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Simple amps

I'm working on building a simple battery powered mini-amp to play my CBG's through. Inspired by the creations of nation member smojo, which he displayed at the recent UK fest in Birmingham, I'm experimenting with designs based on an LM386 integrated circuit. These tiny chips allow the construction of some amazingly compact yet great sounding amps (some of smojo's elegant little amps are shoehorned into very small tins).

I've found a lot of useful information at the websites of Beavis Audio (http://www.beavisaudio.com - see the "Smokey" and "Cricket amps") and runoffgrove (http://www.runoffgroove.com - info on "Little Gem" and "Ruby" amps). I've also investigated Maplin's LM386-based 1w mini amp and I downloaded the LM386 datasheet from National Semiconductor. However there are still a few things I'm struggling to figure out (either because they aren't well covered by the sources I've found or, more likely, because my electronics knowledge isn't sufficient). I wonder if any nation members have worked with these circuits and if so whether they can provide answers.

Firstly, some designs have a capacitor wired between pin 7 of the LM386 and ground (in fact the only design I can see where it's omitted is the Little Gem). The only description or explanation I can find is on the LM386 data sheet where pin 7 is described as "bypass". Any idea what they mean by "bypass" and what effect it might have on the sound of an amp if this is connected to ground via different capacitance values?

Also, I note some designs have a capacitor on the input (eg. Little Gem) while others don't (eg. Smokey and Maplin 1w). My first build doesn't have an input cap (partly because it was based on a Maplin PCB for convenience) and it seems OK. Can you suggest any reasons either in favour of or against adding an input cap?

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Permalink Reply by Justin Mantelli on November 12, 2011 at 9:33am

This will also help when building http://www.instructables.com/id/The-Process-of-Building-a-Cigar-Box...

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Permalink Reply by Mitchell Montgomery on June 10, 2012 at 3:04am

http://www.ebay.com.au/itm/250530515447?ssPageName=STRK:MEWAX:IT&am...

would this be a good start? Mitc6hell

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Permalink Reply by Mitchell Montgomery on June 10, 2012 at 3:03am

http://www.ebay.com.au/itm/250530515447?ssPageName=STRK:MEWAX:IT&am...Would this be a good start? Mit6chell

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Permalink Reply by Jim Woods on June 30, 2012 at 9:54am

Yes, That was one of my first amps to build. I soldered in a 1k pot for gain adj instead of the jumper.

After a couple Lil Gem builds, I settled on the Noisy Cricket. If you get addicted and are going to build a few, buying the components from china, you can build 10 for about $100. If you just want one, buy a kit.

I did find out you only want to use mylar (gumdrop) capacitors for the non-electrolytic, not the ceramic ones..

I have been giving them away when giving a CBG. Everyone is amazed at the sound given a lttle 9v battery. Have fun!!

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Permalink Reply by ron carlson on July 1, 2012 at 3:31am

I was going to build my own also but not being too overly excited about soldering on a little circuit board, decided to give the 5w amp "harness" fro Guitarfuel. I like it so much that I ended up building two and have plans for a third.

I'm not sure what op amp chip it uses or configuration but produces upwards of 5w instead of the .5/1w for the LM386. I've found that it can support a little more substantial driver than the one that's provided. Within reason of course.

I used a Jensen P8R in the one build and a Quam oval from a console in the other. Both sound very nice, great tone and surprising volume.

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