caps now. I thought that was a voltage divider, but I was not sure. This is all pretty new to me. From what I read from the datasheet, this chip get's it's negative voltage on pin 3 and positive voltage on pin 5. But I can't seem to find a voltage divider there, is that what Q1 and Q2 do invert the power? The dual rail circuit in the datasheet is much simpler - and easier for me to understand. Could you guys point me in the direction I need to include those two transistors for the double boost in power?

DocZ

Ok I get it, what about C1, that goes between the two input resistors? Is that some kind of filter? Again how will different values effect it?


DocZ

That electrolytic cap that is on the positive lead to the speaker, what is it's purpose? Is it just to block DC? Can I get away with different values?

DocZ

I stumbled onto this circuit, that uses a TDA2030 and TIP31/TIP32 for a total of 30W, you guys think it will work good together with that preamp circuit I found?

http://www.elecfree.com/electronic/wp-content/uploads/2008/06/circuit-30w-amp-otl-by-tda2030-transistor.jpg

And how do I know what sort of load impedance the power amp can handle?

DocZ

Also about the preamps, will this work as a preamp for that TDA2030 amp? Or will I need something between this circuit and the TDA to get the right impedance?
http://www.erikhansen.net/diy/schematics/misc/2203-RevB.png

DocZ

What did you mean "Burn 4 a week"? 4 chips? 4 grand? 4 ears?

DocZ

Cool, ok I just found a transformer. It is certfied for up to 150W, it's got four secondary taps of 12VAC (actually 8 I believe don't know if it is 8 phases of 6V or 12V I will test, it is made to power up four 12V spotlights) @ 4,2A Could this be a candidate for something? Maybe that 50W amp?

DocZ

I have a bunch of other stuff to, I just wondered what I could use them for. I just read that datasheet and they said they were 40W so I thought 10W sounded a bit low. I have a bunch of MPF102, J201, a couple TDA7294, a couple TDA2030, a bunch of op amps 4558D TL072 and LM386, bunch of 2N5401, 2N5551, buckets of 1N4148, 1N4007 a lot of pots, caps, resistors of different values. And I have sockets, plates for chassises, drivers, and a healthy supply of old wall warts from 5 - 16V. The only I don't have is a real deal transformer. But I'm looking for ideas on what I can build from all this stuff. I bought them for some stompboxes I wanted to build, but now that I have built them I have a lot of spare parts and I thought I'd turn some of them into an amplifier. I really want something in the 20 - 100W range I don't know what is possible. But I'm open to suggestions, I guess a 10 - 15W "ruby" or similar would be cool

Doc-Z

Is there anyway I can get more? Like 50W?

What kind of power can I get out of these?

DocZ

I just found a couple of TIP31 TIP32 transistors, I was thinking maybe I could use them for a power amplifier? Anyone ever tried using those? And anyone who can point me in the direction of a schematic using these that I can study to see if I can use these for guitar purposes?

DocZ

I just posted some pictures and stuff on my blog about this attempt, so you and others can see.
http://krayzyhead.blogspot.com/2010/02/tda2030-power-amp.html

I have a quick question, what do you call those connectors used to connect to pin headers on motherboards and such and what tools do I need to install them?

DocZ