Ruby Amp (LM386-3) Circuit Power Consumption Test

I had to try it. I hooked up my variable power supply to the voltage connector of one of my amps that is soon to be for sale. I was wondering what the current consumption would be for those of us that like 9 volt batteries.

To start off, 9 volt batteries do not function well below 7 volts. Without getting into the engineering aspect, the battery just can’t deliver enough current at this point. The LM386 will work at 5 volts, but once a 9 volt battery gets that low, its voltage sags dramatically. If you don’t believe me, do a Google search on the internal resistance of batteries. :) Continue reading

Adding a power supply to a Cigar Box Amp (REVISED)

This is the first installment of adding a power supply jack to a cigar box amp.

After a little research I’ve discovered that most effects pedals have a negative tip configuration. Diagram Negative TipThe first few cigar box amps that I built and sold with a power supply jack were positive tip. I’ve found that a positive tipped power supply is much harder to come across.
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What’s happening this week @ tech-tut.com? 7-23-2010

This is a quick post to update any followers of the site. I spent the beginning of the week installing laminate floors in my house. I neglected most of my college course work, and now I’m trying to catch up.

I’m working on a 4 speaker Cigar Box Amp. It’ll make it to eBay sometime next week. It’s a working prototype. The electronics are basically the same except that I’m adding an external power jack, a hard battery clip, and a front cover that may or may not look good. I covered most of the front with fabric to cover the speaker holes. I’ll have pictures up next week in the Cigar Box Photo album. I’m also removing the power switch and using a stereo input jack as the switch, and I’ve added an LED to signify that the power is on.

The suitcase amp is still under construction. I do not like version 1.1, and I’m probably going to scrap the 2 watt version for now. It has a horrible “hummmm” when used with wall-warts, and I probably need to add some smoothing capabilities to the incoming power. I am going to test it out with the LM386 circuit and see how that sounds.

That’s about it for Tech-tut.com’s latest updates. I haven’t said this in a while but remember that “it’s more than just a project.”

LM380 2W Samsonite suitcase guitar amplifier

I built this amplifier using the LM380N IC. It was an easy amp to build, but I used a Radio Shack circuit board to do some tinkering. I wanted to have a switchable transistor boost pre-amp, but without using a 3PDT switch and true bypass, I couldn’t think of a way to do it without making the whole thing unusable.

I settled for a clean, 2W amp. The great thing is that it can be used with effects pedals to achieve any sound that could be desired. One aspect of the LM380 chip is the input voltage. The maximum input is 100mVp-p, which has been observed by using a standard electric guitar. The input voltage is reduced using a voltage divider consisting of a simple potentiometer. I soldered the pot directly to the input jack and took the output to the circuit from the wiper. This gives the end user complete control over the amp. Hotter guitars will need to be trimmed down, and hobby guitars built with Cigar boxes can be trimmed up, if needed. I set the amp to work with a Tele-style guitar to work with minimum noise.

This is a springboard project. Version 2.0 is in the works to have distortion capability. I want to have the LM386 as the pre-amp and the LM380 as the power amp. This same circuit will also become the basis of future Cigar Box Amps.

2W amplifier schematic [Version 1.0 - Scrapped]
2W amplifier Schematic [Version 1.1 - added trim pot/removed input cap]

Adding a power jack to the Cigar (cracker) Box Amp

<August 6, 2010> This power supply configuration should only be used if you can find a positive tip power supply. Negative tip is more common in the music scene (effects pedals). General Guitar Gadgets sells a negative tipped power supply for $11. Check out this post for more info…Adding a power supply to a Cigar Box Amp (REVISED)
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