Making an Amp with the Maplin Kit - a bit of help needed! - Forums

Hi All

I would like to make a little amp, to amp my diddly bow

i have the following:

1w amplifer Kit £5 (LM386 kit) http://www.maplin.co.u/Module.aspx?ModuleNo=220054
on/off switch
speaker
solid core bell wire
mini potentiometer 10k http://www.maplin.co.uk/Module.aspx?ModuleNo=2203
9v battery clip
1/4" mono socket
lunch box to put everything in!

questions:

i want to adjust the volume - is the best way to add a potentiometer on the input from the 1/4" socket ?

should the switch be put on the live side of the battery clip?

anything else i need to be aware of??

drawn a little diagram of what i think i'm making - kit diagram available at: http://www.maplin.co.uk/media/pdfs/N48FL.pdf

many thanks !

circuit001.jpg

Replies

Frank July 26, 2010 at 1:16pm

Thanks all for the advice - i built the kit and it works!

right onto the next one now
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Frank July 22, 2010 at 4:26pm

thanks Mark, Tim and Uncle Lou for your replies, its much appreciated.

I will start the build process this weekend and report back

cheers
frank
Mark July 22, 2010 at 4:22am

Best arrangement is to have controls for both input and gain (a common arrangement is a 10k pot on the input and a 1k pot across pins 1 and 8 for the gain). That way you can play around and get a range of dirty and clean tones across a range of volume levels.

One thing you need to change from your diagaram is the way you have the pot wired on the input (you seem to have it wired into one wire, instead you need it wired as a voltage divider)

I played around with a few variations using the Maplin kit and rapidly settled on the following circuit.

http://www.cigarboxnation.com/photo/circuit-diagram-for-simple-amp

Most of the resistors and capacitors are exactly as per the kit. There are two changes: First, on the section between pins 1 and 8, leave out the capacitor and resistor and wire in a 1k pot in their place. (the neatest way is to solder a couple of leads to the holes for the resistor and solder a short piece of wire across where the cap would be. Alternatively you could keep the capacitor in - some circuits include it and I only omitted it because the Little Gem and Smokey circuits use just a pot there.);
Second, wire in a 10k pot in place of the 10k on board trimmer for the input.
(NB. I managed to get my component numbering slightly out of step with the kit instructions so don't read my component numbers as being the same as Maplin's)

In contrast to what Uncle Lou has said, I have no problem playing a piezo straight into my LM386 amp. I'm not entirely sure why some people have problems with piezos but it's not because it's an impossible concept. I think sometimes there are issues with the impedance of piezos but I seem to have avoided these - perhaps by having volume controls on my guitars and on the amp input.
uncle Lou July 22, 2010 at 12:12am

Not sure if this will help but give this a try...http://www.mintellectual.com/mintyamp/Minty%20Amp%20assembly%20inst... With only 1w if your using piezo you`ll need apedal or pre-amp or you won`t be able to hear it. Much better off just getting a used danelectro honeytone or one of these to build.....http://www.designnotes.com/Merchant2/merchant.mvc?Screen=PROD&P...
Hey, TURN IT DOWN! July 21, 2010 at 11:39pm

The resistor sets the gain of the device (386), so it is important, but can be changed. I have to admit I didn't look at Maplin's schematic till just now. If this is your first build, build it per the schematic, with the 10K pot as they show it (wiper to pin 3, one side to ground, the other to the center pin on the input jack.) Less confusing to troubleshoot that way!!

After you get it working, then you can play around with it!!
Frank July 21, 2010 at 5:07pm

thanks Tim

is there a best place to put the volume control, or is either ok? (is that resistor important!)

cheers

frank
Hey, TURN IT DOWN! July 21, 2010 at 4:08pm

Switch in the positive leg of the battery lead, yes. As for the volume control, you can use it on the input, or you can use it in place of the resistor between pins 1 and 8 on the 386. If you use it between pins 1&8, technically it would be called a gain control, but it would serve the same purpose....

The 386 is a very popular amp i/c, and their is ALLOT of information on the interweb about it!!