Crawls Backward (When Alarmed)

IconProjects, musings about guitar builds, guitar repairs, vintage tube amplifiers, old radios, travel, home renovation, and other stuff.

Noisy Cricket Mk II Amplifier Build, Take One

A few months ago the justly famous Toy Making Dad says to me, "Dude, we should make a small guitar amplifier that looks like a <------>.  You do the electronics and I'll do the cabinet."  I'm like, "Ok."  I don't want to give up all the goods on what the "<------>" is just yet, so I'm hoping he'll have more details about his idea on his blog.

Finally I've gotten around to starting a prototype for the amplifier part.  The initial foray will be a simple transistor amp that can be battery or wall-wort powered.  After reading up on some circuits, I figured I'd take a shot at the Noisy Cricket.  I figured it should be straightforward and maybe be a good base to build from.

In an effort to be as lazy as possible make this first attempt straightforward, I decided to use the layout from Beavis Audio - using a Rat Shack board.

So I gathered up the parts.  I had all of them except a switch and the board in my parts bins!  Whoo hoo.

I mostly avoid Radio Shack.  Generally, I get parts from Mouser or Small Bear.  But sometimes I find myself scrounging though their disorganized bins full of questionable quality, way overpriced parts because I have to have it NOW!  (IF, that is, they actually have it).

I'm probably not the only person who keeps waiting for them to go out of business and their subsequent fire sale, so I can snag a few drawers' worth of stuff at the prices it should actually sell for.  On the other hand...meh.  Who needs that junk?

Back to the amp.  I'm going to do one simple mod right off the bat - a switch to choose the 'stock' bass/tone cap value of .047 uF or .1 uF.

Sometimes you read about tinning your soldering iron.  Here's my trusty Weller - tinned and ready to go.  This is what a 'tinned' iron should look like.  Nice and shiny.

I have a sponge in my soldering station that I keep damp and habitually use after every connection to keep the tip clean.

And yes, the tip has a bit of a bend in the end.  I should put a new one on.

Here the amp is all wired up.

Because I figured Toy Making Dad (TMD) will be putting this thing in another cabinet, I made the leads to the controls extra long, figuring that would be A Good Thing.  Maybe it was not.

On the left you can see the volume, tone and gain pots.  The switch on the left near them is for the variable bass.  The switch at the top is the infamous 'grit' switch, and the on/off is the red switch.

So, it sorta worked the first fire up.  However.  It sputters, fuzzes and makes all sorts of ugly noises.

It sounds to me like it's oscillating.  This is a good thing in the front end of radios, but not so much in a guitar amp.

At first I thought the JFET (MPF102) was bad, so I changed it.  Same result.  I'm guessing the lengthy leads are an issue.  I'm going to cut them back.

In the meantime, here's a shot of the board.  I generally don't like this kind of assembly, and it's my own stoopid  fault for going with it.  It was quick to put together, but it's a mess to look at, troubleshoot or replace components on.

It is a prototype, however.  Once I get it going I can experiment with some component values.  I'm also going to try some other circuits.


Post a Comment 1 comments:

  • David Frizzola said...
    June 29, 2016 at 11:55 PM
    BG Micro (and possibly some other electronics stores) has RS parts (pc boards) for sale at prices much lower than RS.

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