Practice guitar amp w/o tubes: Where?

[zener]

I know that this question should be posted somewhere else, but because it is related and people here are very helpful here :wink: , here it is:

I want to build a small guitar practice amp, the usual vol, treble, mid and bass (gain or dist, if possible) that doesn't use tubes (is it what they refer to as solid state?). I have known that tube amps sound great. It is unfortunate for me that in my country, tubes are nowhere . Any site where I can find schematics or can anyone give me one?

Thanks for any help.

[amonte]

how many watts?  If you're looking for a low wattage, simple design, there's a couple floating around, like the Little Gem.  

Let me know if this is what you are looking for.

[aron]

From R.G. re: mini amps:

By the time you do the power supply and heatsink, you've paid 90% of the effort you'd spend getting a TA2030 (20W) or an LM3886 (68W, $5.00) to work. These things need about four resistors and a few caps to make a complete amp circuit. The power supply is worse than the amp.

I would look at those chips he mentions above.

[zener]

Something loud enough for a room. :roll: 10 watts or less, is that loud enough :?:

[Peter Snowberg]

10 watts is amazingly loud. Sound is measured logrithmicly so even if it sounds strange, 10 watts is only twice as loud as 1 watt. 100 watts is only twice as loud at 10 watts.

I built a little amp a while back that I was very happy with. It uses two LM386s. The first 386 is the preamp and it is set to high gain. The output goes to a regular Fender sytle tone stack (using 330pF, .022uF & .022uF) with a volume control and then a second LM386 at low gain to drive the speaker. I put a 500 ohm pot in the speaker line to dial the volume down to bedroom levels. Without the 500 ohm attenuator, that amp was MUCH too loud to use full volume around other people. It worked great until I lost it in a move.

There are many good single chip amplifiers out there. To adapt most of these chips to guitar use, all you need to do is add a JFET buffer to the input to give a high impedance. You could also use an op-amp to preamplify and feed a tone stack. The NE5532 is a great chip for this.

-Peter

[Mark Hammer]

10 watts is plenty loud, if you have a decent speaker, a decent cabinet, and a good preamp stage.  Even though, on paper, they may seem like powerful amps, many small amps will often not be as loud as they might be, given their stated wattage, because the speaker is inefficient, or located in a cabinet that does not allow the bass to come through, or because the preamp stage does not provide as much gain to the input as can be applied.  In fact, because they are designed in anticipation of unknown user conditions, most amps are designed with much more headroom in the preamp section than is actually needed.  If you know what guitar you will be using and what you will be giving the pre/amp for a signal, you can design it to use all the headroom available, and deliver a much hotter signal to the power amp, producing more volume at the speaker.

I've had good luck with the different 6-1/2" and 8" "full-range" speakers that are found in ceiling public address systems.  These can often be bought surplus, and even brand new are pretty inexpensive.  I pay $10 Canadian brand new for the ones I have.  Most are rated at 4 or 8 ohms and 10-20W power handling capacity, which makes them responsive enough to low power amps without being easily burnt out.  In most cases, their bass response will go down low enough and the treble response will go up high enough.  It will NOT sound like a 4x12 stack, but you would be surprised how full a couple of watts into an 8" speaker in a decent cabinet can be.

Just keep in mind that more power = more current needs = bigger transformer.  If you go with a 1-3W amp, an 8-pack of C or D-cells is plenty of power.  If you go bigger than that, you will probably want an adaptor or on-board transformer, and only use batteries if you really need to.  A 12vdc supply is usually what these things will operate best at.

There are plenty of power-amp chips with the KA, TDA, TBA, LM, SK, and STK prefix that will provide between 1 and 10w and run off 12v or less.  Find a chip, download the datasheet by searching for it in google, and there will usually be an application schematic, and maybe even a PCB layout.  Most of the chips over 1W or so will likely need a suitable heat sync of some kind.

Many of the IC companies make dual power-amp chips that are intended for portable music listening.  Many of these chips can be used in bridge mode for even more power from one channel.  Because car stereos are limited to a 12v power supply, many of them use bridge mode as well.  If there is a place near you that sells old computer equipment cheap, many of the early generation sound cards often came with easily unsolderable power amp chips that would pump a couple of watts per channel directly into speakers.  Run those chips in bridged mode and you can easily be cranking 8-12W into your speaker.

[zener]

Forget about the "10 watts or less" :roll: . Just anything loud enough to fill or shake my room .

Thanks.

[Mark Hammer]

I made a 12cdc-powered 1.2W amp from a TBA820 (an 8-pin DIP) using a circuit that appared in Practical Electronics last year, and through a 6-1/2 speaker it was surprisingly loud, and sounded great.  Easily fit your "fill up a room" criterion.  I'll bet they could hear it at least 2 or 3 islands away from you. :twisted:

[Ansil]

the circuit i just sold, to a music store was what i was using is as follows.

lpb1 style clean gain booster,  lm386 set at gain of 100 into eq (hybrid marshall with a mid notch via inductor.) and into another 386 with a gain of 100 into a pot, into two lm380's set in a push pull configuration.  12volts on the 380's and 9.5 volts on the 386's.  heat sink the 380's
total cost of around 10 dollars in new parts.  i had a old peavey shell with a speaker so i just bought some 380's and a few caps and 2 386's.  and a couple of pots.

something like 5 watts, normaly, pushing 8 if you slam it hard.

[RedSweater]

It'd be kinda neat if you included distortion somewhere in the amp. I suggest you finding a soft clipping design that does not  use germanium (The philipines can get hot right? germanium doesnt like heat)