Atari Punk Console with speaker instead of output jack

[guybrush]

Hello, folks. Thought you'd be able to help me with this.

I've successfully built (over the past seven years or so...) about a dozen APCs using Matthew Helm's neat, newbie-proof layout: http://www.getlofi.com/wp-content/uploads/2006/10/atarilayout.gif

I usually build them as gifts. Problem is, most people don't have an amp to plug into. You can use headphones with them but the sound is a little on the low side (which does make sense considering, as I've read it, it's a -4db line out). I figure they should be a better gift with a built-in speaker.

So my questions are:

1) preferably using that layout as a reference with as little change as possible, how can I remove the output jack and add a speaker?

2) by doing that, I assume the circuit must be changed somehow to be slightly louder so that it'll be able to drive a small speaker (if I'm not mistaken, the original circuit was like that, yes?) – how to do that as well?

My building experience is restricted to APCs, a Weird Sound Generator and a couple of simple fuzzes, so speakers baffle me. Instructions as well as technical explanations are very much welcome. Thanks!

[PRR]

There is not enough power in a '556 chip(*) to slap a speaker around.

"Simply" add a power amplifier.

For 9V power and "home play" level, the LM386 chip is perhaps the simplest power amplifier. It needs a few support parts. CanaKit Mini Amp is an example of a complete build. Join the red and black 9V wires together. Run the '556 board out to the '386 board in. Hang a speaker off the end.

Some duplication. Both the '556 board and the '386 board have volume knobs. Conjoined, it is just one after another. You do not need both. The '556 board shows a nice off-board Volume pot, keep that. If you use the CanaKit, turn its volume trimmer full-up and hide it inside.

Since this is personal DIY, after you build and study the LM386 board, you will see that you can etch your own easily, and leave-off the redundant parts. Set the '556 and '386 boards side by side, you can work-out how to combine them into one board for ease of buliding.

Radio Shack used to stock a small amplifier, looked like a pocket transistor radio but a jack instead of a tuning knob. Price was pretty low, makes DIY look expensive, but doesn't have the hand-built appeal of your builds.


(*) EDIT. Actually the '556 is not so weak. It won't fill the house, but it sure can entertain the user working it face-to-face.

Power output is under 0.040 Watts. A small number, but when I turned-up a 0.2 Watt pocket transistor radio the folks downstairs would yell "turn that down!". Certainly worth a try.

You have to scale-down three parts.



The hard part is a 100 Ohm pot with a knob. Knob-pots of such low value are now rare. Trim-pots at 100 Ohms are common, but you'd want to cobble-up a knob.

You can use a speaker L-pad. However these are mostly made for 1,000X the power we need, so they are bulky and costly for a punk project.

Here is a small crude 100 Ohm L-pad, but still more than you need/want ($4!).

A 1K pot will "work", but you won't hear nothing until half-up, most of the action will be between "9" and "10" on the knob. Something to try on the bench, if only to show yourself why we want a low-value pot.

The OUT jack is optional, for players who may sometimes plug-up to a big amp for big performances. Start with Punk volume *down*, set the big amp to "normal" settings, then sneak the punk's volume up slowly until it is plenty loud. It should drive most any instrument or line input, even over a mile of wire.

The 100uFd cap will be bigger than a 10uFd. The wire legs may not want to fit the holes. You can kink them up and make it fit, or etch an extra pad and hole a little further away, as shown above.

[PRR]

Here is what may be the original APC, speaker-only.

I have doubts. With the huge 5K pot the speaker volume will be super-low until nearly full-up. However 5K IS a readily available value. When full-up the '556 sees a pretty heavy load, and may not act right (so turn it down a hair).

This is the same as what you got except the wire from Pin 9, to 5K, to speaker, to +9V (Pin 10). You could just add this to your existing build.

[guybrush]

Wow–thanks a lot for the prompt and super helpful responses. Sounds like all the info I'll need (for now, at least...)

I'll experiment and get back to you! (: