My first Guitar Amp ...Need suggestions for second

[Bismarck]

Hi everybody, this is my first post here since I'm kinda new new to amp building so please be patient with my noobish questions. So far I am amazed at the depth of knowledge this forum has and so I took the liberty to post my first attempt at amp construction. It is just a Little Gem LM386 amp which I installed in an old PC speaker box I had laying around.

Here it is:


Not much to look at, I know, but it was my first attempt at any electronics build, first attempt at circuit etching, soldering, schematics interpretation, resistor-capacitor readings and all that, and it's working pretty well. So I'm pretty proud and moreover encouraged to build something even better.

So here comes my request for your advise. What would be a good guitar amp for me to build next? This amp was around 1/2- 1watt, with only gain and volume controls. So I am looking for something a little more complex, maybe a couple more control pots, up to maybe 15-20W (if that's too much wattage for a simple build let me know). Also I would greatly appreciate it if there were PCB layouts for it.

I hope I am not asking for too much, please fire away with suggestions, comments, anecdotes etc.

[Bismarck]

Come on guys... any suggestions?

I was thinking about that "Little Rebel" amp but it's only 2W... there must be something slightly better than that. 

[joecool85]

I'd consider building an amp around the LM1875 power amp IC.  If you search for LM1875 here you will find a few threads on it.

[Bismarck]

Ok so I decided to built an amp with a LM3886... do you think that would make a decent guitar amp?

I found this one: http://www.generalguitargadgets.com/pdf/ggg_lm3886_amp.pdf
What do you think about it?

Also it says at some point "10 ohm 2 watt resistor with 10-12 turns of #22 insulated wire". I have a 10 ohm 2W resistor but what is that wire deal? Does anyone have a picture of one or know how it's done?

Thanks for the reply joecool85 

[teemuk]

The "wire deal" is an inductor wound around the resistor. You take #22 insulated wire and wind 10 - 12 turns of it around the resistor (as tightly as you can). You solder both ends of the wire to the corresponding leads of the resistor. NOTE: The inductor (and the solder joints) will pass practically all HIGH speaker current and therefore you must make these components appropriately sturdy. The resultant is the (about) 0.7 uH inductor shown in the schematic. Since the inductor forms a resonant circuit the resistor (which also acts as the body of the inductor) is used to damp the resonant peak.

I would also add a shunting combination of 100 nF capacitor and 10R resistor in series from output to ground (in parallel with the speaker or preferably before the RF filter if you can accomodate it). It's known as a "Zobel network" and it can improve the overall stability of the amplifier when it's driving complex loads and long speaker leads. You can likely wire it straight to the speaker output jack. The circuit may become subject to abuse (if amplifier oscillates or something) and it is adviseable to use a self-healing capacitor (e.g. polypropylene) and a high-watt resistor (2 - 10 W).

Also, put a capacitor coupling to the input but do not accomodate it between the potentiometer and the chip since the potentiometer creates the required common reference for the input (and therefore defines DC potential of zero volts to both input and output).

Many people have built guitar amps using that chip - even big name manufacturers of commercial guitar amps so yes, you can make a decent guitar amp with it. The design and layout in question look solid but very often it comes down to how you design the power supply. If you dind't know already, search for "gainclone" for lots and lots of discussion about these kinds of amplifiers.

[Bismarck]

Thank you teemuk, I appreciate the insight and advice.

Speaking of power supply, what do you think would be the appropriate one for this amp? (voltage etc.)