How to create a simple amplifier?

[mikevolta]

I am looking for some help into building a small guitar amplifier with an output voltage range from 4-volts to 9-volts.

I have been looking at the smokey amplifier design range and have read on many sites that the amp is a rip-off at a price of £23. It is supposedly a simple design to recreate and boasts a powerful distorted sound.

Any help would be great as i am a newcomer to amplifier building. cheers

[RDV]

Right here is a good variation on the Smokey.

RDV

[teemuk]

Hi,

I don't know about you guys but i never got the LM386 to work without terrible oscillation with a lesser gain resistor value than 1.2k. I feel this is the absolute minimum.

The Smokey schematic can be found here:

http://www.blueguitar.org/new/schem/_ss/smokey.gif

As you see it´s a pretty basic circuit and therefore prone to oscillation or other misbehavior unless built properly. In my opinion the original LM386 datasheet application with zobel network on the output is a much better and more reliable circuit. You can see that Little Gem and Ruby are pretty similar to it.

Building a low powered application like this for guitar is probably the only choice for your needs, however i'd suggest some improvements:

- The input impedance of LM386 is about 50 kilohms. Any volume potentiometer with a smaller resistance than that in front of the IC will attenuate the input signal.

- Include an automatic gain control, in other words either a limiter or compressor, circuit to the design: This will give you a vacuum-tube-like character and an impression of a greater output power. It will also reduce the amount of distortion. Look for example LDR-based circuits, they´re quite simple and should be easy enough to implement.

- Put a "fenderish" tonestack to the front. An electric guitar sound has a bit too much midrange when it´s totally clean. A tonestack circuit (that attenuates midrange frequencies) will give you that "pinch" to make the guitar sound more acoustic. It will also give you a wider range of tonal possibilities.
You can for example modify the Ruby circuit and turn the jfet buffer into a preamplifier. (Look the Fetzer Valve circuit, also found from the runoffgroove website). You need a preamp that boosts the signal enough to compensate losses caused by the tonestack.

- Do not hook the amplifier to very small speaker(s), otherwise you will get a very "boxy" and cheap tone. The peak power can go over 3 Watts so heed that while choosing the driver.

Teemu K

[aletheian]

I built a couple of these for fun. A bridged version as well. They are not too loud, but they are ful little buggers. I used a jfet buffer in fromt of them.

Check out this site: www.runoffgroove.com

The Lil Gem and the Ruby work well.

[footstony]

Hi mikevolta

I don't hang out here much but I thought I'd chime in.

I like the TDA2003: low volts, low parts count with high current output!


My prototype uses the previous version TDA2002 and works with a small rechargable 9V for me.

I used the low cost bridge application shown in Fig. 20 in the application sheet. Nice and loud for a 9V battery.
Sounds nice also with guitar.

http://home.eunet.cz/rysanek/pdf/tda2003.pdf

Has anyone else used this one?

Regards Philip