| 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 |
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| 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 |
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| 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. |
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| 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 |
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